Posted By Jeffrey S. Sargent,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
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Every electrical inspector has been there, the first time out to approve an electrical installation as the "authority having jurisdiction.” Realizing the importance of his or her role in the safety chain, new electrical inspectors, and for that matter all electrical inspectors, want to perform their duties with a thorough and professional approach. In most cases the electrical inspector is the independent public safety advocate with no stake in a particular project other than to ensure that the end result is a safe installation that complies with all of the applicable NEC requirements. In some cases inspectors may be working as a "clerk of the works” or project inspector for a private concern. The bottom line is, whatever the role of an electrical inspector is for a particular installation, he or she is charged with the responsibility of quality assurance, and the benchmark on which compliance is judged most generally is the requirements of the NEC.
Photo 1. Home under construction
Where to Start?
Electrical inspectors bring varying degrees of background and expertise to their positions. Many have been electricians prior to accepting the role as electrical inspector, but that fact alone does not ensure a seamless transition from installer to inspector. Although they may be well-versed in the NEC requirements from past training and experience, when they are placed in the position of being the authority having jurisdiction (AHJ) their electrical world inevitably expands into the full scope of what the NEC covers. Many electricians have a specific focus as an installer. Industrial electricians may never have used and applied the rules for dwelling units or manufactured homes, and residential electricians probably did not perform many installations involving the installation of large separately derived systems or capacitor banks. Now, in the new role as the electrical inspector, this person is expected to be an expert in all facets of the NEC. Electrical inspectors soon realize that their new position has put them in a new learning curve and most experienced electrical inspectors will tell you that this learning curve is on-going and ever-changing throughout their electrical inspection careers. Certainly there are training and certification programs that enable electrical inspectors to enhance their job performance. However, new and seasoned electrical inspectors will inevitably encounter an installation that is new ground.
When put into the position of having to approve an electrical installation that one has not previously encountered, either as an electrician or as an installer, the logical question is where to start? From a very general sense, a logical approach to the inspection and approval process is determined based on the phase of construction a project is at. Certainly the status of the construction project will direct the focus of the inspection. For new building projects, inspections are generally made incrementally as the building is constructed. Depending on the size of the building and more importantly the complexity of the building’s electrical system, the number and focus of electrical inspections will differ.
The major considerations for "rough wiring” inspections differ from the major considerations for a "final inspection.” Putting this all together into a logical and thorough approach is the challenge faced by the electrical inspector. He or she is compelled by the responsibility placed in his or her hands to ensure that the building electrical system is essentially free from fire and shock hazards.
A systematic approach often will involve the use of some kind of written or mental checklist. As inspectors gain experience in the multitude of electrical installations that they are exposed to, there is a natural maturation in how they perform their duties. Experience promotes efficiency and thoroughness. A key component to this increased efficiency and thoroughness is the development of the inspector’s "inspection system.” Many electrical inspectors approach the inspection task using mental checklists. The development and refinement of these checklists evolves with experience. Like any job, one’s proficiency develops with experience and this definitely holds true for electrical inspectors. Tasks that were at one time daunting become routine through the lessons of experience. But the question remains, as a new electrical inspector where does one start in order to develop a polished inspectional procedure?
A Tool for Inspectors
Unlike apprentice programs for training electricians, the training of electrical inspectors is generally far less formal or structured. For those who have entered the inspection field from a background in electrical installations or design, there is generally a thorough understanding of the NEC and how electrical systems are put together. This background provides a solid foundation for an electrical inspector to build on as he or she changes perspective from installer to approver. Organizations such as the IAEI that promote uniform application of the NEC via their educational programs offered by their local chapters and the International office help electrical inspectors make this transition. This type of meeting provides an excellent forum for the dissemination of knowledge regarding the NEC, however there was a need for an inspectional job-aid that could be used by electrical inspectors on a daily basis. The National Fire Protection Association (NFPA), the developer and publisher of the National Electrical Code has developed a tool to meet this need.
First published in 1999 and based on the 1999 edition of the NEC, the Electrical Inspection Manual with Checklists was developed to fit the needs of anyone who installs or inspects electrical installations. Endorsed by the IAEI, the purpose of this manual is to provide inspectors and installers with a compilation of electrical inspection checklists. These checklists range in coverage from general requirements for all electrical installations to more specific checklists based on type of occupancy, type of equipment or type of location. The checklists are an assemblage of electrical installation requirements that pertain to a respective type of occupancy or equipment and are not intended to dictate a specific inspection order or procedure. Electrical inspectors are individuals and need to develop an inspection system they are comfortable with. There is not one inspection template that will be suitable for every inspector. What works for one inspector will not necessarily work for another. The bottom line is that the inspection is performed efficiently and comprehensively. Use of the Inspection Manual checklists will assist the inspector in developing an approach that meets this objective.
The checklists are comprehensive and in most cases provide all of the necessary references to the NEC requirements that apply to a particular installation. In some cases all of the items in the checklist may not be applicable to a given installation. On the other hand, the checklists are not intended to imply that there may not be other NEC requirements that are applicable to a given installation.
How the Manual Works
The foundation of the manual is the checklists. Each checklist contains a number of inspection activity items and there is a cross-reference to the applicable section of the NEC. An important feature of the manual is the brief explanation that is provided for every inspection activity item. This commentary provides insight on the application of the particular NEC requirement that the inspection activity is based on. This commentary material is numerically linked to the number of the inspection activity item in the checklist. Table 1
An important concept in using the Inspection Manual is its structure. Like the hierarchal arrangement of the chapters within the NEC, the chapters in the Inspection Manual are arranged to provide general overall considerations regarding electrical installations in the first five chapters, while Chapters six through twelve contain specific occupancy or equipment checklists. As an example, the checklist in Chapter 2 of the Inspection Manual contains inspection items from Articles 90 and 110 of the NEC. These checklist items are general requirements that will apply to most electrical installations that the inspector will encounter. However, the checklists in the latter chapters are more specific and do not have the broad scope of the up-front chapters. Like the NEC, it is necessary to use more than one part of the book for any given installation. Chapter Six on Dwelling Units and Mobile/Manufactured Homes is the only chapter that for the most part is self-contained and does not require the use of other chapters. The decision to make Chapter Six a "stand-alone” chapter was based on the fact that in most cases electrical inspectors who work for a city or town will inspect a large number of dwelling unit electrical systems.
Additionally, each checklist contains "key questions” that are germane to that particular inspection checklist occupancy or equipment. The purpose of the key questions is to put the inspector "in the mood” for that particular inspection by providing some general considerations and items to be aware as the inspection is being performed. Like the commentary provided for each of the inspection activities, background information is provided for each of the key questions and uses alphabetical links. The checklists have many different applications. An individual electrical inspector can use them as a self-training tool for developing a personal inspection protocol. The checklists can be used as a template for training groups of electrical inspectors or they can be used during the field inspection process where a comprehensive written record of a particular installation is required.
Using the Dwelling Unit Checklists
The inspection checklists for dwelling units in Chapter 6 provide a slightly different approach than the checklists contained in the other chapters. Chapter 6 takes a residential project from start to finish and provides checklists covering "rough” and "finish” inspections. Another feature of this chapter is that it provides a breakdown of specific rooms or areas within or associated with a dwelling based on the specific NEC requirements for those areas. Beginning with some key questions that are intended to give the inspector some general points to focus on as the project proceeds, the checklist next provides some general requirements that apply throughout the dwelling unit, and then it continues with specific NEC requirements for kitchens, dining rooms, bathrooms, other habitable rooms, hallways, stairways, closets, laundry areas, basements and attics, garages, and outdoors. This area approach provides the inspector with the NEC requirements that are unique to that specific area. This reflects the fact that the NEC, particularly in Article 210 provides more requirements for specific locations within a dwelling than for any other type of occupancy. This type of approach is taken in the NEC since in most cases, the electrical system of a dwelling is laid out by the installer.
The dwelling unit checklist then proceeds into the requirements applicable to the installation of the electric service, the installation of any feeders, and the grounding and bonding provisions for the service equipment. This portion of the checklist also provides the requirements for panelboards that are supplied by service or feeder conductors.
The "finish” inspection checklist is arranged similarly to the "rough” wiring checklist. Beginning with a number of general requirements that apply throughout the dwelling, the checklist proceeds with the room-by-room approach, ensuring that the completed installation in each room meets the NEC requirements that are unique to that area. For instance, during the rough wiring inspection of the kitchen the inspector needs to verify the installation and proper use of the minimum two small-appliance branch circuits, while during the final inspection the inspector is verifying that GFCI protection has been provided for the receptacles serving the kitchen counter area. On the same vein, within the dwelling unit bathroom(s) the inspector has verified the presence of the 20-ampere circuit for the bathroom receptacle outlets, while during the finish inspection it can be verified that GFCI protection has been provided for the bathroom receptacles.
As part of the final inspection checklist, there are also requirements for service equipment and panelboards supplied by feeders. Among the items covered in this portion of the checklist are the verification of the completed grounding system and the identification of the circuits within the panelboard(s).
New for the 2002 edition of the manual is a checklist that covers the NEC requirements for manufactured home site supply wiring. For new manufactured home installations, the electrical inspector does not typically inspect the factory-installed wiring, however the site supply installation and any additional branch circuit or feeder installations are subject to field inspection. Also new for this NEC cycle is the Pocket Guide to Residential Electrical Inspections. This abridged version of the Electrical Inspection Manual contains all of the dwelling unit checklists and associated commentary. In addition, the checklists for general wiring requirements, wiring methods, grounding and bonding and swimming pools are also included.
No two electrical inspectors will perform their field inspections exactly alike. Inspection processes and techniques differ and often are dictated by construction conditions. Thus it is often not possible to "package” the inspection of a dwelling as is neatly laid out in the checklists. This was never the purpose of the book. The purpose was to lay out the applicable requirements in a list format that can be used as an aid to inspectors of dwellings and other occupancies and electrical equipment covered in the manual to develop a system for performing thorough, efficient and effective electrical inspections. As was previously stated, experience and an upfront understanding of how electrical systems operate are two of the most important factors to having a strong foundation on which an inspector can grow from. After all, the method by which the inspection is performed is not nearly as important as is how well the inspection is performed.
Read more by Jeffrey S. Sargent
Posted By Ken McLennan,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
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Section 18 of the CSA Canadian Electrical Code (CE Code) covers the installation of equipment and wiring in locations considered hazardous because of the presence of ignitable or explosive materials. Such locations are divided into three classes:
Class I, which contains explosive gas or vapours
Class II, which contains combustible dust
Class III, which contains combustible fibres.
A major change in the 18th edition of the CE Code, published in 1998, introduced the zone system of dividing Class I locations into three zones instead of the two divisions used in previous editions. This was a significant change, affecting all electrical installations in hazardous locations, and is still not entirely understood by everyone.
It would not be appropriate to simply identify the revisions brought about by this change without discussing the principles behind them.
The Division System
Originally, Class I locations were not divided. A location that was subject to the presence of flammable gas or vapour was simply classified as a Class I location. Electrical equipment and wiring located in such areas had to meet the most stringent requirements that were approved at that time.
It was eventually agreed that there was a need to divide Class I into two divisions. It had become obvious that there were many situations where there was a minimal chance that gas or vapour would be present. In fact, it was not expected that gas or vapour would be present at all during normal working conditions, but it was recognized that an accident or other abnormal condition could result in a release of hazardous gas or vapour.
Locations in which the presence of gas or vapour was unlikely under normal situations, were classified Division 2, and were subject to less stringent requirements for equipment and wiring. All other Class I locations were classified Division 1 and continued to be subject to the more stringent requirements.
It should be noted that the principle behind the division of Class I locations is as significant as the actual practical application. Dividing Class I locations into two divisions introduced the principle of "probabilities.” In other words, when classifying hazardous locations it became acceptable to consider the probability, or likelihood, of gas or vapour being present simultaneously with a source of ignition.
Therefore, in the division system, Division 1 locations are those where the likelihood of explosive gas atmospheres occurring is the highest, and Division 2 locations are those where the likelihood is reduced. The Canadian Electrical Code defines Division 1 and 2 as follows:
(a) Division 1, comprising Class I locations in which:
(i) Hazardous concentrations of flammable gases or vapours exist continuously, intermittently, or periodically under normal operating conditions; or
(ii) Hazardous concentrations of flammable gases or vapours may exist frequently because of repair or maintenance operation or because of leakage.
(b) Division 2, comprising Class I locations in which:
(i) Flammable volatile liquids, flammable gases, or vapours are handled, processed, or used, but in which the liquids, gases, or vapours are normally confined within closed containers or closed systems from which they can escape only as a result of accidental rupture or breakdown of the containers or systems or the abnormal operation of the equipment by which the liquids or gases are handled, processed, or used; or
(ii) Explosive gas atmospheres are not likely to occur in normal operation and, if they do occur, they will exist for a short time only; or
(iii) Explosive gas atmospheres are normally prevented by adequate ventilation but which may occur as a result of failure or abnormal operation of the ventilation system; or
(iv) The location is adjacent to a Class I, Division 1 location, from which a hazardous concentration of gases or vapours could be communicated, unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.1
The Zone System
Just as the division system uses two divisions to describe the specifics of Class I locations, the zone system, first published in the CE Code in 1998, uses three zones. The zone system originated in the international community, in standards developed by standards development organizations such as the International Electrotechnical Commission (IEC) and CENELEC (the European standards writing body).
The following is an excerpt from the IEC Standard 60079-10 and explains the probability principle that is used in international standards. (It is interesting to note that the Canadian Electrical Code has followed this same principle in developing standards for equipment and wiring in hazardous locations since the implementation of the division system).
In most practical situations where flammable materials are used, it is difficult to insure that an explosive gas atmosphere will never occur. It may also be difficult to insure that apparatus will never give rise to a source of ignition. Therefore, in situations where an explosive gas atmosphere has a high likelihood of occurring, reliance is placed on using apparatus which has a low likelihood of creating a source of ignition. Conversely, where the likelihood of an explosive gas atmosphere occurring is reduced, apparatus constructed to a less rigorous standard may be used.”2
In the zone system, Zone 0 represents that area where there is the most likelihood of an explosive gas atmosphere being present, Zone 1 is that area where the likelihood is reduced somewhat, and Zone 2 is that area where the likelihood is reduced even further.
The Canadian Electrical Code Rule 18-006 defines Zones 0, 1, and 2 as follows:
(a) Zone 0, comprising Class I locations in which explosive gas atmospheres are present continuously or are present for long periods;
(b) Zone 1, comprising Class I locations in which:
(i) Explosive gas atmospheres are likely to occur in normal operation; or
(ii) Explosive gas atmospheres may exist frequently because of repair or maintenance operations or because of leakage; or
(iii) The location is adjacent to a Class I, Zone 0 location, from which explosive gas atmospheres could be communicated.
(c) Zone 2, comprising Class I locations in which:
(i) Explosive gas atmospheres are not likely to occur in normal operation and, if they do occur, they will exist for a short time only; or
(ii) Flammable volatile liquids, flammable gases, or vapours are handled, processed, or used, but in which liquids, gases, or vapours are normally confined within closed containers or closed systems from which they can escape only as a result of accidental rupture or breakdown of the containers or systems or the abnormal operation of the equipment by which the liquids or gases are handled, processed, or used; or
(iii) Explosive gas atmospheres are normally prevented by adequate ventilation but may occur as a result of failure or abnormal operation of the ventilation system; or
(iv) The location is adjacent to a Class I, Zone 1 location from which explosive gas atmospheres could be communicated, unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.3
The process of changing a two-division system to a three-zone system was simplified by the knowledge that the rather broad allocation of "”Division 1″” would be more specific when split into two parts. These two parts are relative to the frequency and duration of exposure to a release of gas or vapour, i.e.,
Areas having a high likelihood of release (continuous, long periods of time) match the definition of Zone 0.
Areas having a lower likelihood of release (expected but will not occur for long periods) match the definition of Zone 1
Division 2 became Zone 2
Impact on Section 18 (installation rules)
Rule 18-000 Scope
Because of the significance of the changes made to the CE Code, the scope had to be worded to make it clear that any new installation undertaken, subsequent to the adoption of the 1998 edition of the code, would be subject to the zone system of classification. Subrule (1) covers this by stating that Section 18 (which uses the zone system) applies to all locations classified as Class I.
At the same time, there had to be enough flexibility for those existing facilities, already classified to the division system, to continue to operate, expand, or be modified, without an enforced reclassification. As well, the rules related to the division system had to be kept up to date and be available for use with those facilities.
This was accomplished by expanding the Scope from the previous two subrules to the present five. The Scope now includes provisions for the continued use of the division system in specific cases (Subrule 18-000(3)), and mandates the division system rules, located in Appendix J, for those cases (Subrule 18-000(4)).
Rule 18-002 Terminology
There is some new terminology in Section 18 that is particularly important to the application of the zone system.
"Adequate Ventilation.”This term has never been defined in the CE Code prior to the 1998 edition. Adequate ventilation simply means ventilation, either natural or artificial, that is sufficient to prevent the accumulation of vapour/air or gas/air mixtures in concentrations above 25 percent of their lower explosive limit. Both artificial ventilation and natural ventilation are considered in this definition. In previous issues of the code natural ventilation was never a consideration.
"Degree of Protection”and"Methods of Protection.”These definitions appear to be related but the difference is quite significant and warrant some discussion.
Degree of protection signifies the degree to which equipment will prevent ingress of foreign bodies such as dust or liquids.
Methods of protection are the methods used in the manufacture of equipment to ensure that it does not become or provide a source of ignition. These terms will appear in several of the revised rules in this section.
"Explosive Gas Atmosphere.”This is defined as a mixture of gas or vapour and air that is within its flammable limits. The term simplifies the previous reference to "flammable gases or vapours which may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.”
"Normal Operation.”This term is used in much of the literature dealing with the zone system and has been defined as the situation when the plant or equipment is operating within its design parameters. An abnormal operation would result in a release of gas or vapour sufficient to develop an explosive gas atmosphere.
Methods of Protection
The division system uses the basic protection features of explosion-proof equipment, purged or pressurized equipment or intrinsically safe equipment. The zone system introduces a number of additional protective principles.
They are defined in the Canadian Electrical Code, so the following is intended as a paraphrase only. (Included in brackets after the name is the symbol that is used to identify each one.)
"Intrinsically Safe” (Intrinsic Safety i, ia, or ib).Intrinsic safety (i) is the intrinsic safety that has been part of the division system. The IEC standards have introduced two new classifications of intrinsically safe:
- Intrinsic safety (ia) provides the same level of protection as intrinsic safety (i) used in the previous edition of the code. During testing, it must continue to provide explosion protection after two countable faults have been applied (countable faults are faults to components of the equipment being tested, not field wiring components).
- Intrinsic safety (ib). Equipment certified with intrinsic safety (ib) does not have quite the same level of backup protection as (ia) or (i). During testing, it must continue to provide explosion protection after only one countable fault has been applied.
"Flameproof” (d).Flameproof equipment provides the same type of protection as explosion-proof. The principle of both is to contain an explosion within the enclosure. Hot gases cool as the increased pressure forces them out though an engineered flame path and will not ignite the surrounding hazardous atmosphere.
"Increased Safety” (e).Equipment which is considered approved under the increased safety standard will have:
- a high impact type of enclosure,
- protection against the ingress of dust and moisture,
- a high degree of safety in the terminals, i.e., splices will not be permitted in an increased safety enclosure, and
- improved tracking distances between terminations.
In general, an increased safety enclosure is one in which steps have been taken to increase the safety that is provided by the enclosure and the equipment that is inside. There will be no arc producing, heat producing or sparking apparatus enclosed in an increased safety enclosure.
The following four methods of protection use similar principles:
- "oil immersed” (o)
- "pressurized” (p)
- "powder filled” (q)
- "encapsulation” (m)
Because of the special type of manufacture, gas or vapour is excluded from contact with those parts of the equipment that produce arcs, sparks or high temperatures. Ignition will therefore not occur.
"Non-sparking” (n).This is a more generalized term and will cover many types of equipment. Basically, the equipment will not produce arcs, sparks, or high temperatures, and it is unlikely that a fault will occur within the equipment.
Refer to the Canadian Electrical Code, Appendix B notes, page 577 for further information, including the standard number, for each method of protection covered in the CAN/CSA – E79 series of standards.
Rule 18-050, Electrical Equipment
Standards governing the manufacture of equipment for use in hazardous locations have traditionally been part of the C22.2 or CAN/CSA C22.2 group of standards. When referring to equipment certified under these standards, the code has stated that equipment that is required to be approved for a class of location, i.e., Class I, must also be approved for the specific gas or vapour that will be present. To simplify this process, gases and vapours having similar properties are grouped together. Group designations used with the division system for Class I locations are Groups A, B, C, and D.
To take full advantage of the move to the zone system, new standards were required to cover the manufacture of equipment intended for Class I, Zone 0, 1, and 2 locations. Standards, based on the IEC standards, were developed and adopted under the CAN/CSA E79 series of standards. To follow the IEC standards as closely as possible, the IEC method of naming gas groups IIA, IIB, and IIC was also adopted.
It is critical to recognize that the gases contained in Group IIA do not correspond to those in Group A. Instead, Group IIA gases correspond to those in Group D. Similarly, Group IIB gases correspond to those in Group C, and Group IIC gases correspond to those in Groups A and B combined. This means greater attention needs to be paid to the marking on the equipment (i.e., is the equipment suitable for Group A or Group IIA gases?)
A complete listing of typical gases and vapours along with a cross reference between the two types of group names is shown in the Canadian Electrical Code Appendix
Rule 18-052 Marking
All electrical equipment must bear a certification mark such as the CSA mark, to confirm that the equipment has been certified, as required by Rule 2-024.
In addition, the marking convention for equipment intended for hazardous locations under the division system includes the class of location, gas group, and temperature or temperature code. A typical marking may be:
Class I, Group D, T4
The marking convention under the zone system includes the Ex or EEx mark to indicate that the equipment is explosion protected, the symbol for the method of protection (d, e, etc.), the gas group, and the temperature code. A typical marking may be:
Ex d IIA T4
The marking conventions between the division and zone systems are quite different and we can expect to see either one on equipment used in Class I hazardous locations. An important point is that the latter does not include the "”class of location”" and, therefore, equipment with this marking is not permitted in a Class I Division 1 location unless it has had the class of location added.
A table showing the types of equipment permitted and the methods of protection acceptable for use in the zone and division systems is given in the Canadian Electrical Code, Appendix J.
Rule 18-090 Equipment and Wiring in Class I Zone 0 Locations
While a Class I Division 1 location includes the area designated under the zone system as Zone 0, there is a difference between the two systems in the rules for electrical equipment and wiring.
Rules for Class I Division 1 locations include:
explosion-proof equipment and wiring,
equipment and wiring that is pressurized or purged with a protective gas (see Rule 18-002 Special Terminology), or
equipment approved as intrinsically safe and associated wiring that is designed and installed as intrinsically safe.
Rules for Class I Zone 0 locations require intrinsically safe equipment and wiring of the (i) or (ia) types only.
Rule 18-090 also includes the requirements for seals in conduit runs where they leave the Zone 0 location and in cable runs at the first termination in the Zone 0 location.
Rules 18-106 Wiring Methods Class I Zone I
Although the wiring methods for Class I Zone 1 locations are quite similar to those normally permitted in Class I Division I locations, Subrules 18-106(3), (4), and (5) indicate that there are some significant differences.
Subrules (3) and (4) cover the requirements for threaded joints. Subrule (3) permits the use of straight threads in equipment required to be explosion-proof or flameproof design (tapered threads must still be used on the conduit as required in Rule 12-1006). Subrule (4) covers the need for approved adapters in cases where the threads may be metric rather than the more commonly used National Pipe Thread (NPT).
Another point to consider in dealing with threaded joints in a hazardous location is the number of fully engaged threads that are required. With the division system, the requirement is for 5 fully engaged threads in any hazardous atmosphere. With equipment used in the zone system, 5 fully engaged threads are required in Group IIA or IIB atmospheres, but at least 8 fully engaged threads are required in a Group IIC atmosphere.
Subrule 18-106(5) covers the need for care when terminating conduit or cable in enclosures with the method of protection "”e”" (increased safety). Such entries are to maintain the degree of protection provided by the enclosure. The increased safety principle includes preventing the ingress of dust or moisture into the enclosure. When such an enclosure is installed in the field, steps must be taken to ensure that principle is not compromised.
Rule 18-108 Sealing, Class I, Zone 1
There are two basic differences in the rules for sealing brought about by the move to the zone system.
The type of enclosure that is permitted in a Class I Zone 1 location is significant. For instance, seals will not be required on cables terminating at enclosures with the method protection "e” when run within the zone. Also cables that leave a Zone 1 location will not require a seal providing the cable is greater than 10 m (32.8 ft) in length and there are no excess process or atmospheric pressures involved that may force gas or vapour through the cable.
The need to seal conduit entries into enclosures that are not required to be either explosion-proof or flameproof is another significant difference. There are two reasons for this: the need to ensure dust and moisture cannot enter an increased safety enclosure, and the need to ensure the integrity of an explosion-proof or flameproof wiring system (i.e., a wiring system intended to contain an explosion). A seal must be installed at the transition to a wiring system that is not required to be explosion-proof or flameproof.
Rule 18-156 and Rule 18-158 cover wiring methods and sealing for Zone 2 locations. Since a Class I Zone 2 location is considered equivalent to a Class I Division 2 location, there are no significant differences in either the type of equipment that is permitted, the wiring methods or the requirements for sealing.
1 Canadian Electrical Code – C22.1 – 02
2 CEI IEC Standard 79-10 (60079-10) Third edition, 1995-12
3 Canadian Electrical Code – C22.1 – 02
Read more by Ken McLennan
Posted By David Young,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
| Comments (0)
About fifteen years ago, on a beautiful Saturday in September, my then nine-year-old son and I had just finished a wonderful day of sailing. Five hours earlier, when we put in at a new boat ramp, there were very few cars with trailers in the parking lot because the stiff wind was scaring the power boaters away. When we arrived back at the ramp, the parking lot was almost full. As I pulled my boat out of the water, I had to park on the far side of the parking lot well away from the water. As I pulled into the parking space to down rig the mast, I noticed a power line between the front of my car and the adjacent roadway. The high voltage conductors seemed too low for their location adjacent to an area that the National Electrical Safety Code (NESC) would clearly define as an established boat ramp and associated rigging area.
Photo 1. The utility quickly replaced the poles with taller ones. Photo 1 shows the line before it was corrected.
As my son and I lowered the short mast of our day sailor well away from the power line, another family backed their 22-foot day sailor into the parking space next to ours. I asked the man the length of his mast. He replied twenty-nine feet as he and his wife and two children prepared to raise the mast. I identified myself as an engineer with an electric power company and called his attention to the high voltage power line directly above the stern of his sailboat. If he raised the mast, it would surely hit the phase conductor. He acknowledged the hazard and then got irritated at me because he now had to move the trailer.
The next day, I contacted the utility and inquired about the line. The utility was not aware of the new boat ramp. The clearances were fine for a line along a coastal road, but they were dangerous next to a boat ramp. The people who built the boat ramp had created the hazard when they did not contact the utility. The phase conductor was only 24 feet above the ground. The utility quickly replaced the poles with taller ones. Photo 1 shows the line before it was corrected. The NESC minimum clearance of conductors over boat ramps and associated rigging areas is a function of the minimum clearance over the adjacent water.
Photo 2. Photo 2 shows an example of an obstruction that would prevent the passage of a sailboat.
The minimum clearance of conductors over water is covered by Rule 232 (page 71) and rows 6 and 7 of Table 232-1 (page 78). An "unobstructed surface” is a body of water where there is no fixed bridge or other obstruction preventing large sailboat access from a larger body of water. The larger the surface area of the body of water, the higher the clearance. For rivers, streams and canals, the surface area shall be the largest surface area of any one-mile segment that includes the crossing (Footnote 19). If a river, stream or canal has an unobstructed connection to a larger body of water, the clearance shall be based upon the water surface area of the larger body of water. Photo 2 shows an example of an obstruction that would prevent the passage of a sailboat. In photo 2, the power line crossing is actually between two fixed bridges 500 feet apart. The water surface area is less than 20 acres and thus the minimum clearance over that body of water is only 20.5 feet for phase conductors up to 22 kV phase to ground. If the body of water on the power line side of the bridge was directly connected without obstruction to the ocean, then the minimum clearance becomes 40.5 feet for phase conductors up to 22 kV to ground. Drawbridges are not considered obstructions. For bodies of water where the water level is controlled, the surface area and corresponding clearance shall be based upon the design high water level (Footnote 17). For bodies of water where the water level is not controlled, the surface area shall be that enclosed by its annual high-water mark. The clearance shall be based upon the normal flood level. If available, the 10-year flood level may be assumed as the normal flood level (Footnote 18). Note that some utilities have run into problems crossing shallow streams that become deep rivers at flood level. During storms, people out in sailboats often go up rivers to find a safe haven to weather the storm. Let us hope that they don’t find out in a flash that it wasn’t the safest move.
For boat ramps and associated rigging areas, the minimum clearance is specified in Rule 232 and in row 8 of Table 232-1 to be five feet greater than that specified over water in row 7. For the ramp and rigging area I spoke of previously, the minimum clearance for a 25 kV line (14,400-volt phase to ground) is 45.5 feet since the body of water next to the ramp is a river connected to the Atlantic Ocean.
The minimum clearances shall be met when the conductor is under maximum sag conditions. The three conditions that can create maximum sag conditions are spelled out in Rule 232A1, 2, and 3. The clearance shall be met with the conductor temperature of 120°F. If the crossing is designed for a maximum operating temperature exceeding 120°F; the clearance shall be met at the maximum operating temperature. In the medium and heavy loading districts, the clearance shall also be met when the conductor is at 32°F, with radial thickness of ice as specified in Rule 250B for the district.
National Electrical Safety Code® and NESC® are registered trademarks of the Institute of Electrical and Electronics Engineers.
Read more by David Young
Posted By Leslie Stoch,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
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This article looks at effective grounding and bonding, how it is defined by the code, and its importance to electrical safety.
The Canadian Electrical Code, Rule 10-500 Effective Grounding defines and specifies that: "The path to ground from circuits, equipment or conductor enclosures shall be permanent and continuous, and shall have ample ampacity to conduct safely any currents likely to be imposed on it, and shall have impedance sufficiently low to limit the voltage above ground, and to facilitate the operation of the overcurrent devices in the circuit.”
Appendix B offers some additional guidance by specifying that the impedance of the circuit fault return path must be sufficiently low so as to ensure that the overcurrent protection trips when it should to limit voltages on exposed metal and to permit minimum 5 x rated current to flow during a ground fault. "Rated current” is considered to be the rating of protection ahead in the circuit.
This article reviews several possible ground-fault return paths— the effective ones and the not so effective ones. When required, the Canadian Electrical Code requires that bonding conductors be installed in the same cable or raceways as circuit conductors. How important is that requirement and how critical is conductor spacing? The code does not specify any restrictions on the lengths of metal conduit or EMT when used as the equipment bonding means. Can metal raceways provide an equally effective fault path without any restrictions as to maximum length?
Let’s start with bonding conductor spacing. Tests have shown that bonding conductors must be close and parallel to the circuit conductors for the lowest impedance path for ground-fault currents. Inductive reactance increases with the distance between the circuit and bonding conductors and increases total impedance in the fault current return path. Inductive reactance always forces more current to flow along the paths closest to the circuit conductors.
Tests also show that the most effective fault return paths are bonding conductors inside cables or raceways, or metal conduit enclosing circuit conductors. Ineffective fault current paths are connections to grounded (or ungrounded) building steel, and bonding conductors external to raceways or cables. Also, due to its method of construction, metallic cable armour presents a higher impedance than metallic sheaths.
It can easily be demonstrated by testing that only an internal bonding conductor can divert a sizable amount of fault current from a metal raceway (approximately a 50-50 division). None of the other possible paths (building steel or external bonding) will have any appreciable effect on the direction of current flow.
The Canadian Electrical Code specifies no maximum length restrictions when metal raceway is used for equipment bonding. The cross-sectional area of a metal raceway is considered adequate to carry the available fault currents when selected in compliance with Tables 6 to 10. But is this enough?
The total circuit impedance of metal raceway consists of the raceway impedance, the couplings and the arc fault impedance. To determine the maximum length of metal conduit when used for equipment bonding, we must know:
- The minimum permissible ground-fault current (for effective grounding— at least 5 x the circuit overcurrent protection setting)
- The conduit impedance (from manufacturer’s data)
- The arc voltage (assume 50 volts)
- And allow a 50% margin of safety
Example – To calculate maximum ground fault impedance, for a 120/208-volt, 400-ampere circuit, assume a minimum fault level of 400 x 5 = 2000 amperes. Subtract the assumed arc voltage and divide by 2000 amperes.
120 – 50 volts = .035 ohms maximum
Next, find the conduit impedance at 2000 amperes per 100 feet (from wire and cable manufacturer’s data), apply a 50 percent safety factor and divide the permissible ground-fault return path (in this example .035 ohms) impedance by conduit impedance with safety factor to obtain the maximum permissible length of conduit. Although the Canadian Electrical Code does not specify it, maximum length is required by implication by Rule 10-500.
Based on the circuit protection rating, minimum bonding conductor sizes are selected from Table 16, but as a rule of thumb, they should have no less ampacity than 25 percent of overcurrent protection ratings. Bonding conductors must carry available fault currents during the clearing times of fuses or circuit breakers without any damage to wiring insulation, and without any risk of burning off.
Manufacturers can provide damage curve tables showing how much fault current and the lengths of time during which different size wiring can withstand faults without damage. Burn off tables are also available to show the melting points of copper and aluminum conductors at different fault currents and protection clearing times.
As mentioned above, distances between bonding and circuit conductors will affect bonding conductor impedance and resulting voltage drop during a ground fault. A higher impedance creates an increased risk of electric shock due to contact with exposed metal parts.
As in the past, you should check with the electrical inspection authority in each province or territory as applicable for a more precise interpretation of any of the above.
Read more by Leslie Stoch
Posted By James W. Carpenter,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
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Many questions have arisen since the announcement that the IAEI Board of Directors, recognizing the need for additional revenue, voted to increase the dues to $90.00 per year effective January 1, 2003.
Let us review what the purpose and objectives of the International Association of Electrical Inspectors are. Our founders, some 75 years ago, saw the need for an organization that could represent the electrical inspector in the national and international arena. In fashioning the Articles of Association they set forth in Article II, Section 1 the details of what the objectives of the IAEI shall be.
(a) To cooperate in the formulation of standards for the safe installation and use of electrical materials, devices and appliances.
(b) To promote the uniform understanding and application of the National Electrical Code and other electrical codes.
(c) To promote cooperation between inspectors, the electrical industry and the public.
(d) To collect and disseminate information relative to the safe use of electricity.
(e) To represent the Electrical Inspectors in all matters which are dealt with nationally and internationally by the electrical industry.
(f) To cooperate with other national and international organizations in furthering the development of the electrical industry.
Back 75 years ago the emphasis was on the national scene but today, in 2003, the scene is moving globally.
What do these objectives mean to the local one-person inspection department in small town America or the largest municipality? Why does the inspector need to belong to an international organization? What does the inspector member or the associate member get for $90.00 a year?
The IAEI sponsors two members, a principal and an alternate, on each of the nineteen NEC code making panels, and a principal and an alternate on the Technical Correlating Committee. The IAEI also has members on other standards making panels. This is done to fulfill the first objective to cooperate in the formation of standards. Even though the members are volunteering their time to do this important work of assuring that the inspectors’ voice and viewpoint is presented in the standards making process, the IAEI finances the travel, lodging, and meals of these 40 plus people. This happens on a three-year cycle so funds must be available for the ROP and ROC meetings. Even the smallest building in the most remote location must have a safe electrical installation and use safe electrical materials, devices, and appliances. The IAEI objective of cooperating in the formation of recognized standards IS important to every citizen living or working where electricity is used.
To promote the uniform understanding of electrical codes and standards, the IAEI produces publications on various aspects of the electrical code. These publications are on such timely code subjects as grounding, wiring of one- and two-family dwellings, and analysis of changes of the NEC. These books are priced to defray the cost of production and to return some extra funds to the association but printing must be paid for up-front. The IAEI decided to make these books available in the year that the NEC came out instead of spreading the production out over three years. The IAEI has an outstanding and hardworking staff writing material for the various books but they can’t do it all, so others are contracted to help write—another expense.
The Education Department is also producing and conducting seminars on a variety of timely subjects. The IAEI provides these educational experiences in many different ways. We conduct on-site seminars using our staff as instructors or contract with others to provide the instruction. We can partner with local chapters or divisions to conduct seminars, and we make available materials for chapters and divisions to conduct their own seminars.
The Education Department and the Publication Department combine to collect information (Education Department) and disseminate information (Publication Department) on the safe installation and use of electricity. Our representatives on code panels provide valuable information and insight on the code changes that is used by the Education Department to compose the text for the books. The Publication Department does an excellent job of editing and laying out the text and illustrations to produce an award-winning IAEI News and other technical books. This work does not just happen. Talented people are necessary and proper support in the form of advanced computers and software is required.
To represent the electrical inspector in the national and international arena and to cooperate with national and international organizations, the IAEI joins with others on the United States National Committee to represent the U.S. on the International Electrotechnical Commission (IEC).
Of course all this requires a support staff in the Customer Service Department. With the turn-over in customer service personnel, we have had problems with errors with our database. This seems to be what most people notice first about the association. We must do something to keep staff longer so they will be more sensitive to the members’ needs and realize what it means when errors are made.
Other things are needed to support the carrying out of the objectives. We have an office building that we must keep up to protect the investment— new roof, maintenance, taxes, and utilities. Also legal fees are incurred to protect our intellectual properties and to keep us out of trouble in contracts and agreements we enter into with other parties.
When all things are considered, I believe when one stops and reflects on them, one can see that a $90.00 membership fee to belong and support the IAEI is still "The Best Bang for the Buck.” I also believe that you only get out of anything, what you put into it. So take advantage of Section, Chapter and Divisions meetings. Participate in the education programs provided or better yet share your knowledge with others through the IAEI!
Read more by James W. Carpenter
Posted By Underwriters Laboratories,
Saturday, March 01, 2003
Updated: Thursday, February 14, 2013
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Question: Light curtains on industrial machinery
Does UL List light curtains that are used on industrial machinery to prevent personal injury?
Yes, light curtains are Listed under the category Active Opto-Electronic Protective Devices (NIPF), located on Page 60 of the 2002 General Information for Electrical Equipment Directory (White Book).
In January 2002 UL published new standards for Electro-Sensitive Protective Equipment, UL/ ANSI 61496-1 and 61496-2. UL 61496-1 contains general requirements and tests for all Electro-Sensitive Protective Equipment; UL 61496-2 contains specific requirements for Active Opto-Electronic Protective Devices, otherwise known as light curtains.
Light curtains are commonly used in industrial settings for the safeguarding of machinery that presents risk of personal injury. Light curtains typically consist of an emitter/ receiver pair. The length of the light curtain, number of light beams and spacing of light beams may vary depending upon customer application. When one or more beams of light are broken, due to for instance a hand in a point of hazard zone, within milliseconds a signal is sent to shut down machine operation. Signal redundancy and continuous selfchecking are among the requirements for light curtains.
In addition to an evaluation for fire and electric shock hazards, light curtains undergo a stringent investigation of their safety-related performance features. This includes evaluations of software reliability, Failure Mode and Effect Analysis (FMEA), EMC immunity, and resistance to mechanical and environmental stresses.
Question: USE and USE-2
Are Type USE and USE-2 suitable for exposure to sunlight?
All UL Listed service entrance cables are required to be sunlight resistant as part of their UL Listing. Both the cable assembly and the individual inner conductors are sunlight resistant, and neither is required to be marked. This information is noted in the UL Guide Information for Service Entrance Cable (TYLZ) located on page 104 of the 2002 White Book.
As a side note, individual insulated conductors, such as THWN, that are not part of a service entrance cable assembly are not sunlight resistant, unless so marked, (i.e., "sunlight resistant”).
Question: Electric sign
Does each individual part of an electric sign require a "Section ____ of _____” marking?
A UL Listed sign may be shipped in sections only when the sections form a complete sign and complete instructions for field assembly are provided. Each major subassembly is required to bear an electric sign section marking.
For example, separate channel letters and remote neon power supplies are considered major subassemblies and each subassembly requires a section marking. Sign faces, trim and mounting hardware are not considered major subassemblies.
The "section” UL Label has changed. The UL Guide information was revised to require each section to bear an "Electric Sign Section” Listing Mark in lieu of the "Section _____ of _____” marking where each section of the sign was assigned a number. The Electric Sign "Section _____ of ______” Listing Mark is still acceptable until the stock is depleted.
Electric signs are Listed under the category, "Signs” (UXYT). The UL Guide Information can be found on page 105 of the 2002 White Book or visit the UL Online Certification Database atwww.ul.com/database.
Question: Shower lights
Are lights installed in showers required to have GFCIs?
UL Listed luminaries are evaluated for compliance with the Standard for Luminaires, UL 1598. The UL Standard does not require integral GFCI protection for luminaries. If the manufacturer’s installation instructions require GFCI protection in the installation, then Section 110.3(B) of the NEC would be applicable. Also note that for some special occupancies in Chapter 5, the NEC requires GFCI protection to be provided for the equipment in the installation. The UL Guide Information for luminaires (IETX) can be found on page 40 of the 2002 General Information for Electrical Equipment Directory (White Book).
It is important to note that combination ceiling-insert exhaust fan/lights are Listed under the product category Electric Fans (GPWV) and are required by the Standard for Electric Fans, UL 507, to be marked, "Acceptable for use over a bathtub or shower when installed in a GFCI protected branch circuit.” This information is detailed in the Guide Information for this category located on page 203 of the 2002 White Book. In this case, the UL Standard does not require integral GFCI protection in the product. However, the product must be marked to indicate that a GFCI protected branch circuit should be used to supply power to the product. Section 110.3(B) of the NEC is applicable.
Question: Listing mark on outlet box
Why isn’t the UL Listing Mark always required on an outlet box? I’ve seen the Mark on packaging, but once it’s discarded, it is difficult to verify Listing.
For some products, the UL Mark is on the smallest unit container. This is due to the size and/or shape of the products, which physically does not allow the UL Mark on the product itself. For outlet boxes, the UL Listing Mark is required on the product, or the UL symbol can be marked on the product and the complete Listing Mark of Underwriters Laboratories Inc. is marked on the smallest unit container. This practice has been in place for many years. This information is detailed in the UL Guide information for "Metallic Outlet Boxes” (QCIT) located on page 81 of the 2002 General Information for Electrical Equipment Directory (White Book).
For all UL Listed or Classified products, the Guide Information for each product category contains a description of how the product is to be marked to identify that the product is UL Listed or Classified under that product category.
UL Question Corner
Posted By Brian Haydon,
Wednesday, January 01, 2003
Updated: Thursday, February 14, 2013
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In Canada, CSA is one of four nationally accredited Standard Development Organizations (SDO) and publishes Canada’s electrical code and electrical product standards.
The Canadian Electrical Code (CE Code) is the governing electrical code for the majority of Canada, and consists of two parts. The CE Code, Part I establishes requirements for electrical work and the installation of electrical equipment operating or intending to operate at all voltages in electrical installations for buildings, structures and premises across Canada. The 2002 CE Code, Part I is the 19th edition of the code, and was first published in 1927.
Requirements for electrical equipment are included in a list of more than 500 individual product standards, collectively referred to as the CSA CE Code, Part II. CSA Part II electrical equipment standards include product specifications, test methods, design requirements, classifications, recommended practices and other requirements to which electrical products are certified in order to bear the appropriate certification mark in Canada.
Standards are living documents, continually revised and refreshed to address changing requirements and emerging technologies. Standards are reviewed at least every five years as part of this process of continual improvement.
Accreditation of a Standards Development Organization (SDO) is the formal recognition of their competence to develop standards, and comply with specific accreditation criteria as determined by the accreditor.
The Standards Council of Canada (SCC), a division of Industry Canada, a Federal Crown Corporation, has responsibility for co-ordination of the National Standards System (NSS) in Canada. To achieve and maintain accreditation, a SDO must adhere to the principles governing the consensus process used in Canada for the development of consensus standards. This includes, but is not limited to, undergoing a public review process and not being framed in such a way that it will act as a restraint to trade. Further, standards should be consistent with or incorporate appropriate international standards as well as pertinent national standards.
Anyone can come forward and request a standard. Often it is a consumer organization, trade/industry association or a government department, which has observed a need. The SDO then evaluates the usefulness of a potential standard in meeting the need and assesses the level of support in the community and industry.
In the standards development process, the SDO functions as a neutral third party, providing a structure and a forum for developing the standard. Standards are developed using committees created using a "”balanced matrix”" approach. This means that each committee is structured to capitalize on the combined strengths and expertise of its members— with no single interest group dominating. In CSA’s development process, under which the CE Code, Parts I and II are developed, committees are divided into distinct interest groups including producers, regulatory authorities, end users and general interest.
The standards development process requires the technical committee to consider the views of all participants and develop the details of the standard by a consensus process, which includes the principles of inclusive participation, and respect for diverse interest and transparency. Substantial agreement among committee members, rather than a simple majority of votes, is necessary. When a draft standard has been agreed upon, it is submitted for public review, and amended if necessary.
The CE Code, Parts I and II, as well as all other standards facilitated by CSA, are developed by sub-committees and technical committees, consisting of recognized experts, who volunteer their time, resources and efforts to the standards development process.
Input on changes and maintenance of the CE Code Part I come from forty-two subcommittees each representing a section of the CE Code Part I. Using a similar process, over five hundred CE Code Part II product standards have been developed and maintained over the last 70 years. The present committee hierarchy includes five CSA technical committees, supported by 224 CSA technical subcommittees with over 1,200 voluntary members.
In accordance with the National Standards System, a consensus development process is followed to create and maintain CSA Part II electrical equipment standards. This process is used in the development of new standards, amendments to standards or new editions. Because of the immense size and scope of the CE Code Part II, each standard is identified as a project, with a schedule established and monitored by a CSA-assigned project manager. Time to completion is dependent on member commitment to the task, available resources, and the need to move the project through defined stages of development. The flow, followed for each project, is shown in the following diagram.
The complete process is described in eight stages.
To begin, a request for the development of a new standard, new edition or amendment, may come from any interested person, organization or committee. At the preliminary stage, an evaluation is conducted and the project submitted for authorization. The evaluation determines if the product and process selected, for example, an amendment versus a new edition, will be an appropriate solution to the problem. In addition, the result must have value for the stakeholders, and the result must be achievable. After a defined evaluation process, a decision is reached on whether the project can proceed.
Organizations, industries, regulatory authorities, etc., that have been identified as having an interest in the project are requested to participate. To complement this, a public notice of intent is made to improve input early in the process. This provides unidentified stakeholders the opportunity to request to participate, to offer comments, or keep abreast of the progress of a project.
Assignment of the project to an appropriate CSA Technical Committee (TC) is made at this stage. For the CSA electrical program, the six established CSA TCs are Wiring Products, Industrial Products, Consumer and Commercial Products, General Requirements, International Standards, and Fuel Cell Technologies. Each TC receives strategic leadership from the Strategic Resource Group (SRG), a steering committee for electrical standards development, and policy direction from the Standards Policy Board (SPB). The SPB, SRG and TC(s) committees are balanced, with voting members maintained within a minimum and maximum range, in defined categories, for example, regulatory, manufacturer and general interests. Each TC may assign detailed technical work to a Technical Subcommittee (TSC), while maintaining responsibility for formal approval of a standards technical content.
In the preparatory stage, the items considered are harmonization, copyright, resources to develop a working draft, and the project schedule.
Harmonization:A recommendation on harmonization may occur at an earlier stage. This issue is now given full consideration. First preference is to harmonize with an international standard. For products in the electrical field, an IEC standard may be adopted. Minor technical deviations from the original IEC standard are allowed to satisfy Canadian needs. These may include unique conditions such as environment, government regulation, the electrical installation code, or industry practice.
Second preference, when not feasible or appropriate to harmonize with an international standard, is the development of a regional standard. This is a joint standard, typically tri-national or bi-national, formally approved and published by CSA and the SDO of one or more other countries. The CANENA (a Spanish acronym for Council for Harmonization of Electrotechnical Standards of the Nations of Americas) forum has been established in North America to facilitate the harmonization of standards and promote the reduction of non-tariff trade barriers for electrotechnical products between Canada, Mexico, and the United States of America. Currently, there are over 40 CANENA Technical Harmonization Committees. Their role is to help facilitate the development of harmonized seed documents for consideration by each country and its participating SDO. In August 2000, the first tri-national harmonized series of standards in the electrical sector, CSA C22.2 No. 248.1 – 248.16 (Low-Voltage Fuses) was published by the participating SDOs and is recognized in all three countries. Currently, CSA has published 25 bi- and tri-national electrical standards where the harmonized seed document was developed within the CANENA forum.
Third and least used for electrical products, a national standard unique to Canada would be established, where no standard exists elsewhere.
Copyright:At stage 2, copyright issues are addressed. The Standards Council of Canada has been granted copyright control within Canada for standards of the IEC. In turn, the Standards Council of Canada can permit these rights to be used by CSA for developing National Standards of Canada. A National Standard of Canada (NSC) is a consensus standard prepared by an accredited standards-development organization and where the development process has been approved by the Standards Council of Canada.
For regional standards, an existing standard from another standards-development organization may be used as a start point. For such material, copyright agreements are established or reaffirmed at this stage.
Resources:With the aid of a CSA-assigned project manager, preparation of a working draft can now begin in accordance with CSA Directives and guidelines through the TC, a subsidiary committee(s), or a single technical expert. A subsidiary committee may be a task force, or as indicated earlier, a technical subcommittee (TSC).
Project schedule:CSA staff, in consultation with the TC, establish target dates for key milestones, including public and internal review, TC approval, final edit, and publication. A schedule is formed at this stage to ensure the availability, on a timely basis, of needed resources to advance the project.
The committee stage involves the development of technical content of a draft. CSA technical subcommittees for specific electrical product sectors are well established, providing balanced expertise to prepare a draft on a consensus basis. For regional electrical standards, a CANENA technical harmonization committee (THC) may prepare the draft, prior to review by a CSA TSC or TC. The THC typically will include selected members from the corresponding CSA TSC, as well as technical experts from the other participating countries.
The technical content of a draft is developed at meetings (either in person or by video/teleconference), by correspondence, or by electronic means. Internet-based meeting methods are now appearing, providing a combination of teleconferencing with PC-based Internet access to the draft under development. Using this method, committee members can provide input, without the necessity of travel, while one person controls and updates the draft in real time.
During development, consideration is given to corresponding international activity, including relevant international documents and the work of the Canadian Subcommittee for IEC, where one exists. In the electrical safety sector, integration of CSA technical subcommittees with Standards Council of Canada, Canadian Subcommittees to the IEC is a current initiative underway at CSA.
All decisions regarding technical content are determined by consensus. Consensus on the technical content, which is the responsibility of the TC, is confirmed by letter ballot or recorded vote.
At this stage, the draft is offered to the public for review and comment. The comments are then passed on to the appropriate committee for consideration, and if the draft is subsequently revised, the draft is re-circulated to the committee.
An internal review of the draft by CSA staff verifies compliance with CSA policy, format and editorial style. This is to ensure that all users of the standard will be able to reach a common understanding of its contents.
First phase:The TC approves the technical content by letter ballot or recorded vote. The criterion for approval asks the questions, are the technical requirements reasonable and justifiable considering the state of the art in the particular field? Does the draft meet the defined need, and is the scope of the draft consistent with the technical requirements included?
For approval, defined numerical requirements for voting must be met, negative votes must be suitably dispositioned, and comments must be considered.
Second phase:In the first phase, the approval of technical content by the TC is final. The second phase, Second Level Review, is a strict procedural review by an internal CSA committee to verify that all required steps during development have occurred in accordance with CSA Directives and guidelines.
Completion of the previous stage is a prerequisite to proceeding with publication. When this stage is reached, a final edit by CSA staff verifies conformance with applicable editorial requirements. Then the standard is published. CSA Part II electrical equipment standards are available in a number of formats, including hard-copy text, PDF files (on-line) and CD-ROM.
The final standard may be voluntarily adopted for use, or may be referenced in legislation. Additionally, if in compliance with Standards Council of Canada requirements, CSA is authorized to publish the standard as a National Standard of Canada.
The standard is maintained with the objective of keeping it up-to-date and technically valid. The same consensus development process as defined earlier, if required, develops amendments or new editions. A systematic (five-year) review of all CSA Part II standards is made, and reaffirmed as written, or a new edition, if appropriate, is produced.CSA CE Code, Part II standards provide the product requirements for certification of electrical equipment in Canada. Only products bearing one of the marks or labels applicable for Canada, from an accredited certification organization are normally considered approved by Canadian regulators, within their authority and jurisdiction to approve electrical products.
For harmonized standards that are regional or international, national differences applicable strictly to Canada, if any, appear within the Part II standard. Products bearing one of the marks or labels, applicable for Canada, indicate approval for use in Canada through compliance with the Part II standard, and must include compliance with any requirements for national differences for Canada.
CSA International, a division of CSA Group that offers global conformity assessment services, is an OSHA-accredited testing laboratory in the United States. Electrical inspectors accept products certified by CSA International to U.S. standards if they are adorned with the CSA/US certification mark.
In summary, for Canada a list of CSA Canadian Electrical Code, Part II, Safety Standards for Electrical Equipment appears in Appendix A of the CSA Canadian Electrical Code, Part I. Each of these electrical equipment standards have been developed and maintained, using CSA’s consensus standards development process.
Read more by Brian Haydon
Posted By George Gregory,
Wednesday, January 01, 2003
Updated: Thursday, February 14, 2013
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Arc-fault circuit interrupters (AFCIs) have just become required for installation in residences under the 2002National Electrical Code(NEC). Not surprisingly, questions have been raised regarding their application and even the need for them. There have been marketing pitches, technical opinions and, quite frankly, intentional misinformation floating around various industry channels. The intent of this article is to bring out the truth about what AFCIs are and what they are not.
This is Part I of a two-part article produced to directly address some of the questions and the misinformation about AFCIs. Part I focuses on the technology, the AFCI product standard and what the NEC is written to accept. Part II will focus on questions related to application and installation in accordance with the NEC.
Contrary to popular belief, AFCIs are not "new.” They are certainly in their infancy relative to many products, but they are not new. Square D began research in this area in the late 1980s and early 1990s; at about the same time the Consumer Product Safety Commission identified a concern with residential fires of electrical origin. A large number of these fires were identified to be in the branch-circuit wiring system.
The need for AFCIs became more apparent as the Electronic Industries Association (EIA) initiated a project and ultimately code proposals to the 1993 NEC to change the instantaneous trip levels of 15 and 20 A circuit breakers. EIA had studied the issue of arcing fires and determined that some level of additional protection from effects of arcing faults would be beneficial. EIA attempted to improve protection by requiring that the instantaneous trip level of a circuit breaker be reduced to the 85 A level. However, it became clear that lowering the instantaneous levels below the minimums already in the market would result in nuisance operation of the circuit breaker due to inrush currents.
The CPSC study and the EIA efforts led to the first proposals to require AFCIs during the revision cycle to create the 1999 NEC.
Figure 1. 210.12, Arc-fault Circuit-Interrupter Protection
NEC Code-making Panel 2 (CMP-2) was presented with numerous proposals ranging from protection of basically all 15- and 20-A circuits in dwelling units to protection of living and sleeping areas. After listening to many presentations, reviewing large amounts of data, conducting extensive discussions and giving consideration to the issues, CMP-2 concluded that AFCI protection should be required for branch circuits that supply receptacle outlets in bedrooms. The panel placed an effective date of January 1, 2002, for the requirement to become effective. CMP-2 members unanimously passed this action. Subsequently, the requirement was retained in the 2002 NEC with enhancements.
The Need for Arc-Fault Protection
Just as we only need a smoke alarm or a circuit breaker when a problem occurs, we also only need AFCI protection when a problem occurs—then we really need it. A fuse or circuit breaker cannot detect hazardous arcing current that is below its time-current opening characteristic. Arcing faults are frequently below the characteristic. The data on fire origin shows the need for this protection.
A recent report by the National Association of State Fire Marshals states:
According to the National Fire Protection Association and the National Fire Incident Reporting Sys- tem data, during the five-year period from 1994- 1998, there were an average of 73,500 total electrical fires annually, which were responsible for 591 Deaths, 2,247 injuries, and property damage totaling $1,047,900,000. The electrical problems that lead to these fires went undetected by conventional circuit breakers. Of these 73,500 electrical fires, 60,900 or 82% were caused by arcing and not by overloads or short circuits. 1
It may not be realistic to expect AFCIs to detect 82 percent of the conditions that cause fires from electricity and the cited report does not expect that. However, the conclusion indicates the high percentage of cases in which at least one authoritative source finds arcs to be a fire cause worthy of attacking. The AFCI does just that and does it effectively.
AFCIs address a real cause of home fires. Below is a list of reported incidents in which AFCIs detected arcing conditions that could have developed into fire causes.
- An appliance plug damaged by impact repeatedly caused tripping of the AFCI until the problem was discovered. When the appliance cord was replaced, no further tripping of the AFCI occurred.
- A room air conditioner that had developed a defect tripped the AFCI. The performance of the AFCI was questioned until the offending appliance was discovered and disconnected. The AFCI continues in service with no further tripping.
- An AFCI installed in a new building tripped repeatedly until damage caused by a nail through insulation was discovered and corrected.
- An AFCI installed as a retrofit in an older building tripped as soon as it was turned on. The installing electrician found the problem with extensive evidence of arcing in an old lighting fixture.
- Another damaged lamp with line-to-ground arcing was found when an AFCI was installed in an existing circuit. The AFCI tripped when the circuit was first energized after the installation.
- An AFCI tripped when retrofitted into an existing circuit. Examination of the circuit disclosed that wire insulation had burnt back exposing bare conductors near their connection to a receptacle. The exposed wires had been arcing through the charred insulation. It appeared that heat from a loose connection at the receptacle had caused the wires to burn back.
Table 1. Table 1 briefly compares the capabilities of the three types plus the outlet branch circuit AFCI.
As you might guess from that list, the greatest number of fires from electrical causes is in homes ten years old and older where changes have been made to electrical circuits by various owners and where insulation is deteriorating with age, use and misuse. However, fires from electrical arcs are recorded for residences of all ages. Besides, all homes become older homes. If the protection is not present before they age, they will remain unprotected as they age.
NEC 210.12 Requirement
NEC 210.12 defines an AFCI as "a device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected.” The AFCI has two basic functions, which are recognizing arc characteristics and de-energizing the circuit when it recognizes them. There is no protection unless the source of voltage is disconnected from the hazard, once the hazard is detected.
The requirement of 210.12(B) states, "All branch circuits that supply 125-volt, single-phase, 15- and 20-ampere outlets installed in dwelling unit bedrooms shall be protected by an arc-fault circuit interrupter listed to provide protection of the entire branch circuit.”
This requirement in the 2002 NEC reads the same as that in 1999, except for two points. First, "outlets” read "receptacle outlets” in 1999. The change indicates that CMP-2 intended that all fixed wiring be protected. The protection extends also to extension and appliance cords. Second, the word "entire” is added, again indicating the intention to protect the fixed wiring of the entire branch circuit.
The only devices covered by the UL 1699 Standard for Arc-fault Circuit Interrupters that also satisfy these NEC requirements are the branch/feeder and combination AFCIs, when they are installed at the source of the branch. The branch/feeder AFCI is the circuit-breaker type that has been the topic of discussion since the AFCI was first proposed for the 1999 NEC. Branch/feeder AFCIs are listed by at least four manufacturers and are readily available. A combination AFCI has not yet appeared commercially, but at least two manufacturers have mentioned development of them.
There are six devices covered in UL 1699, three of which are defined there as follows:
Branch/feeder AFCI — A device intended to be installed at the origin of a branch circuit or feeder, such as at a panelboard. It is intended to provide protection of the branch-circuit wiring, feeder wiring, or both, against unwanted effects of arcing. This device also provides limited protection to branch-circuit extension wiring. It may be a circuit-breaker type device or a device in its own enclosure mounted at or near a panelboard.
Outlet circuit AFCI — A device intended to be installed at a branch-circuit outlet, such as at an outlet box. It is intended to provide protection of cord sets and power-supply cords connected to it (when provided with receptacle outlets) against the unwanted effects of arcing. This device may provide feed-through protection of the cord sets and power-supply cords connected to downstream receptacles.
Combination AFCI — An AFCI which complies with the requirements for both branch/feeder and outlet circuit AFCIs. It is intended to protect downstream branch-circuit wiring and cord sets and power-supply cords.
Definitions of the cord or portable AFCIs or the leakage-current detector-interrupter are not provided here because they are for specialized applications and are not intended for general protection of branch circuits.
Table 1 briefly compares the capabilities of the three types plus the outlet branch circuit AFCI.
This table, together with the definitions, is intended to help clarify the differences between these three types. So far, only the branch/feeder AFCI has been offered commercially, to the knowledge of the authors. It is the commonly available AFCI in circuit-breaker form. The outlet circuit AFCI is intended for protection of extension and appliance cords. It could also be produced in "feed through” form to protect fixed wiring on its load side. Located at a receptacle outlet, it would not protect the entire branch and would not satisfy the NEC 210.12 requirement.
The combination AFCI is intended to combine the performance of the other two in a single device. Its location is not specified in the definition; however, it can be configured in a form, such as in a circuit breaker, to be located such that it will protect the entire branch circuit, including fixed wiring plus extension and appliance cords in accordance with the UL 1699 Standard.
Branch/feeder AFCI Performance
One of the major reasons for development of AFCI technology is that a number of fires are caused by arcing short circuits in fixed wiring that are not detected by an overcurrent protective device before the fire starts. An overcurrent protective device (a circuit breaker or fuse) has an intentional time delay to allow for elevated current such as would be experienced when operating a microwave oven or starting a vacuum cleaner motor. In other words, when starting a vacuum cleaner, the elevated current is essential and is contained within the conductors. When the current is an arc, it is causing damage continuously. The AFCI distinguishes between the hazardous arc and normal current flow.
As discussions of a standard began in 1994, a rough but scientific experiment was conducted to determine the time and current within which an arc will ignite tissue paper. It was found that arcs above 5 amperes were likely to cause fire ignition if they persisted for a second and those below 5 amperes were much less likely to cause fire. Since then, other experiments have been conducted that suggest that fire can be ignited with lower current levels, but none have been definitive.
The branch/feeder AFCI was the first type to be developed. The intention was to protect branch-circuit wiring primarily and to also provide protection for extension and appliance wiring to the extent it could. The 5-ampere level was found to be difficult to achieve in line-to-neutral arcing at the time AFCIs were first developed, since it is essential to also avoid nuisance operation for the broad range of signals in electrical circuits. In any general-use branch circuit, a variety of dimmers, computers, motors, entertainment appliances and other equipment that produce arcs as part of normal operation may be installed or connected. The 5-ampere detection requirement was set for series arcs that include arcing to grounded conductors.
The 75-ampere level was taken from a survey conducted by UL for the EIA that reported that the lowest short circuit level available at a receptacle within the United States is 75 amperes. This means that a line-to-neutral fault in a branch circuit will have 75 amperes or more available. Correspondingly, AFCI testing verifies that the AFCI will detect an arc in a circuit with 75 amperes available. Therefore, the 75-ampere detection level will identify and de-energize arcing short circuits that are known fire causes.
During the tests, actual current flowing is somewhat less than 75 amperes. The test circuit has 75 amperes available before the arc is introduced. The arc current will be lower because of the impedance of the arc itself. The AFCI must detect the arc current.
Questions have arisen about the ability of the branch/feeder to detect series arcs. The UL 1699 Standard requires that the branch/feeder detect arcs in circuits that deliver 75 amperes and higher fault current. It does not distinguish between series and parallel. These are short-circuit conditions—and are the conditions that drove the industry to develop arc detection. We know that fires occur from these higher energy arcs. This means that true series arcs with no arcing to a grounding conductor, which are at load current values well below 75 amperes, are not detected.
Outlet Circuit AFCI Performance
In considering a device located at the receptacle, it was clear as the standard was being written that the primary function of such a device would be protection of extension and appliance wiring. Detection of series arcs at the lower current level of a single appliance would be important. The device was envisioned to be electrically closer to the appliance and not necessarily in the circuit with the variety of products and conditions on a general branch circuit. Therefore, for the envisioned outlet circuit (OC) AFCI, a 5-ampere detection level was required in the standard for line-to-neutral, line-to-ground and series arcs.
There is a place for each of these devices. As we look at the need addressed by NEC 210.12(A), a branch/feeder AFCI is necessary to protect the entire circuit. Protection would be enhanced if an outlet circuit AFCI were added for extension and appliance wiring.
The ideal device is the combination AFCI located at the source of the branch. The combination AFCI combines the performance of the branch/feeder with that of the outlet circuit in a single unit. With the technology available, why not require combination performance to provide the best available protection for the entire branch?
Causes of Tripping of the Branch/Circuit AFCI
The circuit-breaker branch/feeder AFCI incorporates functions of both an overcurrent protective device and an arc-detection device. It is designed to trip under the following conditions.
Overcurrent.For any current above its current rating it will trip according to its circuit breaker time-current characteristic.
Hazardous arcing.For arcing at current levels of about 75 amperes and above, the AFCI will trip. Commercially available AFCIs will actually operate at some level below 75 amperes. The AFCI will operate faster than a fuse or circuit breaker under short-circuit overcurrent conditions up to about 125 amperes.
Arcing ground faults.The standard requires tripping on faults of 5 amperes and greater. Commercial units will actually detect ground faults of 50 milliamperes and greater. Tripping will be instantaneous, with no intentional delay.
Neutral grounding.If the neutral conductor (grounded-circuit conductor) of an AFCI protected circuit touches grounded metal, the AFCI will trip if the impedance to ground is very low impedance.
Abnormal environments.Some abnormal events may also cause tripping, such as high voltage surges from lightning or utility line surges, voltage or frequency fluctuations from poorly regulated backup generators, or mechanical shock.
More To Come
Part II of this article addresses such questions as which circuits must be protected under the NEC and how to check and troubleshoot installed AFCIs. Look for these questions in the next edition of this magazine.
1. "AFCI Inquiry and Report” by the Consumer Product Safety Task Force of the National Association of State Fire Marshals, August 1, 2002.
Read more by Alan Manche
Posted By Michael Johnston,
Wednesday, January 01, 2003
Updated: Thursday, February 14, 2013
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The purpose of electrical codes is practical safe guarding of persons and property from the hazards associated with electricity. Numerous prescriptive requirements address safety from the minimum standpoint. Codes and standards are the minimum rules for electrical safety, so one can easily surmise that for electrical safety one must do at least what is required by the codes.
Many rules in the codes require installation of protective devices and equipment to be in place for the user and occupant long after the final electrical inspection and certificate of occupancy (C of O) is issued. One type of protective equipment for use by the occupant and by service personnel is the disconnecting means required for electric motors and air-conditioning or refrigeration equipment. There are also rules for service disconnects, disconnects for appliances, electric signs, and other equipment throughout electrical codes. This article takes a close look at the minimum requirements for locations of safety disconnects for motors and air-conditioning equipment as specified in NEC Articles 430 and 440.
The primary purpose of the Code is safety. Compliance with minimum Code rules will generally result in an electrical installation that is essentially safe and free from hazards to persons and property. More specific to motors and air-conditioning equipment, the Code requires a necessary safety disconnecting device for workers and building occupants to remove the electrical power during service operations and also to be able to disconnect the equipment in emergency conditions, such as electrical fires or explosions associated with the equipment. With electrical events or problems, such as explosions or mechanical failures, the natural reaction is to disconnect the power as soon as possible. The disconnecting means required for motors and equipment falling under the scope of Articles 430 and 440 are safety disconnects. In the interest of safety for anyone who may need to react swiftly to adverse conditions or situations, electrical design and installation should not take the location of disconnects lightly. In the electrical field it is vital that safety be first priority, always.
Disconnect Locations for Motor Controllers
Article 430 includes the minimum requirements for electrical motors. Provisions for locations of motor disconnects are included in 430.102. There are two components of Section 430.102, the controller in 430.102(A) and the motor in 430.102(B). Let’s look at the controller first. Section 430.102(A) requires a disconnect in sight from the controller and it must disconnect to be located in sight from the controller and it shall disconnect the controller from the source. A closer look at the definition of the term in sight from is in order here; by definition, it means that one component can be seen from the other and the distance between must not exceed 15 m (50 ft). The disconnecting means must be visible from the motor and equipment. Visible through a glass partition or window does not meet the requirements of this section (see figure 1).
Section 430.81 indicates clearly that the controller is the device that starts and stops the motor, by making nd breaking the motor-circuit current. An example of a controller is a combination magnetic motor starter. Controllers require servicing from time to time and the required disconnect is a means of safety for the worker performing those service operations. The disconnect also serves to allow compliance with the general provisions in OSHA 1910.333, one of which requires electrical equipment to be worked on while de-energized. Of course during some troubleshooting and testing procedures, the equipment will be required to be worked while energized, and the qualified service person then must wear the appropriate personal protective equipment to provide a reasonable level of protection should an arc flash or arc blast event occur (see OSHA 1910.335 for additional information about personal protective equipment). Some requirements for disconnecting means locations in the OSHA Standards also are similar to what is required in NEC 430.102 and 440.14 (see OSHA 1910.333) for information about lockout and tagging procedures for safety). This article focuses primarily on the rules of the NEC, but compliance with installation rules found in the Code often results in conformance to OSHA provisions also. Knowledge of all possible applicable standards results in increased safety relative to the electrical installation and also assists with worker safety.
The disconnect ahead of the controller allows safe replacement of overloads, fuses, worn contacts, and so forth. Most individual combination magnetic motor starters or starters that are part of a motor control center include both the controller and the disconnect within the same enclosure. Compliance with 430.102(A) is inherent to these types of combination controllers that include both the disconnect and the controller as an assembly. Disconnects and motor controllers can also be installed as individual units and must be located with respect to the provisions of 430.102(A).
Disconnect for Motor(s) and Driven Machinery
Requirements for the motor and driven machinery disconnect(s) are found in 430.102(B), which stipulates that the disconnecting means to be located within sight from the motor and driven machinery location (see photo 1). The disconnect that is provided to meet the requirements of 430.102(A) can also serve as the disconnect for the motor if it is located within sight from and not at a distance greater than 15 m (50 ft) from the motor and equipment. At least one of these disconnects is required to be readily accessible in accordance with 430.107 (see figure 2).
This disconnect is a safety device and provides reasonable protection for personnel that may be servicing the motor or the equipment driven by the motor. Service personnel are able to visually monitor the safety disconnect when it is located in accordance within the limits of the in-sight-from rule.
Two exceptions permit the motor disconnect required in 430.102(B) to be located out of sight from the motor and driven machinery location. These provisions are worth a closer look as this alternative is limited and has become even more restrictive by recent changes to NEC 2002.
The first exception allows the disconnect to be located remote (out of sight) from the motor and equipment in installations or systems where locating the disconnect in sight from the motor is impracticable or introduces additional increased hazards to persons or property. Although this is generally in the judgment of the AHJ, the revision in this section gives a clearer indication of what is intended by the rule in the first place. Some examples are also provided of situations where the location would be impracticable. This information is helpful to designers as well as installers.
The second exception to this disconnect rule is intended to be applied to industrial installations under controlled conditions: (1) that qualified persons service the installation, and (2) written safety procedures are in place. Another fine print note provides guidance and direction to NFPA 70 E (Standard for Electrical Safety Requirements for Employee Workplaces), which includes information about acceptable lockout/tag out procedures. If the installation can meet the restricted conditions set forth in this exception, the disconnects can be remotely located but must be individually capable of being locked in the open position. The provisions for the locking means must be permanently installed on or at the switch or circuit breaker used as the disconnecting means. Portable types of lockout devices are no longer acceptable under this provision (see figure 3).
Air-conditioning and Refrigeration Disconnecting Means
Requirements for air-conditioning equipment disconnecting means are found in 440.14 and 440.13. The requirements and reasons for the disconnects at air-conditioning and refrigeration equipment are basically the same. The decision whether or not to use the rules in Article 440 rather than Article 430 is related to the type of motor employed within the equipment.
Basically, if the motor or equipment incorporates a hermetic refrigerant motor compressor, then the rules in 440.14 apply. Both types of motors are used with air-conditioning and refrigeration equipment and systems, so it is important to establish which Code article and rules apply for a given installation (see photos 2 and 3).
If the air-conditioning equipment incorporates or is driven by a standard motor, meaning a motor that is not hermetically sealed, then the rules in 430.102 have to be applied. It is helpful to visit the definitions in 440.2 for additional clarification on hermetic refrigerant motor compressors. Section 440.3(A) clearly indicates that if the equipment does not have a hermetic refrigerant motor compressor, then 440 does not apply and reference is made back to Articles 422, 424, or 430 as applicable. An example of refrigeration equipment falling under the scope of Article 430 is the typical fan coil unit installed in a walk-in refrigerator or freezer. The disconnecting means would need to be provided for such equipment in accordance with 430.102 (see photo 4).
If the air-conditioning or refrigeration unit falls under the scope of Article 440, the disconnecting means location requirements of 440.13 or 440.14 would apply.
Cord and Plugs as Disconnects
Section 440.13 includes the disconnect provision for room air-conditioners and similar utilization equipment where cord and plug connection can serve as the required means of disconnect. Section 440.63 places a within-sight-from requirement for the disconnecting means for room air-conditioners, and also requires it to be readily accessible from the unit. Section 440.64 also places length limitations on cords of room air-conditioners that are related to the voltage rating of the unit (see figure 4). For 120-volt room air-conditioners, the length of cord must not be longer than 3.0 m (10 ft); and for 208- or 240-volt rated room air-conditioners, the length of cord is limited to not longer than 1.8 m (6 ft).
Section 440.14 includes the disconnect location requirements for air-conditioning and refrigeration equipment in types other than those that are cord- and plug-connected.
The requirements are relatively straight-forward and simple. The disconnecting means must be located within sight from and also readily accessible from the equipment it supplies (see figure 5). Readily accessible is defined in Article 100 as "Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth.”
It should be clarified that the wording in 440.14 requires ready access from the equipment. This is slightly different and more restrictive than the rules in 430.102. The disconnect is permitted to be located adjacent to the equipment. Generally, disconnect switches have a height limit of not greater than 2.0 m (6 ft 7 in.) above the floor or working platform as indicated in 404.8(A). Exception 2 to 404.8(A) relaxes this requirement and allows greater heights to meet the provisions of 440.14 for these types of equipment. Examples of applications using the exception to the height limitations are heat pumps installed in hollow spaces above suspended ceilings. The disconnect is permitted to be installed on or within the equipment; and where it is installed on the equipment, it must not obstruct access panels that are removable for servicing (see photo 5).
Two alternatives are allowed by exception to this basic rule in 440.14. One exception refers to the cord- and plug-connected equipment as specified in 440.13, and the other exception is applicable to controlled conditions in industrial applications. In order to qualify for the alternatives in the exception, the refrigerating or air-conditioning equipment must be essential to an industrial process in a facility that includes conditions of maintenance, and the supervision available to ensure that only qualified persons service the equipment. In these cases, a disconnecting means within sight from the equipment shall not be required. Where the disconnecting means normally required by 440.14 is located remotely from the equipment in accordance with the provisions of the exception, it must capable of being locked in the open position (see figure 6).
It is best in electrical design to start with the rules and not the exceptions. It seems as though over several code cycles, the alternatives allowed by the exception to the required disconnecting means for motors and air-conditioning equipment have been incorporated into design. These disconnects ensure safety for personnel and property, and should not be eliminated for reasons other than those specifically included by the exception to the main rule. Some requirements in the OSHA Standards also are similar to what is required in NEC 430.102 and 440.14 [see OSHA 1910.333 for additional information]. Always consult the local AHJ if there are any doubts or if there are any local codes or regulations that require clarification.
Read more by Michael Johnston
Posted By David Young,
Wednesday, January 01, 2003
Updated: Thursday, February 14, 2013
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After completing the soil resistance measurements at the proposed substation site, the next step is the development of a mathematical equivalent soil model that is a good approximation of the actual soil resistance data. The most common models are the uniform soil model and the two-layer soil model. The uniform soil model should only be used when there is very little variation in the average resistivity with position and depth. The average resistivity referred to in IEEE Standard 81-1983 is the same as the apparent resistivity referred to in IEEE Standard 80-2000. Further discussion of the uniform soil model can be found in Clause 13.4.1, page 56 of Std. 80. More commonly, the resistivity varies greatly with depth. The following plot of soil resistivity versus rod spacing is a more typical example of soil resistance variation with depth. [See Figure 1]
There are three ways to develop the two-layer model. Clause 13.4.2, page 57 of Std 80, describes a graphical method for approximating a two-layer soil model. Appendix B, page 38 of Std 81, presents a mathematical method for determining the two-layer soil model. The mathematical method described in Appendix B is the basis for several computer programs that can be used to develop a two-layer soil model that best fits the resistance data. One such program is available from the Electric Power Research Institute.
Clause 16.4, page 88 of Std 80, presents a step-by-step procedure for the design of a substation grounding system. The forty design parameters, which must be calculated to verify the design meets the safety requirements of Clause 4, are listed in Table 12, page 89 of Std 80. Annex B, page 129 of Std 80, presents sample calculations. Computer programs based upon Std 80 and 81 are also available to do most of the calculations.
Read more by Leslie Stoch