In the 1958 edition, calculations were similar to the calculations of today with the main difference in the calculations being the basic load. The basic load covering lighting and convenience outlets was 3,500 W for a residence with a living area up to 500 ft² (46.5 m²). For a residence with a living area over 500 ft² and up to 1500 ft² (139.4 m²), the basic load was 4,500 W with an additional 1000 W for each 1000 ft² (93m²) or portion thereof. The 1958 basic load requirements stayed the same until the twelfth edition dated 1975 when the basic load was increased to the requirements of the current code.

Rule 8-200 of the 2012 CE Code covers load calculations used to determine the minimum feeder or service size for single dwelling units. To start off, we should establish what a dwelling unit is. Section 0 defines a single dwelling unit as "a dwelling unit consisting of a detached house, one unit of row housing, or one unit of a semi-detached, duplex, triplex, or quadruplex house,” and a dwelling unitas "one or more rooms for the use of one or more persons as a housekeeping unit with cooking, eating, living, and sleeping facilities.” Subrule (1) of Rule 8-200 is divided into two items (a) and (b). Item (a) details the specific criteria for calculations and Item (b) mandates the absolute minimum allowable ampacity of the service or feeder size – based on the floor area. 100 A is required by the Code where the floor area of the single dwelling, exclusive of basement floor area, is 80 m² (861 ft²) or more, and 60 A is the minimum permitted service/feeder ampacity – where the floor area of the single dwelling, exclusive of basement floor area, is less than 80 m². Item (a) is further divided into seven items (i) to (vii).

Items (i) and (ii) detail a basic load for the dwelling unit. This basic load includes 120 V 15- and 20-amp convenience outlets, lighting loads and motor loads rated up to 1500 W. The basic load for the dwelling unit is 5000 W for the first 90 m² (968 ft²) of living area plus an additional 1000 W for each 90 m² or portion thereof in excess of 90 m². The living area is determined as 100% of the ground floor, 100% of any area used for living purposes on the upper floor, plus 75% of the basement area of the dwelling unit.

The next step in Item (iii) is to add the electric space-heating and air-conditioning loads. Where it is known that the installed electric space-heating and air-conditioning loads will not be used simultaneously, the larger of the electric space-heating load or the air-conditioning load is added to the base load. For electric space-heating systems consisting of electric thermal storage heating, duct heater, or an electric furnace, the connected heating load is calculated at 100% of the equipment ratings. Where the electric heating installation is provided with automatic thermostatic control devices in each room or heated area, the electric space-heating load is 100% of the first 10 kW of connected heating load plus the balance of the connected heating load at a demand factor of 75%.

Photo 2. A 11 kW electric range used in the article example

The next loads to add are any electric ranges.Item (iv) allows 6000 W for a single range to be added to the basic load provided the range does not have a rating in excess of 12 kW. In the event the electric range is rated more than 12kW, 40% of any amount exceeding 12 kW will need to be added as well.

Now we add water heaters. Item (v) indicates any electric tankless water heaters or electric water heaters for steamers, swimming pools, hot tubs, or spas are added to the basic load at 100% of equipment ratings.

Item (vi) is new for the 2012 CE Code and requires that any electric vehicle charging equipment loads also be added to the basic load at 100% of equipment ratings.

The final step in Item (vii) is to add any additional loads at 25% of the rating of each load with a rating in excess of 1500 W if an electric range has been provided for, or 100% of the rating of each load with a rating in excess of 1500 W up to a total of 6000 W plus 25% of the load in excess of 6000 W if an electric range has not been provided for.

Photo 3. The nameplate of a 1500 W microwave oven

Photo 4. A 1500 W microwave oven used in the article example

As an example we will look at a 269 m² (2900 square foot) residence with the following loads:

• lighting load
• 4 small appliance branch circuits
• laundry circuit 1500 W
• natural gas heating
• air conditioner 6000 VA
• electric range 11,000 W
• hot tub 8000 W (2 hp motor)
• Level II electric vehicle charger 7200 W
• electric dryer 5000 W
• garbage disposal 800 W
• microwave 1500 W
• dishwasher 1200 W
• electric water heater 4500 W

Example Calculation:

The calculated load for the 2900 ft² (269 m²) single dwelling in this example is 173.1 amps.

The basic load is calculated based on the floor area of the single dwelling. The load for the first 90 m² is 5000 W, leaving 179 m² of floor area. The next 90 m² has a load of 1000 W, and an additional 1000 W for the remaining 89 m². The total basic load of 7000 W includes the lighting, convenience receptacles, small appliance branch circuits, laundry circuit, garbage disposal, and the dishwasher.

The heating of the single dwelling is a gas furnace and no electric heat is installed, leaving the 6000 W air-conditioning load added with a demand factor of 100%.

The electric range for this single dwelling is less than 12 kW providing a load for the calculation of 6000 W.

The 8000 W hot tub and the 7200 W electric vehicle charging equipment are now added with a demand factor of 100%.

Any additional loads with a rating in excess of 1500 W are now added with a demand factor of 25%. In this example, the additional loads over 1500 W are the 5000 W dryer and the 4500 W storage type water heater; 25% of the 9500 W gives us 2375 W to be added to the calculation.

Table 1. Summary of the single dwelling service load calculation

Now that we know the calculated load, we can determine the minimum service and conductor size. The ampacity of the load is 173.1 amps (41550 / 240 = 173.1). In most installations, the continuous load on a service is limited to the continuous load rating of the equipment being used. Subrule (3) of Rule 8-104 considers all loads continuous unless it can be shown that in normal operation the load will not persist for a total of more than one hour in any two-hour period for loads not exceeding 225 amp, or a total of more than three hours in any six-hour period for loads in excess of 225 amp. In the case of single dwelling units Subrule (2) of Rule 8-200 allows these loads to be considered as a non-continuous load for application of Rule 8-104. However, although Section 86 considers the EV charging equipment to be a continuous load, when this load is calculated for the purpose of defining the ampacity of a service in a single dwelling, such EV charging equipment load is not considered as continuous load, similarly to all other loads under this Rule. This means 100% of the calculated load for a single dwelling can be used to determine the service equipment ampere rating. For our 269 m² example a standard rating of 175 amp overcurrent device could be selected in the service box as the calculated load is 173.1 amp. Typically 175 amp rating of the overcurrent device will necessitate installation of the 200 A rated service box, as 175 A rating for the service fused disconnect or the service circuit breaker for residential installations is not available. In most cases a 200-amp service would be installed with a 175-A or 200-A trip setting or rating. Let’s consider that the trip setting of the service overcurrent device was selected at 200 A.

The size of the service conductors are now established using Rules 4-004, 4-006, and 14-104. As all distribution equipment presently available has a temperature limitation of 75⁰C, Rule 4-006 requires the allowable ampacity to be based on the 75⁰C column of either Table 2 or 4 for conductors installed in a raceway. The smallest 75⁰C conductor allowable ampacity from Tables 2 and 4 for the calculated load of 173.1 amp are 2/0 copper with an allowable ampacity of 175 amp, or 4/0 aluminum with an allowable ampacity of 180 amp.

Photo 5. The nameplate for a 1200 W dishwasher used in the article example

The next step is to verify the conductor selected meets the requirements of Rule 14-104. Rule 14-104 requires the overcurrent device to have a setting not higher than the allowable ampacity of the conductors being protected. Where the conductor allowable ampacity does not correspond with the overcurrent protection commercially available, Table 13 provides details on acceptable limits for over protection settings. Based on the fact that a 200-amp service will be installed with a main 200-amp trip setting for the breaker, Table 13 limits the conductor allowable ampacity to be not less than 176 amps. In the case of the copper conductors, the 2/0 copper conductor with the allowable ampacity of 175 amp is undersized. At this point some code users will try to apply "the 5% rule” in Subrule (1) of Rule 8-106 to the 175 allowable ampacity of Table 2. Subrule (1) of Rule 8-106 allows loads calculated in accordance with Section 8 to be within 5% of the allowable ampacity of the conductors selected. This means the 5% allowance can be applied to a calculated load. Applying the "5% rule to a conductor allowable ampacity table is a misapplication of Subrule (1).

Load calculations in the National Electrical Code have evolved over many decades. It was in the 1933 NEC that load calculation requirements began to resemble a format that the modern code user would find familiar. Since then, many things have changed, but the primary requirement remains the same — service equipment and conductors must be sized to handle the expected load.

Article 220 of theNational Electrical Code lays out the primary requirements for performing load calculations that are necessary for determining the size of a residential service. The calculations are based on the expected loads present in a dwelling unit, along with appropriate demand factors that are used to account for the diversity of electrical use by occupants. There are two methods available, standard and optional calculations. Optional calculations require fewer steps and generally result in smaller conductors, but the dwelling unit must meet more restrictive requirements. We will only be considering one-family dwelling units in this article, including single family residences, apartments, etc.

Be aware that some authorities having jurisdiction adopt the International Residential Code for One- and Two-Family Dwellings (IRC) and use the method for calculating the service size using the requirements found in Chapter 36. The IRC calculations are based on the National Electrical Code, but are not identical. Always check with your local jurisdiction to find out what method(s) are acceptable.

Photo 1. Electric range

Standard Method

The standard method for calculating service sizing is found in Part III of Article 220. Of course, we can’t find all the requirements in this Part, so we will also be looking at additional requirements in Articles 210, 220, 230, 250 and 310. An example load calculation using the standard method is shown in Table 1.

Table 1

Lighting Load

The first thing we need to determine is the lighting load. Table 220.12 requires that for dwelling units, we multiply the floor area (based on the outside dimensions of the dwelling unit) times 3 volt-amperes/square foot. Section 220.14(J) states that the following loads are also included in the general lighting load calculations:

• all general-use receptacle of 20-ampere rating or less, including the receptacles connected to the bathroom branch circuit required in 210.11(C)(3),
• the outdoor outlets in 210.52(E),
• the receptacle outlets in basements, garages, and accessory buildings in 210.52(G), and
• the lighting outlets required in 210.70(A), which includes habitable rooms, a variety of additional locations, and storage or equipment spaces.

Table 220.42 gives us demand factors for lighting loads. Most homes will take the first 3000 VA at 100% and the remainder at 35%. (If you are calculating a multifamily dwelling service, you might use the third demand factor category, where anything over 120,000 VA is taken at 25%.)

Small Appliance and Laundry Loads

Section 210.11(C)(1) requires a minimum of two small appliance branch circuits. Section 220.52(A) tells us that we must use a minimum load of 1500 VA for each of these circuits, but also allows the small appliance branch circuits to be included with the general lighting load when applying the demand factors in Table 220.12. Section 220.52(B) requires that 1500 VA be added for the required laundry circuit in 210.11(C)(2). This circuit can also be added to the general lighting load and demand factors may be applied.

Photo 2. Washer/dryer

Electric Dryers and Cooking Appliances

Section 220.14(B) refers us to requirements for electric dryers in 220.54 and electric cooking appliances in 220.55. Electric clothes dryers are calculated at either the minimum of 5000 watts or the nameplate rating, whichever is larger. The demand factors in Table 220.54 may be helpful if there are more than four dryers, but this is unlikely in a one-family dwelling unit, so we will not use this table for the examples in this article. Electric ranges and other electric cooking appliances (rated in excess of 1.75 kW) shall be permitted to be calculated in accordance with Table 220.55, which takes up an entire page and has five notes. There are also informational notes directing the code user to Annex D for examples. It is worthwhile to review this table and read all the notes and examples to become familiar with the various options.

Fixed-appliance load

If there are four or more fixed appliances in the residence, 220.53 permits all of these loads to be totaled and then a demand factor of 75% applied. Fixed-appliance loads include items such as a water heater, garbage disposal, dishwasher, microwave, etc.

Photo 3. Garbage disposal

Largest motor load

Section 220.14(C) tells us that motor loads shall be calculated in accordance with the requirements in 430.22, 430.24 and 440.6. For the service calculation, this means that we must determine the largest motor load and add 25% of its value to the total calculation. Common motor loads in residential applications include air conditioning, water pumps, disposals, blowers, etc. Often, the largest motor load in a home is the air conditioner. Even if the air conditioning is dropped from the total load calculation in favor of electric heating (see below), you may still be required to use the AC motor load for this calculation. Check with your jurisdiction to see what the policy is locally. Many jurisdictions publish residential load calculation worksheets to help with determining the size of the service.

Noncoincident loads

When two loads are not likely to be energized at the same time, 220.60 allows us to use only the largest load for the calculation of the service. This is typically applied to dwelling units with both electric heating and air conditioning, since they are not expected to run at the same time.

Specific appliances or loads

There are certain loads that may be found in residences that are not included in the previous list. Section 220.14(A) requires that an outlet for a specific load or appliance not covered elsewhere must be calculated based on the ampere rating of the load served. Some examples might include a spa, RV hookup, etc. These must be included in the load calculation at their full value.

Optional Method

The optional method is much simpler than the standard calculation, but is restricted in 220.82 to "... a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.” Most one-family dwelling units meet this requirement, so the optional method is used frequently. An example calculation using the optional method is shown in Table 2.

Table 2

General Loads

For the purposes of the optional method, everything except heating and air conditioning is considered to be a general load. For this method, the general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of all loads other than heating and air conditioning.

Lighting and general-use receptacles are again based on the outside dimensions of the dwelling unit multiplied by 3 volt-amperes/square foot. The small-appliance branch circuits and laundry branch circuit are each included at 1500 VA.

The next step is to determine the nameplate rating of each of the following items:

• all appliances fastened in place, permanently connected, or located to be on a specific circuit
• ranges, wall-mounted ovens, counter-mounted cooking units
• clothes dryers that are not connected to the laundry branch circuit
• water heaters

For all permanently connected motors not included in the previous list, the nameplate or kVA rating must be included in the calculation.

Heating and Air Conditioning

The largest heating and air-conditioning load must be chosen from six options:

• 100 percent of the nameplate rating of the air conditioning and cooling
• 100 percent of the nameplate rating of the heat pump when it is used with no supplemental electric heating
• 100 percent of the nameplate rating of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems (If the heat pump compressor is prevented from operating at the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.)
• 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units
• 40 percent of the nameplate ratings of electric space heating if four or more separately controlled units
• 100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value.

Comparing Standard and Optional Calculations

To see how the two methods compare, let’s take a look at a 2900 square foot residence with the following loads:

• lighting load
• 4 small appliance branch circuits
• laundry circuit 1500 W
• natural gas heating
• air conditioner 6000 VA
• electric range 11,000 W
• hot tub 8000 W (2 hp motor)
• Level II electric vehicle charger 7200 W
• electric dryer 5000 W
• garbage disposal 800 W
• microwave 1500 W
• dishwasher 1200 W
• electric water heater 4500 W

The standard calculation method is shown in Table 1 and the optional calculation method is shown in Table 2. Using the standard calculation, our total load is 47,520 VA. Dividing that by 240 volts gives us 198 amps. Using the next standard service rating requires that we use a 200-amp service. Since we have a 120/240-volt single-phase dwelling service, we are allowed to use NEC Table 310.15(B)(7) and use either 2/0 AWG copper or 4/0 AWG aluminum service conductors.

Using the optional calculation, our total calculated load is 34,160 VA. Dividing that by 240 volts gives us 142 amps. Using the next standard service rating requires that we use a 150-amp service. Once again, we are allowed to use NEC Table 310.15(B)(7), which requires either 1 AWG copper or 2/0 AWG aluminum conductors.

For this example, it is clear that the optional calculation permits a smaller service. From a practical perspective, due to equipment availability, it is likely that a 200-amp service will be installed rather than a 150-amp service.

Neutral Load

Neutrals are permitted to be smaller than the phase conductors in most residential service installations. Section 220.61 requires that the neutral load be determined by calculating the maximum unbalanced load between the neutral and any one ungrounded conductor. The values used for calculating the neutral size when using the standard or optional methods will often be different, as shown in Tables 3 and 4.

Section 230.42 states that the grounded conductor for a service shall not be smaller than the minimum size as determined in accordance with 250.24(C). If we have a single raceway (as is most common for service conductors), 250.24(C)(1) tells us that the conductor cannot be smaller than specified in NEC Table 250.66, but is not required to be larger than the ungrounded conductors.

For our standard service calculation, our minimum ungrounded conductor size was a 2/0 AWG copper or a 4/0 AWG aluminum. Using NEC Table 250.66 would require a neutral no smaller than a 4 AWG copper or a 2 AWG aluminum. In Table 3, we found that our calculated neutral load is 28,035 VA. Dividing that by 240 volts gives us 117 amps, which will require either a 2 AWG copper or 1/0 AWG aluminum from Table 310.15(B)(7). These sizes are larger than the required minimum, so we choose one of these conductors.

Table 3

For our optional service calculation, our minimum ungrounded conductor size was a 1 AWG kcmil copper or 2/0 AWG aluminum. Using NECTable 250.66 would require a neutral no smaller than 6 AWG copper or a 4 AWG aluminum. In Table 4, we found that our calculated neutral load is 30,320 VA. Dividing that by 240 volts gives us 126 amps, which will require either a 1 AWG copper or 2/0 AWG aluminum from NEC Table 310.15(B)(7). Since these sizes are larger than the required minimum, we would choose one of these conductor sizes.

Table 4 

Note that for this example in our optional method calculation, the neutral conductor is the same size as our phase conductors. However, if a 200-amp service is installed based on the standard calculation, the neutral is significantly smaller due to the calculation method. Table 5 shows a summary of the ungrounded and neutral conductor sizes for our example using both the standard and optional calculation methods.

Table 5

Conclusion

For one-family dwellings and the individual dwelling units of two-family and multifamily dwellings, service and feeder conductors supplied by a single phase, 120/240-volt system shall be permitted be sized in accordance with 310.15(B)(7)(a) through (d).

(a) For a service rated 100 through 400 amperes, the service conductors supplying the entire load associated with a one-family dwelling or the service conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling shall be permitted to have an ampacity not less than 83% of the service rating.

(b) For a feeder rated 100 through 400 amperes, the feeder conductors supplying the entire load associated with a one-family dwelling or the feeder conductors supplying the entire load associated with an individual dwelling unit in a two-family or multifamily dwelling shall be permitted to have an ampacity not less than 83% of the feeder rating.

(c) In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that of its 310.15(B)(7)(a) or (b) conductors.

(d) Grounded conductors shall be permitted to be sized smaller than the ungrounded conductors provided the requirements of 220.61 and 230.42 for service conductors or the requirements of 215.2 and 220.61 for feeder conductors are met.

Informational Note No. 1: It is possible that the conductor ampacity will require other correction or adjustment factors applicable to the conductor installation.

Informational Note No. 2: See example DXXX in Annex D.

Read more by Christel Hunter

The fourth edition of the SPE-1000 Model Code for the Field Evaluation of Electrical Equipment (SPE-1000) is scheduled to be published by June of this year. The SPE-1000 was first published in 1994 providing requirements used by inspection bodies accredited by the Standards Council of Canada when field evaluating unapproved electrical equipment. Used in conjunction with the requirements of the Canadian Electrical Code (CE Code), Part I, the SPE-1000 document provides construction requirements for the equipment being evaluated along with testing criteria, and minimum marking for equipment nameplates, warning and caution notices. The SPE-1000 does not cover the field evaluation of equipment for use in hazardous locations, medical electrical equipment, equipment connected to line voltage in excess of 46 kV, and individual stand-alone components such as conductors, cable, wiring devices, switches, relays, and timers.

Photo 1. Testing of a photovoltaic module

The changes in the fourth edition focused on the addition of specific requirements for industrial control equipment, high-voltage equipment, solar photovoltaic modules, wind turbines, inverters, and additional requirements for instrument transformers, energy usage metering devices, and associated equipment. During these additions, the SPE-1000 Working Group identified the need for general requirements for transformers, motors, switches, receptacles, enclosures for outdoor use, conductor ampacities, and supplementary protectors. New clauses have been added for the allowable ampacity for wires and cables. These new clauses reference allowable ampacities in the CE Code Part I for conductors external to control panels and to a new table that matches Table 18 from CSA Standard C22.2 No 14 Industrial Control Equipment for conductors within control panels. In addition the temperature limitations of CE Code Part I Rule 4-006 have been added to align the SPE-1000 with the CE Code Part I and existing equipment testing in CE Code Part II standards. For supplementary protectors a new definition has been added to the definition section of the SPE-1000 in Clause 2.2, and a new clause has been added detailing the limited acceptability for supplementary protectors.

New clauses have been added for industrial control equipment. These clauses include details for wire bending space including new tables from C22.2 No 14, disconnection means for control panels, protective devices, control transformer protection, minimum allowable conductor size, permanent connection provisions, terminal size requirements, enclosure thermal insulation limitations, observation windows, intrinsically safe equipment requirements, and additional marking requirements for control panels.

Photo 2. 27.6kV Switchgear modified to metering specification of the supply authority then field evaluated to the requirements in the SPE-1000

The high-voltage equipment requirements added to the SPE-1000 are limited to certified deadfront indoor enclosed and an outdoor enclosed assembly of switchgear and components that have been modified, and then only where adequate testing and review is performed or where documentation is provided to demonstrate that all type testing and mechanical review have been conducted as detailed in CSA Standard C22.2 No. 31 or CSA TIL D-25, as applicable, on a similar design of equipment. These clauses for high voltage equipment are not intended to approve a new design of high-voltage equipment where all relevant sections of CSA C22.2 No. 31 or another recognized document (ORD) are deemed necessary. The requirements in the clauses for high voltage equipment include construction, grounding and bonding, conductor spacing, circuit breakers and switching devices, force-cooled equipment, pad-mounted switchgear, and requirements switchgear intended to be used for service entrance. Testing for high voltage equipment includes all tests from CSA Standard C22.2 No 31 Switchgear, and additional requirements for short-circuit withstand rating, and dielectric strength testing.

New clauses have been added for solar photovoltaic modules. These clauses provide separate direction regarding additional testing and markings required for modules that have been either certified to UL 1703 or tested in accordance with IEC 61730-1 and 61730-2. Modules without UL 1703 certification or appropriate IEC 61730-2 testing cannot be field evaluated using the SPE-1000.

Wind turbines clauses have also been added to the SPE-1000. These clauses include details for generators and motors, generator overcurrent protection, wind turbine components, overcurrent protection for all components of the wind turbine, emergency blade pitch control power supplies, capacitors, low and extra low voltage cables, high voltage cables, grounding and bonding, lightning protection, disconnection means, and safety controls. In addition, clear direction is given for the main nameplate, and warning and caution markings.

Specific requirements for inverters/converter have also been added to the SPE-1000 with separate details for inverter components, and utility interconnected inverters. These clauses tie closely with the requirements and testing in CSA Standard C22.2 No 107.1 General Use Power Supplies.

Photo 3. Modified distribution panel with CTs installed for non-utility metering; ready for a field evaluation inspection

Additional requirements for instrument transformers, energy usage metering devices, and associated equipment have been added to the SPE-1000. These clauses were added as a direct result of the addition of Subrule (4) for CE Code Part I Rule 12-3032 allowing enclosures for overcurrent devices, controllers, and externally operated switches to be used as a raceway for wiring associated with instrument transformers and energy usage metering devices. These new clauses address the wiring space, wire bending space, and additional marking requirements when current transformers CTs are added to a panelboard.

In addition to the changes detailed in this article, tables have been added for

• Wire bending space
• Wiring space
• Full-load motor-running currents in amperes corresponding to ac horsepower ratings
• Full-load motor-running currents in amperes corresponding to dc horsepower ratings
• Allowable ampacities of insulated copper conductors inside industrial control enclosures
• Maximum acceptable rating of primary overcurrent device for control transformers
• Maximum acceptable rating of secondary overcurrent device for control transformers
• Minimum spacings for high-voltage power circuits
• Impulse and corona-extinction test voltages for high-voltage switchgear assemblies
• Dielectric strength test voltages for high-voltage switchgear assemblies, and
• Voltage and frequency operation limits

Two new figures have also been added, one for an articulated finger probe, and one for the typical arrangement of intrinsic safety barriers.

One more major change is in the process and scheduling of future editions of the SPE-1000. Future changes for the SPE-1000 will use a similar approach as the CE Code Part I in that separate proposals will be addressed when submitted then sent for ballot. The existing process held proposals until a sufficient number were received, and then a working group would work on all the proposals at once. The new process will address proposals sooner in an effort to encourage more proposals. The cycle for the SPE-1000 will also change to a three year cycle with new editions being published following the publication of the CE Code Part I.

There were 120 proposals submitted to raise the 600-volt threshold in the NEC to 1000-volts in the 2014 NEC cycle. These proposals were submitted by the High Voltage Task Group (HVTG), which was appointed by the NEC Correlating Committee. The HVTG was charged to review all NEC requirements and/or the lack of requirements for circuits and systems operating at over 600-volts.

FPN reference to NESC deleted

The origin of this task group began at the end of the 2008 NEC cycle when a fine print note (FPN) [now Informational Notes] referencing the National Electrical Safety Code (NESC) was deleted from 90.2(A)(2). The substantiation provided in the proposal to delete the FPN stated that "conductors on the load side of the service point are under the purview of the NEC, and the FPN sending NEC users to the NESC creates serious confusion for designers, installers and the authority having jurisdiction (AHJ) working on premises wiring at voltage levels over 600-volts”. The proposal was supported by comments that pointed out conflicts that place the AHJ in a very difficult position and the FPN was deleted in the 2008 NEC. The NEC Correlating Committee then appointed the High Voltage Task Group to address issues with installations over 600 volts”.

Article 399 created

In the 2011 NEC, a proposal submitted by the HVTG created a new Article 399, Outdoor Overhead Conductors over 600 Volts. This new article was developed to provide the AHJ with NEC requirements to address the outdoor installations referenced in 90.2(A)(2) without a broad reference to another standard. It is interesting to note that most of the requirements in Article 399 are performance based. The requirements for conductor support and structures outline the installation requirements to consider without being prescriptive. In each case there must be documentation of an engineered design submitted by a licensed professional engineer engaged primarily in the design of such systems. This new article permits an engineer to design the installation in accordance with NESC requirements provided the design is documented and available to the AHJ.

Photo 1. XHHW cable labeled 600 volts

Raising the voltage threshold

The work of the High Voltage Task Group continued into the 2014 NEC cycle with a primary focus on raising the voltage threshold in the NEC from 600 to 1000 volts. This is not the first coordinated attempt to raise the voltage threshold. In the 1990 NEC revision cycle, a Correlating Committee task group tried unsuccessfully to raise the voltage threshold. Finding substantiation on how the NEC settled at 600 volts is difficult. The threshold was raised from 550 to 600 volts in the 1920 NEC. In 1990 it was difficult to substantiate a need to raise the voltage threshold. Today, emerging technologies are operating at just over the 600-volt threshold. We need product standards and installation requirements to facilitate their safe installation. The electrical industry is changing rapidly and codes/standards must keep pace; otherwise, we will be forced to use the International Electrotechnical Commission (IEC*) products and installation standards other than the NEC.

Is going from 600 to 1000 volts the right number? Small wind electric systems often operate at 690 volts AC but solar photovoltaic (PV) systems are currently being installed at dc voltages over 600 volts up to and including 1000 volts, 1200 volts, 1500 volts, and 2000 volts dc. These dc systems are expanding and have become a more integral part of many structures. Small wind electric systems and solar photovoltaic (PV) systems are employed regularly in and on all types of structures from dwellings units to large retail and high rise construction.

Photo 2. Cube fuses labeled 600 VAC or less

The first direction that the Higher Voltage Task Group took was to simply suggest revisions in Chapter 6 of the NEC for Special Equipment. It was quickly understood that changes throughout the NEC were required. Chapter 6 requirements simply modify and/or supplement the rules in Chapters 1 through 4. A review of the UL White Book reveals that UL has many products that are utilized in these systems rated at and above 600 volts, including but not limited to, 1000-V dc PV switches, 1500-Vdc PV fuses, and 2000-V PV wiring. The HVTG realized that the NEC must recognize those products through installation requirements or we will continue to have problems installing and inspecting systems for PV and small wind. The HVTG proposals to raise the voltage threshold recognize emerging technologies that are in many cases operating at just over 600 volts. Everyone needs to play a role in this transition. The present NEC requirements would literally require that a PV system operating at 1000 volts dc utilize a disconnecting means rated at 5 kV. The manufacturers, research and testing laboratories, and the NEC must work together to develop installation requirements and product standards to support these emerging technologies.

Moving the NEC threshold from 600 volts to 1000 volts will not, by itself, allow the immediate installation of systems at 1000 volts. Equipment must first be tested and found acceptable for use at the higher voltage(s). The testing and listing of equipment will not, by itself, allow for the installation of 1000-volt systems. The NEC must include prescriptive requirements to permit the installation of systems that are over 600 but less than or equal to 1000 volts. It will take both tested/listed equipment and changes in our installation code, the NEC, to meet the needs of these emerging technologies that society demands.

Eighty-two percent of the proposals submitted to raise the voltage threshold were accepted in some form. Where a code-making panel felt there was a safety issue or where manufacturers did not want to pursue having their products evaluated at 1000 volts, the Higher Voltage Task Group agreed to reject.

Moving the NEC to 1000 volts is just the beginning. This is just the first step of many to recognize emerging technology with prescriptive requirements to ensure that these systems and products can be safely installed and inspected in accordance with the NEC.

*The IEC is a nonprofit, nongovernmental international standards organization that prepares and publishes international standards for electrical and electronic technologies.

Think you might know what lurks behind the meter cover? Chances are you will think twice after reading this article!

Electrical Metering Devices

Meter enclosures are part of every electrical system. But how often do you look inside the enclosure after it has been installed and energized? A utility provider provides electricity to a customer in order to make a profit. Typically, this is accomplished by metering the electrical system at the point of connection. Electronic receiver/transmitter (ERT) meters are becoming more of the norm in today’s electrical metering systems. They provide many benefits to the electric utility provider and to the customer. But, this could allow for many unforeseen problems as well.

Photo 1. A 400-ampere, single-phase meter enclosure located at the front entrance of a church and preschool. Men, women, and children visiting this location walk by this meter enclosure on a daily basis. What’s located behind the cover could prove deadly! And chances are it will not be discovered until there is a problem.

The Good Ole Days and the Standard Electrical Meter

For many years the measurement of electricity went relatively unchanged. These metering devices worked adequately for the utility provider to accomplish the goal of registering electrical usage so that a utility bill could be generated. The customer received the monthly statement and would pay his or her bill.

In the event the customer fell in arrears and did not pay the monthly bills, a customer service representative would visit the location and disconnect the power. To accomplish this, the meter seal would be cut, the electric meter removed and booted off, and then reinserted into the meter base. The cover is then reinstalled and re-sealed until a time in which the customer pays the outstanding bill and any reconnection charges. In the event of tampering, the meter would either be removed and a blank inserted or the service conductors cut and disconnected at the weatherhead or utility pole.

Photo 2. Within the meter enclosure unknown to daily passersby are several potential dangers as can be seen, such as corrosion, effects of overheating to busbars and conductors, insulation failure as well as conductor damage.

When the service is ready to be reconnected, the customer service representative then returns to the property, cuts the meter seal, removes the meter, removes the boots and reinserts the meter. The cover is then installed and another seal applied. This returns electricity to the customer and usage is recorded for the next monthly billing cycle.

During this entire process there were several opportunities for the utility representative to notice and report any problems developing within the meter enclosure. Upon discovery, action could be taken to alleviate potential problems before they happened. Technology has changed the way that utilities gather billing information and even the disconnection of delinquent accounts. This has in turn made it even more imperative that electrical work within the meter enclosure be installed in a code-compliant fashion.

A statement must be mentioned concerning safety regarding this issue. Unbelievably, some customers take it upon themselves to reconnect their electricity without the approval of the serving utility. This has resulted in additional fees being accessed by utility and the electrical meter being removed or the conductors disconnected at the weatherhead or utility pole. This illegal activity can result in electrical accidents up to and including death. Qualified personnel are necessary to reconnect these services to assure the safety of the electrical system. Never attempt to reconnect your electrical service! Contact your friendly utility provider for help with this situation.

Photo 3. The interior of this meter enclosure depicts damage due to overheating and corrosion. Remember, none of this damage is visible from the outside of the meter enclosure.

The ERT Meter

An electronic receiver/transmitter meter (ERT meter) is used in a network meter reading environment. It can be retrofitted into existing meter enclosures and is available in single- phase and three-phase models. The meter uses electronic modules to communicate power consumption and power quality to the utility provider. The meter also allows two-way communications from the utility provider to the customer. This allows the utility provider the opportunity to be aware of outages that occur and to respond much more quickly.

The use of ERT meters saves the utility provider from physically visiting the meter location on a monthly basis. The ERT meters have a low-powered radio device that permits them to be read from a distance. This allows meter readings to be collected electronically with a mobile data collector (usually a laptop computer) or with a handheld receiver. Technicians are able to download the readings for multiple meters at one time rather than walking from house to house to look at each individual meter.

In some cases, the utility can also disconnect and reconnect the customer remotely. This can be for nonpayment of their monthly bill or to head off high demand issues on the utility system. This can be handy during high usage periods where the provider needs to disconnect loads within structures to prevent brownouts or blackouts from affecting the system. Many household devices are being produced with communication features that communicate with the electronic meters. Utilities can disconnect AC units briefly to prevent issues on the system from occurring. Most generally the customer is unaware that this has even taken place. Some consumers have expressed concerns regarding this issue as it applies to privacy. Many customers enjoy the features of ERT meters. This technology allows the customer to monitor their electrical usage. This has also allowed the customer to change some of their usage patterns in order to save money on their electrical bills by using electricity in the off-peak periods.

As you can see, the use of this technology removes the "hands on, eyes in the field” that may have visited the enclosure and discovered a problem. This can result in minor situations arising that develop into major issues. These issues can be lessened by proper equipment installation and inspection.

Photo 4. Conductor damage due to insulation failure that is not detectable from the exterior of the meter enclosure.

Preventing These Problems Begins with You

The first line of defense in addressing this issue starts with the electrical contractor. The contractor must make sure that all material used for the installation is listed and labeled as per requirements found in NEC 110.3(B). Proper application of NEC requirements will help ensure a safe and compliant installation. NEC Article 110 covers the requirements for electrical installations. Requirements found within this article include working clearances, interrupting rating, mechanical execution of work, mounting and cooling of equipment, illumination, electrical connections, arc-flash, and field marking. There are other requirements that are useful and required throughout the NEC as well.

Care must be taken to follow the manufacturer’s installation instructions. Special care must be taken to use anti-oxidant compounds as required by the NEC and the manufacturer. These requirements are found in NEC 110.14. Conductors should be stripped and prepared properly so as to not damage the conductor. Specialized tools are necessary to assure that the specific torque requirements are followed for the lugs and conductors. Informative Annex I includes recommended tightening torque values to be used in the absence of the manufacturer’s recommended torque values. These values are taken from UL Standard 486A-B.

The next line of defense lies with the electrical inspector. The inspector needs to assure the customer and utility provider that the electrical contractor has followed the guidelines for properly installing the metering equipment. A good understanding of the NEC and any additional electrical requirements required by the utility provider are necessary. Some of these requirements have been previously discussed. Additionally, the inspector needs to make sure that proper grounding and bonding has been accomplished. Grounding and bonding requirements can be found in NEC Article 250. Also, remember that the insulated fitting required at NEC 300.4(G) is required due to conductor size, not conduit type. Bushings are required for various conduit types throughout the NEC such as at 344.46 for rigid metal conduit. There have been many instances where the electrical installation has been turned down by an inspector due to a missing conduit bushing or insulated fitting.

Photo 5. For years a standard 2s meter was adequate for the needs of the utility company. Today’s technological advances have spurred changes within the utility industry in order to compete and reduce operation costs. Electronic radio transmission (ERT) meters may be able to control some electrical devices within the structure through the electrical utility to prevent system problems. These include the refrigerator, the air conditioner or some other high usage item. Privacy issues have been expressed by some people.

Arc Flash and Available Fault Current, a Deadly Combination

New to the 2011 NEC are 110.16 and 110.24 which deal with arc-flash and available fault current markings and requirements. Section 110.16 states that the marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment. This includes meter socket enclosures as well as switchboards, panelboards, industrial control panels and other motor control centers. These requirements do not apply to dwelling units.

Service equipment must be marked with the maximum available fault current per NEC 110.24. This Code requirement further states that the field marking shall be legible and include the date that the fault-current calculation was performed. It must also be sufficiently durable to withstand the environment in which it has been installed. Modifications require that this calculation be verified and recalculated as necessary to ensure the service ratings are sufficient for the maximum available fault current at the line terminals of the equipment. An exception exists for industrial installations where conditions of maintenance and supervision ensure that only qualified persons service the equipment. Again, as previously stated these requirements do not apply to dwelling units.

These requirements help to ensure that whoever works on this equipment in the future is aware of the potential available fault current. This also brings up an interesting question. Who is responsible to adjust the modification markings to the existing equipment as per the requirements found within 110.24? Suppose the providing utility changes out the transformer to the building. Suppose the impedance is different from the existing transformer to the newly installed transformer. Who makes the changes to the marking at the service equipment? Is the building owner aware that these changes have been made and what effect it has on the available fault current to his equipment? Does the utility provider even know that this requirement is found within the NEC? How does this information get upgraded on the electrical equipment?

Photo 6. This electrical service location has a meter blank installed and the meter retired or taken out of service. This could be due to non-payment for services, tampering or because the electrical equipment is no longer in service.

Most utilities work under the guidelines of the National Electrical Safety Code (NESC). During a power outage at 2:00 A.M. in the pouring rain and lightning, who will make these adjustments in the field? Is there communication between the utility provider and the customer concerning these changes? What happens when the utility changes the substation feeder to this area of town from one substation to another? There are different characteristics present in both substations that will affect the calculations towards what is marked on the service equipment. These are just a few questions and situations that could arise and affect the accuracy of the field markings for these installations.

Interestingly, during the 2011 NEC Report on Proposals (ROP) and Report on Comments (ROC) meetings these situations were vigorously debated and discussed. The inclusion of the date of when the calculation was conducted was agreed upon and included so that the future electrical contractor would be aware of when the calculation was conducted. Under no circumstances should the electrical contractor rely on a marking on the equipment to determine the level of personal protective equipment (PPE) required. Changes to the system may have taken place after the date the calculation was performed, changing the available fault current at the terminals of the equipment.

Technology Always Has its Ups and Downs

In conclusion, a properly installed and inspected electrical service should provide years of service to the customer. If the customer increases the electrical load by adding new electrical appliances, the service size may need to be re-evaluated. There are many existing older homes and commercial locations with electrical services that were acceptable at the time they were built. Over the years with the addition of new electrical appliances, these services may no longer be adequate for their situation. An electrical contractor should review these services and determine if modifications are needed.

Believe it or not, there are still several locations within utility territories that have only 120-volt services. Usually these are only 60-amp services. This service was all that was necessary to provide electricity to the few devices available at that time. Technology has brought us many new items to add comfort and convenience to our daily life. Many homeowners are shocked when they purchase a new air conditioner or electric dryer to find out that they will need to modify their electrical service to utilize the equipment. Many tend to be elderly and on a fixed income.

Field markings are crucial to the safety of the equipment, the electrician and the electrical inspector. All attempts should be made by the utility and the customer to maintain the accuracy of these markings. Doing so may mean the difference between life and death!

And remember to consult the utility provider and to secure the required permits from the authority having jurisdiction (AHJ) before beginning the electrical upgrade. The utility provider may need to re-evaluate transformer sizes and make adjustments to their system due to your planned modification. What worked for the utility years ago may need modification today.