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Underwriters Laboratories

Underwriters Laboratories® (UL) is an independent product safety certification organization that has been testing products and writing Standards for Safety for over a century. UL evaluates more than 19,000 types of products, components, materials and systems annually with 20 billion UL Marks appearing on 66,000 manufacturers products each year. UL's worldwide family of companies and network of service providers includes 68 laboratory, testing and certification facilities serving customers in 102 countries. UL is also the only National Certification Body (NCB) for PV in North America and an OSHA-accredited Nationally Recognized Testing Laboratory (NRTL). For more information, visit


Operating Portable Generators

When a hurricane downs power lines, electricity is often one of the initial services to fail. In response, many people use portable generators to weather the inconvenience until power is restored.

Chinese National Sentenced to Prison for Dealing in Counterfeit Merchandise

U.S. Attorney Michael Shelby announced on February 16, 2005, that Zheng Xiao Yi, a citizen of the Peoples Republic of China who owned and operated an import and wholesale business in the Harwin Drive area of Houston, has been sentenced to more than five years in federal prison for trafficking in counterfeit goods.

A Century of Safety Standards – UL Celebrates 100 Years of Developing Safety Standards

Underwriters Laboratories Inc. celebrates the 100th anniversary of its first safety standard. UL, whose familiar Mark appears on billions of products each year, is one of the world’s leading standards writing organizations. UL has published more than 880 Standards for Safety since 1903 — the not-for-profit company was founded in 1894 — for products ranging from fire-rated building materials to information technology equipment to electrical household appliances.

UL Adopts Enhanced Standards Development Process

In July 1, UL introduced a significant enhancement to the way it develops and maintains UL Standards for Safety. This new process allows greater input from interested parties—consumer groups, regulatory officials, government agencies, insurance companies, academics and others—at the earliest stages of development.

UL Question Corner

Does UL Certify Air Compressors?

Yes, UL certifies (Lists) air compressors under the product category Compressors, Vacuum Pumps and Pneumatic Paint Sprayers (QDGS), located on page 330 in the 2013 UL White Book. By accessing UL’s Online Certifications Directory at and entering QDGS at the category code search field, you can access the nearly 60 manufacturers that have certification under this category.

If the nylon on THHN is scuffed, is the insulation damaged?

In the process of pulling THHN conductors through raceway we encountered some scuffing and scraping of the outer nylon conductor covering at the final fitting. The engineer says we ruined the conductor and wants it replaced. Does damage to the nylon covering constitute damage to the conductor insulation?

Fire Resistive Cable Update

Has there been any progress made on changes to UL2196 and ULC-S139? Are the standards still active? Are there any new certifications? Yes to all three questions. Initial research has been completed and a joint U.S. and Canada standards working group of the consensus based technical committee has been formed to determine what upgrades in requirements are necessary to deliver a single, harmonized bi-national standard. The group will focus on a strategy to address installation variables, sampling requirements for testing, and the need for any further research.

Are All Grounding Lugs Listed for PV?

Can I use any UL Listed grounding lug evaluated to UL 467 for grounding a photovoltaic (PV) panel or supporting rack system? What devices are evaluated for grounding and bonding PV modules and mounting racks to comply with 2011 NEC Section 690.43(C), (D), and (E)?

Does UL List (Certify) Paint Spray Booths?

UL certifies (Lists) paint spray booths under one of two categories, depending on whether fire protection systems are provided as part of the paint spray booth. The two categories are Paint Spray Booths without Fire Protection Systems for Use in Hazardous Locations (QEFA) and Paint Spray Booths with Fire Protection Systems for Use in Hazardous Locations (QEFY), both are located on page 317 in the 2012 UL White Book or online at

UL Certifies First Modular Data Center

With the advent of cloud computing, there seems to be a lot of modular data centers popping up. Does UL certify (List) modular or containerized data centers that are typically housed in an enclosure like a shipping container and are filled with computer servers?

UL Certifies First Stand-Alone Replacement LED Tube

Yes, recently UL has certified (Listed) the first stand-alone LED tube for direct replacement of a fluorescent tube in a fluorescent luminaire. The replacement tubes operate in the existing ballast circuit present in the fluorescent luminaire. They have been evaluated to operate in the ballast circuit so that the LED tube does not adversely affect the ballast operation in the luminaire.

Is there a way to interact with UL’s Regulatory Services Department Staff on social media?

Yes, UL’s Regulatory Services Department has a discussion group on, entitled "UL Codes and Technical Services”. To join, go to, become a member, then select "groups” from the search pull down menu at the top right of the screen and then enter "UL Codes” in the search field. Once you are a member, you can enter the conversation or post a new topic to discuss.

Has UL Certified any small wind turbines?

Yes, UL has certified small wind turbines under the product category Small Wind Turbine Generating Systems (ZGEN), located on page 466 in the 2012 UL White Book or you can check online at UL’s Online Certification Directory at by entering ZGEN at the category code search field. This category covers small wind turbine generating systems (WTGS) investigated for risk of fire and shock, including safety-related control system electrical performance and utility (grid) interconnection performance for Utility Interactive models.

Is the XO Jumper Sized Correctly?

Is the XO bonding jumper strap provided in certified (Listed) dry type core and coil transformers used in typical commercial installations adequately sized?

DC AFCIs for Photovoltaic Systems Now Certified

2011 NEC 690.11 requires DC arc-fault circuit interrupter protection in DC photovoltaic (PV) circuits. Are there any certified (listed) DC arc-fault circuit interrupters (AFCIs) for use in PV circuits? What requirements are used for certification?

Does UL certify (list) Photovoltaic (PV) module tracker devices?

Does UL certify (list) Photovoltaic (PV) module tracker devices? What about grounding lugs for PV modules? Where can I find this information?

Is there anything new in wind turbine certifications?

Yes, recently UL has created two new wind turbine certification product categories, Wind Turbine Drive-train Systems and Equipment (ZGDT) and Wind Turbine Tower Assemblies (ZGTA) both of these categories can be found in a list of Wind Power Systems product categories located on page 34 in the 2012 UL White Book.

Are there LED retrofits for emergency lighting? Are two light sources required?

Product category Emergency LED Drivers (FTBV) covers battery packs that can be factory- or field-installed into specific LED luminaires. These battery packs are functionally parallel to fluorescent luminaire products commonly referred to as "inverter-charger packs.”

Does UL Certify (List) Circuit Breaker Pad Locking Devices?

Yes, UL certifies both circuit breaker lock-on and lock-off devices under the product category Circuit Breaker Accessories (DIHS), located on page 96 of the 2011 UL White Book. These devices are evaluated for compliance with the Standard for Safety for Molded Case Circuit Breakers, Molded-Case Switches and Circuit-Breaker Enclosures, UL 489.

Have any electric vehicle (EV) level 3 DC fast chargers been UL certified (Listed)?

Yes. A few manufacturers have had their electric vehicle DC fast chargers UL certified. Electric vehicle DC fast chargers can fully charge an electric vehicle battery in as short as 15 to 30 minutes. These fast chargers will most likely be installed at electric vehicle charging locations in public/commercial settings, such as traditional gas or service stations.

Are flat cord extension cords equivalent to hard usage or extra hard usage cord?

Yes. Convention center cord sets are required to be constructed with cord that is evaluated as being equivalent to extra hard usage or "Type S” cord. These cords are typically constructed of a flat type of jacketed cord, which is suitable for the abuses that it may be subjected to by being laid on a floor in an exhibit hall.

Certified Ceiling Grids that Power Lighting Systems

Yes. UL certifies ceiling grids that power lighting systems under the UL product category Suspended-ceiling-grid Low-voltage Lighting Systems (IFFA) found on page 176 of the 2011 UL White Book. UL also certifies low-voltage luminaires and other accessories for these systems under the UL product category Suspended-ceiling-grid Low-voltage Lighting System Accessories (IFFC) on page 177 in the 2011 UL White Book. Both of these product categories can also be found on UL’s Online Certifications Directory at; simply enter the four letter category code (IFFA or IFFC) at the Category Code search field.

LED Retrofits for Luminaires and Signs

I see many kits to retrofit or convert incandescent and fluorescent luminaires and signs as well as neon signs to LED lighting sources. Does this impact the UL certification of these existing luminaires and signs? Does UL certify these retrofits and conversions kits?

When is the 2011 UL White Book available, and what is new for 2011?

The 2011 UL White Book started distribution April 1, 2011. The UL White Book is considered by many as "Part 2 of the Code.” That is because without the White Book, it is difficult to determine compliance with the National Electrical Code (NEC).

Has UL investigated the effects of spray-on foam insulation on Type NM cable jackets or individual conductor insulation?

UL has not specifically investigated the effects of spray-on foam building insulation on the jacket or insulation materials of NM cable. UL Lists NM cable under the product category Nonmetallic Sheathed Cable (PWVX), located on page 293 in the 2011 UL White Book and online at and enter PWVX at the category code search field.

Is there anywhere I can get a repository of UL Question Corner columns in one place and organized by topic?

Yes, UL has a repository of UL Question Corner columns going back to the year 2000 located on UL’s recently enhanced Code Authorities web pages located at The Code Authorities page on is the website for UL’s Regulatory Services Department that is charged with supporting the UL Mark by supporting you, the users of UL’s certifications.

Can a manufacturer add labels to a UL Listed product in the field, even if the label is not a Listing Mark?

No, when you add labels to a Listed product after it leaves the factory, it is considered a Field Modification. The product was never reviewed to determine if the attribute identified on the added label or marking is accurate or continues to comply with UL’s requirements. In order for UL to determine if that product still complies with UL’s requirements, UL would have to conduct a Field Inspection or Field Evaluation to determine if the modifications are still in compliance with the UL’s requirements.

Are there certified AFCIs that can be installed into another manufacturer’s panelboard?

Yes, UL Classifies molded-case circuit breakers, including arc-fault circuit-interrupter combination type and branch-feeder-type circuit breakers for use in other manufacturers’ panelboards under the product category Circuit Breakers, Molded-Case, Classified for Use in Specified Equipment (DIXF), located on page 99 in the 2010 UL White Book. The Guide Information can also be found online at and entering DIXF in the category code search field.

Can I install a general use ordinary location ICP to control a circuit that extends into a hazardous classified location?

No, industrial control panels Listed for use in ordinary locations are Listed under the product category Industrial Control Panels (NITW), and are not intended for controlling circuits extending into a hazardous classified location. Industrial control panels (ICPs) that would be suitable for this application are Listed under the product category Industrial Control Panels Relating to Hazardous Locations (NRBX), located on page 249 in the 2010 UL White Book.

Are wire connectors that are filled with silicone Listed to splice THWN conductors in an open bottom handhole for an outdoor parking lot light?

Unless the wet locations connectors or their shipping carton or installation instructions state that they are for use with THWN conductors, then they are not Listed for use with THWN insulated conductors.

Is it permissible to stub up conduits into the bottom of a stationary generator enclosure and continue the conductors out of the conduit directly into the generator itself, or...

It is permissible to stub up conduits into a generator enclosure and have exposed conductors inside of the generator enclosure provided that the generator is mounted on a non-combustible surface such as concrete.

Does UL List LED Tube Lamps and LED Edison Screw-Type Base Lamps?

LED tube lamps intended to replace fluorescent tubes are not eligible for Listing as a stand-alone lamp at this time. Currently the industry has two types of products on the market that are certified by UL: lamps that are intended to operate directly from line voltage (120 V) or lamps in combination with a remote, line voltage driven power supply. The output of the power supply goes onto the lamp. Both products can be used in the construction of new luminaires but of greater interest is the ability to use the lamps for conversion of existing luminaires.

Luminaire Ballast Retrofits and Conversions — How Does that Effect the Luminaire Listing?

The short answer is that the impact is unknown. The presence of the UL Mark on a modified luminaire is essentially no different than when on a luminaire that has been serviced or repaired.

Can Listed Water Heaters be Cord-and-Plug Connected?

Has UL Listed any cord-and-plug connected central air-conditioning units, central heating furnaces or storage tank water heaters? No, UL has not Listed cord-and-plug connected central air-conditioning equipment or central heating furnaces.

Does UL apply a Listing Mark to a product based on evaluation to an Outline of Investigation?

Yes, in cases where a published UL Standard does not cover a product submitted for investigation and certification, an Outline of Investigation may be used and contains basic requirements for such products.

Is all Type PLTC cable sunlight-resistant or is it sunlight-resistant only if marked?

All listed power limited tray cable or Type PLTC is sunlight-resistant and may be marked "sun res” or "sunlight resistant” but is not required to be so marked. PLTC cable is listed under the product category Power Limited Circuit Cable (QPTZ) located on page 320 in the 2010 UL White Book. The Guide Information for (QPTZ) in the 2010 White Book doesn’t make it clear that the jacket is sunlight-resistant even if it isn’t marked.

Can a sealing gasket be installed on the interior of the enclosure to maintain the rating?

No, UL lists sealing gaskets under the product category "Outlet Bushings and Fittings, (QCRV).” Guide Information for this category can be found in UL’s Online Certifications Directory at and on page 296 in the 2010 UL White Book.

Circuit breakers and old panelboard; will anything work?

I have an old panelboard made by a company that was sold and no longer produces panelboards or circuit breakers under their old name. How do I find circuit breakers listed for use in the panel when the manufacturer is no longer in business, can I use any circuit breaker that fits?

When is the UL White Book published every year?

Historically, the UL White Book has been published in late June every year. However, effective with the 2010 edition, the UL White Book will now be available in early April. So look for the 2010 UL White Book from the UL representative at your local IAEI meeting or download a copy online at

UL and Installations of Alternative Power Equipment?

Does UL have any additional information available to AHJs or installers regarding installations of photovoltaic systems, wind turbines and other alternative power source equipment?

Was the Fire Protection Research Foundation’s (FPRF) Residential Electrical System

I understand UL conducted research on old homes to determine the effects of aging on residential electrical wiring systems. Is that research project complete, and where can I get the report and any recommendations from the research?

Do Stacked AFCIs Cause Panelboards to Overheat?

I have noticed that arc-fault circuit-interrupter (AFCI) circuit breakers tend to be warmer to the touch than regular circuit breakers. Now that the 2008 NEC requires most circuits in a dwelling to be protected by a combination-type AFCI circuit breaker, and there will be more AFCIs stacked into a panel, will the added heat affect the operation of the circuit breakers in the panelboard or create a hazard?

What types of emergency lighting are listed by UL under the product category Emergency Lighting and Power Equipment (FTBR)?

Luminaires that are specifically for use as emergency lighting are listed under the product category Emergency Lighting and Power Equipment (FTBR), located on page 142 in the 2009 UL White Book. Luminaires listed under (FTBR) would be evaluated for compliance with the Standard for Safety for Emergency Lighting and Power Equipment, UL 924.

Can the wiring of normal and emergency power circuits be intermixed in luminaires?

I have an installation of a series of ten, row-mounted, 2 by 4 fluorescent troffer luminaires listed as surface-mounted fluorescent luminaires. They are provided with two circuits integral to the luminaire and also with wiring harnesses to connect those two circuits from one luminaire, end-to-end to another in a row-mount application. Every third luminaire is on the emergency lighting circuit. One of two circuits in the luminaire is connected to the normal power circuit and the other is supplied by the emergency power circuit. Do these rows of luminaires count as one emergency luminaire?

Manufacturers explain that modifications were made to meet specific customer requirements, or for some unknown reason, the UL Mark or markings were not applied at the factory. What is UL’s position on this practice?

UL requires markings to be on UL Listed and Classified products constructed under UL’s Follow-Up Services (FUS) Program before they leave the factory. If a product is altered or a label is added after it leaves the factory, there is no way that UL can discern whether the product still complies with UL requirements without an evaluation. In such cases, UL conducts a Field Inspection.

Can Power Outlet Listed for Temporary Location be used in Permanent One?

Can a power outlet Listed as suitable for use as temporary service equipment be used as service equipment in a permanent installation for other than a temporary wiring installation?

Power Pedestals Listings for Various Locations

Question: Power Pedestals Listings for Various Locations What is the difference between power pedestals Listed for RV parks, mobile homes, temporary sites, marinas, etc.? Are they Listed under different product categories?

Wind turbines and wind turbine related equipment

I have heard that UL has developed requirements for wind turbines and is able to perform listing evaluations and field evaluations on this type of equipment. We have had a number of these turbines installed in our area and would like to require listing on the entire assembly...

Luminaire disconnects and motors?

Are the luminaire disconnect connectors that are used to comply with NEC 410.130(G) evaluated for other uses such as a disconnecting means for a motor?

How do I use the UL White Book?

I received a UL White Book at an IAEI meeting. It seems to contain a wealth of information for electricians and electrical inspectors; however, I do not know how to use it. Does UL have an online presentation that can show me how to use the UL White Book?

Grounding permanently mounted portable luminaires

Are permanently mounted portable luminaires required to be grounded? I have seen some wall-mounted portable luminaires that are cord connected with a polarized plug, even though these products often have quite a bit of exposed metal.

Can Listed cable have dual ratings such as Type TC, 600V, direct burial cable that is also marked NPLF 150V?

The cable in question is dual rated as both, Type TC, Power and Control Cable (QPOR), page 275 in the 2008 UL White Book rated 600V and for direct burial and Non Power Limited Fire Alarm Cable (HNHT), located on page 144 in the White Book, NPLF cable rated 150V and marked appropriately.

Does UL have special product categories for these types of LED lights?

Yes, UL is keeping pace with the changes in LED lighting technology and has developed many product categories to address the many types of LED luminaires and accessories.

Does the unit switch on a household dishwasher qualify as a disconnect in accordance with NEC 422.34?

No, the unit switch in a household dishwasher is not required to disconnect all ungrounded conductors from the source of supply and does not qualify as a disconnect in accordance with NEC 422.34.

A contractor indicated that a UL Listed fiber optic swimming pool light was not provided with installation instructions. Are these instructions required as part of the Listing?

As with most UL Listed products, installation instructions are required to be provided with fiber optic swimming pool luminaires. UL lists fiber optic luminaires for swimming pools and spas under the product category "Luminaires and Forming Shells for Swimming Pools and Spas (WBDT).”

Are receptacles and switches Listed for use with stranded conductors?

UL Listed receptacles are evaluated for use with solid and stranded conductors; however, they are not Listed for use with spade terminals. Receptacles are Listed under the product category Receptacles for Plugs and Attachment Plugs (RTRT) located on page 295 in the 2008 UL White Book and (RTRT7) on page 434 in the 2008 Canadian White Book. The Guide Information for (RTRT) and (RTRT7) states under the heading of Terminals, "Terminals of the wire-binding screw, setscrew, or screw-actuated back wired clamping types are suitable for use with both solid and stranded building wires. Screwless terminal connectors of the conductor push-in type (also known as "pushin-terminals”) are restricted to 15 A branch circuits and are for connection with 14 AWG solid copper wire only.” They are not intended for use with aluminum or copperclad aluminum wire, 14 AWG stranded copper wire, or 12 AWG solid or stranded copper wire.

Are receptacles that are provided with more than one set of terminals Listed for tapping off more than one circuit, utilizing both the side and back wiring terminals?

The short answer is yes for receptacles Listed for the U.S. market and no to receptacles Listed for the Canadian market. This is due to the difference in certification requirements between the two countries. Receptacles evaluated to UL 498, The Standard for Receptacles for Plugs and Attachment Plugs requires receptacles to be tested using the side terminal and rear terminals on the receptacles concurrently, where the Canadian Standard, CSA C22.2 No. 42-M1984, General Use Receptacles, Attachment Plugs and Similar Devices does not address testing for this application. Receptacles for the U.S. market are Listed under the product category Receptacles for Plugs and Attachment Plugs (RTRT) located on page 295 in the 2008 UL White Book.

My jurisdiction recently adopted the 2008 NEC and I was wondering when UL is going to add the 2008 NEC to the Code Correlation database?

UL has completed the correlation of 2008 NEC to UL product categories and the information is now included in UL Code Correlation Database on the Regulators page of The database can be accessed at

Why does the Listing limit these meter sockets for residential use only?

The "Residential Use Only” marking is permitted by UL 414, the Standard for Safety for Meter Sockets, for meter sockets that are intended for use on 120/240-volt, 3-wire, single-phase dwelling services in accordance with NEC 310.15(B)(6). This Code section provides a different ampacity table for "3-wire, single-phase dwelling services and feeders.”

Does UL have a quick reference guide that I can carry around in my pocket that includes UL Mark information as well as UL policies and contact information?

Yes, recently UL developed a shirt pocket sized reference guide titled "Product Guide to Inspections.” The UL Product Guide to Inspections includes information on contacting UL, UL’s Certification Marks, UL’s Field Evaluation Services and Field Modification policy as well as information on CE Marking and UL’s Anti-Counterfeiting Programs.

How do I know if a switchboard or panelboard is Listed for top or bottom feed or both?

Switchboards are Listed under the category Deadfront Switchboards (WEVZ), located on page 325 in the 2007 UL White Book. This information can also be located using UL’s Online Certification Directory at entering "WEVZ” at the UL Category Code Search.

How do I know if a meter socket was evaluated for a top or bottom feed or both?

UL Lists meter sockets under the product category Meter Sockets (PJYZ) located on page 233 in the 2007 UL White Book. This information can also be located using UL’s Online Certification Directory at by entering "PJYZ” at the UL Category Code Search.

How can these computer carts in hospital rooms be Listed when they conflict with the XBYS Guide Information?

As indicated in the question, the Guide Information for Relocatable Power Taps (XBYS) located on page 343 of the 2007 UL White Book states that relocatable power taps are not intended for use in general or critical patient care areas of a hospital.

I have seen these power strips that pop up out of a counter in a kitchen, are these power strips Listed for use in kitchen counters?

UL Lists power strips under the product category "Relocatable Power Taps (XBYS).” Guide Information for this product category can be found on UL’s Online Certification Directory at, and on page 343 in the 2007 UL White Book.

What is AWM and can I use it for field wiring and comply with the NEC?

I encountered some wire that was marked AWM and was marked with a style number, yet there was no type marking on the insulation that is mentioned in Article 310 in the NEC. What is AWM and can I use it for field wiring and comply with the NEC?

Some ground-fault circuit interrupter (GFCI) receptacles that carry a rating of 20 amps are provided with a 15-A NEMA configuration receptacle. Can you tell me why the GFCI is not the same?

Ground-fault circuit interrupters are Listed under the category of the same name with the category code (KCXS) located on page 170 in the 2007 UL White Book. Ground-fault circuit-interrupter receptacles are evaluated for compliance with the Standard for Safety for Ground-Fault Circuit Interrupters, UL 943.

In the 2008 NEC, Section 406.8(A) and (B) require receptacles installed in damp or wet locations to be weather-resistant. How will these be identified?

Weather-resistant receptacles are Listed under the category Receptacles for Plugs and Attachment Plugs, (RTRT), located on page 284 in the 2007 UL White Book. The UL Guide Information for RTRT in the 2007 White Book does not include the marking information for weather-resistant receptacles; however, the information is available on UL’s Online Certification Directory at and enter RTRT at the category code search.

How are Listed tamper-resistant receptacles identified?

Tamper-resistant receptacles are Listed under the product category Receptacles for Plugs and Attachment Plugs, (RTRT), located on page 284 in the 2007 UL White Book or on UL’s Online Certification Directory at and enter RTRT at the category code search. The Guide Information for RTRT will be updated in the 2008 White Book to reflect the requirements in dwelling units as indicated below.

Are concentric and eccentric knockouts on panelboards Listed for bonding at over 250-volts? How about on outlet boxes?

No. Enclosures for panelboards as well as enclosed switches are evaluated using requirements in the UL Standard for Safety for Enclosures for Electrical Equipment, UL 50. Requirements in UL 50 do not include an evaluation of concentric and/or eccentric (also known as tangential) knockouts for bonding. UL did have requirements in place at one time, which detailed construction, and performance requirements for evaluating concentric and/or eccentric knockouts for this purpose. Subsequent to actions taken by the UL 50 Standards Technical Panel (STP) in 2005, these requirements were withdrawn.

Is a CE Mark the same as a NRTL mark?

No, a NRTL Mark is the certification mark of a nationally recognized test lab as accredited by the Occupational Health and Safety Administration (OSHA). You can determine which test labs are nationally recognized testing laboratories (NRTLs) as well as the scope of their accreditation (which standards they can certify to as a NRTL) by accessing www.osha. gov/dts/otpca/nrtl The UL Mark is the most well known and accepted NRTL Mark.

Has UL listed any CSST? Does UL list connectors to bond CSST?

As of this writing (June 2007), UL has not Listed any CSST or any grounding or bonding fittings intended for use on hexagonal shaped CSST fittings intended to bond CSST. Corrugated Stainless Steel Tubing (CSST) is a flexible corrugated tubing made of stainless steel with a polymeric jacket that is used in many areas of the country for distribution of natural gas. The technical bulletin in question recommends the use of a ground clamp secured around the hexagonal compression nuts on CSST fittings to bond the CSST gas piping system to the grounding electrode system.

If underground service entrance cable Type USE conductor insulation is not marked as an RHW conductor, can USE cable be used inside for premise wiring?

Underground service-entrance cable Type USE, is not Listed for use inside for premises wiring except for termination at the service equipment or metering equipment. Multiconductor USE conductors utilize insulation that is equivalent to RHW or XHHW conductors when additionally marked as type RHW or XHHW. Single conductor Type USE cable does not have conductor insulation which is equivalent to RHW or XHHW type insulation or any other type of building wire.

I was told that I could not plug one extension cord into another on a construction site. The NEC does not seem to prohibit this practice. Where do I find such information?

UL Lists what every one knows as "extension cords” as cord sets under the product category Cord Sets and Power Supply Cords (ELBZ), located on page 65 in the 2006 UL White Book or online at and enter ELBZ at the Category Code search. Cord sets and power supply cords are evaluated for compliance with the Standard for Safety for Cord Sets and Power Supply Cords, UL 817.

I am a Canadian electrical inspector and want to know what is the UL White Book and is there a UL White Book for Canada?

The UL White Book is a regulatory reference tool that UL provides to AHJs and others to verify the Listing scope of UL Listed electrical products installed in the field. The Guide Information for each UL product category details the scope of the Listing, important installation and marking information, identification of the standard or other requirements used for Listing as well as how to identify products Listed under the product category.

Are all split bolt clamps Listed to be used for connecting copper grounding electrode conductors to steel rebar direct buried in earth, and if so how can these clamps be identified?

Typical split bolt connectors are not Listed for connection of a grounding electrode conductor to rebar, they are intended for connection of two conductors in an ordinary dry location inside an enclosure and are Listed under the category Wire Connectors, (ZMVV) located on page 307 in the 2006 UL White book or online at and entering ZMVV at the Category Code Search. These type of split bolts connectors are not intended to be used for grounding applications to connect a grounding electrode conductor to rebar or any other component of the grounding electrode system. The Listing Mark on the connector or packaging would identify it as a wire connector.

Does UL List the spiralshaped compact fluorescent lamps (e.g. light bulbs)?

UL does List the spiral shaped types of compact fluorescent lamps (CFLs) that are very popular right now. These types of lamps consist of a self-contained fluorescent tube and ballast in an enclosure with a medium base screw shell adapter that will screw into any medium base lamp holder. This category also covers self-ballasted lamps employing light emitting diode (LED) lights.

I see that the 2006 White Book now includes an index that correlates the 2005 NEC to UL product categories, is there a UL code correlation database online that I can access?

The answer is yes; there is a UL code correlation database on In the past several issues of the UL Question Corner, we discussed all the new features in the 2006 UL White Book that make it the companion tool to the NEC. One of those features is the Index of Product Categories Correlated to the 2005 NEC, the index is a code correlation index. UL took that data and incorporated that into an online version in a database form that correlates the 2005 NEC to UL product categories and also includes various building, mechanical and gas codes.

Are low-voltage landscape luminaires (lighting fixtures) Listed to be installed in the ground 3 feet from a swimming pool?

UL Listed low-voltage landscape luminaires are for installation not less than 10 ft from a swimming pool, whether in or on the ground, and are not for use where supplied by a Listed swimming pool transformer or any other power source other than a Listed landscape power unit.

The Index of UL Product Categories Correlated to the NEC-2005 seems like a great tool, how do I use the index to determine compliance with the NEC?

The new Index of Product Categories Correlated to the NEC-2005 provides a direct link between individual sections within the NEC and corresponding UL product categories that may be applicable to that section of the code. The index starts on page 311, and is simple to use, just look up a particular NEC section number and read across to locate the corresponding UL category code and page number on which the complete guide information for the category is located. This will direct you to the UL Guide Information for the product category, which provides important information regarding the applications for which the products covered under the product category are Listed.

The 2006 UL White Book is much larger than the 2005, what has changed and how do I use the White Book in the field?

The 2006 UL White Book has under gone many changes and can be considered THE Companion Tool to the National Electrical Code, NEC. Besides a new name, 2006 Guide Information for Electrical Equipment, White Book and a new look, here are some of the highlights

What are the new listing requirements for GFCIs and when will they go into effect?

Effective July 28, 2006, new requirements go into effect in the Standard for Safety for Ground Fault Circuit Interrupters, UL 943. These requirements are to address new requirements for an end of life test and for a revised miswiring test.

What happens if I use the factory provided holes in the bus?

Switchboards are Listed under the product category Deadfront Switchboards, (WEVZ), located on page 264 of the 2006 White Book or online at and enter the Category Code WEVZ. Switchboards are not Listed for drilling holes in the buswork in the field and tapping branch circuits off of the bus.

Are EMT offset connectors or any EMT connectors or fittings Listed for use with threaded hubs, such as on a conduit body or Myers hub?

All hubs are intended for use with threaded conduit, not fittings. Hubs are provided with a tapered thread, and so is threaded conduit such as rigid metal conduit or intermediate metal conduit (IMC). EMT fittings have a straight thread and are designed for use with a lock nut, intended to secure to an enclosure through a knock out or punched hole.

Are there any Listed MC cable connectors for use with this cable?

There is a new type of MC cable for use in dry locations only, that is of the interlocked metal tape–type. It is constructed with a bare aluminum grounding/bonding conductor that is sandwiched between the Mylar wrap around the conductors and the interlocked metal tape armor. That construction ensures intimate metal contact of the grounding/bonding conductor and the metal armor sheath of the cable.

Is it permitted to paint the face of a receptacle to match the paint in a room?

Receptacles are Listed under the category Receptacles for Plugs and Attachment Plugs (RTRT), located on page 109 in the 2005 White Book. Receptacles Listed under this category are evaluated for compliance with the Standard for Receptacles for Plugs and Attachment Plugs, UL 498.

Can a Listed panelboard be retrofitted into an existing cabinet that may be cemented into an existing wall?

Panelboards are Listed under the category Panelboards (QEUY) located on page 92 in the 2005 UL General Information Directory for Electrical Equipment, the White Book. The Guide Information for QEUY states panelboards are intended for mounting in cabinets or cutout boxes, which may be provided with the panel or provided separately. Only panelboards marked to indicate that they are for use in a specific box and panelboards labeled as ‘‘Enclosed Panelboards’’ have been investigated to determine that box wiring space is adequate.

I know that UL provides strong support for the IAEI at section meetings, but what support do you provide for IAEI divisions or chapters?

UL and the IAEI work together on a common public safety goal. As you noted this is done in a number of ways, including providing technical support at all the section meetings, not merely attending and providing cute trinkets as handouts. We also publish technical articles for IAEI News as well as this column, provide complimentary White Books and other technical aides and support the IAEI in many other fashions.

Do these conductors have to be routed in the same cable or raceway or can the signal wire be routed separately?

Many hard-wired smoke alarms illustrate the interconnection of smoke alarms in their installation instructions depicting 3 wires, hot, neutral and the signal wire and indicate the signal wire can be as small as 18 AWG. Do these conductors have to be routed in the same cable or raceway or can the signal wire be routed separately?

Is it permitted to replace a sign face on a listed sign?

This question was addressed in the March/April UL Question Corner column and since the publication, UL received a number of follow-up questions regarding this issue. It should be noted that UL 48, the Standard for Electric Signs anticipates that sign faces may likely be changed from time to time due to commercial changes in product and property ownership as well as damage that may occur to sign faces.

Are fire alarms listed as a system and not just listed components?

Fire alarm equipment is listed as individual products; however, these products are evaluated as part of a complete system. The compatible Listed equipment that forms the alarm system is specified in the installation instructions/wiring diagram referenced on the Listed product’s marking, by part number and revision level, and included with the product. The compatibility may be identified in the installation instructions for either the control unit or the device connected to the control unit.

Are commercial cooking appliances such as commercial electric ranges listed for use in a household?

Commercial cooking appliances, such as commercial electric ranges, are not listed for use in a household. UL lists commercial cooking equipment including commercial electric ranges under the category Commercial Cooking Appliances, (KNGT), located on page 231 of the 2004 White Book. The Guide Information states, "This category covers cooking equipment intended for commercial indoor use, such as…ranges, and other appliances for use in commercial kitchens, restaurants, or other business establishments where food is dispensed.”

Is it permitted to replace a sign face on a listed sign?

Depending on the sign design and the location of the sign, either dry or wet location, a sign face may provide many functions. In some cases the sign face may provide a weather shield, in other cases it may also provide the electrical enclosure for the sign. In either case the sign face material is required to have specific properties that must be verified if that sign is going to maintain its UL Listing.

Other than the typical fire and shock hazards, are there other safety concerns with motor-operated door systems that are commonly used for security in stores such as on pharmacy service counters?

Yes. Motor-operated door systems are listed under the category Door, Drapery, Gate Louver and Window Operators and Systems, (FDDR), located on page 224 of the 2004 General Information on Electrical Equipment Directory (The White Book). The standard is UL Standard for Safety for Door, Drapery, Gate, Louver, and Window Operators and Systems, UL 325.

What is the new process for performing a field evaluation?

UL’s Field Evaluated Product services have changed during the past year to include new processes, a uniform pricing schedule and improved delivery. But one thing hasn’t changed: field evaluations still often occur as unplanned have-to-get-it-done-today-or-mybusiness-can’t-open” events. UL conducts field evaluations to meet customers’ needs and to provide AHJs the information they need to "approve” installations. A field evaluation can be broken down into four phases, all often taking place in a few days: the request, dispatching of qualified field engineers, the evaluation and the report.

What are the types of equipment that can be subject to a field evaluation?

First, it is important to understand why field evaluations are performed. Section 90.7 of the 2002 National Electrical Code outlines specifific considerations for approval of equipment by the AHJ. Inherent in this language is the recognition that equipment should be evaluated to specific parameters by an organization with proper facilities to evaluate the construction and components of the equipment. Without third-party evaluated equipment, a jurisdiction would be faced with judging equipment based on NEC requirements alone. NEC requirements primarily focus on the installation of equipment and therefore, are not suitable for the evaluation of internal wiring and components used in many products.

Can I get an email update from UL when new information is added to UL’s Regulators page?

Yes, as of January 2004, the UL Regulators page at has added a function where you can register for email updates and select your interest area, such as electrical, building or fire and you will receive an ULtimate Email update when UL information that is of interest to you is developed. In order to register, just log on to and a popup window will appear. Complete the registration form and you will be registered to receive ULtimate email updates, so that you will always be the first to know.

Can low-voltage luminaires marked "for recreational vehicle use” be used in other locations?

Luminaires intended for RV use are listed under the category Low Voltage Luminaires for Recreational Vehicle Use (IFDQ) located on page 48 in the 2003 General Information for Electrical Equipment Directory (the White Book).

How can we tell if a UL Listing Mark is counterfeit?

For over a century, the UL Mark, has been considered the American Symbol of Safety. Each day, employees at UL go to work for a safer world. On the other end, counterfeiters go to work to profit at the expense of the public’s well being and a company’s reputation.

What should we do if we experience a nuisance trip on a UL Listed arc-fault circuit interrupter (AFCI)?

Most circuit breaker type AFCIs are Listed under the category Arc Fault Circuit Interrupters, Branch/Feeder Type (AVZQ) located on page five of the 2003 General Information for Electrical Equipment Directory (the White Book).

What UL Standard is used to evaluate portable power distribution units used at construction sites?

Portable power distribution units used at construction sites are evaluated for compliance with UL 1640, the Standard for Safety for "Portable Power Distribution Units.” These products are Listed under the product category Portable Power Distribution Units and Devices (QPSH), located on page 93 of the 2003 General Information for Electrical Equipment Directory (the White Book).

Is the flange that sticks down through the ceiling that the trim mounts through considered part of the points of support?

Type Non-IC recessed incandescent fixtures are Listed under the product category Incandescent Recessed Luminaires (IEZX), the UL Guide Information is located on page 45 in the 2003 White Book and includes important explanations of installation markings.

Are Listed wet location polymeric electrode insulator boots for neon lighting

There is one manufacturer that has a UL Listing for a wet location on their boots and it is only acceptable for use with GTO cable sleeving by that same manufacturer. Only the specific combinations identified in the instructions for a Listed polymeric electrode insulator boot have been found suitable for use in wet locations. You should always ask for and refer to the installation instructions provided with the Listed product for the proper component correlation.

Some outlet boxes are sold with clamps packaged in bulk, rather than included?

UL Listed outlet boxes may or may not be provided with clamps. When clamps are provided, they are required to be already mounted in place or provided in the carton with the outlet box. If the outlet boxes are bulk packaged, the clamps may be in a separate bag, but are still required to be provided in the same carton. An exception to this requirement is applicable when the box is marked for use with a specific clamp.

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).

Is Type RHH wire in EMT, with a two-hour fire rating Listed as circuit integrity cable?by Underwriters Laboratories

Fire resistive cables are Classified under the category "Fire Resistive Cables” (FHJR). The UL guide information can be found on page 233 of the 2001 White Book. Cables under this category are intended for installation in specific Electrical Circuit Protective Systems (FHIT) – located on page 232 of the 2001 White Book – as marked on the product or the smallest unit container. An example of the marking is noted below.

Are dry type transformers with expanded metal bottoms suitable for installation on combustible floors?

Dry type transformers with expanded metal bottoms are not suitable for installation on combustible floors. They are required to be enclosed. The enclosure houses all uninsulated live parts. However, the bottom of the enclosure does not need to be provided (or may have openings) for transformers intended to be pad mounted.

Is a meter socket with a marked rating of 160A/ 200A max intended to be installed on a 160 A or 200 A circuit?

A meter socket rated 160 A/ 200 A is intended for a continuous load of 160 A or a maximum non continuous load of 200 A. These products are Listed under the category Meter Sockets (PJYZ).

Can Power Strips be Daisy Chained or Plugged Directly into a Wall Receptacle?

GTO cable is Listed by UL under the product category, Gas Tube Sign and Ignition Cable (ZJQX). Listing information for GTO cable can be found on the UL Online Certification Directory at, or on page 119 of the 2001 print edition of the General Information for Electrical Equipment Directory (White Book). There currently are no stand-alone GTO cables that are UL Listed under ZJQX that do not need to be installed in a raceway.

With the soaring cost of energy and deregulation of the U.S. electrical power grid, alternate sources of power generation such as photovoltaic and fuel cell technology is on the increase. Does UL List this type of equipment?

UL currently Lists these types of alternative power sources and generation equipment Distributed Generation equipment includes but is not necessarily limited to photovoltaics, fuel cells, engine generator sets, and microturbines. The inverters or converters used to control grid interconnection are also considered to be DG equipment.

Modifications Affect UL Listing

The UL Mark applies to products as they were originally manufactured. UL does not know the effect modifications in the field will have on a product. Therefore, unless the modifications are specifically tested and evaluated by UL, UL cannot say that the modifications void the UL Mark, or that the product continues to comply with UL’s safety requirements. The exception would be when the product has specific replacement markings.

Are AFCIs required to undergo monthly testing like GFCIs?

Similar to GFCIs, UL 1699, the Standard for Arc-Fault Circuit Interrupters does require monthly testing. This requirement is communicated in the installation instructions. The installation instructions are also standardized to reduce the likelihood of miswiring.

Bi-national Standards for Luminaires Now in Effect

A new, bi-national standard that combines safety requirements for both the United States and Canada went into effect on January 31, 2001. This binational Standard, UL 1598/CSA 250 (or UL 1598/CSA-C22.2, No. 250.0) Standard for Safety for Luminaires, replaces three of the UL 1570 series of Standards for Safety for lighting products, including Fluorescent Lighting Fixtures (UL 1570), Incandescent Lighting Fixtures (UL 1571), and High Intensity Discharge Fixtures (UL 1572), and the Canadian lighting products standard SAC22.2, No. 9.096, General Requirements for Luminaires or CSA Spec. 9.

Prefabricated Buildings are Categorized and Given One Classification Mark

Occasionally the word "recommended” appears in manufacturers’ installation instructions. For example, "it is recommended that this product be used on a separate branch circuit.” Does the installer need to follow manufacturers’ "recommendations” to comply with Section 110-3(b) of the National Electrical Code (NEC)?

UL Can Help Determine Equipment Replacement During Natural Disasters

The product you mentioned was probably an older power supply cord. At one time, UL did permit power supply cords for connection to electrical appliances to bear Listing Marks indicating that such cords were in compliance with UL Standards for Safety. Although the product identifier on the label indicated that the product covered by the Listing Mark applied only to the power supply cord, UL discontinued marking power supply cords because consumers were under the mistaken impression that the Mark applied to the entire electrical appliance.

UL Requires American Standard-Sized Mounting Hardware

All UL Listed luminaires must be equipped with American standard-sized mounting hardware. Over the past few years, UL received a limited number of field reports regarding luminaries being provided with metric mounting hardware. UL Listed luminaires exported to the United States are required to be equipped with American standard-sized hardware.

Metallic and Non-metallic Outlet Boxes Used in Fire-rated Assembly

Metallic Outlet Boxes are Listed under the category Metallic Outlet Boxes (QCIT), in the UL Electrical Construction Equipment Directory. The Guide Information for QCIT specifies the installation requirements for use in fire-rated assemblies. Information about UL-Listed metallic outlet boxes, including the Guide Information, can also be found by accessing UL’s online product certification database at

Five New Categories for AFCI Devices Under UL 1699

In the March-April issue of IAEI News’ "UL Question Corner,” UL indicated that arc-fault circuit interrupters (AFCIs) were covered under the product category of Circuit Breakers, Molded Case, Classified for Mitigating the Effects of Arcing Faults (DIWL). Since then, the UL engineers responsible for AFCIs have pointed out that this category has been phased out and replaced by five new categories specifically for AFCI devices, now covered under UL 1699, Standard for Arc-Fault Circuit Interrupters.

Does UL review installation instructions?

Yes, during Listing and Classification investigations, UL does evaluate the manufacturer’s installation instructions provided with UL certified products. Many UL Standards specify numerous requirements for the content of the installation instructions. UL reviews installation instructions to verify proper content and determine if the product can be installed and operated as intended in accordance with the applicable UL Standards, which are compatible with the installation codes. For electrical products, the National Electrical Code (NEC), NFPA 70, is the applicable code.

The new Section 210-12 of the 1999 National Electrical Code (NEC) requires arc-fault circuit-interrupter protection for some branch circuits. Does UL List such devices?

Arc-Fault Circuit-Interrupters (AFCIs) are currently covered under the category Circuit Breakers, Molded Case, Classified for Mitigating the Effects of Arcing Faults (DIWL). The Guide information can be found on page 11 of the 1999 General Information for Electrical Equipment Directory (white book). This category covers Listed molded case circuit breakers, which are also Classified after being evaluated for their ability to mitigate the effects of arcing faults that may pose risk of fire ignition under certain arcing conditions.

Modifications Affect UL Listing

The UL Mark applies to products as they were originally manufactured. UL does not know the effect modifications in the field will have on a product. Therefore, unless the modifications are specifically tested and evaluated by UL, UL cannot say that the modifications void the UL Mark, or that the product continues to comply with UL’s safety...

How does UL assess water-damaged electrical equipment?

How does UL assess water-damaged electrical equipment?

I recently encountered a lightning protection system on a water treatment plant that was certified by UL. What is a "Letter of Findings”?

I recently encountered a lightning protection system on a water treatment plant that was certified by UL with what was referred to as a ‘Letter of Findings.’ The only type of lightning protection certification I’m familiar with is the UL Master Label. What is a ‘Letter of Findings,’ and what other types of certifications currently are available for lightning protection systems?

Which GTO cable types may be used in electric signs?

Question: Which GTO cable types may be used in electric signs? I am especially interested in the cable that looks like a coaxial cable.

Outlet boxes for Ceiling Fans

Question: For outlet boxes that support ceiling suspended fans, does UL consider out-of-balance fans?

Variations in Exit Signs

UL listed exit signs must meet the requirements outlined in UL 924, the Standard for Emergency Lighting and Power Equipment. These fixtures are intended for installation in accordance with the National Electrical Code, ANSI/NFPA 70, and the Life Safety Code, ANSI/NFPA 101. Some of the listing requirements are as follows.