Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to codefaqs@gmail.com. Answers are based on the 2014 NEC.

What is a knife switch?

While preparing for a shutdown, we ran into an interesting situation. The owner was involved in the shutdown planning, preparation and execution. To create an electrically safe working condition, we were following our written lockout/tagout program and NFPA 70E requirements. Part of the shutdown required the opening of multiple 480-volt (V) loads with 600-ampere (A) fused disconnects. The owners’ representative informed us that, since the NEC prohibited a knife-blade-type switch rated over 1,000A from being opened under load, they wanted another procedure even though these disconnects were rated at 600A. We argued that the fused disconnects were rated to be opened under load and that there was no issue. Eventually, we agreed and arranged to shut down the majority of their facility. Does the NEC prohibit a knife-blade-type disconnect from being opened under load?

The issue here is the lack of defined terms and a general misunderstanding of the term “knife switch.” The NEC requirements that the owner referenced are located in Section 404.13, Knife Switches. This requirement prohibits knife switches rated more than 1,200A at 250V or less and more than 1,000A at 251V to 1,000V from being used to open a load. At the above ratings, they are only permitted as isolating switches. The NEC does not define “knife switch,” “dead front switch” or “enclosed switch.”

The UL product category descriptions clear up the confusion. A knife switch, as Section 404.13 references, falls under the product category WIOV, which covers open-type knife switches. The 600A fused disconnects you referenced are not open-type knife switches. They are enclosed switches, which fall under the UL product category WIAX. This category does not prohibit enclosed switches from being opened under load.

In addition, dead-front switches are covered under UL product category WHXS. Dead-front switches have all current-carrying parts enclosed in a panelboard or dead-front switchboard. This category does not prohibit dead-front switches from being opened under load. Perhaps the NEC should define these terms to provide clarity with respect to the requirements of Section 404.13.

Authority having jurisdiction

The definition of authority having jurisdiction (AHJ) seems to be clear. However, the informational note that accompanies the definition explains that, in many circumstances, the property owner can assume the role of AHJ. Why was that inserted in the definition? Could it be that, where public safety is concerned, an inspector is needed, but where private premises are involved, the property owner could override any other AHJ?

The definition of AHJ is intentionally written in a broad manner. The NEC is a consensus code. It is not a law or regulation that can be enforced unless it is formally adopted by a municipality, township, county, state or other body.

Where the NEC is formally adopted, it is enforced in many different ways. Typical enforcement begins with a requirement to obtain an electrical permit, which would initiate an electrical inspection. In some areas, there may be city or municipal inspectors; in others, those responsibilities are delegated to a third party.

There are many reasons for requiring an electrical inspection. The primary reason is public safety. The informational note clarifies that, where public safety is primary, the AHJ may be a federal, state, local or other regional department or individual such as a fire chief; fire marshal; chief of a fire prevention bureau, labor department, or health department; building official; electrical inspector; or others having statutory authority. The informational note explains that, in some situations, the property owner or a designated owners’ agent assumes the role of the AHJ.

In some large, industrial installations, local codes require compliance with the NEC but do not provide inspection services. In these cases, the owner is the AHJ. This does not mean that a homeowner, for example, can override an electrical inspector where the local requirements assign the inspector with the duties of the AHJ.

High-voltage warning signs

Does the NEC require all pull boxes for high-voltage conductors to be marked as such? We recently had to add warning signs on all junction and pull boxes for 15-kilovolt (kV) feeders we had previously installed.

Yes, the NEC requires warning signs to be posted at all points of access to conductors in all conduit systems and cable systems where the voltage is more than 1,000V nominal. This is a general requirement that applies to all wiring methods containing conductors at more than 1,000V.

This requirement is located in Article 300, which contains general requirements for all wiring methods and materials. Part II contains general requirements for wiring methods and materials operating at more than 1,000V nominal. This marking must be located at “all points of access to conductors in all conduit systems and cable systems,” meaning all junction/pull boxes as well as all distribution and utilization equipment. Prescriptive text is provided for the warning signs as follows:


Equivalent insulation?

In Section 110.14(B), there is a requirement that all splices “shall be covered with insulation equivalent 
to that of the conductors.” I assume 
that means equal to the voltage rating, 
not the mil thickness. How would one achieve this requirement?

Section 110.14 contains requirements for all electrical connections. As you have stated, the first level subdivision 110.14(B) contains a specific requirement that mandates the insulation used for all splices to be equivalent to the insulation on the conductors being spliced. An equivalent insulation for splices requires an understanding of the properties of the conductor insulation involved, the environment and the products used to make the splice. Multiple ratings must be considered including, but not limited to, system, voltage, temperature and exposure to damp or wet locations.

It is important to note that 110.14(B) also requires splices to be made with “devices identified for the use.” Article 100 defines the term “identified” as being “recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.”

The accompanying informational note explains that this determination of suitability for the intended purpose is typically done by qualified testing laboratories through listing and labeling, an inspection agency, or other organizations concerned with product evaluation. This essentially means we need to use splicing devices that are included by the equipment manufacturer or listed devices.

Many types of listed splicing devices are available on the market today, the most common of which is the wire nut. These listed devices must be used in accordance with their listing and labeling and may include devices listed for applications, such as wet locations or direct burial.

MC cable jacket

On a recent service call, we found isolated grounding-type receptacles that were fed with standard type MC cable. The insulated green conductor in the MC cable was terminated on the isolated equipment-grounding terminal on the receptacle. The metal box was grounded only by the metal jacket on the MC cable. This did not seem right. Can one use the metal jacket of type MC cable as an equipment grounding conductor (EGC)?

Section 110.18 lists all types of permitted EGCs. List item 250.118(10) addresses MC cable. Three different permitted methods are listed. I assume by “standard type MC cable,” as stated in your question, that this installation consisted of MC cable with an interlocked metal sheath (not a solid jacket) and a single insulated EGC. In that case, the interlocked metal sheath alone is not recognized as an EGC, and the installation would be in violation of the NEC. 

If the jacket on the MC cable was smooth or corrugated tube-type MC cable that is listed and identified as an EGC, this would be a compliant installation. MC cable manufacturers have product offerings for every type of installation. Where an installation requires an isolated EGC, it is typical to see MC cable made for this specific purpose with two EGCs, one for the isolated EGC termination and one for general grounding requirements.

Readily accessible

The definition of “readily accessible” uses the word “obstacle.” What does that mean? Is a couch in front of a GFCI- or AFCI-type receptacle an obstacle?

The NEC does not define commonly used terms such as the word “obstacle.” In this case, we must look in the dictionary and find that an obstacle is considered to be “a thing that blocks one’s way or prevents or hinders progress.”

The NEC uses the term “readily accessible” where it recognizes that users of electrical equipment must be able to quickly access equipment. Sections 210.8 and 210.12 require GFCI and AFCI devices to be readily accessible. A couch in front of a GFCI- or AFCI-type receptacle installed in accordance with sections 210.8 or 210.12 would be considered an obstacle, rendering those devices not readily accessible due to the fact that obstacles must be removed to gain access. Installers can easily avoid this type of violation by placing these devices at a switching location, which would not typically have ready access hindered by an obstacle.