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. Send questions to [email protected]. Answers are based on the 2020 NEC.

Battery rooms

What is a battery room? The local authority having jurisdiction (AHJ) is requiring doors that open in the direction of egress with listed panic hardware for an electrical equipment room, but not as required in 110.26(C)(3). There are also four large battery racks installed in this room as part of a UPS system. Is the AHJ correct?

The requirements for personnel doors that open in the direction of egress with listed panic hardware or fire exit hardware in 110.26(C)(3) are based on the presence of equipment rated  at 800 ampere (A) or more and the distance from this equipment to the door(s) intended for entrance/egress from the working space.

The NEC does not provide any criteria for the designation of a “battery room.” If drawings designate that space as a battery room, this requirement will apply. The AHJ may also have the authority to designate the space as a battery room. Section 480.10(E) provides requirements for egress from battery rooms and requires personnel doors intended for entrance to, and egress from, rooms designated as battery rooms to open in the direction of egress, and they must be equipped with listed panic or listed fire exit hardware.

Portable receptacles

Can metal electrical boxes be mounted on portable tool carts and wired with flexible power cords? I have seen such carts for sale with metal boxes or a power strip flush-mounted on the top or side. I have also seen mechanics with portable tool carts where they screwed or bolted on a metal electrical box with a flexible power cord to power a duplex receptacle or two. What NEC rules apply here? Is a GFCI required?

The scope of the NEC in 90.2(A) covers the installation and removal of electrical conductors, equipment and raceways outlined in six list items. List item (1) identifies public and private premises, including buildings, structures, mobile homes, recreational vehicles and floating buildings. While the NEC does cover appliances, it does not cover a receptacle outlet installed in a portable manner on a cart with wheels. The equipment you have described is not an appliance because it does not use electrical energy.

Where this type of equipment is sold as a complete unit, the installation of a receptacle(s) would be covered in the applicable product standard. Where such a portable tool cart is used in construction, the OSHA 1926 construction standard would apply as well as the requirements of NEC Section 590.6 (GFCI). GFCI protection is required and could be provided at the receptacle outlet where the cart is plugged in, at the source of the circuit (circuit breaker), through a listed GFCI identified for portable use or in the male cord cap supplied on the cart.

New emergency disconnects

In the new requirements for an outdoor emergency disconnect for services supplying one- and two-family dwellings, I understand a meter disconnect but disagree with list item (3), which will permit a circuit breaker and it would not be the service disconnect! We’ve never allowed that before; why now? These disconnects should be renamed because many will think the disconnect is for an emergency system! What if the homeowner locks the disconnect?

I understand that this new requirement in the 2020 NEC for emergency disconnects may be hard for the installer and inspector to initially buy into because we have always been taught that the first disconnect and OCPD is the service disconnect. That mindset has served us well for many years. The technical committee that developed this text discussed each of your concerns at length.

This requirement is in Section 230.85 and requires all service conductors supplying one- and two-family dwelling units terminate in a disconnecting means with a short-circuit current rating equal to or greater than the available fault current, and it must be installed in a readily accessible outdoor location. If there is more than one service disconnect, the emergency disconnects must be grouped.

There are three permitted methods for installing this disconnect, giving installers options. List item (1) permits the service disconnect to be installed outdoors. It is common in some areas to see service equipment for dwelling units installed outdoors. This option can be applied anywhere and compliance is easy; all they need to do is label the disconnect as both the “emergency disconnect” and the “service disconnect.” List item (2) permits a meter disconnect and the enclosure is required to be labeled as “Emergency disconnect,” “Meter disconnect” and “Not service equipment.” List item (3) permits other listed disconnect switches or circuit breakers on the supply side of each service disconnect that are suitable for use as service equipment. The required label would be “Emergency disconnect, not service equipment.” This includes a molded-case circuit breaker and is a cost-effective option.

There are many possible devices that could be used including, but not limited to, molded-case switches, disconnects and SUSE rated transfer switches. This requirement is for a disconnect that first responders can open in the event of fire or emergency. Using a circuit breaker makes sense because they are economical and readily available. Eliminating permission to use a circuit breaker as an emergency disconnect because it provides a level of protection is not a persuasive argument in this case. The term “emergency disconnect” was discussed at length and chosen as the proper identification. Emergency systems are not used in one- and two-family dwelling units. Fire service professionals are quite capable of removing any lock.

Conductor protection

I think you misinterpreted the question regarding conductor protection in your October 2019 article. He is probably running NM inside the dwelling and then changing over to THWN in the whip to the disconnect on the exterior. If we were using something other than type NM to go outdoors, what is permitted?

This question has generated multiple responses. Thanks so much for reading and commenting, and please keep sending your questions and comments!

There are multiple items to address here. Type NM cable is not permitted in wet locations. It is very common to see Type NM cable run from the inside of a dwelling unit and then in LNFMC for example, going directly to outdoor disconnects and AC condensing units. That is not permitted. When sizing branch-circuit conductors, overcurrent protection and overload protection for AC units, Article 440 applies. In general, 440.6(A) requires the rated-load current marked on the nameplate of the equipment in which the motor-compressor is employed to be used in determining the rating or ampacity of the branch-circuit conductors, the branch-circuit short-circuit and ground-fault protection, and the separate motor overload protection. However, many air conditioners (HVAC equipment) are considered as multimotor and combination-load equipment, and the requirements of 440.4(B) mandate the equipment be provided with a visible nameplate marked with the minimum supply circuit conductor ampacity, and the maximum rating of the branch-circuit short-circuit and ground-fault protective device (OCPD).

In this case, all of the calculations have been performed, and the installer simply complies with the nameplate information. Is a 40A OCPD permitted to protect a 10 AWG copper conductor? Yes, provided the remaining requirements in Article 440 are met. Where only the rated load current is provided, 440.32 requires the minimum size branch-circuit conductor to be 125% of the rated load current. Section 440.22(A) permits the branch-circuit short-circuit and ground-fault protection to be rated at 175% of the rated current, and permission exists up to 225% if the device sized at 175% is not sufficient for the starting current of the motor. 440.52(A) requires the motor-compressor to be protected against overload and failure. If overload protection is not provided by list items: (1) a separate overload relay, (2) a thermal protector integral with the motor-compressor or (4) another protective system, list item (3) applies and limits the fuse or circuit breaker sized above in 440.22(A) to 125% of the rated load current.