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 [email protected]. Answers are based on the 2014 NEC.


Receptacles and EGC connections


When installing receptacles in metal boxes, I know a wired connection of the equipment-grounding conductor (EGC) to the device is not required as long as I connect the EGC to the metal box. My question is about an installation of electrical metallic tubing with a copper EGC installed as per the drawings. This question is specifically about a receptacle we have to install in a 4-inch-by-1½-inch metal box with a raised cover. Metal contact will be made between the receptacle and the cover, as well as the raised cover to the box. So it seems we can install the device in the raised cover without a wire connection to the EGC. Is that correct?


The NEC permits a receptacle to be installed in a metal box without a wired connection to an EGC if the installation meets prescriptive requirements. Section 250.146 provides requirements for connecting grounding terminals to metal boxes. The general rule is that an equipment-­bonding jumper must be installed to connect the receptacle’s grounding terminal to the grounded box. Where an EGC is installed and spliced within the box or terminated on equipment within or supported by the box, Section 250.148 requires the EGC to be connected. The required equipment-­bonding jumper must be sized in accordance with Section 250.122 based on the rating of the overcurrent protective device supplying the branch circuit.


To address the first statement in your question, Section 250.146(B) permits receptacles that are designed and listed as self-grounding together with the supporting screws on the device to establish the equipment bonding between the yoke on a receptacle and a flush-type metal box. An installation of a receptacle in a raised cover on a surface-mounted box is very different and is addressed in Section 250.146(A). The required equipment bonding for a receptacle installed in a raised cover is recognized only where the combination of the box and cover are listed to provide grounding continuity. In addition, the receptacle must be connected to the raised cover with at least two permanent fasteners or two thread-locking screws/nuts and the corners of the raised cover (where it attaches to the surface-mounted box) must be flat or nonraised to ensure electrical continuity.


Outdoor hot tub


I know your answers are based on the 2014 NEC, but my question deals with the 2011 edition, which we still use in my area. Recently, we did electrical work for a new, outdoor hot tub. Fortunately, the owner contacted us early, and we informed him that, before the concrete was poured, we had to install an equipotential bonding grid. We called the electrical inspector for a rough inspection before the concrete was poured, and he told us that, if we used a listed spa, the equipotential bonding was not required. We left it in because it was already done. I can see this change in 2014 but not 2011. Apparently, there was a midcycle change that we had no idea had occurred. How did that happen?


When an NEC technical committee (TC) realizes there was an oversight or mistake during an NEC revision cycle, two signatory committee members can submit a Tentative Interim Amendment (TIA). The TIA is then balloted through the TC and then the NEC Correlating Committee. The ballot for a TIA looks at technical merit (to ensure the revision is technically sound and correlates with other requirements) and emergency nature (to ensure there is significant reason to make a midcycle change).


In the 2011 NEC, Section 680.43 for indoor spa/hot tub installations was modified with an exception that exempted the need for equipotential bonding in Section 680.26 if the spa/hot tub was a listed self-contained unit installed above a finished floor. The TC decided the same type of change should be made for an outdoor spa/hot tub, so a TIA was submitted, which passed ballot for technical merit but failed for emergency nature. A subsequent appeal to NFPA standards council D#11-2 was upheld, and TIA 11-1 was published on Mar. 1, 2011. Code users should regularly go to www.nfpa.org and check for errata and any TIAs that may have been published for their respective NEC edition. See TIA 11-1 for the revised requirement where the 2011 NEC is still adopted.


Surface metal raceway 
conductors


When calculating the conductor fill in surface metal raceway, is it permitted to determine the allowable fill by using the conductor sizes in square inches from Table 5 and the approximate square-inch measurement of the individual surface metal raceway?


No, Section 386.22 provides requirements for the number of permitted conductors or cables in surface metal raceway. The raceway design will determine the maximum number of conductors permitted, not a calculation. See the manufacturer’s labeling and instructions.


Manufacturers of surface metal raceway provide conductor fill information for all of their products. I suggest you determine the number of conductors the installation needs and the appropriate size of surface metal raceway, to install by visiting the manufacturers’ website before installation.


Fireproofing


On a recent job, we had many discussions about fireproofing openings in fire-rated walls. We struggled, but the electrical inspector was well-versed in applicable building codes and was a big help. Section 300.21 is quite confusing. The first sentence tells us that we must install so that the spread of fire is not “substantially increased.” What does that mean? Is a little fire OK? The rest of the requirement basically tells us to use approved fire-stopping materials. The informational note does steer the user to parties that can provide more information, but this is confusing as well. My research shows the 24-inch spacing always applies. Also, every opening must be fire proofed, not just those without minimum spacing. Why is the NEC so vague here? We should have the exact requirements in 300.21.


No, a little fire is not OK! When we penetrate a fire-rated assembly, it is compromised. Yes, we will fireproof the opening, but it is not equal in rating to a similar assembly without penetration. That is the reason the NEC states, “will not be substantially increased.”


Section 300.21 contains general requirements for the fireproofing of any penetration in any fire-rated wall, floor or ceiling that is made as part of an electrical installation. The requirements for fireproofing openings made in fire-rated assemblies to install raceways, cable assemblies and other electrical equipment are outside of the NEC’s scope. Other codes and standards will provide prescriptive requirements for fireproofing these openings. Section 300.21 is a performance-based requirement. We cannot get prescriptive because there are far too many different scenarios encountered when fireproofing.


Also, the building codes that address fireproofing are subject to change. The requirements themselves may change, and the authority having jurisdiction determines which edition of applicable codes and standards applies in your area. I do believe the informational note should be expanded or a new informational note added to reference applicable sections in building codes for NEC users. Be sure to submit your ideas in the form of a public input for the 2020 NEC.


Branch circuit or 
receptacle ratings


When installing branch circuits at 15 and 20 amperes (A), the NEC has strict rules on the rating of receptacles with respect to the size of the branch circuit. If we have a load such as a standard dwelling-unit refrigerator, and we put it on its own 20A branch circuit, why must we install a 20A receptacle when the cord is a 15A configuration? The same holds true for a 15A branch circuit: why can’t I just use a 20A receptacle? The 15A breaker will never allow more than 15A.


The general NEC requirement for single receptacles on an individual branch circuit in Section 210.21(B)(1) requires the receptacle to have an ampere rating not less than the branch circuit rating. This is based on the fact that this is an individual branch circuit, which by definition supplies only one piece of utilization equipment. 


The intent of this rule is to size the receptacle to allow for a single utilization equipment with the same rating of the branch circuit to be supplied. While your question discusses a single dwelling-unit-type refrigerator with a 15A cord cap, there are refrigerators that are rated and supplied with a 20A cord cap. Where a 15A branch circuit is installed, the NEC prohibits the installation of a 20A receptacle. This is to prevent utilization equipment rated at 20A from exceeding or overloading the 15A branch circuit.