Location, Location, Location, Field Markings and More

By Jim Dollard | Feb 15, 2023
Photo of a well lit operating room
Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at [email protected]. Answers are based on the 2023 NEC.




An operating room is a wet procedure location

Article 517 has rules for wet procedure locations in 517.20. Is a standard doctors’ office a wet procedure location?

No, see Article 100 for the definition of a “wet procedure location.” It is an area in a patient care space (see the definition of patient care space category) where a procedure is performed that is normally subject to wet conditions while patients are present, including standing fluids on the floor or drenching of the work area, either of which condition is intimate to the patient or staff. An operating room is an excellent example of a wet procedure location, and the requirements of 517.20 include isolated power systems to provide an increased level of safety in these areas.

Woodshop as hazardous location

Is a woodshop a hazardous location? How do we make that determination? This is in a detached structure and feeder supplied from a dwelling unit. However, we also do work for a commercial cabinet shop.

As described in your question, the woodshop is likely to be used as a hobby and not a commercial facility significantly impacting the quantity of dust created. The NEC addresses installations where the presence of commercial dust creates a fire or explosion hazard. See Section 500.5(C) for Class II locations.

It can be difficult for an electrical contractor to determine whether a woodshop is a hazardous location. See informational note No. 1 following 500.5(C)(2) that explains the quantity of combustible dust and the adequacy of dust removal systems are factors that must be considered in the determination. There are other NFPA codes/standards that may also apply. For example, see NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities. This document will provide valuable information to help the owner make the determination. This standard references a deflagration hazard, which means the action of heating a substance until it burns away rapidly. NFPA 664 clearly states that the facility owner/operator is responsible for implementing the requirements of the standard (4.1.2). Additionally, it provides prescriptive criteria (4.1.3) to determine if a deflagration hazard exists, including a dust hazard analysis in Chapter 7.

Panelboard locations

Why does the NEC prohibit a panelboard in clothes closets and bathrooms? I have been doing residential work for over 40 years and never had an issue. In my area, the inspectors will not allow us to add to or upgrade a panelboard in a closet, creating significant financial hardship for owners. A panelboard in a bathroom is only an issue if it can be reached from the tub.

The two requirements referenced are typical issues in existing dwelling units. See 240.24(D), which prohibits overcurrent protective devices from being located in the vicinity of easily ignitible material, such as the clothes in closets. This requirement exists because an overcurrent device opening to clear a fault may vent or fail based on the fault level, the operating condition and condition of maintenance, which creates temperatures that can ignite “easily ignitible material.”

The second issue mentioned is in 240.4(E), which now prohibits overcurrent protective devices, other than supplementary overcurrent protection, from being installed in any bathrooms, showering facilities or locker rooms with showering facilities. The safety issues here are significant. Occupants with wet feet on grounded tile floors will access devices in a bathroom panelboard. 

The NEC does not address the cost to repair or replace an existing Code violation.

Colors for field markings

An inspector asked us to modify multiple field-applied labels we installed. Where can we find information on colors, font size, etc.?

Section 110.21(B) provides performance-­based requirements for field-applied labels or signs. This requires labels/signs to be sufficiently durable for the environment involved and warn of the hazards using effective words, colors, symbols or any combination thereof. No specific colors are mentioned. Two informational notes are provided following 110.21(B) and send the Code user to ANSI documents that contain useful guidance how to design, apply, use and properly place safety signs and labels.

Conduit fill

How can we apply the conduit fill tables in Annex C when it is just information and not enforceable? When calculating fill for multiconductor cables, where do we get the area in square inches for the cables? The manufacturer does not provide that information. I have a situation where I need four cables in EMT.

NEC requirements for conduit fill are located in the XXX.22 section, Number of Conductors, in each raceway article. This mandates that the number of conductors does not exceed that permitted by the percentage fill specified in Table 1, Chapter 9. Cables are also addressed here, and where they are permitted in a raceway, they too must not exceed the allowable percentage fill specified in Table 1, Chapter 9. See the table notes that accompany Table 1, Chapter 9. These are not informational notes; table notes are enforceable requirements. Note 1 sends Code users to Annex C, where all the conductors involved are of the same size, for example ten 12 AWG XHHW-2 conductors in EMT. Annex C has very simply done the math for us, and we can quickly access the right table to determine compliant conduit fill.

When a multiconductor cable is involved, the user must apply Note 9 to Table 1, which requires that a multiconductor cable, optical fiber cable or flexible cord of two or more conductors must be treated as a single conductor for calculating percentage conduit or tubing fill area. They key here is that the cable contains two or more conductors, but this does not address individual conductors. 

Your question mentions four cables in EMT, and as an example, we will consider four multiconductor cables in EMT. We must measure the outside diameter of the cable and get into Table 5 in Chapter 9. A multiconductor cable with an outside diameter of ½ inch is comparable (a bit smaller to work conservatively) to the larger diameter of a 2/0 AWG THHN conductor at 0.532 inches listed in Table 5. In a mix of conductors and cables, each cable can be considered as a 2/0 AWG THHN when calculating. Additionally, we can reference Annex C and would need 2-inch EMT for the four multiconductor cables. Note that if you directly convert diameter to area in square inches first, Table 4 can be applied and may result in a smaller raceway.

Mounting a panelboard sideways?

In a really tough situation, is it permitted to mount a 100A panelboard sideways? If not, we will need to add a junction box and extend existing branch circuits over 20 feet.

No, see Section 240.33. Circuit breakers are permitted to be installed horizontally, meaning that the off and on positions are achieved by moving the circuit breakers left or right. Circuit breakers must comply with Section 240.81, which requires circuit breaker handles that are operated vertically rather than rotationally or horizontally. The “up” position of the handle must be the “on” position.

shutterstock / Terelyuk

About The Author

DOLLARD is retired safety coordinator for IBEW Local 98 in Philadelphia. He is a past member of the NEC Correlating Committee, CMP-10, CMP-13, CMP-15, NFPA 90A/B and NFPA 855. Jim continues to serve on NFPA 70E and as a UL Electrical Council member. Reach him at [email protected].


featured Video


Why Vive Lighting Controls - The Benefits of Wireless

Vive by Lutron is a simple, scalable, wireless lighting control solution designed to meet today’s energy codes and budgets in both new and existing commercial buildings. Vive wireless systems install up to 70% faster than wired solutions, saving time, money, and labor costs.


Related Articles