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Code Quandaries

Feb 1, 2004 12:00 PM, By Mike Holt, NEC Consultant

Q.

How is the working space width requirement of 110.26(A)(2) measured?

A. The working space must be a minimum of 30 inches wide, but in no case may it be less than the width of the equipment. The width of the working space is measured from left to right, right to left, or simply from the center line of the equipment. In all cases, the working space must be of sufficient width, depth, and height to permit at least a 90° opening of all equipment doors (Fig. 1).

Q.

Is GFCI protection required for a 20A, single-phase 208V pool pump motor that's hard wired?

A.

No, but it would be required if a receptacle provided power for water-pump motors and other loads directly related to the circulation and sanitation systems located within 10 feet of the inside walls of the pool [680.22(A)(1)].

The Code requires GFCI protection for all 15A and 20A, 120V through 240V receptacles that supply cord-connected pool-pump motors [680.22(A)(5)].

Q.

Can a 24V Class 2 cable that contains conductors for control or signaling be run in the same raceway with 120V power conductors?

A.

The general requirement is that Class 2 circuit conductors shall not be placed in the same raceway with conductors of power or Class 1 conductors [725.55(A)]. However, a Class 2 circuit can be installed with power or Class 1 circuits if they're reclassified as Class 1 and installed in accordance with the requirements for Class 1 circuits (Art. 725, Part II). In addition, the Class 2 marking on the equipment must be removed, and overcurrent protection be provided in accordance with 725.23 [725.52(A)(1) Ex. No. 2].

Class 1 circuits may only be located in the same cable, enclosure, or raceway with power-supply circuits where the equipment powered is functionally associated with the Class 1 circuit [725.26(B)(1)].

Q.

Can communications cable be installed within supply and return air ducts?

A.

Yes. Communications cables can be installed in ducts, plenums, and other spaces used for environmental air as long as the cable is Type CMP [800.53(A)].

Q.

This question is in reference to separately derived systems under 600V installed within a building. Why does the NEC require a separately derived system to be grounded to a grounding electrode in accordance with 250.30(A)(2) and (A)(4), if the system ‘xo’ terminal is bonded to the system equipment grounding (bonding) conductor?

A.

I don't think there is any technical reason to ground a separately derived system to an electrode if the system is under 600V — especially if it's located indoors. Since a separately derived system is bonded to the metal parts of the electrical installation [250.30(A)(1)], a zero system reference is established, the system voltage is stabilized, and the system-bonding conductor provides the low impedance path necessary to clear a ground fault.

Don't forget that system bonding automatically grounds the system to the building grounding electrode system via the effective ground-fault path.

Q.

I learned today that the state electrical inspector doesn't require electrical equipment to be listed or labeled. As a result, unlisted equipment is typically installed in our industrial facility. Does the inspector have the right to wave this significant NEC requirement?

A.

The NEC doesn't require all electrical equipment to be listed, it specifies that the authority having jurisdiction (AHJ) is responsible for deciding on the approval of equipment and materials (90.4 and 110.2). The key to understanding this concept is that electrical equipment is required to be “approved” by the AHJ, not “listed or labeled.” Approved means “acceptable to the authority having jurisdiction” (Art. 100). However, listing and labeling is often the basis for approval (90.7), and 110.3 provides guidance for the evaluation of equipment by the AHJ.

Q.

I'm planning to run three rigid nonmetallic conduits that each contains 500 kcmil conductors to supply a 1,200A panel from the service disconnect. According to Table 250.122, I need to supply a 3/0 AWG ground wire. Do I have to pull a ground wire in each conduit?

A.

Well, let's first get the feeder conductor properly sized. A 1,200A feeder requires 600 kcmil conductors, not 500 kcmil. This is because the ampacity of 500 kcmil is only rated 1,140A (380A × 3) at 75°C [110.14(C) and 240.4(C)].

Now, back to your question. The equipment grounding (bonding) conductor must be a minimum of 3/0 AWG, and it must be installed in each of the raceways.

Q.

We use cords for motor connections in a Class I hazardous location in our industrial facility. I've been told that the cord must be explosionproof. Is there such a thing as an explosionproof cord?

A.

There's no such thing as an explosionproof cord. The NEC only requires that the cord be of a type listed for extra-hard usage in accordance with Table 400.4 (501.11).

Need some help with an installation? Clashing with the local inspector? E-mail Mike at mike@mikeholt.com with a description of the situation.