NEC Code Quandry
 

Questions and Answers - April 2000

Question:

I am an apprentice electrician and I was told that the 1999 NEC requires wall-mounted receptacles for commercial buildings to be mounted so that the bottom of the cover plate is no less than 15 inches from the floor. Is this True?

Answer: No. There is no NEC requirement on the height of wall-mounted receptacles in residential, commercial, or industrial facilities.

Question:

I recently installed a 480/120-208 volt transformer and I bonded the X0 terminal (neutral) to the case of the transformer and I ran a grounding electrode conductor to effectively grounded building steel. A co-worker insists that the X0 terminal (neutral) should only be bonded to the case of the transformer and not to the building steel. He cited recent changes in Articles 230 and 250. Whoís correct?

Answer: You are correct. The NEC Section 250-30 specifies that the system grounded (neutral) conductor be bonded to the equipment grounding conductor on the secondary side of the transformer. In addition, the same Code rule requires a grounding electrode conductor to be run from the secondary grounded (neutral) conductor to an effectively grounded structural metal member of the structure, or an effectively grounded metal water pipe within 5 ft from the point of entrance into the building. If both of the above electrodes are not available, then any electrode specified in Sections 250-50 or 250-52 can be used, Figure 1.

Note: Figures not on Internet.

Question:

Is there any distance a switch must be located from a bathtub, shower space, or hydromassage bathtub?

Answer: No. However, Section 380-4 does require switches not be installed within the wet location of a tub, shower space, or hydromassage bathtubs, see Section 680-71, Figure 2.

Note: Switches must be located 5 feet from pools, fountains, spas, and hot tubs, see Sections 680-6(c), 680-12, 680-38, 680-41(c).

Question:

I know a 20 ampere circuit is required for the washing machine in a dwelling laundry room, but am I required to install a single receptacle or could I use a duplex receptacle?

Answer: The NEC does not require a separate receptacle for the washing machine. It requires at least one receptacle for the laundry area [210-52(f)]! Section 210-11(c)(2) specifies that one 20 ampere branch circuit must be provided to supply the laundry area receptacle outlets. Therefore, the laundry area receptacle branch circuit can supply more than one receptacle, either single or duplex. For example, the circuit could have a duplex receptacle for the washing machine and the gas dryer motor, and a second duplex receptacle for convenience, Figure 3.

Note: The laundry area receptacle branch circuit is not permitted to supply any other outlets.

Question:

Is there a Code rule that requires a raceway seal to prevent water and moisture from entering underground raceways? I have owned my home for over 6 years and recently water has been entering my house through the electrical system. Water enters the meter enclosure from the underground service raceway, and then it drains into the panel, which then pours into the walls of my home via the electrical raceways. Is there a Code rule to prevent this?

Answer: Yes, there are a few on this subject.

1. Where a service raceway enters a building from an underground raceway, it must be sealed in accordance with Section 300-5(g), [230-8].

2. Underground raceways through which moisture may contact energized live parts shall be sealed or plugged at either or both ends [300-5(g)].

Note: Water entering a building from an underground raceway occurs with the building is located downhill from the service transformer.

Question:

We recently had a contractor bond the neutral and grounds at both the transformer case and at the secondary disconnect. When asked about bonding at two separate locations, he said that the transformer is the same as the power companyís transformer and the secondary disconnect is the same as the service entrance equipment. Is their thinking correct?

Answer: No. Transformers (separately derived systems) can only be bonded at one location. This connection can be made at any point on the separately derived system from the source to the first system disconnecting means [250-30(a)(1)].

A new exception was added to Section 250-30(a)(1) to permit a bonding jumper at both the source and the first disconnecting means, where doing so does not establish a parallel path for the grounded circuit conductor. I have spent many hours thinking about this new exception and the only way I figure you could use it is if the building does not have any metal members (no metal studs, no metal water pipe, no steel framing, etc.), and all of the electrical raceways are nonmetallic. Therefore, for all practical purposes, the neutral-to-ground bond should only be done at one location, either at the source or at the first system disconnecting means.

Question:

I have been in the practice of installing speakers for sound and public address systems on to metal poles for sports fields for years. We have always installed our cables inside a nonmetallic raceway within the pole to assure our speaker wiring was separated from the power wiring. We take care to separate our Class 2 or 3 cables from the power wiring by having internal dividers and boxes. Does the NEC prohibit us from continuing this practice?

Answer: Maybe and maybe not. Letís review a few Code rules to understand this issue better.

1. Changes to Section 410-15(b) in the 1999 NEC was made to recognize that metal poles could be used as a raceway to enclose lighting fixture supply conductors.

2. Section 640-9(a)(3) requires Class 2 or 3 cables used for sound and public address systems to be installed in accordance with the requirements of Article 725.

3. The exception to Section 725-54(a)(3)indicates that separation between Class 2 and/or Class 3 cables and power conductors is not required if either the Class 2 and/or 3 cables or the power conductors are installed in a raceway.

Okay, here are my opinions.

1. Nonmetallic Pole - Itís okay for Class 2 or Class 3 cables to be inside a raceway within a nonmetallic pole (concrete, fiberglass, etc.) with the poleís power conductors.

2. Metal Pole - I still feel Class 2 or Class 3 cables inside a raceway within a metal pole with the poleís power conductors would be just as safe, but Iím sure some inspectors will not permit this practice.

Question:

I am with the Army & Air Force Exchange Service. We are constructing a new data center and I have a question about the requirements for cables under raised floor. Are short (30 feet or less) jumper cords or power cords that plug into underfloor outlets required to be plenum rated?

Answer: No, the cords are required to be listed as Type DP (data processing cable). Section 300-22(d) identifies that electric wiring in air-handling areas beneath raised floors for information technology equipment must be in accordance with Article 645. Section 645-5(d) requires power, connecting, and interconnecting cables associated with information technology equipment be listed for data processing rooms and be marked Type DP. Type DP cable is constructed to have adequate fire-resistance characteristics suitable for use under a computer room raised floor [645-5(d)]. However, listed low-voltage and limited-energy cables are not required to be Type DP or plenum rated, Figure 4.

Note: All proposals (to the 2002 NEC) to allow short length power cords (non DP rated) to plug into underfloor outlets beneath raised floors for information technology equipment were rejected.

The above questions and answers (including graphics) by Mike Holt are in EC&M magazine. Click here for more magazine articles.

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