Here are the latest short answers to questions posted on our Web site. In our discussion, we will cover topics from Secs. 250-30, 250-50, 250-52, 300-22(d), 380-4, 410-15(b), 640-9(a)(3), 645-5(d), 680-6(c), 680-12, 680-38, 680-41(c), 680-71, 725-54(a)(3) and Arts. 230, 250, 645, and 725 of the National Electrical Code (NEC).
Q. I recently installed a 480/120-208V transformer. I bonded the X0 terminal (neutral) to the case of the transformer and ran a grounding electrode conductor to effectively grounded building steel. A coworker insisted that I should only bond the X0 terminal (neutral) to the case of the transformer and not to the building steel. He cited recent changes in Arts. 230 and 250. Who's correct?
A. You are correct. Sec. 250-30 specifies you should bond the grounded (neutral) conductor to the equipment grounding conductor on the secondary side of the transformer. In addition, the same Code rule requires you to run a grounding electrode conductor 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 you can use any electrode specified in Secs. 250-50 or 250-52.
Q. Are there any distance restrictions or requirements regarding how close you place a switch to a bathtub, shower space, or hydromassage bathtub?
A. No. However, Sec. 380-4 does prohibit you from installing switches within the wet location of a tub, shower space, or hydromassage bathtubs (see Sec. 680-71).
Note: You must install switches 5 ft from pools, fountains, spas, and hot tubs, see Secs. 680-6(c), 680-12, 680-38, and 680-41(c).
Q. I've installed speakers on metal poles for sound and public address systems for sports fields for years. We've always installed our cables inside a nonmetallic raceway within the pole to assure our speaker wiring remained separate 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?
A. Maybe, maybe not. Let's review a few rules to understand this issue better.
1. Changes to Sec. 410-15(b) in the 1999 NEC was made to recognize that you could use metal poles as a raceway to enclose lighting fixture supply conductors.
2. Sec. 640-9(a)(3) requires you to install Class 2 or 3 cables (used for sound and public address systems) in accordance with Art. 725.
3. The exception to Sec. 725-54(a)(3) indicates that separation between Class 2 and/or Class 3 cables and power conductors is not required if you install either the Class 2 and/or 3 cables or the power conductors in a raceway.
So now what? Here are my opinions. When working with nonmetallic poles, it's okay for Class 2 or Class 3 cables to be inside a raceway within a nonmetallic pole (concrete, fiberglass, etc.) along with the pole power conductors. However, I still feel Class 2 or Class 3 cables located inside a raceway within a metal pole along with the pole's power conductors would be just as safe. But I'm sure some inspectors will not permit this practice.
Q. 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. Must short (30 ft or less) jumper cords or power cords that plug into underfloor outlets be plenum rated?
A. No, the cords are required to be listed as Type DP (data processing cable). Sec. 300-22(d) identifies electric wiring in air-handling areas beneath raised floors for information technology equipment must be in accordance with Art. 645. Sec. 645-5(d) requires power, connecting, and interconnecting cables associated with information technology equipment be listed for data processing rooms and marked Type DP. Type DP cable has adequate fire-resistance characteristics suitable for this environment. However, listed low-voltage and limited-energy cables are not required to be Type DP or plenum rated.
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.