NEC Questions and Answers

 

By Mike Holt for EC&M Magazine

 

Q1.Can a panel be installed in a residential bathroom? What about a bedroom?

A1. The NEC does not permit overcurrent protection devices to be located in the bathrooms of dwelling units, or guest rooms or guest suites of hotels or motels [240.24(E)]. Nothing in the code prohibits panels from being installed in bedroom.

 

Q2. Must I use a flexible wiring method for a 112.5 kVA dry-type transformer?

A2. No. Rigid metal conduit is often use in industrial installations for this purpose.

 

Q3. What are the rules on mixing emergency circuits in the same raceway or enclosure with nonemergency circuits?

A3. To ensure that a fault on the normal wiring circuits will not affect the performance of emergency wiring or equipment, all wiring from an emergency source, or emergency source distribution overcurrent protection, to emergency loads must be kept entirely independent of all other wiring and equipment, except as permitted for [700.9(B)]:

(1)       Wiring in transfer equipment enclosures

(2)       Wiring supplied from two sources in exit or emergency luminaires

(3)       Wiring from two sources in a common junction box, attached to exit or emergency luminaires

 

Q4. I recently saw an advertisement that red EMT conduit was required for emergency circuits. Is this a code requirement?

A4. No, only boxes and enclosures, including transfer switches, generators, and power panels for emergency circuits must be permanently marked as components of an emergency system [700.9(A)].

 

Q5. Can power conductors for an intercom system be mixed in the same raceway with the audio output conductors?

A5. No. Audio output circuits using Class 2 or Class 3 wiring methods must not be placed in any enclosure, raceway, or cable with conductors of electric light, power circuits [640.9(C) and 725.55].

 

Q6. What are the limitations on the use of rigid nonmetallic conduit underground for a gasoline dispenser?

A6. Rigid nonmetallic conduit can be installed underground below a Class I location if the raceway is covered with not less than 2 ft of earth, concrete, or asphalt [514.8 Exception 2]. However, threaded rigid metal or threaded intermediate metal conduit must be used for the last 2 ft of the underground run.

 

Q7. I have a house with a detached garage for aircraft. Are there any special rules that I need to know about?

A7. Yes Article 513 has lots of very stringent requirements for buildings or structures in which aircraft might undergo service, repairs, or alterations.

 

Q8. What are the NEC requirements for using electrical metallic tubing (EMT) to physically protect NM cable?

A8. For one, a nonmetallic bushing or adapter must be installed at the point where the cable enters the raceway [300.15(C)] and in unfinished basements the raceway and metal outlet boxes must be grounded (bonded) to an effective ground-fault current path in accordance with 250.148 [334.15(C)].

 

Q9. Does the NEC require safety chains on a high bay lighting fixtures?

A9. No, although your locally adopted building code might have rules for seismic restraint. Check with your local building inspector for information.

 

Q10. Can NM cable be used to wire a hot tub? What about a hydromassage bathtub?

A10. Outdoor hot tub motors must be installed in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or Type MC cable listed for the location (sunlight-resistant or for direct burial) [680.21(A)]. Indoor installations of hot tubs can be connected by any of the wiring methods contained in Chapter 3 [680.43]. Hydromassage tubs are also allowed to be installed by using any of the Chapter 3 wiring methods.