advanced search

Code Quandaries

Jul 1, 2007 12:00 PM, By Mike Holt, NEC Consultant

Stumped by the Code?

All questions and answers are based on the 2005 NEC.

Q. Can I pass conductors from one panel through another panel? If so, what are the restrictions?

A. Yes, cabinets, cutout boxes, and meter socket enclosures can be used as a raceway for conductors that feed through if the conductors do not fill the wiring space at any cross section to more than 40% [312.8], as shown in the Figure.

Service conductors and other conductors are permitted to be installed in the same enclosure [230.7]. Splices and taps can be installed in cabinets, cutout boxes, or meter socket enclosures if the splices or taps do not fill the wiring space at any cross section to more than 75% [312.8].

Q. What are the rules for installing fluorescent luminaires in clothes closets?

A. There are specific clearances that must be maintained for either fluorescent or incandescent luminaires installed in a clothes closet. Here are the rules from 410.8(D):

1. Surface-mounted, totally enclosed, incandescent luminaires must maintain a minimum clearance of 12 inches from the storage space.

2. Surface-mounted fluorescent luminaires must maintain a minimum clearance of 6 inches from the storage space.

3. Recessed incandescent luminaires with a completely enclosed lamp must maintain a minimum clearance of 6 inches from the storage space.

4. Recessed fluorescent luminaires must maintain a minimum clearance of 6 inches from the storage space.

Q. What are the disconnecting means requirements for transformers?

A. The NEC does not have specific requirements for disconnecting means at a transformer; however, you must follow the overcurrent protection requirements of Art. 450 and Art. 240.

Q. In what rooms of a home is an electrical panel with breakers prohibited?

A. Overcurrent protection devices should not be located where they would be subjected to physical damage or in areas where they might create a fire or safety hazard [240.24(C)]. Some specific locations are prohibited in dwelling units. They include:

• Near easily ignitible material, such as in clothes closets [240.24(D)]. The purpose of keeping overcurrent protection devices away from easily ignitible material is to prevent fires — not to keep them out of clothes closets.

• In the bathrooms of dwelling units, or guest rooms or guest suites of hotels or motels [240.24(E)]. The service disconnecting means must not be located in a bathroom, even in commercial or industrial facilities [230.70(A)(2)].

Q. Can Type NM cable in a dwelling unit be used to wire recessed light fixtures that require the circuit conductors to have at least a 90°C rating?

A. Yes, Type NM conductors are rated at 90°C [334.104], even though the ampacity is required to be selected based on the 60°C column of Table 310.16 [334.80].

Q. I have noticed that some light fixtures located in the attics and crawl spaces of numerous residences have been damaged unintentionally. Does the NEC require fixtures in these locations to be suitably guarded against accidental damage?

A. Nothing in the NEC requires guarding of light fixtures in the attics of dwelling units. When installed around combustible material, luminaires are required to have guards to limit the temperature around the combustible material [410.5].

Q. A 30kVA, 480V/208V transformer is fed by a 60A, 3-pole breaker from a 480V panel. This transformer secondary then feeds a 120V/208V panel, which is located within 10 feet of conductor length. Is secondary overcurrent protection required for the secondary conductors?

A. The NEC permits 10 feet of secondary conductors without secondary conductor protection if [240.21(C)(2)]:

• The ampacity of the secondary conductor must not be less than:

  a. The calculated load in accordance with Art. 220,

  b. The rating of the device supplied by the secondary conductors or the overcurrent protective device at the termination of the secondary conductors, and

  c. Not less than one-tenth the rating of the overcurrent device protecting the primary of the transformer multiplied by the primary-to-secondary transformer voltage ratio.

• The secondary conductors must not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply.

• The secondary conductors must be enclosed in a raceway. Secondary overcurrent protection is not required for the secondary conductors, but overcurrent protection is required for lighting and appliance branch-circuit panelboards. This protection is required to be located on the secondary side of the transformer [408.36(D)].

---

Acceptable Use Policy blog comments powered by Disqus

Browse Back Issues Select an Issue November 2009 October 2009 September 2009 August 2009 July 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 1, 2009 December 2008 November 2008 October 1, 2008 September 2008 August 2008 July 2008 June 1, 2008 May 2008 April 2008 March 2008 February 2008 January 2008 December 2007 November 2007 October 2007 September 2007 August 2007 July 2007 June 2007 May 2007 April 2007 March 2007 February 2007 January 2007 December 2006 November 2006 October 2006 September 2006 August 2006 July 2006 June 1, 2006 May 1, 2006 April 2006 March 1, 2006 February 2006 January 2006 December 2005 November 2005 October 2005 September 2005 August 2005 July 2005 June 2005 May 2005 April 2005 March 2005 February 2005 January 2005 December 2004 November 2004 October 2004 September 2004 August 2004 July 2004 June 2004 May 2004 April 2004 March 2004 February 1, 2004 January 1, 2004 December 1, 2003 November 1, 2003 October 1, 2003 September 1, 2003 August 1, 2003 July 1, 2003 June 1, 2003 May 1, 2003 April 1, 2003 March 1, 2003 February 1, 2003 January 1, 2003 December 1, 2002 November 1, 2002 October 1, 2002 September 1, 2002 August 1, 2002 July 1, 2002 June 1, 2002 May 1, 2002 April 1, 2002 March 1, 2002 February 1, 2002 January 1, 2002 December 1, 2001 November 1, 2001 October 1, 2001 September 1, 2001 August 1, 2001 July 1, 2001 June 1, 2001 May 1, 2001 April 1, 2001 March 1, 2001 February 1, 2001 January 1, 2001 December 1, 2000 November 1, 2000 October 1, 2000 September 1, 2000 August 1, 2000 July 1, 2000 June 1, 2000 May 1, 2000 April 1, 2000 March 1, 2000 February 1, 2000 January 1, 2000 December 1, 1999 November 1, 1999 October 1, 1999 September 1, 1999 August 1, 1999 July 1, 1999 June 1, 1999 May 1, 1999 April 1, 1999 March 1, 1999 February 1, 1999 January 1, 1999 December 1, 1998 November 1, 1998 October 1, 1998 September 1, 1998 August 1, 1998 July 1, 1998 June 1, 1998 May 1, 1998 April 1, 1998 March 1, 1998 February 1, 1998 January 1, 1998 December 1, 1997 November 1, 1997 December 1, 1996 November 1, 1996 October 1, 1996 September 1, 1996 August 1, 1996 July 1, 1996 June 1, 1996 May 1, 1996 April 1, 1996 March 1, 1996 February 1, 1996 January 1, 1996 December 1, 1995 November 30, 1995 November 1, 1995 October 1, 1995 September 1, 1995 August 1, 1995 July 1, 1995 June 1, 1995 May 1, 1995 April 1, 1995 March 1, 1995 February 1, 1995

browse e-newsletters