advanced search

Stumped by the Code?

Jan 1, 2010 12:00 PM, By Mike Holt, NEC Consultant

All questions and answers are based on the 2008 NEC.

Q. Do I need a grounding conductor for a pole light, or is the ground rod good enough?

A. You absolutely need an equipment grounding conductor. Metal parts of electrical raceways, cables, enclosures, or equipment must be bonded together (and to the supply system) in a manner that creates a low-impedance path for ground-fault current that facilitates the operation of the circuit overcurrent device [250.4(A)(5)].

Because the earth is not suitable to serve as the required effective ground-fault current path, an equipment grounding conductor is required to be run with all circuits.

Danger: Because the contact resistance of an electrode to the earth is so high, very little fault current returns to the power supply if the earth is the only fault current return path. What’s the result? The circuit overcurrent device will not open, and all metal parts associated with the electrical installation, metal piping, and structural building steel will become and remain energized.

Q. We are told that we must GFCI protect our drinking fountain, but the receptacle is buried behind the unit. Do we really have to do this?

A. All electric drinking fountains must be GFCI-protected [422.52], but if you are really concerned about accessibility, you can always use a GFCI breaker for protection.

Q. What are the NEC requirements when replacing 15A or 20A, 125V receptacles?

A. See 406.3(D) as follows: Grounding-type receptacles. Where an equipment grounding conductor exists, grounding-type receptacles must replace nongrounding-type receptacles, and the receptacle's grounding terminal must be connected to an equipment grounding conductor in accordance with 406.3(C) or 250.130(C).

Nongrounding-type receptacles. Where no equipment grounding conductor exists in the outlet box for the receptacle, such as old 2-wire Type NM cable without an equipment grounding conductor, existing nongrounding-type receptacles can be replaced in accordance with one of the following:

• Another nongrounding-type receptacle.
• A GFCI-type receptacle marked "No Equip¬ment Ground."
• A grounding-type receptacle, if GFCI protected and marked "GFCI Protected" and "No Equipment Ground."

Caution: The permission to replace nongrounding-type receptacles with GFCI-protected grounding-type receptacles doesn't apply to new receptacle outlets that extend from an existing outlet box that's not connected to an equipment grounding conductor. Once you add a receptacle outlet (branch circuit extension), the receptacle must be of the grounding type — and it must have its grounding terminal connected to an equipment grounding conductor of a type recognized in 250.118, in accordance with 250.130(C).

When existing receptacles are replaced in locations where GFCI protection is currently required, the replacement receptacles must be GFCI protected. This includes the replacement of receptacles in dwelling unit bathrooms, garages, outdoors, crawl spaces, unfinished basements, kitchen countertops, rooftops, or within 6 ft of laundry, utility, and wet bar sinks. See 210.8 for specific GFCI-protection requirements.

Author's comment: GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor because the circuit equipment grounding conductor serves no role in the operation of the GFCI-protection device. See the definition of "ground-fault circuit interrupter" for more information.

Q. A conduit contains six current-carrying 10 AWG THHN conductors on a roof for a photovoltaic system, where the ambient temperature 94ºF and the ambient temperature add is 60ºF in accordance with Table 310.15(B)(2)(c). How do I determine the conductor ampacity for this condition of use?

A. When conductors are installed in an ambient temperature other than 78°F to 86°F, ampacities listed in Table 310.16 must be corrected in accordance with the multipliers listed in Table 310.16. Where the number of current-carrying conductors in a raceway or cable exceeds three, the allowable ampacity of each conductor, as listed in Table 310.16, must be adjusted in accordance with the adjustment factors contained in Table 310.15(B)(2)(a) and 310.15(B)(2)(c). When both of these conditions exist, you must do both calculations, but you can start with the 90°C ampacity for the calculations [110.14(C)(1)].

Table 310.16 ampacity if 10 AWG THHN is 40A

Ambient temperature correction [Table 310.16] = 0.58, based on 154ºF

Conductor bundle adjustment [310.15(B)(2)(a)] = 0.80, six current-carrying conductors

Adjusted ampacity = 40A x .58 x 0.80

Adjusted ampacity = 18.56 or 19A

Q. We got written up for having our underground conduits too close together. I know you can't bundle cables together, but I didn't think this applied to raceways too. Does it?

A. Actually, it does. In 310.15(B)(2)(b), it states that spacing between conduits, tubing, or raceways must be maintained, even though the Code doesn't say what the spacing is — or how to adjust when the spacing is not maintained. Hopefully, the next Code cycle will have better language for this rule.

---

Acceptable Use Policy blog comments powered by Disqus

Browse Back Issues Select an Issue EC&M Magazine | April 2012 March 2012 February 2012 January 2012 December 2011 November 2011 October 2011 September 2011 August 2011 July 2011 June 2011 May 2011 April 2011 March 2011 February 2011 January 2011 December 2010 November 2010 October 2010 September 2010 August 2010 July 2010 June 2010 May 2010 April 2010 March 2010 February 2010 January 2010 December 2009 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 February 1, 1995 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

browse e-newsletters