Ecmweb 2257 001ecmcqfig1
Ecmweb 2257 001ecmcqfig1
Ecmweb 2257 001ecmcqfig1
Ecmweb 2257 001ecmcqfig1
Ecmweb 2257 001ecmcqfig1

Stumped by the Code? January 2010

Jan. 1, 2010
Do I need a grounding conductor for a pole light, or is the ground rod good enough?

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.

About the Author

Mike Holt

Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.

Voice your opinion!

To join the conversation, and become an exclusive member of EC&M, create an account today!

Sponsored Recommendations

Electrical Conduit Comparison Chart

CHAMPION FIBERGLASS electrical conduit is a lightweight, durable option that provides lasting savings when compared to other materials. Compare electrical conduit types including...

Fiberglass Electrical Conduit Chemical Resistance Chart

This information is provided solely as a guide since it is impossible to anticipate all individual site conditions. For specific applications which are not covered in this guide...

Considerations for Direct Burial Conduit

Installation type plays a key role in the type of conduit selected for electrical systems in industrial construction projects. Above ground, below ground, direct buried, encased...

How to Calculate Labor Costs

Most important to accurately estimating labor costs is knowing the approximate hours required for project completion. Learn how to calculate electrical labor cost.