If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2011 NEC.
Bonding both ends of a raceway
A recent job required me to bond both ends of a raceway to the grounding-electrode conductor. The raceway was enclosing the grounding--electrode conductor. What is the purpose of this requirement?
If a ferrous (iron) metal raceway is used to enclose the grounding-electrode conductor, the grounding-electrode conductor must be bonded to the raceway at both ends [250.64(E)] to ensure the raceway and the conductor are in parallel. This is to prevent an inductive choke on the grounding-electrode conductor. When current is flowing in the grounding--electrode conductor, the condition creates a magnetic field around that conductor. The build up and collapse of this magnetic field with the alternating-current flow induces a current flow in the raceway. This current flow is in an opposite direction and opposes or chokes the current flow on the grounding--electrode conductor. Paralleling the raceway and the grounding-electrode conductor prevents this choke effect.
Concrete-encased electrodes vs. grounding rods
Why do the people who make the NEC believe the “concrete-encased electrode” is better than the two ground rods in “direct” contact with the ground?
Extensive testing has shown that ground rods deteriorate over time, and their effectiveness is reduced considerably. Concrete-encased electrodes have greater contact with the earth and will be there as long as the building is there.
The cause of GFCI nuisance tripping
What causes nuisance tripping of ground-fault circuit interrupters (GFCIs)?
A GFCI will open when it senses a current flow to ground of 4 to 6 milliamps (mA). If it opens without 4 to 6 mA flowing to ground, it is defective. If the installer follows the manufacturer’s instructions [110.3(B)], there should be no tripping, nuisance or otherwise, unless there is a ground fault.
Code oversight with regard to enclosure location
Why do enclosures in wet locations above ground not have the same clear statement as shown in 300.5(B) for underground installations? Have I missed something, or can terminations in above-ground enclosures installed in a wet location be other than ones listed for a wet location? It seems to me that, if I run my raceways with the fittings to make them “raintight “ (225.22) and the inside of the raceway is still considered a wet location, the same thought should apply to enclosures installed with the same integrity.
The accepted proposal for considering the interiors of raceways—installed in wet locations above ground—as wet locations did not include enclosures (as 300.5(B) shows for underground locations). However, the absence of the requirement to include enclosures installed above ground outdoors does not mean the enclosures are considered a dry location. The conductors installed in outdoor raceways above grade must be listed as suitable for use in a wet location [310.10(C)(3)]. The enclosures are subject to the same condensation effects as the raceway. I thought this oversight would be corrected in the 2011 NEC, but we’ll have to wait for the 2014 Code.
Moisture inside and outside raceways
Can you explain “arranged to drain” in 225.22 and 230.52? Is this in reference to moisture inside or outside of the raceway?
This requirement covers the moisture that accumulates within the raceway due to condensation caused by the temperature difference between the air inside and surrounding the raceway. Properly installed raceways on the exterior of a building will prevent the entrance of water from rainfall. Raceways installed on the exterior of a building can be arranged to drain by providing weep holes at low points in the run and in junction boxes.
I am curious about your response in the January issue about tamper-proof receptacle requirements. It would seem that the building (a woodworking workshop) could have receptacles that are not dedicated to machinery and could be considered convenience outlets. NEC 210.52(G)(1) provides a requirement for receptacle outlets in addition to those for specific equipment. Would not such convenience receptacles be required to be tamper-proof?
Upon further review, I believe you are correct. At least one receptacle outlet is required by 210.52(G)(1) in the accessory building and must be tamper-resistant in accordance with 406.12. However, note that “tamper-proof” is not the terminology used; the correct term is “tamper-resistant.”
Ground-fault protection minimum
I am installing a 1,200-amp (A) I-line panel as a service entrance with four breakers: 600A, 400A, 250A and 225A. NEC 230.71 allows me to do this without a main disconnect. However, my customer and I would prefer to install a 1,200A main breaker in this panel so that only one handle pull would be required to disconnect the service. According to 230.95, I need ground-fault protection on a service disconnect of 1,000A or larger. My understanding is that the four breakers used by themselves as the service-disconnecting means would not require ground-fault protection under 230.95. Are we required to have ground-fault protection on a main breaker installed in this same panel as long as there are six or less individual breakers all under 1,000A?
Ground-fault protection of equipment is required only for service disconnects rated 1,000A or more on grounded wye services of more than 150 volts to ground (230.95). If you install a 1,200A main disconnect on a grounded wye service, it falls under this requirement, and ground-fault protection of equipment is required.
Bath fan/light and ground-fault protection
If an approved bath fan/light is installed directly above a bathtub or in a shower stall, where in the Code does it state that the circuit supplying it has to be ground-fault-protected?
There is no requirement that a bath fan/light be ground-fault-protected. However, it can be installed on the ground-fault protected 20A branch circuit required by 210.11(C)(3) where it is a single bathroom and the exception is used. The exception refers to 210.23(A)(1) and (A)(2).
Hot tub wiring in dry locations
In regards to using Type NM cable for a hot tub in a dwelling unit, does the Code permit the use of NM cable in dry locations for hot tub wiring?
NEC 680.21(A)(4) permits Type NM cable to be used for hot tub wiring in the interior of dwelling units. Where run in a cable assembly, the equipment--grounding conductor can be uninsulated, but it shall be enclosed within the outer sheath of the cable assembly.
I was just reading the question about Article 312.8 in your column in the January 2011 issue of Electrical Contractor. I have always seen 312.8 to allow the splices as long as the cross-sectional area restrictions were applied. I can see where some get their opinion about the adequate space needed to be identified somehow, but I feel that it is being taken out of context.
NEC 312.8, regarding the wiring space for enclosures for switches and overcurrent devices, has been revised for the 2011 edition. A new third condition requires a warning label to be applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors. The 2011 NEC shows the adequate spacing and requires approval from the authority having jurisdiction (AHJ).
ASDs and bypass devices
I think you misread the Code rule in 430.122. Your answer in the November 2010 issue indicates that the rule requires conductors sized based on the motor current. That is not the case with the supply conductors to an adjustable speed drive. The conductors are required to be sized at a minimum of 125 percent of the rated input current of the drive. The size of the motor does not enter into this, and there is no exception that would permit a smaller supply conductor even in the cases where the drive has been oversized.
Yes, you are correct. I should have been more specific. NEC 430.122(B) applies to an adjustable speed drive system that uses a bypass device. The circuit conductors shall be the larger of either of the following: (1) 125 percent of the rated-input current to the power conversion equipment or (2) 125 percent of the motor full-load current rating as determined by 430.6. For an adjustable speed drive system, other than one that uses a bypass device, the branch-circuit conductors must have an ampacity not less than the 125 percent of the rated input current to the power conversion equipment [430.122(A)].
Sheet metal lining panelboard
We have installed a piece of sheet metal to the inside lining of the bottom of a panelboard in order to cover up all the old knockouts. Does this invalidate the Underwriters Laboratories’ rating of the panelboard?
NEC 110.12(A) requires unused openings to be closed to afford protection substantially equivalent to the wall of the equipment. I don’t see a problem with it, depending on the workmanship of the installation; however, it is subject to the AHJ’s approval.
TROUT answers the Code Question of the Day on the NECA NEIS website. He can be reached at email@example.com.