NEC Questions Based on the 2008 NEC
June Part 1
Here is the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent yesterday so you can see how you did.
By Mike Holt, for EC&M Magazine
Q1. What are the requirements for installing fixtures in bathroom?
A1. No part of chain-, cable-, or cord-suspended luminaires, track luminaires, or ceiling paddle fans can be located within 3 ft horizontally and 8 ft vertically from the top of the bathtub rim or shower stall threshold. Luminaires located within the actual outside dimensions of a bathtub or shower to a height of 8 ft from the top of the bathtub rim or shower threshold must be marked for damp locations. Where subject to shower spray, the luminaires must be marked for wet locations [410.10(D)].
Q2. Is the required working space for a panel measured from the panel guts inside the panel, or from the panel cover?
A2. The working space is measured from the enclosure front [110.26(A)(1)].
Q3. What are the requirements for installing communications cable underground?
Q4. Can a three pole breaker be used on a single phase (two-wire) load in a three phase panel?
A4. Yes. According the UL White Book (Product Category DIVQ), multipole common trip circuit breakers rated 125/250V are suitable for use for a single-phase multiwire circuit, with or without the neutral connected to the load.
Q5. Is there a minimum and/or maximum height when installing circuit breakers?
A5. There is no minimum height, except for manufactured homes [550.32(F)], which is two feet above grade. Circuit breakers must be installed so the center of the grip of the operating handle of the fuse switch or circuit breaker, when in its highest position, isn’t more than 6 ft 7 in. above the floor or working platform [240.24(A)].
Q6. What are the requirement for the placement of general-purpose receptacles in nondwelling unit occupancies? Is it every 12’ like dwelling units?
A6. No. The NEC is not a design manual, and therefore it does not have any requirements for convenient receptacle placement. This is all up to the designer.
Q7. Is a warning ribbon required for underground service conductors if installed in a raceway?
A7. No, only direct-buried service-lateral conductors not under the exclusive control of the electric utility [90.2(B)(5)] must have their location identified by a warning ribbon placed, in accordance with the requirements of 300.5(D).
Q8. Is a warning ribbon required for service conductors installed by directional boring?
A8. No. The only way to install a warning ribbon 12-inch above a bored hole containing service conductors would be to drill an additional hole with the ribbon inserted in the hole and pulled through from one location to another or to dig a trench to a depth 12-inches above the cable. In addition, since the ribbon would be installed in a drilled hole, the inspector would not be able to verify the depth of the ribbon as being 12-inches above the service conductors.
Q9. What are the requirements when installing a 120V switch in the same box with a 277V switch?
A9. Snap switches must not be grouped or ganged in enclosures with other snap switches, receptacles, or similar devices if the voltage between devices exceeds 300V, unless the devices are separated by barriers [404.8(B)].
Q10. What is the maximum number of bathroom receptacles that can be placed on the 20A 120V bathroom receptacle circuit in a single family dwelling?
A10. There are two options for wiring receptacles in dwelling unit bathrooms [210.11(C)(3)]:
- One 20A, 120V branch circuit can supply the all of the receptacle outlets required by 210.52(D) for dwelling unit bathrooms. This 20A bathroom receptacle circuit is not permitted to serve any other outlet, such as bathroom lighting outlets or receptacles in other rooms. In this case, the Code doesn’t have a limit on how many receptacles can be on the bathroom receptacle circuit.
- A single 20A, 120V branch circuit is permitted to supply all of the receptacle and lighting outlets as well as other loads in a single bathroom, as long as no single load fastened in place is rated more than 10A [210.23(A)].
Q11. Does the NEC limit voltage drop for parking lot lighting?
A11. Maybe. Electrical equipment must be installed in accordance with manufacturer’s instructions, which typically indicate that the maximum voltage drop is limited to 10% of the luminaire voltage rating. Many believe that the NEC requires conductor voltage drop to not exceed 3 percent, as per Fine Print Note 4 of 210.19(A)(1). Although this is often a good practice, it’s not a Code requirement because FPNs are only advisory [90.5(C)].
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