NEC Questions and Answers
May Part 1 of 2
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 rules in sizing a gutter?
A1. What many in the field call a ‘gutter’ is actually identified by the NEC as a Wireway, so we need to get the requirements from Article 376. A wireway must be sized to accommodate the maximum conductor fill, which is limited to 20 percent of the cross-sectional area of the wireway [376.22] and the conductors plus any splices and taps must not fill more that 75 percent of the wiring space at any cross section [376.56(A)].
Sizing for Conductor Bending Radius. Where conductors are bent within a metal wireway, the wireway must be sized to meet the bending radius requirements contained in Table 312.6(A), based on one wire per terminal [376.23(A)].
Wireway Used as Pull Box. Where conductors 4 AWG or larger are pulled through a metal wireway, the distance between raceway and cable entries enclosing the same conductor must not be less than required by 314.28(A)(1) and 314.28(A)(2) [376.23(B)].
Q2. Is the required width for working space around electrical panels measured from the center or edge of the enclosures?
A2. The width of the working space can be measured from the edge measuring left-to-right, from the right-to-left, or simply centered on the equipment and must be no less than 30 in. or the width of the equipment, whichever is greater [110.26(A)(2)]. Working space can overlap the working space for other electrical equipment.
Q3. Can the receptacles of two dwelling unit bathrooms be connected to the same 20A branch circuit or must they each be on a separate circuit?
A3. A single 20A, 120V receptacle branch circuit can be used to supply multiple bathroom receptacles, including receptacles in different bathrooms. One 20A, 120V branch circuit must be provided for the receptacle outlets required by 210.52(D) for a dwelling unit bathroom. This 20A bathroom receptacle circuit must not serve any other outlet, such as bathroom lighting outlets or receptacles in other rooms [210.11(C)(3)].
As an alternate method, a single 20A, 120V branch circuit is permitted to supply all of the outlets in a single bathroom, as long as no single load that is fastened in place is rated more than 10A [210.23(A)] and no outlets from outside the bathroom are included on this circuit [210.11(C)(3) Ex].
Q4. Must a multiwire branch circuit be on a two pole breaker, or can you use two single pole breakers?
A4. Individual single-pole circuit breakers without handle ties, individual single-pole circuit breakers with handle ties identified for the purpose, or a breaker with common internal trip, can be used for a multiwire branch circuit [240.20(B)(1)].
Multiwire branch circuits that supply devices or equipment on the same yoke (also called a strap) must be provided with a means to disconnect simultaneously all ungrounded conductors that supply those devices or equipment at the point where the branch circuit originates [210.4(B)]. This can be accomplished by individual single-pole circuit breakers with handle ties identified for the purpose or a breaker with common internal trip.
Caution: This rule is intended to prevent people from working on energized circuits that they thought were disconnected.
Q5. Is there anything in the Code that stipulates a distance that a light fixture can be
from a sprinkler head?
A5. The NEC does not have any requirement for this, but check with your local building officials as fire safety codes and the fire sprinkler manufacturer address this for surface mounted light fixtures (and other obstructions projecting below the ceiling) that might interfere with the sprinkler water spray coverage pattern.
Q6. How do you find the ampacity of a copper busbar?
A6. Multiply the cross sectional area of the copper busbar times 1,000A [366.23(A)].
For instance, the maximum ampere rating of a 4 in. x ½ in. copper busbar installed in an auxiliary gutter is:
4 in. x 0.50 in. = 2 sq in.
1,000A x 2 sq in. = 2,000A
Q7. Does the Code permit 15A duplex receptacles on a 20A circuit?
A7. Yes. Where connected to a branch circuit that supplies two or more receptacles, receptacles must have an ampere rating in accordance with the values listed in Table 210.21(B)(3), which allows 15 and 20A rated receptacles on a 20A rated circuit.
Q8. What are the disconnect requirements for outdoor spas or hot tubs?
A8. A maintenance disconnecting means is required for an outdoor spa or hot tub. The maintenance disconnecting means must be readily accessible and located within sight from the spa or hot tub [680.12], but not less than 5 ft horizontally from the inside walls of the spa or hot tub unless separated by a solid fence, wall, or other permanent barrier [680.22(C)].
In other than a single-family dwelling, a clearly labeled emergency spa or hot tub water recirculation and jet system shutoff must be supplied. The emergency shutoff must be readily accessible to the users and located not less than 5 ft away, but adjacent to and within sight of the spa or hot tub. [680.41]. Either the maintenance disconnecting means required by 680.12 or a pushbutton that controls a relay located in accordance with this section can be used to meet the emergency shutoff requirement.
Q9. What are the GFCI requirements for outdoor spas or hot tubs?
A9. GFCI protection is required for cords 15 ft or less in length used for cord and plug connection of outdoor spas and hot tubs [680.42(A)(2)]. Also, all receptacles rated 15 or 20A, 125V through 250V supplying cord-and-plug connected pump motors for a permanently installed outdoor spa, or outdoor hot tub must be GFCI protected [680.22(A)(5)].
Q10. What are the GFCI requirements for 15 or 20A, 125V receptacles located near outdoor spas or hot tubs?
A10. All 15 and 20A, 125V receptacles located within 20 ft of the inside walls of a permanently installed pool, outdoor spa, or outdoor hot tub must be GFCI protected [680.22(A)(5)].
Q11. Is a room that contains both a switchboard and a dry-type transformer considered a "transformer vault"?
A11. No. The definition of a vault is determined by certain construction specifications, not simply by the fact that a room contains a transformer. Transformer vaults are required for oil-insulated transformers installed indoors [450.26].
Article 450 provides some specific requirements in regard to transformer vaults including:
- Ventilation to the outside air [450.41 and 450.45]
- Floors, walls, ceilings, and roofs of vaults must have adequate structural strength [450.42].
- Fire resistant [450.42 and 450.43(A)]
- Tight-fitting doors [450.43(A)]
- Vault doors must swing out, be equipped with panic bars or pressure plates so the door can open under simple pressure, and must be provided with locks only accessible to qualified persons [450.43(C)].
Q12. We have a standby generator with a circuit breaker mounted on the generator and an automatic transfer switch installed on the load side of the service disconnect. Is an additional disconnecting means required for the generator feeder conductors entering the building?
A12. Where an outdoor-housed generator is equipped with a readily accessible disconnecting means located within sight (within 50 ft) of the building or structure, an additional disconnecting means isn’t required on or at the building or structure for the generator feeder conductors that serve or pass through the building or structure [700.12(B)(6)].
Q13. We have a 70A circuit breaker protecting the conductors feeding a 100A panelboard with a connected load of 30A, 240V. What is the minimum size conductors required to the panel?
A13. Circuit conductors must have sufficient ampacity, after adjustment, to carry the load, and the conductors must be protected against overcurrent in accordance with their ampacity [110.14(C), 215.3 and 240.4]. You can use 4 AWG copper conductors since it‘s rated 70A in the 60°C column or 85A in the 75°C column of Table 310.16 [110.14(C)].
Q14. Does the Code prohibit locking a circuit breaker handle in the “ON” or “OFF” position?
A14. No.
Q15. Are exposed electric fences that carry 5 kV to 12 kV pulses used to enclose livestock covered by the NEC?
A15. No. The scope of the Code indicates that the Code covers premises wiring, not equipment [90.2(A)]. Electric fencers are utilization equipment, and as such should be installed in accordance with the listing instructions.
Q16. What are the GFCI protection requirements for a self-contained indoor spa or hot tub?
A16. According to 680.44, the outlet that supplies a self-contained indoor spa or hot tub must be GFCI-protected. Because this rule applies to all outlets and not just receptacle outlets, a hard-wired indoor self-contained spa or hot tub would require GFCI protection [Article 100, outlet].
GFCI protection for the outlet isn’t required for a listed self-contained spa marked to indicate that integral GFCI protection has been provided for electrical parts within the unit or assembly.
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