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NEC Questions and Answers - August 2006
 

 
Topic - NEC Questions
Subject - NEC Questions and Answers - August 2006

September 5, 2006  

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NEC Questions and Answers August 2006

 

By Mike Holt for EC&M Magazine

 

Q1. Can the sum of the ampere rating of circuit breakers in a panel exceed the rating of the panelboard?

A1. Yes, because each lighting and appliance branch-circuit panelboard [408.34(A)] must have overcurrent protection not greater than that of the panelboard [408.36(A)].

 

Q2. Can I use a different manufacturer’s breaker in my panel as long as it fits?

A2. Only if the circuit breaker is listed or classified to be used in the specific panelboard [110.3(B)].

 

Q3. If an outdoor generator has a disconnect, do I need an additional disconnect where the conductors enter the building?

A3. Where an outdoor-housed generator is equipped with a readily accessible disconnecting means located within sight (Article 100 - 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 the building or structure [700.12(B)(6), 701.11(B)(5) and 702.11].

 

Q4.  Can I use 12-3 NM cable to wire the bathroom and laundry circuits in a dwelling?

A4. Yes, however continuity of the grounded (neutral) conductor of a multiwire branch circuit must not be interrupted by the removal of a wiring device [300.13(B)]. Therefore, the grounded neutral conductors must be spliced together, and a pigtail must be provided for the wiring device.

 

Q5 How far away must a receptacle outlet be from a shower or bathtub?

Q6. Receptacles must not be installed within or directly over a bathtub or shower stall [406.8(C)], but they can be installed next to a bathtub or shower. Hydromassage bathtubs are treated like bathtubs [680.70].

 

Q6. Can Table 310.15(B)(6) (reduced size wire for dwelling unit service) be used to size the service neutral conductor for a single family dwelling?

A6. Yes this table can be used to size the grounded neutral conductor of a 3-wire single-phase 120/240V service or feeder that serves as the main power feeder, based on the feeder calculated load in accordance with 220.61.

 

Q7. Can an AFCI type receptacle be used to meet the AFCI requirements of the NEC?

A7. Yes, if the AFCI is located within 6 ft of the branch-circuit overcurrent device as measured along the branch-circuit conductors, if the circuit conductors are installed in a metal raceway or a cable with a metallic sheath [210.12(B) exception]. But no manufacture makes an AFCI receptacle…

 

Q8. Do I need to bond the metal parts of a diving board and ladder of a fiberglass swimming pool pump motor?

A8. Yes, all metal fittings within or attached to a permanently installed pool, outdoor spa, or outdoor hot tub structure, such as ladders, diving boards and handrails must be bonded together, even if the pool is of fiberglass construction [680.26(B)(3)].

 

Q9.  I have two receptacles on two different circuits in the same outlet box. Am I required to use a two pole breaker for these circuits?

A9. No. A two pole breaker or two single breakers with handle ties identified for the purpose is only required if the two circuits are on the same receptacle [210.4(B) and 210.7(B)].

 

Q10. How many 12 AWG conductors can I install in 4 x 4 x 1½” box if the box has a plaster ring listed for 3.3 cubic inches and there are no cable clamps or fixture support fittings in the enclosure.

A10. According to Table 314.16(A), the box has a capacity of 21.0 cubic inches.  Table 314.16(B) tells us that each 12 AWG conductor is considered as 2.25 cubic inches, so:

Step 1. Determine the total volume of the box assembly [314.16(A)].
Box 21 cu in. + 3.3 cu in. plaster ring = 28.3 cu in.

 

Step 2. Determine the number of 12 AWG conductors permitted in the box.

24.3 cu in. /2.25 cu in. = 10 conductors

 
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Comments

  • love the q&a's, especially reading the comments. I was scratching my head on your initial answer to Q#9, because my first response would have been a 2p C/B would have been required. However, the comments, and your subsequent answer(s) to those comments made me view the question in a broader perspective.

    fred stephenson
    Reply to this comment

  • Hi Mike, Just wanted to say I love these newsletters. They are very informative and timely. I enjoy reading them. I use them as study guides and references at my fingertips. Keep up the good work. Thank you.

    Michael

    Michael
    Reply to this comment

  • Many of the new pool pump motors have plastic housing and do not have a lug for bonding. It is my understanding that the bond wire must be run to the motor area incase the motor is replaced with a metal cased motor. So the bond would be to the ladder, diving board, the grid around the pool deck and a tail to the motor.

    Steve Thomas
    Reply to this comment

  • Very good! Nice q and A series!!

    Jim Gintner
    Reply to this comment

  • I agree that 12-3 (multiwire branch circuits) may be used to wire a laundry and/or bathroom circuit, but care will need to be taken to ensure that the GFCI devices for these circuits operate correctly. A 2-pole GFCI device may be required which will probably negate the savings achieved by using the multiwire circuit. The neutral current from circuit "A" will be seen as an imbalance in circuit "B" and vice-versa.

    Don
    Reply to this comment

  • Question 9. Modify answer. Yes, if on the same yoke. No if on differert yokes.

    Wesley Gerrans
    Reply to this comment

  • Question #9 should be clarified - if two circuits terminate to a device on the SAME YOKE, a two-pole breaker shall be used. A duplex receptacle actually has TWO receptacles on the same yoke.

    Jim
    Reply to this comment

  • On Q10 there are 10 volumes allowed for 12 AWG, but wouldn't there be one taken up for the equipment grounding conductors and two each for the 2 switches or receptacles mounted in the box, leaving only five actual conductors allowed in the box?

    Rick Mack
    Reply to this comment

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