NEC Questions and Answers – Based on the 2011 NEC
December 2011
By Mike Holt for EC&M Magazine
Here’s the follow up to Monday's newsletter. This includes all of the answers to the questions sent, so you can see how you did.
Q1. Is it acceptable to use a portable cord with male cord caps on both ends to connect a portable generator?
A1. No. Attachment plugs must be installed so their prongs, blades, or pins aren’t energized unless inserted into an energized receptacle or cord connector [406.7(B)].
Q2. Is the service neutral conductor allowed to perform bonding between the meter can and disconnect?
A2. Yes. Electrical continuity at service equipment, service raceways, and service conductor enclosures can be established by bonding the metal parts to the service neutral conductor [250.92(B)(1)]. Figure 250-92B1 01
A3. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers must terminate in one of the following methods [250.8(A)]:
Q4. What panelboard identification is required for a panelboard that contains a 3 phase 4-wire, 120/240V delta-connected system?
A4. A switchboard or panelboard containing a 4-wire delta-connected system where the midpoint of one phase winding is grounded shall be legibly and permanently field-marked as follows [408.3(F)(1)]:
“Caution _____ Phase Has _____ Volts to Ground”
Q5. When a panelboard is supplied by a 4-wire, delta-connected, three-phase (high-leg) system, where must the high-leg conductor terminate?
A5. Panelboards supplied by a 4-wire, delta-connected, three-phase (high-leg) system must have the high-leg conductor (which operates at 208V to ground) terminate to the “B” phase of the panelboard [408.3(E)] . Figure 408-03E0 02
Ex: The high-leg conductor can terminate to the “C” phase when the meter is located in the same section of a switchboard or panelboard.
Note: Orange identification, or some other effective means, is required for the high-leg conductor [110.15 and 230.56].
Warning: The ANSI standard for meter equipment requires the high-leg conductor (208V to neutral) to terminate on the “C” (right) phase of the meter socket enclosure. This is because the demand meter needs 120V and it gets it from the “B” phase.
WARNING: When replacing equipment in existing facilities that contain a high-leg conductor, use care to ensure that the high-leg conductor is replaced in the original location. Prior to 1975, the high-leg conductor was required to terminate on the “C” phase of panelboards and switchboards. Failure to re-terminate the high leg in accordance with the existing installation can result in 120V circuits being inadvertently connected to the 208V high leg, with disastrous results.
Q6. What must be done to protect Type NM cable where it is run through or parallel to framing members?
A6. Type NM cable installed through or parallel to framing members or furring strips must be protected against physical damage from penetration by screws or nails by 1¼ in. of separation or by a suitable metal plate [300.4(A) and (D) and 334.17]. Figure 334-17 02
If Type NM cable passes through holes in metal studs, a listed bushing or listed grommet is required [300.4(B)(1)] to be in place before the cable is installed.
Q7. What is the Code rule for sizing branch circuit conductors?
A7. Conductors must be sized no less than 125 percent of the continuous loads, plus 100 percent of the noncontinuous loads, based on the terminal temperature rating ampacities [110.14(C)(1)] as listed in Table 310.15(B)(16), before any ampacity adjustment [210.19(A)(1)].
Ex 1: If the assembly and the overcurrent device are both listed for operation at 100 percent of its rating, the conductors can be sized at 100 percent of the continuous load.
Example: What size branch-circuit conductors are required for the ungrounded conductors of a 44A continuous load, if the equipment terminals are rated 75ºC?
(a) 10 AWG (b) 8 AWG (c) 6 AWG (d) 4 AWG
Answer: (c) 6 AWG
Since the load is 44A continuous, the ungrounded conductors must be sized to have an ampacity of not less than 55A (44A x 1.25). According to the 75ºC column of Table 310.15(B)(16), a 6 AWG conductor is suitable, because it has an ampere rating of 65A at 75ºC before any conductor ampacity adjustment for ambient temperature [310.15(B)(2)(a)], conductor bundling [310.15(B)(3)(a)], or both.
Q8. What does the NEC recommend in regard to voltage drop when sizing conductors?
A8. The Code recommends: to provide reasonable efficiency of operation of electrical equipment, branch-circuit conductors should be sized to prevent a voltage drop not to exceed 3 percent. In addition, the maximum total voltage drop on both feeders and branch circuits shouldn’t exceed 5 percent. [210.19(A)(1) Note 4 and 215.2(A) Note 2] Figure 210-19A1 02 N4
Q9. Is AFCI protection required in hotel guest rooms?
A9. No, the Code requirements for AFCI protection are for dwelling units only.
All 15A or 20A, 120V branch circuits in dwelling units supplying outlets in family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similar rooms or areas must be protected by a listed AFCI device of the combination type [210.12(A)].
210.12(A) Note 3: See 760.41(B) and 760.121(B) for power-supply requirements for fire alarm systems.
Q10. What labeling does the Code require in regard to arc-flash hazard warning?
A10. Electrical equipment such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers in other than dwelling units that are likely to require examination, adjustment, servicing, or maintenance while energized must be field-marked to warn qualified persons of the danger associated with an arc flash from short circuits or ground faults. The field-marking must be clearly visible to qualified persons before they examine, adjust, service, or perform maintenance on the equipment [110.16].
110.16 Note 1: NFPA 70E, Standard for Electrical Safety in the Workplace, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.
For more NEC Practice purchase Mike Holt's NEC Practice Questions book, Based on the 2011 NEC.
