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NEC Code Quandry

Questions and Answers - February 2000

Question 1.

How many duplex receptacles are allowed downstream from a feed-through GFCI receptacle?

No Limit. There’s no limit on the number of receptacles (on one strap) fed from a feed-through GFCI receptacle, but the NEC limits the number of receptacles on a circuit in occupancies other than dwelling units. The maximum number of receptacles (on one strap) permitted on a commercial or industrial circuit is based on the 180 VA per outlet and the VA rating of the circuit [220-3(b)(9)].

Example. What is the maximum number of duplex receptacles permitted on a 20 ampere, 120 volt circuit, Figure 1?

Note: Figure are not posted on the Internet.

Step 1. Determine the circuit VA rating, 120 volt x 20 ampere = 2,400 VA

Step 2. Number of duplex receptacles permitted 2,400 VA/180 VA* = 13

*Receptacles are not considered a continuous load.

Author’s Comment: The NEC is not specific on the requirements for determining the number of receptacle outlets permitted on general lighting circuits in dwelling units [220-3(c)(10). However, the NEC Handbook (published by the NFPA) clarifies that there is no limit as to the number of receptacle outlets on a dwelling unit circuit, because residential receptacles are lightly used, Figure 2.

CAUTION: Check with your local building/electrical code. Some local areas have a maximum number of receptacles permitted on a circuit for dwelling units.

Question No. 2

Can No. 14 wire be used for receptacle taps from a 20 ampere circuit?

No. Section 240-3(e) identifies that the rules for branch circuit tap conductors are contained in Section 210-19(d). Exception No. 1(c) to Section 210-19(d) permits No. 14 wire taps for other than receptacle outlets, Figure 3.

Question No. 3

When sizing conductors and short circuit protection for motors, do we use the motor nameplate current or the Table FLC as listed in the Codebook?

Table FLC. According to Section 430-6(a), the FLC values given in Table 430-147, 430-148, or 150 are to be used to determine the ampacity of conductors or ampere ratings of switches, branch circuit short circuit and ground-fault protection instead of the actual current rating marked on the motor nameplate, see Sections 430-22(a) and 430-24, Figure 4.

Note: The motor nameplate current rating shall be used where separate motor overload protection is provided to comply with Section 430-32,

Question No. 4

Can buried conductors for 12 volt landscaping lighting be spliced without using a junction box?

Yes. Section 300-5(e) specifies that direct-buried conductors or cables can be spliced or tapped without the use of splice boxes, but the splices or taps must be made with wire connectors or splicing means listed for direct burial [110-14(b)].

Question No. 5

How many consecutive feet of rigid nonmetallic conduit can be run before a junction box is needed?

No limit. The only limitations would be the length of the conductors and there shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points [347-14].

Question No. 6

When using nonmetallic sheath cable for temporary wiring at carnivals, does Article 305 or 525 apply? Are splices and joints required in junction boxes?

Article 525. Section 525-1 states that Article 525 covers the installation of portable wiring and equipment for carnivals, circuses, exhibitions, fairs, traveling attractions and similar functions.

Junction boxes required. Section 525-13(d) specifies, “Flexible cords or cables shall be continuous without splice or tap between boxes or fittings,” Figure 5.

Question No. 7

Is it a Code violation for armored or metal clad cable to be in contact with copper water piping?

No. The Code does not prevent the contact of armored or metal clad cables with copper water piping, but Sections 345-3 (Rigid), 346-3 (IMC) and 348-5 (EMT) states that where practicable, contact between dissimilar metals shall be avoided to eliminate the possibility of galvanic action. Naturally, we would like to keep the metal armor of electrical wiring from making contact from copper water piping, but this is not a Code requirement.

Question No. 8

Does the NEC require coaxial cable used for security cameras to be installed within a raceway?

No. Chapter 8 is independent of the other chapters in the NEC [90-3] and there is no requirement in Article 820 requiring coaxial cable to be installed within a raceway, Figure 6.

The above questions and answers (including graphics) by Mike Holt are in EC&M magazine. Click here for more magazine articles.