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.
Answer. 13 duplex receptacles,
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
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
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.