If you have a problem related to the National Electrical Code (NEC), are experiencing difficulty in understanding a Code requirement, or are wondering why or if such a requirement exists, ask Charlie, and he will let the Code decide. Questions can be sent to email@example.com. Answers are based on the 2011 NEC.
Fridge branch circuit
In your January 2011 Code FAQs, you responded that a duplex receptacle was not allowed on a separate branch circuit for the refrigerator. If the circuit is rated at 20 amperes (A), it can be considered one of the “two or more” required small appliance branch circuits. In this case, a duplex receptacle is allowed.
I believe I wrote that, when using Exception No. 2 to 210.52(B)(1), which permits supplying the receptacle outlet for refrigeration from an individual branch circuit rated 15A or greater, a single receptacle must be used. Article 100 defines an individual branch circuit as “a branch circuit that supplies only one utilization equipment.” A duplex receptacle or greater would allow the use of more than one utilization equipment. NEC 210.21(B)(1) shows the requirements for a single receptacle on an individual branch circuit. Note that a 15A circuit is permitted. Your suggestion, while valid, has nothing to do with the exception.
Drilling weep holes
When I read the May 2011 Code FAQs comment, “Arranged to Drain,” I was concerned about certain consequences of drilling weep holes at the low points of raceway. I’m not clear whether raceways are investigated for such installation or whether such modification violates their listing. When the raceway is galvanized steel, I am afraid that drilling through its wall could expose unprotected steel to accelerated corrosion. Some boxes are designed with weep holes, but I am not clear that adding holes through the wall of, say, EMT, is suitable. Can you say something about these issues, Charlie?
Yes, you are correct. Drilling weep holes in circular raceways probably wouldn’t get by the authority having jurisdiciton. Proper installation will prevent the entrance of water in raceways installed in wet locations above grade, but moisture will still accumulate due to the temperature difference between the interior and exterior of the raceway. Conductors installed in raceways in wet locations above grade must be listed for use in wet locations in accordance with 310.10(C).
Minimum size conductor revisited
Under “Minimum size conductor,” in the June 2011 Code FAQs, the reader is looking for the size of the equipment grounding conductor (EGC). He stated that a 3,000A service is being fed underground from a metering cabinet. He may be misled because he does not say this is a feeder but does say it is feeding his main switchgear. If this is the main service and there is no overcurrent protection on the line side, then he doesn’t need an EGC. Section 250.142 allows the grounded--circuit conductor to ground equipment and raceways on the supply side of the service disconnect.
Yes, you are right. Thanks for contributing your insight. A good example of this is shown in 250.28 where a main bonding jumper is required. The main bonding jumper connects the grounded conductor (neutral bar) to the panelboard enclosure, which could be accomplished with the screw with the green head or a conductor.
Conductor temperature rating
If you use three sets of Type 2 THHN/THWN 500 kcmil (90° wire) copper conductors rated at 430A, does the Code allow you to use a 1,200A switch? Will the terminal lugs also be required to be rated 90°?
NEC 110.14(C) requires that the temperature rating of a conductor associated with the ampacity of a conductor must be selected so as to not exceed the temperature rating of the termination. Conductors rated 90° must be used at their 60° or 75° rating to match the termination rating.
120V receptacle requirement
Are you required in commercial offices and industrial applications to have all 120V duplex receptacles on 20A circuits rated at 20A? I see a lot of 15A devices on 20A circuit breakers.
There is no NEC requirement to have 120-volt (V) duplex receptacles on 20A circuits rated at 20A in commercial and industrial applications. NEC 210.21(B)(3) permits the use of 15- or 20A receptacles on 20A rated branch circuits.
Minimum outlet height
On one of our current commercial jobs, the electrician is insisting there is a minimum height requirement for outlets. Does the NEC address this?
The NEC does not have a minimum height requirement for receptacle outlets. You should be more specific when using the term outlet. There are receptacle outlets, lighting outlets, smoke alarm outlets, and utilization equipment outlets. See the definition of outlet in Article 100.
Is schedule 40 PVC permitted to be run inside the building, such as in the ceiling, etc.?
Yes, NEC 352.10(A) permits PVC conduit to be run in walls, floors and ceilings. Schedule 80 PVC is suitable for use wherever Schedule 40 may be used.
Solar system AC disconnect
I just had a solar power system installed, and the installation company insists that the alternating current (AC) disconnect box must be mounted on my outside garage wall, next to the regular utility company meter/electrical closet even though the solar disconnect box will easily fit inside the electrical closet. They are citing NEC 690, and Southern California Edison (SCE) Rule 21 (readily accessible clause), but in my research I still can’t see why it can’t be mounted inside the closet. It is still “readily accessible,” just like the SCE connections are. Any idea on why I can’t have them move that solar disconnect box inside my electrical closet?
Apparently the installers do not feel that the electrical closet meets the readily accessible requirements, and this judgment is their responsibility. Check with the local authority having jurisdiction.
Grounded well casing
Is it required to ground the well casing at a residence if the water line is PVC?
The metal well casing is grounded by its contact with the earth. Article 100 defines “grounded” as being “connected to earth or to some conducting body that serves in place of the earth.” However, unless the metal well casing is bonded to the equipment-grounding (bonding) conductor there is no path for ground-fault current other than through the earth, which of course is a path of very high resistance and is prohibited by 250.4(A)(5) and 250.54. NEC 250.112(M) requires that where a submersible pump is used in a metal well casing, the metal well casing shall be bonded to the equipment-grounding (bonding) conductor of the circuit that supplies the submersible pump.
Twist-lock receptacle requirement
Is there a requirement for a twist-lock receptacle for a storable pool pump motor?
No. The only locking configuration required is in 680.22(A)(1)(2) for receptacles for pool pump motors, installed for permanently installed pools, that are within 6 feet and 10 feet from the inside wall of the pool.
Am I required to leave 6 inches of conductor extending from a box where I am just pulling through the box? (I’m not terminating at a device installed in that box.)
NEC 300.14 requires that at least 6 inches of free conductor, measured from the point in the box where it emerges from the raceway or cable sheath, be left at each outlet box and be long enough to extend at least 3 inches outside the box opening. If the conductors are not terminated or spliced at the outlet box, there’s an exception to this requirement. This exception permits these conductors to be pulled in tightly. However, I believe it’s better to be safe than sorry and always leave enough slack so that one could use the conductors in the future if necessary. NEC 314.16(B)(1) permits each conductor that passes through the box without termination or splice to be counted once but doesn’t restrict the length of the conductor loop.
Nonmetallic in metal
Can electrical nonmetallic boxes be used with metal raceways?
According to NEC 314.3, nonmetallic boxes can only be used with nonmetallic raceway and nonmetallic cable wiring methods, unless the requirements of Exceptions No. 1 or No. 2 are followed. Basically, this requires a means of ensuring the electrical continuity of the metal raceways and a provision for attaching an equipment-grounding jumper inside the box, which can be accomplished by running an equipment-grounding conductor with the circuit conductors and providing a grounding terminal or clip in the box.
TROUT answers the Code Question of the Day on the NECA website. He can be reached at firstname.lastname@example.org.