Editor’s note: Charlie Trout is moving on to retirement. This edition of Code FAQs will be the last collection of questions and answers he will provide. For the next few months, tune in for a “best of” series of Code Questions of the Day by Charlie. A new writer will be introduced in January. If you want to wish Charlie the best in his retirement, please drop him a note to email@example.com.
NM cable in a drop ceiling
Can nonmetallic sheathed cable be used in a drop ceiling area that is used as a return air system for a basement family room in a dwelling unit?
Nonmetallic sheathed cable cannot be used in a plenum area. NEC 300.22(C)(1) describes the wiring methods that may be used in “other spaces used for environmental air.”
Copper conductor in a raceway
Can the grounded (neutral) service-entrance conductor be installed as a bare copper conductor in a metal raceway?
NEC Section 230.41 Exception (1) permits a bare copper grounded conductor to be used in a service raceway or as part of a service cable assembly.
Terminals for multiple conductors
Can I connect more than one conductor on a single terminal, such as a circuit breaker?
Section 110.14(A) requires terminals for more than one conductor to be so identified. In the absence of such identification, only one conductor is permitted to be attached to a single terminal.
Permanently mounted CATV
I’m checking out a job where the TV cable installer ran all the coaxial cables to a spot in the attic near the retractable ladder, made up his connections and dropped the cables into the insulation. Isn’t there a Code requirement that CATV equipment, such as the amplifier and splitters, should be permanently mounted?
There definitely are Code requirements relating to these installations. NEC 820.24—Mechanical Execution of Work requires the installation to be in a neat and workmanlike manner and the cables to be properly secured in accordance with NEC 300.4(D) and 300.11. Amplifiers and splitters have mounting lugs as part of the equipment and should be used in accordance with NEC 110.3(B). NEC 800.24, 820.24 and 830.24 are all explicit requirements for Mechanical Execution of Work.
How can I use 6 feet of flexible metal conduit in a service entrance raceway run, and how can I install an equipment bonding jumper on the outside of the raceway that is not more than 6 feet?
You can’t. Section 230.43 permits flexible metal conduit to be used in a service entrance raceway run (presumably to get around obstructions where you might have to use a bender) but restricts the length to 6 feet and refers you to Section 250.102(E) where the requirements for bonding around the flexible metal conduit are shown. You’re right, not picky. You are restricted to an equipment bonding jumper that shall not exceed 6 feet in length if you run on the outside of the raceway. So you have three choices: limit the length of flexible metal conduit to where 6 feet of bonding jumper will be sufficient; run the equipment-bonding conductor inside the raceway; or buy a bender.
Grounding electrode conductor
Does the grounding electrode conductor have to be connected to the neutral bus, or can it be connected to the ground bus?
NEC 250.24(A)(4) permits the grounding electrode conductor to be connected to the ground bus in the panelboard if there is a wire from the ground bus to the neutral bus. The NEC does not permit the panelboard enclosure to be used as part of the grounding electrode conductor.
Higher rated circuit breaker
Can you help me with a fundamental question? It’s my understanding that the purpose of overcurrent protection (fuse, circuit breaker, etc.) is to protect the wire. Since the Code allows you to choose the next higher circuit breaker, up to 800 amperes (A), it seems to me that it would be possible in some circumstances for the circuit breaker to have a higher rating than the wire it is intended to protect. What is the logic behind that?
NEC 240.4(B) permits using the next higher standard overcurrent device rating (above the ampacity of the conductors being protected) only when all of these three conditions are met:
Condition 1 prevents the circuit from having cord- and plug-connected loads connected to the circuit that would exceed the ampacity of the conductors but not the overcurrent device. Condition 2 prevents using this section where overcurrent devices that match the ampacity of the conductors are available. Condition 3 prevents using this section where the next higher rating exceeds 800A (this is because the next higher standard rating is 1,000A, a giant step upward). Overcurrent devices protect the circuit conductors in two ways. They protect the conductors from overload conditions and from short-circuit or ground-fault conditions. If you put too much of a load on the circuit, the overcurrent device will open. If the circuit has equipment, such as a motor, and it becomes overloaded, the motor overload relays will open. Short-circuit and ground-fault currents are generally of such magnitude that the overcurrent device will open before any damage is done to the conductors.
Hair dryer listing
Why do listed 1,800-watt (W) hair dryers come with a 15A attachment plug?
The hair dryer is rated 1,800W at 125 volts (V). The resistance of the hair dryer element is 8.68 ohms (E² ÷ P). Dividing 1,800W by 125V comes out to 14.4A. If used on a 120V circuit, the resistance of the hair dryer element does not change, but the wattage drops to 1,650W. Divided by 120V, that’s 13.75A.
Separation of conductors
I have a question about Article 830.133 “Installation of Network-Powered Broadband Communications Cables and Equipment.” Part A.1.C states the following: “Electric Light, Power, Class 1, Non-Powered Broadband Communications Circuit Cables. Network-powered broadband communications cable shall not be placed in any raceway, compartment, outlet box, junction box, or similar fittings with conductors of electric light, power, Class 1, or non-power-limited fire alarm circuit cables.” Two exceptions are given. One involves having a permanent barrier; the other involves the power wiring being solely for powering up the equipment. What about a PLC rack where hundreds of 120V wires are installed—e.g., a process line. These PLCs are expected to be networked, and often I find media converters to fiber optics entering the PLC and Cat 5e cable going from the converter to the rack. There are no physical separations made for the network cable, so the installer routes as best as possible. What is the correct method for installing these cables? Often, a single PLC can have up to 10 or 20 Cat 5e cables servicing the system. The same question applies to motor drives that include a Cat 5e connection internal to the drive.
I wish I could give you a more definitive answer, but it probably would take a case-by-case study to determine an answer that would comply with the Code requirements regarding separation of conductors. However, the rules and the intent are clear. The installation of permanent barriers or a listed divider, porcelain tubes, flexible tubing or raceways may be employed to gain the desired separation of conductors. If the equipment manufacturer does not provide these barriers, it becomes the installer’s responsibility.
Code QOTD kudos
Some days your Code Question of the Day really makes me think. I use it in the shop regularly to encourage discussion and get out those Code books. I recently purchased your book, “Electrical Installation & Inspection.” It’s a great tool. The illustrations are especially good and helpful.
Thank you for your nice commentary about Code Question of the Day and especially thank you for the neat reference to my book. I hope that it will be helpful to many more readers. I have tried to keep the answers accurate, helpful, informative and, sometimes, a little entertaining.
Editor’s P.S. to Charlie: Our readers clearly are going to feel your absence. We’re going to miss your great talent and prodigious knowledge of the NEC. All the best to you in retirement.