NEC - Questions and Answers (1-4-2K)
NEC Code Quandary
Q1. Is it acceptable to terminate two wires on a single screw or lug?
Q2. Is it permissible to terminate two circuits on a single circuit breaker?
A. Sometimes. According to 110-3(b) "listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling" and 110-14(a) states "terminals for more than one conductor shall be so identified".
The only time two wires can be installed under a single screw or lug is when the terminal is identified for this purpose. Circuit breakers rated not more than 30 amperes are often identified for the termination of two conductors. This can be verified by reviewing the circuit breaker manufacture's catalog.
Neutral and equipment grounding lugs for panelboards are often suitable for two and sometimes three wires. This information is contained on the label affixed within the panelboard or on the packing container of the equipment ground lug. Often the instructions will identify the number of conductors, the size of the conductors, the conductor material, as well as the torque requirements.
Note: Split-bolt lugs are only permitted for two conductors.
Q. Can a panelboard be installed with the main breaker upside down, so the "up" position of the handle is the "off" position?
A. No. Sections 240-81 and 380-3 require "circuit breakers that are operated vertically be installed with the "up" position of the handle to be the "on" position.
Q. Does NEC require GFCI protection for receptacle located within 6 feet of a sink in school laboratories?
A. No. GFCI protection is only required at the following locations:
- Agricultural Building - 547-9
- Carnivals, Circuses and Fairs - 525-18
- Commercial Garages - 511-10
- Dwelling Units - 210-8
- Elevator Pits - 620-85
- Health Care Facilities - 517-20(a), 517-21
- Portable or Mobile Signs - 600-10
- Roof Top Receptacles - 210-8(b)
- Swimming Pools - 680-6(a)
- Temporary Wiring - 305-6
Q. A person makes contact with the hot wire and the return wire at the same time. Will this trip the GFCI?
A. No. A ground-fault circuit-interrupter protects against electric shock from an energized conductor or from energized metal parts that are not effectively grounded. It operates on the principle of monitoring the imbalanced current between the ungrounded (hot) and grounded (neutral) conductors. In a typical 2-wire circuit, the current in amperes returning to the power supply will be the same as the current leaving the power supply (except for small leakage). If the difference between the current leaving and returning through the current transformer of the GFCI protection device is 5 milliamperes (+ or 1 milliampere), the solid-state circuitry activates the shunt trip feature to open the switching contacts of the GFCI, thereby de-energizing the circuit.
Sever electric shock or death can occur if a person touches the energized (line or hot) and neutral conductor at the same time, even if the circuit is GFCI protected. This is because the current transformer within the GFCI protection device does not sense an imbalance between the departing and returning current and the switching contacts remain closed.
Q. Does the NEC required phase conductors to be color-coded?
A. No. There is not NEC rule requiring color coding of phase conductors, however 210-4(d) states that where more than one nominal voltage system exists in a building, each ungrounded conductor of a multiwire branch circuit, where accessible, shall be identified by phase and system. This means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means and shall be permanently posted at each branch-circuit panelboard.
This rule applies primarily for commercial and industrial buildings that have 208Y/120 volts for receptacle circuits and 480Y/277 volts for lighting and other equipment loads. If two system voltages are not present, then identification of multiwire branch circuit is not required.
Note: The high-leg conductor must be identified with the color orange, see 215-8 for feeders, 230-56 for service conductors, and 384-3(e) for switchboards or panelboards. When two voltage systems are installed in the same raceway (or enclosure), one system's neutral can be white or natural gray and the other system's neutral must be white with a readily distinguishable different color stripe (other than green), or identified with other effective means; see 200-6(d) and 210-5(a).
Q. Can a single equipment grounding conductor be used for a nonmetallic raceway that contains one 20 ampere multiwire circuit and one 30 ampere, 2-wire circuit?
A. Yes. This issue is covered in 250-122(c), which states that when multiple circuits are installed in the same raceway, a single equipment grounding conductor can be used for all of the circuits, sized to the largest overcurrent device protecting the conductors in the raceway. According to Table 250-122, the equipment grounding conductor for a 30 ampere overcurrent protection device is No. 10.
Q. Is it a code violation to wrap a stranded No. 12 wire around the post of a wiring device screw?
A. No. This is not directly covered by the NEC, but 110-3(b) requires all equipment to be installed in accordance with manufacture instructions. According wiring device manufactures, the screws on wiring devices are listed for the termination of either solid, or stranded No. 14 or No. 12 wire.
Q. I am installing a permanent generator at
my home to be used for optional standby power. I'll be using a manual double pole/double throw switch
with a solid neutral as my transfer switch. The feeder to the subpanel from the main and the generator
is 4-wire (two hots, neutral and ground) and there is no neutral-to-ground connection in the subpanel.
Q1. Is my generator considered a separately derived system?
A1. No. The National Electrical Code requires a neutral-to-ground connection for a separately derived system such as generator at the separately derived system or at the first disconnect after the separately derived system [250-30(a)]. Fine Print Note No. 1 to Section 250-20(d) warns the NEC user that an alternate ac power source is not considered a separately derived system if the neutral from the generator is solidly interconnected to a service system neutral.
Q2. Should I make a neutral-to-ground connection at the generator?
A2. No. Since the neutral is not opened in the transfer switch, the neutral from the generator will be solidly interconnected to a service system neutral. Under this condition, the generator is not considered a separately derived system and a neutral-to-ground connection must not be made at the generator or at it's disconnect.
Q3. Is the generator required to be grounded to the earth?
A3. No. Since the generator is not a separately system, the generator is not required be grounded to a grounding electrode (earth).
The above questions and answers by Mike Holt appeared in EC&M magazine.