Stumped by the Code? January 2011

All questions and answers are based on the 2008 NEC.

Q. What are the grounding requirements for a satellite dish?

A. Article 810 includes the requirements for various antennas, including satellite dishes [810.1]. The antenna mast [810.15] and antenna discharge unit [810.20(C)] must be grounded as follows, according to 810.21 and shown in Fig. 1.

Grounding the lead-in antenna cables and the mast helps prevent voltage surges caused by static discharge or nearby lightning strikes from reaching the center conductor of the lead-in coaxial cable. Because the satellite sits outdoors, wind creates a static charge on the antenna as well as on the cable attached to it. This charge can build up on both the antenna and the cable, until it jumps across an air space — often passing through the electronics inside the low noise block down converter feed horn (LNBF) or receiver. Grounding the coaxial cable and dish to the building grounding electrode system helps to dissipate this static charge.

Nothing can prevent damage from a direct lightning strike, but grounding with proper surge protection can help reduce damage to satellite and other equipment from nearby lightning strikes. Here are some key items to keep in mind.

• Material. The grounding conductor to the electrode [810.21(F)] must be copper or other corrosion-resistant conductive material, stranded or solid [810.21(A)].
• Insulation. The grounding conductor isn’t required to be insulated [810.21(B)].
• Supports. The grounding conductor must be securely fastened in place [810.21(C)].
• Mechanical protection. The grounding conductor must be mechanically protected where subject to physical damage and where run in a metal raceway. Both ends of the raceway must be bonded to the grounding conductor [810.21(D)].

Installing the grounding conductor in PVC conduit is a better practice when the AHJ judges that physical protection is not required. The grounding conductor must be run in as straight a line as practicable [810.21(E)]. Lightning doesn’t like to travel around corners or through loops, which is why the grounding conductor should be run as straight as practicable.

The grounding conductor for the antenna mast and antenna discharge unit must terminate to the intersystem bonding termination, if there is one [Art. 100 and Sec. 250.94]. Bonding all systems to the intersystem bonding termination helps reduce induced potential (voltage) between the power and radio and TV systems during lightning events.

In buildings or structures without intersystem bonding termination, the grounding conductor for the antenna mast and antenna discharge unit terminates to the nearest accessible:

• Building or structure grounding electrode system [250.50].
• Interior metal water piping system, within 5 ft from its point of entrance [250.52(A)(1)].
• Accessible means external to the building, as covered in 250.94.
• Metallic service raceway.
• Service equipment enclosure.
• Grounding electrode conductor or the grounding electrode conductor metal enclosure.

In buildings or structures without a grounding means, the grounding conductor for the antenna mast and antenna discharge unit terminates to:

• Any individual electrodes described in 250.52.
• Structural steel grounded in accordance with 250.52(A)(2).

The grounding conductor can be run either inside or outside the building [810.21(G)], and it must not be smaller than 10 AWG copper or 17 AWG copper-clad steel or bronze [810.21(H)]. Copper-clad steel or bronze wire (17 AWG) is often molded into the jacket of the coaxial cable to simplify the grounding of the satellite dish by eliminating the need to run a separate grounding conductor to the dish [810.21(F)(2)].

If a ground rod is installed to serve as the ground for the radio and TV equipment, it must be connected to the building’s power grounding electrode system with a minimum 6 AWG conductor [810.21(J)].

Termination of the grounding conductor must be by exothermic welding, listed lug, listed pressure connector, or listed clamp. Grounding fittings that are concrete-encased or buried in the earth must be listed for direct burial [250.70] and marked “DB” [810.21(K)].

Q. When does the Code require branch circuit conductors to be pigtailed at receptacles?

A. Continuity of the neutral conductor of a multiwire branch circuit must not be interrupted by the removal of a wiring device. Therefore, the neutral conductors must be spliced together, and a pigtail must be provided for the wiring device according to 300.13(B), as shown in Fig. 2.

The opening of the ungrounded conductors, or the neutral conductor of a 2-wire circuit during the replacement of a device, doesn’t cause a safety hazard, so pigtailing of these conductors isn’t required [110.14(B)].

Caution: If the continuity of the neutral conductor of a multiwire circuit is interrupted (open), the resultant over- or undervoltage could cause a fire and/or destruction of electrical equipment.

Q. When is the neutral conductor allowed to be used as an equipment grounding conductor?

A. The neutral conductor can be used as the circuit equipment grounding conductor for metal parts of equipment, raceways, and enclosures at the following locations [250.142(A)]:

Service equipment — On the supply side or within the enclosure of the service-disconnecting means in accordance with 250.24(B). Danger: Failure to connect the service neutral conductor to the service disconnect enclosure as required by 250.24(C) creates a condition where dangerous voltage from a ground fault will not be removed.

Separately derived systems — On the supply side or within the enclosure of the system disconnecting means in accordance with 250.30(A)(1). Danger: Failure to install the system bonding jumper as required by 250.30(A)(1) creates a condition where dangerous touch voltage from a ground fault will not be removed.

Except for service equipment and separately derived systems, the neutral conductor must not serve as an equipment grounding conductor on the load side of service equipment [250.142(B)].

In existing installations, the frames of ranges, wall-mounted ovens, counter-mounted cooking units, and clothes dryers can be connected to the grounded circuit conductor, according to 250.140, Ex. [250.142(A), Ex 1].

The neutral conductor can be connected to meter socket enclosures on the load side of the service disconnecting means if [250.142(A) Ex 2]:

1. Ground-fault protection is not provided on service equipment,
2. Meter socket enclosures are immediately adjacent to the service disconnecting means, and
3. The neutral conductor is sized in accordance with 250.122, based on the ampere rating of the occupancy’s feeder overcurrent device.

Q. What is the rule on using 16 AWG tap conductors for lighting fixtures supplied by a 20A branch circuit?

A. Fixture wires installed in accordance with Art. 402 and protected against overcurrent in accordance with 240.5(B)(2) are permitted to run from the luminaire to an outlet box located at least 1 ft away from the luminaire, as long as the conductors aren’t more than 6 ft long.

As a general rule, branch circuit conductors must have an ampacity sufficient for the loads served and must not be smaller than 14 AWG [210.19(A) (4)]. Luminaire taps are an exception to this rule [210.19(A) (4) Ex 1], and the overcurrent protection rules for fixture wires in 240.5(B)(2) allow fixture wires to be protected by overcurrent protection devices tapped from the following circuits:

1. 20A – 18 AWG, up to 50 ft of run length
2. 20A – 16 AWG, up to 100 ft of run length
3. 20A – 14 AWG and larger.