Electrode Conductors, AFCIs and More

Article 110—Requirements for Electrical Installations; Article 210—Branch Circuits; Article 250—Grounding and Bonding; Article 392—Cable Trays; Article 408—Switchboards and Panelboards; Article 517—Health Care Facilities; Article 680—Swimming Pools, Fountains, and Similar Installations; The 2006 edition of the Guide Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc. also is mentioned.

Concrete-encased electrode

Q: Does the National Electrical Code (NEC) permit a grounding-electrode conductor smaller than 4 AWG copper for a concrete-encased electrode for a 60-ampere, 3-wire, 120/240-volt service? The service conductors are three 6 AWG copper with THWN insulation.

A: There is nothing in Article 250 that allows the grounding-electrode conductor to be smaller than 4 AWG copper. There also is nothing in Article 250 that requires the grounding-electrode conductor from the reinforcing steel to be larger than 4 AWG copper.

Article 250.66(B), which states the grounding electrode for a concrete-
encased electrode does not have to be larger than 4 AWG copper, covers the connection to the concrete-encased electrode.

Where the concrete slab in contact with the earth does not contain 20 feet or more of ½-inch or larger reinforcing rods, the concrete-encased electrode may consist of at least 20 feet of bare 4 AWG copper placed near the bottom of the concrete foundation. Article 250.52(A)(3) permits this substitution of wire for reinforcing rods. Notice the minimum size wire electrode is required to be 4 AWG bare copper.

Sealing locknuts at weatherproof enclosures

Q: On an outdoor disconnect switch in a 3R enclosure, is it necessary to enter the enclosure above live parts with 1-inch rigid metal conduit? Sealing locknuts will be used at the conduit entry. Does the sealing locknut install on the outside or inside of the enclosure? Are two sealing locknuts required—one inside and one outside?

A: It is necessary to maintain the integrity of the enclosure. Therefore, the conduit penetration must be made weatherproof. According to the Guide Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc., this information appears under the title, Conduit Fittings (DWTT): “Sealing locknuts are intended for use with threaded rigid metal conduit and intermediate metal conduit with one sealing locknut in the outside or the inside and either an ordinary locknut or sealing locknut on the other side of the enclosure for wet locations or liquidtight applications.”

Bonding cable trays

Q: Are all listed metal cable trays suitable for grounding and bonding?

A: Underwriters Laboratories Inc. does not list metal cable trays. However, UL does “classify” metal cable trays that are suitable as a grounding conductor. The cable tray manufacturer may provide the necessary hardware for bonding between sections of the cable tray. Where these materials are not furnished with the cable tray, the installer must provide the necessary fittings and other components to properly bond all sections of the cable tray system.

For proper installation of cable trays, see the Fine Print Note following 392.1. Bonding and grounding requirements for metal cable trays are in 392.7 (A) and (B). Part (B) covers the construction requirements for metal cable trays. Grounding and bonding conductors must be terminated by exothermic welding, listed pressure connectors or listed clamps using threaded bolts. Sheet metal screws are not acceptable for fastening the grounding conductor to the cable tray.

The size of the bonding-jumper grounding conductor is determined from 250.102(D). It is based on the largest ampere rating of the overcurrent device, protecting any of the conductors in the cable tray. This ampere rating is used along with Table 250.122 to obtain the minimum size equipment-grounding conductor.

Neutral bus connected grounded branch-circuit conductors

Q: I connected two branch-circuit grounded conductors to a single terminal on the neutral bus in a panelboard. The electrical inspector said this was not permitted. Installation instructions supplied with the panelboard indicate that up to three 12-AWG conductors are permitted in each terminal of the neutral bus. What am I missing?

A: I assume you are confusing the grounded branch-circuit conductor with the equipment-grounding conductor.

Where the panelboard is part of the service equipment, the neutral bus is bolted or welded to the panelboard enclosure, and this bus may be used to terminate branch-circuit grounded conductors and equipment-grounding conductors provided there are enough individual terminals on the bus.

According to 408.40, “Grounding conductors shall not be connected to a terminal bar provided for grounded conductors (may be a neutral) unless the bar is identified and is located where interconnection between equipment-grounding conductors and grounded circuit conductors is permitted or required by Article 250.” According to 408.41, “Grounded Conductor Terminations. Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.”

Multiple equipment-grounding conductors may be terminated under a single terminal as permitted by the instructions posted on the panelboard, but branch-circuit grounded conductors are limited to one wire per terminal.

Hydromassage bathtub AFCI

Q: Is arc-fault circuit interrupter (AFCI) protection required for the pump on a hydromassage bathtub
located in the master bedroom of a single-
family residence? There also is a bathroom that can be entered from the
bedroom. Do outlets in the bathroom
require AFCI protection?

A: AFCI protection, in addition to ground-fault circuit interrupter (GFCI) protection, is required for the wiring to a hydromassage tub. All 125-volt, single-phase receptacles rated 30 amperes or less and located within 5 feet of the tub must be GFCI-protected to comply with 680.71. Also, all outlets in the bedroom that are supplied from 15- and 20-ampere, 120-volt branch circuits must have AFCI protection, as 210.12(B) requires. Having both devices on the same branch circuit does not interfere with their operation. Both devices will function as intended.

For the bathroom, at least one 20-
ampere branch circuit is required to supply the bathroom outlets. This requirement is in 210.11(C)(3). Also, 15- and 20-ampere, 125-volt receptacles in the bathroom must have GFCI protection to comply with 210.8(A)(1).

Hall lighting branch circuits

Q: Is a “house” service and panel required for an entrance hall that is used for six apartments?

A: Yes, the electrical system must be arranged so that the common area of a multifamily dwelling is not supplied from an individual apartment panelboard. Article 210.25 reads, “Common Area Branch Circuits. Branch circuits in dwelling units shall supply only loads within that dwelling unit or loads associated only with that dwelling unit. Branch circuits required for the purpose of lighting, central alarm, signal, communications, or other needs for public or common areas of a two-family or multi-family dwelling shall not be supplied from equipment that supplies an individual dwelling unit.”

Raceway in healthcare facilities

Q: Is surface metal raceway containing an equipment-grounding conductor along with the branch-circuit conductors suitable for installation in a patient care area of a hospital?

A: Yes, UL-listed surface metal raceway is a recognized equipment-grounding conductor, according to Item 14 of 250.118. Since the metal raceway provides one grounding path and the equipment-grounding conductor installed in the surface metal raceway provides an additional independent ground path, the requirement in 517.13 is satisfied. All fittings used with the surface metal raceway must be those specified and installed in accordance with the manufacturer’s instructions to ensure a low impedance path through the raceway to clear a ground fault.

Switchboard door requirements

Q: Does a single door for a room with a 1,200-ampere switchboard have to swing outward and be equipped with panic hardware where the door is more than 6 feet from the front of the switchboard? The voltage is 208Y/120.

A: The depth of the working space in front of the switchboard is more than double the working space required by Table 110.26(A)(1). Therefore, one entrance door is acceptable. However, the door must feature panic hardware or a pressure plate and swing outward from the room. This required door must be at least 24 inches wide and 6.5 feet high. Also, the door opening must be at least 3 feet from the switchboard if it is located on a side wall.

Relocating electrical equipment

Q: A manufacturing company is moving from one building to another. Some of the electrical equipment is not listed or labeled. Is there any requirement in the NEC that covers this situation?

A: The authority having jurisdiction has the responsibility for approval of electrical equipment and for granting special permission as allowed by some of the rules in the NEC. After a thorough inspection of the electrical materials and equipment, the inspector should be able to accept some, if not all, of the electrical products. Items that are not accepted may be field-evaluated by a recognized testing laboratory or replaced.   EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.


About the Author

George W. Flach

Code Q&A Columnist
George W. Flach was a regular contributing Code editor for Electrical Contractor magazine, serving for more than 40 years. His long-running column, Code Q&A, is one of the most widely read in the magazine's history. He is a former chief electrical in...

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