For multiwire branch circuits, the Code states, “All conductors shall originate from the same panelboard or similar distribution equipment;” where is a similar requirement for those other than multiwire branch circuits? Although it is poor practice, it is common knowledge that electricians making repairs will grab the closest grounded (may be a neutral) conductor in a box to create a new two-wire circuit.
This unprincipled electrician makes no effort to track this grounded conductor back to the panelboard—if it provides the necessary voltage, the electrician will use it. It is very possible to load this neutral conductor beyond its ampacity, thus creating a hazard due to overheating of the insulation. It is doubtful that an electrician with this sort of work ethic would have taken out a permit for the work. Even if it was inspected, is it likely that the inspector would have traced the circuit back to the panelboard(s)? Thus the two conductors may be from different circuits. Though unlikely, they could possibly be from different panelboards.
The only requirement in the Code I can find is in Article 408, Switchboards and Panelboards, where 408.3(B) requires that “The arrangement of busbars and conductors shall be such as to avoid overheating due to inductive effects.” I believe this was intended to cover the interior routing of wiring within a switchboard, but it could just as well apply to conductors for the same circuit taken from different panelboards or switchboards. Of course, 110.3(B) could be used, which states, “Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.” But would it not make more sense to cover the situation specifically with a requirement in Article 210?
This seems to be such a basic requirement that everybody knows you cannot take a circuit from two different panelboards, but there are other Code requirements just as basic that electricians also seem to forget about.
A frequently overlooked requirement is that a metallic raceway enclosing a service grounding-electrode conductor must be bonded at both ends. This requires the same types of bonding hardware as those used for a service conduit—in other words, locknuts and bushings will not do. The basic requirement is in 250.92, Services, which states, “The non-current-carrying metal parts of equipment indicated in 250.92(A)(1), (A)(2), and (A)(3) shall be effectively bonded together.
“(1) The service raceways, cable trays, auxiliary gutters, cablebus framework, or service cable armor or sheath except as permitted in 250.84
“(2) All service enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor
“(3) Any metallic raceway or armor enclosing a grounding electrode conductor as specified in 250.64(B). Bonding shall apply at each end and to all intervening raceways, boxes, and enclosures between the service equipment and the grounding electrode.”
The methods permitted are in 250.92(B), Method of Bonding at the Service, which states, “Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:
“(1) Bonding equipment to the grounded service conductor in a manner provided in 250.8
“(2) Connections utilizing threaded couplings or threaded bosses on enclosures where made up wrenchtight
“(3) Threadless couplings and connectors where made up tight for metal raceways and metal-clad cables
“(4) Other listed devices, such as bonding-type locknuts, bushings, or bushings with bonding jumpers
“Bonding jumpers meeting the other requirements of this article shall be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair the electrical connection to ground. Standard locknuts or bushings shall not be the sole means for the bonding required by this section.”
Sometimes the raceway is used for only part of the run of grounding-electrode conductor, for protection against physical damage and where the rest of the run is considered protected without the raceway. In this case, the termination of the raceway must be bonded to the grounding-electrode conductor [250.64(E)].
The best raceway enclosure for a grounding-electrode conductor, however, is PVC rigid nonmetallic conduit. With PVC there is no concern with magnetic fields around the grounding-electrode conductor, and no bonding is required. If physical damage is possible, use schedule 80 PVC.
The best electricians use the Code and exceed its requirements through improvisation and ingenuity. Some who do it “by the book” would criticize them as risk takers, but for all those who play it safe, the Code is certainly the dependable place to go for guidance. Don’t mistake improvisation for risk taking. Don’t mistake laziness for craftiness either. EC
SCHWAN is an electrical Code consultant in Hayward, Calif. He can be reached at firstname.lastname@example.org.