• Todd Engle

Distribution Panels stay safe!


Remote Distribution Panels

Although this topic is covered in other areas, because the emphasis is on safety, it's important to review.

The National Electrical Code (NEC) does not recognize the term "sub panels." From a code standpoint, there are two types of panels:

Service Panels

A service panel is a distribution or load center that contains the main disconnecting means. This is the ONLY panel where the neutral and grounds should be joined (bonded) together.

Distribution Panels

Distribution panels, or load-side panels, are downstream from the panel containing the main service disconnect(s). In these panels, the neutral and grounds should be separate, and the neutral bus should be isolated from the panel enclosure.

The only exception to this is in existing detached structures where no metallic path exists between the structures. In this exception, a connection between the grounded conductor and the metal case via a bonding jumper is permitted. According to the 2008 NEC, this is not allowed in new construction, so, in all cases, a 4-wire feed to the detached structure is required in order to isolate the grounded conductors from the equipment grounding conductors.

There are two methods of providing ground continuity back to the service panel:

1. four conductor feeders with:

  • two hot or ungrounded conductors;

  • one neutral or grounded conductor; and

  • one grounding conductor.

2. three conductor feeders with:

  • two hot or ungrounded conductors;

  • one neutral or grounded conductor; and

  • equipment grounding through conduit/tubing, electrically linking the two panels (allowed by section 250.118 of the NEC).

Inspecting Service Panels

  1. Are the neutral and ground connected (bonded)?

  2. Is the panel enclosure connected (bonded) to ground?

  3. Does each neutral conductor terminate at a separate lug on its bus?

Inspecting Distribution Panels

  1. How is the service grounded back to the service panel?

  2. Are the neutrals and grounds separated?

  3. Is the neutral bus isolated from the panel enclosure?

  4. Is the panel enclosure connected (bonded) to the grounding bus?

  5. Does each neutral conductor terminate at a separate lug on its bus?

An important note: Every structure is required to have a grounding electrode system. If they are present in the structure, they must all be bonded together. If a detached structure has a remote distribution panel located at the structure, then it requires a grounding electrode system of its own. The equipment grounding conductor in a 4-wire feeder does not take the place of the required grounding electrodes. It is also important to understand that if the detached structure is being fed by a single branch circuit, and it contains an equipment grounding conductor which is used for grounding the non-current-carrying metal parts of equipment, then no grounding electrode system is required. Complements of InterNachi



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