Most properties today, whether residential, commercial, or industrial, include at least one building or structure on that property. Often there are multiple buildings on a single property. Some include buildings that are each supplied by its own utility service and others have an electrical service at one point and deliver electrical power to the other buildings or structures by feeder(s) or by branch circuit(s). This article takes a closer look at the grounding and bonding requirements and methods for separate buildings or structures supplied from other than a service. //

The second method for grounding and bonding at a separate building or structure is allowed where the feeder does not provide an equipment grounding conductor, but does include a system grounded (often a neutral) conductor. This second method is a bit more difficult to utilize because there are more specific restrictions that must be considered and adhered to. Three conditions must exist before one may use the grounded conductor for grounding purposes at a separate building or structure.

Figure 4. Grounding and bonding at separate buildings or structures using the grounded conductor by the method specified in Section 250.32(B)(2)

The first condition is that an equipment grounding conductor, of any form specified in 250.118, is not provided or run with the supply to the structure. This means that only the phase conductor(s) and the system grounded conductor either as direct burial, in nonmetallic conduit underground, or as overhead conductors are included. The key is that no equipment grounding conductor is included.

The second condition is that no continuous metallic paths exist or are otherwise present, and that are bonded to the grounding system in both buildings. Examples of continuous metallic paths could be metal water piping, building steel, metallic conduit, cable shields, metal ducts, and so forth.

The last condition that must be met prior to utilizing this method is that no equipment ground-fault protection is installed on the supply service or feeder, as neutral-to-ground connections on the load side of this equipment can nullify or desensitize the equipment protection.

If all of these conditions are met, then the grounded conductor of the feeder or branch circuit is permitted to be used for grounding and bonding the electrical equipment. It must be connected to the structure disconnecting means enclosure to which the required grounding electrode conductor is also connected. The minimum size of the grounded conductor of the feeder or branch– circuit must satisfy two minimum sizing requirements. First, it must be adequate to carry the maximum load on the grounded (often a neutral) conductor as specified in 220.22. Second, it also must not be smaller than the required equipment grounding conductor for the feeder or branch circuit using 250.122, based on the size of fuse or circuit breaker ahead of it.