Figure 7-6. - Definition of fixed equipment.
proper mounting, coupling, and terminating of the conductor or raceway intended to serve as the grounding conductor. The installation must be made so that it can be inspected by an electrical inspector, the design engineer, or any other authority concerned. A continuity test with a meter, a light, or a bell will assure that the path is "continuous."
2. That every grounding conductor has the capacity to conduct safely any fault current likely to be imposed on it. Refer back to the section of the Code that specifically establishes a minimum required size of grounding conductor.
Part (a) of NEC ® , section 250-61, permits the grounded conductor (usually the neutral) of a circuit to be used to ground metal equipment enclosures and raceways on the supply side of the service disconnect. Figure 7-7 shows such applications. At (A), the grounded service neutral is bonded to the meter housing by means of the bonded neutral terminal lug in the socket. The housing is thereby grounded by this connection to the grounded neutral, which itself is grounded at the service equipment as well as at the utility transformer secondary supplying the service. At (B), the service equipment enclosure is grounded by connection (bonding) to the grounded neutral, which itself is grounded at the meter socket and at the supply transformer. These same types of grounding connections may be made for cabinets, auxiliary gutters, and other enclosures on the line side of the service entrance disconnect means, including the enclosure for the service disconnect. At (C), equipment is grounded to the neutral on the line (supply) side of the first disconnect fed from a step- down transformer (a separately derived system).
Aside from the permission given in the five exceptions to the rule of part(b) of section 250-61, the Code prohibits connection between a grounded neutral and equipment enclosures on the load side of the service. So bonding between any system grounded conductor, neutral or phase leg, and equipment enclosures is prohibited on the load side of the service (fig. 7-8). The use of a neutral-to-ground panelboard or other equipment (other than specified in the exceptions) on the load side of service equipment would be extremely hazardous if the neutral became loosened or disconnected. In such cases, any line-to- neutral load would energize all metal components connected to the neutral, creating a dangerous potential for electrocution. Hence such a practice is prohibited. This prohibition is fully described in figure 7-9.Continue Reading