Q. What are the rules for grounding and bonding service equipment?
Find the Answer
A. Service equipment supplied from a grounded system must have the grounding electrode conductor (GEC) terminate in accordance with Sec. 250.24(A)(1) through (5). Let’s see what parts 1, 4 and 5 of this section have to say on the subject.
1) A GEC must connect the service neutral conductor to the grounding electrode at any accessible location, from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral, up to and including the service disconnecting means.
Some inspectors require the service neutral conductor to be grounded (connected to the earth) from the meter socket enclosure, while other inspectors insist that it be grounded (connected to the earth) only from the service disconnect. Grounding at either location complies with this rule.
4) When the service neutral conductor is connected to the service disconnecting means [250.24(B)] by a wire or busbar [250.28], the GEC is permitted to terminate to either the neutral terminal or the equipment grounding terminal within the service disconnect.
5) A neutral-to-case connection isn’t permitted on the load side of service equipment, except as permitted by Sec. 250.142(B).
If a neutral-to-case connection is made on the load side of service equipment, dangerous objectionable neutral current will flow on conductive metal parts of electrical equipment [250.6(A)]. Objectionable neutral current on metal parts of electrical equipment can cause electric shock and even death from ventricular fibrillation, as well as a fire.
A main bonding jumper [250.28] is required to connect the neutral conductor to the equipment grounding conductor within the service disconnecting means [250.24(B)].