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Tuesday, October 18, 2022
Question:
Dear Code Guy, thanks so much for your daily questions and answers. They are always a joy to read. My question is: where does the Equipment Grounding Conductor system begin in a single-family dwelling? Specifically, we have an underground fed meter combo with a 120/240V revenue meter and a 200A main breaker. In this combo box, the main bonding jumper is installed and also the grounding electrode conductor terminates. From the combo box, we go 70 feet into the building to the panelboard. So, do we take two ungrounded conductors and a grounded conductor into the dwelling, OR do we take two ungrounded conductors, a grounded conductor, and the equipment grounding conductor into the dwelling? NEC 250.130(A) seems to indicate since the main bonding jumper is in the combo box we take four wires into the dwelling. It seems as though the location of the main bonding jumper is the starting point of the ECG system.
Thanks,
Robert Frye
A
Answer:
Hello Robert, glad to hear you are enjoying the CQD. Based on the information in your question, the combo (Meter/Main) equipment, with installed 200A Breaker, would be the service disconnect. The Grounded (Neutral) Conductor and the Equipment Grounding Conductor are bonded together in the service disconnect as well. The wiring installed from the load side of the Service Disconnect to the panel inside the building is considered a feeder. In addition to the 2 ungrounded conductors, the feeder would be required to have 1-Grounded (Neutral) Conductor, sized in accordance with the load served, and 1 qualifying type of Equipment Grounding Conductor as specified in Section 250.118. If the Equipment Grounding Conductor installed is of copper or aluminum conductor type, then Table 250.122 must be used to size the Equipment Grounding Conductor. In general, the Grounded (Neutral) Conductor would not be permitted to connect to the Equipment Grounding Conductor on the load-side of the service, at the feeder location per Section 250.142(B).