National Electrical Installation Standards

Standards as High as Your Own

Thursday, August 27, 2020


Great job, please keep up the good work. I have a question regarding the supplemental ground connection point when a whole house generator is installed. I installed a non-separately derived 200A service rated transfer switch, which houses a 200A main breaker as the first means of disconnect since the exterior meter socket has no disconnecting means. From the meter to the transfer switch I ran 4/0 AL SEU cable and from the transfer switch to the existing circuit breaker panel/load center, I ran 4/0 AL SER cable. In the existing load center I removed the neutral to ground bonding screw, then separated the grounds and neutrals and moved the main ground wire coming from the water main over into the transfer switch where the neutral and ground are bonded together. All good so far, but the question was raised where the supplemental ground needs to be attached. It is my understanding it can be attached virtually at any ground point in the meter, the transfer switch, or on the newly installed ground bar in the existing load center. What say you?

Richard Cressotti




Thanks for the question and the kind words. The question included the term "supplemental ground connection." Based on the way the question is worded, you are seeking the acceptable connection point for the required grounding electrode conductor for the service. Since the new transfer equipment is the service disconnect and is so rated, the grounding electrode conductor should be connected in the service rated transfer equipment. The Section 250.24(A)(1) indicates that the grounding electrode connection at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to, including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means. separating the neurals (grounded conductor) and equipment grounding terminal bars in the load side panelboard meets the requirements in 250.24(A)(5). Note: Supplemental grounding electrodes are covered in Section 250.53(A)(2) and 250.53(D)(2) if you are using a metal water pipe grounding electrode.

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