National Electrical Installation Standards

Standards as High as Your Own

Thursday, June 2, 2022


Hello Code Geeks,

We have a service for a billboard signs. The inspector said a 4 AWG grounding electrode conductor is required and two ground rods must be installed.  I don’t see that 4 AWG GEC is required. In fact, I don’t see that the “second” ground rod is even necessary except to assure the required 25 ohms resistance. One ground rod and 6 AWG appear to be all that is necessary for this installation. As more and more water supply lines were converted to plastic, a supplemental ground became necessary but this is only a service for a billboard. Can you assist with an opinion on this?

Thanks for all you do.

Peter White



Hi Peter,

Yes, the connection of the grounding electrode conductor to a ground rod is shown in 250.66(A) which is a 6 AWG copper for a sole connection. But first, let’s clear up the requirement for a “second” ground rod. NEC 250.53(A)(2) requires that a single rod be supplemented by an additional electrode (could be a ground rod). However, the exception to 250.53(A) relaxes the requirement for a supplemental electrode where the resistance requirements of the exception are met. Generally, to avoid the work involved in determining resistance by the fall of potential method or using a clamp-on meter, a second rod is installed. The requirements cover all electrical installations including billboards. Hope this is useful.

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