Greg Asked:
In order to place two grounding rods, what is the distance required by the NEC away from the electrical panel? And what is the distance they should be from each other (the rods)?
Our Answer:
The National Electrical Code (NEC) Article 250 does not have a requirement for how far the grounding rod needs to be placed in relation to the electrical panel. Generally speaking “best practice” would indicate that the closer you install the rod to the panel, the better. Now, if you are installing the grounding rod really far away, the NEC may require you to increase the conductor size to ensure that you don’t have an impedance issue.
That said, it is becoming quite common for local governing authorities (building inspectors), to issue rules requiring the installation of grounding rods within some specified distance from the panel. We think this is a good idea for a number of reasons. While it may be difficult (or unsightly) to install a ground rod near the panel, as you may need to core through some concrete, the advantages of proximal grounding outweigh the effort. Remember, if you do core through concrete, you must install a PVC sleeve to prevent accidental contact between the rod and any rebar in the slab.
As far as spacing of the grounding electrodes goes, NEC 250.53 (B) requires a minimum of 6-ft between electrodes. However, in NEC 250.56 they note that spacing’s greater than 6-ft will improve the efficiency of the electrode. The spacing of electrodes deals with a theory known as the Sphere of Influence. Basically you want to space your electrodes out 2-times (2X) the length of the electrode. So, if you are installing 10-ft grounding rods, you would want them spaced at 20-ft intervals.