No problem, sorta.The Code is a permissive document, in other words, if it doesn't say you can't, then you can. In the case of a ground rod in the crawl space, how do you deal with the dryness issue in the future when the soil dries out? I know the rod extends down about 10 feet (length of the rod plus the depth of the crawl space), but I would think it would still be dryer than the surrounding area. Remember the Code is a minimum standard.I would not feel comfortable with the idea.
Charlie: In this case the rod would be an additional 4' below outside grade due to the crawl space depth and next to the foundation outside wall. Becuse of this I believe the ground resistance would be less in this case.
By chance I found an answer to this from Charlie Trout (Code Message of the Day) from 2000. He says it is allowed but questions why you would want to direct a lightning strike to that point. He adds that driving two rods might save time rather than having to prove a 25 ohm resistance from the rod in dry soil.
Are we talking supplemental electrode or supplementary electrode there is a difference.
ie, supplemental electode 250.56 and suplementary grounding electrodes and their conductors are not required to comply with the bonding requirements of article 250.50/
Supplementary electrodes are usually used for signal reference 250.54.