UFER Ground
- Thread starter chrisd
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- Illinois
- Occupation
- retired electrician
rbj,
There is no "supplementary" grounding electrode at a second building. 250.32 requires a grounding electrode with the grounding electrode conductor sized per 250.66. The table would require a #4 GEC, and since the grounding electrode being used is a concrete encased electrode, there is no reduction in sized permitted. If it was a ground rod, then 250.66(A) would permit the #6.
Don
There is no "supplementary" grounding electrode at a second building. 250.32 requires a grounding electrode with the grounding electrode conductor sized per 250.66. The table would require a #4 GEC, and since the grounding electrode being used is a concrete encased electrode, there is no reduction in sized permitted. If it was a ground rod, then 250.66(A) would permit the #6.
Don
Don,
Does the 200 A Service main GEC sizing mandate all UFER installations to be #4 even if a 60A sub is installed at a distant structure. I perused through 250.32 earlier and associated the compliance to 250.66 as being relevant to the subpanel supplied using the multi-wire exception. I know there is a wide spread for interpretation here but the 250.32 is pretty well stated
In theory the remote #4 UFER doesn't really hold for transient effects over distance from the main panel, but from a lightning event imposed at the remote structure equipment I can see that rational application. So installing 100 A mains using #6 GEC's on slab footers is the limit....I've installed a few combined garage-agri wells 100A mains way back in the 70's. Now I wonder when 250.32 came into effect? Thanks for the good input. rbj
Does the 200 A Service main GEC sizing mandate all UFER installations to be #4 even if a 60A sub is installed at a distant structure. I perused through 250.32 earlier and associated the compliance to 250.66 as being relevant to the subpanel supplied using the multi-wire exception. I know there is a wide spread for interpretation here but the 250.32 is pretty well stated
In theory the remote #4 UFER doesn't really hold for transient effects over distance from the main panel, but from a lightning event imposed at the remote structure equipment I can see that rational application. So installing 100 A mains using #6 GEC's on slab footers is the limit....I've installed a few combined garage-agri wells 100A mains way back in the 70's. Now I wonder when 250.32 came into effect? Thanks for the good input. rbj
- Location
- Illinois
- Occupation
- retired electrician
rbj,
Don
No, the GEC size at the second building is based on the size of the feeder conductors that serve the second building.
The exception that you are speaking of does not apply here. It only applies to branch circuits, and in this case we don't have a branch circuit, we have a feeder and the grounding electrode is required by the code rules.
Don
The key word 'feeder' is defined with an equivalent final ocpd/disconnect protecting it at the sub panel. I used supplementary incorrectly and I apologize. I have been using the sub ocpd current rating as a base compared to the feeder conductor sizing you have been using as a base per 250.66. We are discussing the same thing from two directions and I think we share a 'gold spike'. The #4 GEC used in a garage UFER connection is good enough to cover all bets for me. Thanks Don. rbj
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