Grounding electrodes and Transformer GEC

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Isaiah

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Location
Baton Rouge
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Electrical Inspector
There's a very large (4 feet diameter), thick wall steel pipe that runs about 50' through a building. The pipe contains air only. They're installing a 3ph, 45kVA delta-wye dry-type transformer/panelboard near the pipe for temporary construction power. There are no available grounding electrodes other than two ground wells that lie about 150' away, outside building.
Construction wants to take the transformer's GEC to the pipe - i.e. bolts/footing. Although the pipe does not qualify as a grounding electrode per 250.52, construction is arguing its not unsafe and will suffice for temp power of about 3 weeks.
Any thoughts?
 
The nec, starting in 250.52, has prescriptive rules on what a GE can be. So your question is easily amswered by those rules, but you also need to review 250.30 ish on SDS.
 
Isaiah said:
There's a very large (4 feet diameter), thick wall steel pipe that runs about 50' through a building. The pipe contains air only. They're installing a 3ph, 45kVA delta-wye dry-type transformer/panelboard near the pipe for temporary construction power. There are no available grounding electrodes other than two ground wells that lie about 150' away, outside building.
Construction wants to take the transformer's GEC to the pipe - i.e. bolts/footing. Although the pipe does not qualify as a grounding electrode per 250.52, construction is arguing its not unsafe and will suffice for temp power of about 3 weeks.
Any thoughts?
Click to expand...
Does the building have a structural steel frame? Take a look at 250.68 (C) (2).
 
petersonra said:
Does the building have a structural steel frame? Take a look at 250.68 (C) (2).
Click to expand...

The building is very old and hardly any drawings exist. None of the steel appears to be tied to earth electrode defined in 250.52. It sits upon concrete pedestals.


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210 C 2 allows you to use the steel frame as a grounding electrode conductor or as a GEC bonding conductor. So you could potentially use it to get to an existing grounding electrode.
 
petersonra said:
210 C 2 allows you to use the steel frame as a grounding electrode conductor or as a GEC bonding conductor. So you could potentially use it to get to an existing grounding electrode.
Click to expand...

The structural steel frame unfortunately is not exposed. They’d have to chip thru 2”-3” of concrete -which has an additional sort of ‘floor tile’ finish - in order to reach the steel.


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