Grounding Table 250.66 vs Table 250.122

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Str1ve13

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Orlando, FL


Hey Guys Question about grounding sizes,
As you can see in my image I have an existing trough system with 4 sets of 4#500MCM AL coming from the utility transformer feeding into a wireway. The wireway is being fed by a 250MCM AL GEC.

Now I am adding a 200A Service to this trough and my question is out of the trough do I use table 250.66 to size the tap for the 200A fused disconnect switch (Note#4). Then from the disconnect to the tenant's panel can that be considered an EGC and use table 250.122 (Note #3)?

Also, I haven't heard a problem of mixing Aluminum and Copper, are there any by chance?

Thanks
 
When there is no conductor over current protection on the supply end of the conductors 250.66 applies.

When there is conductor over current protection on the supply end of the conductors 250.122 applies.

So at Note 4 use 250.66 at Note 3 use 250.122.
 
Brad, What do you mean by mixing copper and aluminum ? There certianly

can be problems if they are not seperated from each other.
 
benaround said:
Brad, What do you mean by mixing copper and aluminum ? There certianly

can be problems if they are not seperated from each other.
Click to expand...
Click on his image and you will see the diagram he has presented us.
 
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