equipment ground

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green2012

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I have a 10 HP compressor that im hooking up. Its recommended to be o a 200 amp fast acting fussed disconnect. This is 480 3phase. Its piped in 2inch EMT from panel to disconnect. Piped out of disconnect and changes over to a 10 foot section of sealtite. 3/0 THHN. Now here is the question. Im getting 3 different answers on the size of the equipment ground. The sales company and their field tech say #8 because the compressor wires are oversized and should be 2/0. The manufacturer has a sticker that says to use #2! And the NEC 250-122 says a number 6 is all I need. Im not going with the sales tech, but why would the manufacturer recommend a number 2? Is there something Im missing?
 
No idea as to why they recommend a #2.
A #6 would be the "normal" for a 200 amp fuse, but since you have increased your wire size and argument could be made that you need to upsize to a #4.

On a side note, I'm a bit dubious about the "fast acting" fuse at 200 amp on a 100 HP motor if it's across the line start.
 
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#2/0 is the correct conductor size. {124 amps * 125% = 155 amps} As Augie stated you would need to go up one size for the EGC when using #3/0.
 
green2012 said:
I have a 10 HP compressor that im hooking up. Its recommended to be o a 200 amp fast acting fussed disconnect. This is 480 3phase. Its piped in 2inch EMT from panel to disconnect. Piped out of disconnect and changes over to a 10 foot section of sealtite. 3/0 THHN. Now here is the question. Im getting 3 different answers on the size of the equipment ground. The sales company and their field tech say #8 because the compressor wires are oversized and should be 2/0. The manufacturer has a sticker that says to use #2! And the NEC 250-122 says a number 6 is all I need. Im not going with the sales tech, but why would the manufacturer recommend a number 2? Is there something Im missing?
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the emt can serve as the EGC up to the point it transitions to flex. I would be inclined to use #2 from the point, and only because the sticker says to do so.
 
augie47 said:
No idea as to why they recommend a #2.
A #6 would be the "normal" for a 200 amp fuse, but since you have increased your wire size and argument could be made that you need to upsize to a #4.
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Where is this required in the Code? Table 250.66 would require it, but it's an EGC, not a GEC.
 
Pharon said:
Where is this required in the Code? Table 250.66 would require it, but it's an EGC, not a GEC.
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250.122(B):

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.
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If you increase the size of ungrounded conductors for any reason you must increase the size of the EGC by an equal proportional amount.

OP has 3/0 conductors where 2/0 conductors would otherwise be sufficient - so the EGC must be increased by the same proportional amount.
 
Ah, okay -- thanks. I was wondering why 250.66 would have that note but not 250.122. I guess I should have looked harder, lol.
 
Pharon said:
Ah, okay -- thanks. I was wondering why 250.66 would have that note but not 250.122. I guess I should have looked harder, lol.
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250.66 doesn't need such a requirement, if you use a larger conductor your GEC will be larger - if it gets into a different line of the table, where 250.122 is based on the overcurrent device instead of the conductor size
 
kwired said:
250.66 doesn't need such a requirement, if you use a larger conductor your GEC will be larger - if it gets into a different line of the table, where 250.122 is based on the overcurrent device instead of the conductor size
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Good point. I was misreading note #1 in the table.

Time for some more coffee...
 
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