Wire Sizing 90 degree C

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etinkham

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DC, MD , VA
We have contractors currently installing a UPS. The wire size for the primary input of the UPS is 3 #2/0 + 1 #6 ground in 2" rigid conduit (per drawing). The wire type is XHHW-2. When the UPS arrived it had a 200-amp circuit breaker instead of 175-amp. Do we need to upgrade the wire size to 3/0? The terminations in the UPS are NOT labeled and listed for 90 degrees, therefore I believe the 75 degree C rating on Table 310-16 must be used.
 
augie47

augie47

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Tennessee
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State Electrical Inspector (Retired)
The over-current device ahead of your conductors would be the protection for the conductors. If you protect your 2/0s at 175 amps and they feed the UPS breaker it makes no difference what size that (UPS) breaker is.
 
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etinkham

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Location
DC, MD , VA
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I need to make clarifications. The UPS breaker is 200-amp. The contractor cannot get a 175 amp breaker for the old switchgear and they are going to install a 200-amp breaker. The wire size is 2/0. The Engineer is claiming the 2/0 wire size is okay based on the current rating on the 90 degree scale on 310-16 for XHHW-2 wire. The terminations in the UPS and the new breaker going in the switchgear are not labeled and identified for 90 degree terminations. I believe the wire size must be based on the 75 degree scale on 310-16 which is 3/0 for 200-amps.
 
Dennis Alwon

Dennis Alwon

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Chapel Hill, NC
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etinkham said:
I need to make clarifications. The UPS breaker is 200-amp. The contractor cannot get a 175 amp breaker for the old switchgear and they are going to install a 200-amp breaker. The wire size is 2/0. The Engineer is claiming the 2/0 wire size is okay based on the current rating on the 90 degree scale on 310-16 for XHHW-2 wire. The terminations in the UPS and the new breaker going in the switchgear are not labeled and identified for 90 degree terminations. I believe the wire size must be based on the 75 degree scale on 310-16 which is 3/0 for 200-amps.
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I would disagree with the engineer.
 
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Volta

Senior Member
Location
Columbus, Ohio
etinkham said:
... The terminations in the UPS and the new breaker going in the switchgear are not labeled and identified for 90 degree terminations. I believe the wire size must be based on the 75 degree scale on 310-16 which is 3/0 for 200-amps.
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I agree. They cannot upsize the protection under 240.4(B) either as 175 is a standard size.
 
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