Replacing a 480v RTU

S

Sparky202

Member
Location
Washington DC
Occupation
Supervisor
We currently have a 480V 3-Phase RTU with a 132amp MCA and 150amp MOP that needs to be replaced. The new RTU has a higher amperage, with a 147amp MCA and 175amp MOP. The question is whether we can continue to use the existing (3) 1/0 THHN feeder on a 150amp breaker for the new RTU. The feeder is 92ft long. The building engineer is confident that the existing feeder and breaker will suffice, but the building inspector advises against it. Any guidance on this matter would be greatly appreciated. Thank you.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Sparky202 said:
so if we change the breaker to 175amp and that’s OK using 1/0 THHN wire? I just wanna make sure we’re all on the same page.
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Yes you'll need a 147 amp or larger conductor so #1/0 copper is good. The 150 amp OCPD will probably work but you can change it to a 175 if needed I would try the 150 first.
 
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