Transformer Disconnects - Electrician Talk - Professional Electrical Contractors Forum

GEORGE D · 04-14-2011, 10:48 PM

Ok, no code book handy. Do I have to have a disco on primary and secondary of tranny? Secondary terminates about 25' away into a machines disco switch. Primary will be fed from a fused disco in electrical room 250' away. I'm gonna guess the primary should have to be within sight. Any help is appreciated

Greenblinker · 04-15-2011, 12:18 AM

Searching the 08' NEC I don't see anything regarding disconnects for XFMRs. I do see plenty of rules for overcurrent protection though. My guess is your disco rules are gonna be more specific to the loads they are serving.

raider1 · 04-15-2011, 10:22 AM

Under the 2008 NEC there is no requirement for a local disconnecting means on the primary of the transformer.

Under the 2011 NEC a new section was added that requires either a local disconnecting means or a label on the transformer denoting the location of the upstream breaker and the upstream breaker must be capable of being locked in the open position. (See 450.14)

As for the secondary remember that 240.21(C) provides the requirement for overcurrent protection for the secondary conductors. So the machines disconnect that you are terminating the secondary conductors in must meet the requirements of 240.21(C)(6)(2) (The 25' secondary conductor rule).

Chris