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#189171 - 09/22/09 10:06 PM Secondary of transformers  
SJT  Offline
Member
Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
I was looking at a job that had a 225KVA transformer suspended from the ceiling in a large utility room of Building. Below the transformer there are 2 - 400amp disconnects. The secondary conductors go to these two switches. Is this allowed, or do you need one single disconnect? I believe the transformer is 3 phase 480V to 208V. There is a breaker on the Primary side also. Is there a section in the code about the number of disconnects allowed on the secondary side?
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#189173 - 09/22/09 10:26 PM Re: Secondary of transformers [Re: SJT]  
Yoopersup  Offline
Member
Joined: Mar 2003
Posts: 822
Michigan
240.21 (C) Each set of conductors feeding seperate loads Shall be permitted to connected to a transformer secondary. (Notice EACH)Devices must be grouped to meet 450.3 (B) note 2
NEC 2005 Handbook Details this clearly on page 170.
Yoopersup


#189174 - 09/22/09 10:27 PM Re: Secondary of transformers [Re: SJT]  
JBD  Offline
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Joined: Jul 2001
Posts: 599
WI, USA
The transformer is protected under article 450.3. If the primary disconnect is sized at not more than 125% of the primary FLA, a single disconnect is not required on the secondary.

The secondary conductors are protected by the tap rules in 240.21(C). There are situations where a set of tap conductors can feed multiple devices.

Last edited by JBD; 09/22/09 10:29 PM.

#189183 - 09/22/09 11:00 PM Re: Secondary of transformers [Re: JBD]  
SJT  Offline
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Joined: Jul 2002
Posts: 241
PATCHOGUE, N.Y.
I checked that 240.21 (C) and you were right on with that. We may leave the 2 Disconnects alone and change a distribution panel downstream from those.
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