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#189171 - 09/22/09 07:06 PM Secondary of transformers
SJT Offline

Registered: 07/24/02
Posts: 242
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 07:26 PM Re: Secondary of transformers [Re: SJT]
Yoopersup Offline

Registered: 03/04/03
Posts: 826
Loc: 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.

#189174 - 09/22/09 07:27 PM Re: Secondary of transformers [Re: SJT]
JBD Offline

Registered: 07/12/01
Posts: 599
Loc: 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.

Edited by JBD (09/22/09 07:29 PM)

#189183 - 09/22/09 08:00 PM Re: Secondary of transformers [Re: JBD]
SJT Offline

Registered: 07/24/02
Posts: 242
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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