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#54597 - 08/02/05 06:37 PM Tap for Transformer
master66 Offline

Registered: 04/18/02
Posts: 260
Loc: Masontown, PA, USA
Is this OK?

In a school, there is a 150 KVA transformer (480V delta Primary / 120/208Y secondary) installed 6" away from a MLO panel.

The MLO panel is fed from the MDP (located in an electrical room on the other side of the building) via a 400A Fused switch.

The transformer is fed from the feed-thru lugs in the MLO panel with 4/0 copper in flex.

The transformer then feeds a 120/208Y panel (6" away) with paralleled 4/0 copper in flex terminating in a 400A main breaker.

Does this meet all requirements of articles 240.21 and 450? (2005 NEC)

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#54598 - 08/03/05 03:01 AM Re: Tap for Transformer
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA

The primary current of the 150 KVA transformer is about 180 amps.

Table 450.3(B) allows the primary overcurrent protection to be 250% of the primary current when secondary protection is provided.

180 x 2.5 = 450 amps.

On the secondary side we are allowed 125% and we can round up to the next standard size OCP.

The secondary current of a 150 KVA transformer is 416 amps.

They could have gone higher than 400 amps on the secondary side.
Bob Badger
Construction & Maintenance Electrician

#54599 - 08/03/05 03:51 AM Re: Tap for Transformer
Dnkldorf Offline

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
How and where does the GEC terminate?



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