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#54597 08/02/05 08:37 PM
Joined: Apr 2002
Posts: 257
M
Member
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)

#54598 08/03/05 05:01 AM
Joined: Jan 2003
Posts: 4,391
I
Moderator
Sure. [Linked Image]

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. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#54599 08/03/05 05:51 AM
Joined: Dec 2004
Posts: 1,064
D
Member
How and where does the GEC terminate?


Dnk......


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