112.5 KVA transformer

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ronaldrc

Senior Member
Location
Tennessee
On a job I am doing I am installing a 480 volt to 120/208 three phase transformer.

I installed a 150 amp. 3 pole breaker on the primary to protect the transformer and conductors.

My question is would it be a code violation to double barrel the secondary lines of the transformer and feed two different 200 amp. panels each 200 amp. panel will be protected with a 200 amp. 3 pole breaker set just a few feet from the transformer?

Ronald :)
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: 112.5 KVA transformer

Morning Ronald,

I agree with Ron as 125% of the secondary current would be 390 amps and you can move up to the next size breaker.

Also your 150 amp primary protection is under 125% of the primary current of this 112.5 transformer.

That being the case you are not required to have any secondary protection, you could add as many panels as you wanted to the secondary side, all you would have to think about is the total connected load along with panel and conductor protection.

Bob
 
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ronaldrc

Senior Member
Location
Tennessee
Re: 112.5 KVA transformer

Ron and Bob I thought I was all right the way I read the code but doesn't hurt to here it from others that no what there doing. Thanks a bundle.Have a great day.

Ronald :)
 
ron

ron

Senior Member
Location
New York, 40.7514,-73.9925
Re: 112.5 KVA transformer

Bob,
Always a confusing issue for me, is
240.21(C)(1).
It says that the secondary conductors cannot be considered to be protected by the "primary only" scheme, as it is a multiphase (other than delta-delta 3-wire). So you would need secondary protection within 10' of the secondary connection anyway, 400A or less, right (240.21(C)(2)?
 
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ronaldrc

Senior Member
Location
Tennessee
Re: 112.5 KVA transformer

Maybe I wasn't clear enough.The mains for the panels feeds are ,feed through breakers 250 volt 200 amp. fed with 2-1/2" flex and right beside the transformer. Oh the conductors are primary 1/0 copper and 200amp. conductor are 3/0 copper.

Ronald :)

[ March 25, 2004, 03:15 PM: Message edited by: ronaldrc ]
 
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templdl

Senior Member
Location
Wisconsin
Re: 112.5 KVA transformer

For what it's worth consider the following:
This is the way I look at primary protection and any of your comments would be very much appreciated.
Table 450.3(B) allows you to size the pri. breaker up to but no more than 250%. However,one would also need to apply the 25' tap rule, a distance of which would be measured from the pri. break to the secondary breaker so you don't have just carte blanche as to where you can locate the pri. breaker.
The transformer is already protected from being overloaded by the sec. OCPD. The pri. breaker is there to take the transformer off line should the transformer fail such as from an internal fault.
The reason that I bring this up is the possibility of tripping the primary breaker upon energizing the transformer because of inrush. The 250% can provide so latitude when sizing the pri. breaker.
It should be noted that energy efficient transformers have a higher inrush than common general purpose transformer and the K-factor transformers have even higher inrushes.
Personally, I always like to know the possibly problems before they bit you such as panels which can only accommodate breakers of up to 100a or 150a for example that locks you into the maximum pri. breaker that you can use.
Dave
 
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ronaldrc

Senior Member
Location
Tennessee
Re: 112.5 KVA transformer

Dave thanks for the input

I used the 125 percent and set the primary breaker at 150 amps. on my primary for another reason besides protecting the transformer and primary conductors it will also protect the secondary since it could approach 400 amps if both panels where loaded to the gills.

Ronald :)
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: 112.5 KVA transformer

Ron, I could be wrong but I believe as long as he leaves the transformer with two sets of conductors that each terminate in a single circuit breaker or set of fuses he will be in compliance with 240.21(C)(6)(2).

I do not see the 25' rule limiting the number of secondary conductors.
 
R

ronaldrc

Senior Member
Location
Tennessee
Re: 112.5 KVA transformer

Ron I agree with Bob

I think its talking about unprotected conductor on the 25 ft. rule my 200 amp. breakers are located right beside the transformer and there are also mains in the panels which I no I didn't really need but I got them for the same price as main lug.Why not?

The job is already installed havn't had it inspected yet just hope for the best.

Ronald :)
 
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