Circuit type

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ryan_618

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Are primary and secondary conductors to and from a transformer considered a circuit...such as feeder or branch or service, or are they just primary and secondary?

[ January 28, 2004, 08:59 PM: Message edited by: ryan_618 ]
 
Re: Circuit type

Hello Ryan, is this a trick? ;)

Roger
 
Re: Circuit type

I would have to agree with Bob simply for the definition of feeder. Also 215.2(B)(1) would cover the primary side.

The secondary side of the utility transformer would be "service conductors".

Roger

[ January 28, 2004, 09:36 PM: Message edited by: roger ]
 
Re: Circuit type

Feeders...thats probably what I would say too.

With that in mind, 215.2(A)(1) tells us that the feeder conductors must have an ampacity not less than required to supply the load as computed in parts 2,3 and 4 in Art. 220.

Example: A 75KVA transformer's secondary conductors feed two panels (120/208V). The first panel is a main breaker (225A) with feed through lugs to the second panel, which is main lug only. The computed load of the panels are about 65,000W and 50,000W. Total of 115,000 Watts.

Questions:
1) Does the transformer have to be sized sufficient to provide the computed load?
2) Since Article 215 only address the feeder conductors, is question #1 valid?

[ January 28, 2004, 09:34 PM: Message edited by: ryan_618 ]
 
Re: Circuit type

OK, I'll bite...assuming load side of a service, not the poco.

Primary - yes
Reasoning: there's an upstream OCPD and the xformer could be considered an "outlet" (at minimum, it generates heat :) )

Secondary - no
Reasoning: no OCPD yet on the wires coming directly out of the xformer
 
Re: Circuit type

Ryan is the transformer utility owned?

Roger
 
Re: Circuit type

Ryan, I'd say you would be right in forcing this issue with the engineer and let him explain his design.

Roger
 
Re: Circuit type

[EDIT: I am presuming this is a 3-phase, 480-120/208 V system. No voltage levels were given in the question.]

If ?the engineer? used a 225 amp panel to serve 115KVA of computed load (equivalent to 319.4 amps), then I would call it a ?bad design.? It?s not unsafe, just bad. By that I mean that it will not serve the customer?s needs. The main breaker would trip under a load that is lower than the computed load. But that is not an NEC issue.

Is the transformer adequately protected? For the secondary, I would say ?yes.? 75KVA equates to 208 amps. Add 25% and you get 260. The 225 amp main breaker on the first panel is lower than 260, so it does not violate the limits of Table 450.3(B). You gave us no information on the primary side protection.

Are the conductors properly sized? We can?t say, because you did not tell us what size(s) ?the engineer? specified.

What?s the bottom line? If I were the owner, I would fire ?the engineer.? But if I were the Inspector, I would have to let it go (unless there are other issues that you have not listed here). I?ve never been an Inspector. I don?t know if your duties and obligations require you to advise the owner that the design ?meets code but is inadequate.? But if they do not prohibit you from doing so, then I would definitely suggest pointing out the design weakness to the owner.

[ January 29, 2004, 04:56 PM: Message edited by: charlie b ]
 
Re: Circuit type

Hi Charlie, and thanks for your response. The OCPD's are properly sized (I don't have the plans here, so I can't give you the numbers). The conductors are also properly sized to the OCPD, but they are not sized large enough to handle the computed or the connected load. The Transformer, however, is undersized.

I have considered calling the engineer to ask how he/she justifies this, but as you wrote, I need the NEC to help me out.
 
Re: Circuit type

I plan on finishing my review of these plans over the weekend, and once I am done I plan to call the engineer to discuss this apparent inadequacy. Does anyone else have any thoughts on this before I call the engineer?
 
Re: Circuit type

Originally posted by ryan_618:
I plan on finishing my review of these plans over the weekend, and once I am done I plan to call the engineer to discuss this apparent inadequacy. Does anyone else have any thoughts on this before I call the engineer?
Ryan, you're a great to check that over, because Engineer's make mistakes too. I'm sorry, Charlie. :)
 
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