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#174416 - 02/04/08 11:15 AM (Part 2 ) 12470 Disconnect & Switch Question
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
On the load side of theses (two) 2500 KVA 12470 / 277-480 volt transformers. The runs into the Building Allow how many disconnect Switchs between them. I got my Idea wanna know yers . 2 , 6, 12??? I want other ideas without where I;m getting mine in the code.
Yoopers

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#174417 - 02/04/08 11:58 AM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: Yoopersup]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
NEC2005 240.21(C)(4) allows as many as you want as long the the sum does not exceed the ampacity of the conductors.

side note:
I didn't think there were any cities in da UP that needed 5000kVA of power.



Edited by JBD (02/04/08 11:59 AM)

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#174429 - 02/04/08 05:09 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: JBD]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
What about Article 225.33 , 450.3(A) also 240.21 C(4)note two says Terminate in a single circuit breaker or single set of fuses. note 240.92 (B)(2) if it applys says 6. Hey this is a residental Service up here fer thoses with Electric Heat!!!
So Again Two, Six , or twelve .


Edited by Yoopersup (02/04/08 05:17 PM)

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#174437 - 02/04/08 07:12 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: Yoopersup]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
 Originally Posted By: Yoopersup
What about Article 225.33 , 450.3(A) also 240.21 C(4)note two says Terminate in a single circuit breaker or single set of fuses. note 240.92 (B)(2) if it applys says 6. Hey this is a residental Service up here fer thoses with Electric Heat!!!
So Again Two, Six , or twelve .


225.30 Applies if the building is fed on the load side of a service disconnect. Because this is a customer owned transfromer it is not a service. But even if it is applicable 225.30(C) allows multiple feeders when the capacity is in excess of 2000A.

225.33 allows six disconnects per supply allowed by 225.30.

450.3(A) allows up to six disconnects unless Note 3 (supervised transformer location) applies. Which probably the case unless your HO (the one with electric heat) is maintaining this size oil-filled transformer.

240.21(C)(4) is per set of conductors not per transformer or supply, as is 240.92(B)(2).

I done gradgitated from da Tech.

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#174459 - 02/05/08 10:31 AM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: JBD]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Ernie— My answer would be 2 (one for each feeder). This is based on 240.21(C)(4). I would also say that these Secondary taps give the structure two sources of supply allowed by 225.30(C). There appears to be two structures on this property if you count the Service as a structure. The key point is however, as you pointed out, each xformer tap must terminate in a single disconnect.
_________________________
George Little

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#174468 - 02/05/08 02:41 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: George Little]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
George
225.30 (C) in excess of 2000 amp. We have 3000 Amps on each transformer on the Secondary. So are we now allowed 4 feeders each with a Main?? And if it Falls under Supervised Industrial Instllations 240.A (2)Overload Protection (2)
Now how many . This is a Real time question about a Job up here.
Yoopers
HI JDB miss the Snow???

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#174481 - 02/05/08 05:50 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: Yoopersup]
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Ernie— A few things: I don't know what your referring to in 240 because you are missing the section reference in your post. Secondly, you can have as many taps as you want on the secondary, assuming your not trying to protect the transformer with the overcurrent protection on the secondary side as allowed by Article 450. As for the number of Disconnects inside the building you are limited to 6 in one location per 225.33(A). Each tap must terminate in a single overcurrent device sized to protect the secondary tap conductors feeding it. 240.21(C)(4)(2)
_________________________
George Little

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#174482 - 02/05/08 05:55 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: Yoopersup]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
For what its worth, I try to treat supervised transformer secondaries the same way as I services.

I would allow up to 6 disconnects per set of conductors, however I see very little reason not to have a single disconnect per transformer.

So,
Is this location supervised?
Do both of these transformers feed the same building?
Is there a good reason to have multiple sets of supply conductors per transformer?
What answer do you want, lots of disconnects or just 2?

And even though it does snow down here, I occasionally miss the +250" up nordth dere.

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#174517 - 02/06/08 11:42 AM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: JBD]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
Both Transformers feed the Same Building,
(Sorry George 240.92 (B) (2) 2
Allowes six disconnect Switches per set of Conductors if a Supervised Industrial Installation.
Also 240.30 (B) Have Several Exceptions to the one disconnect Rule .225.33 Maxium # of disconnects says six for EACH suppy!So could you have four feeders , They say PER SUPPLY , here we would have several supplys Right
Reason not to have single disconnect Switch you ask. COST Ground Fault Protection. any breaker over 1000 amps on a Wye Requires it. If you can get your breakers under 1000 amps its not required.


YES ITS SNOWING!

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#174523 - 02/06/08 03:29 PM Re: (Part 2 ) 12470 Disconnect & Switch Question [Re: Yoopersup]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
 Originally Posted By: Yoopersup
COST Ground Fault Protection. any breaker over 1000 amps on a Wye Requires it. If you can get your breakers under 1000 amps its not required.


30yrs ago I often designed services without GFP for installed cost reasons, now I wouldn't think of it. If ground faults are common in your facility then add a second level of GFP like they do in hospitals or use a high resistant ground scheme instead

Having a single main device, especially if it is in a barriered enclosure or a separate enclosure, makes reducing arc flash incident energy levels easier as well as providing a convenient means to disconnect the service for de-energized work.

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