Transformer Secondary going to Buss Gutter then To Multiple Disconnects

[TrickleCharge]

I have a project where the EE is proposing that the secondary on the transformer land on a buss gutter and just bellow that go to 5 fused disconnects. Is there something that applies to having multiple OCPD on the secondary? Or does simply just going off of 240.21(C) will suffice, in that the total OCPD will not exceed the XFMR secondary rating AND the conductors will be rated not less than the total load on the secondary side? Thanks

 

[don_resqcapt19]

What is a buss gutter? If it is a conductor that is connected to the transformer secondary terminals, then you would not be permitted to extend other conductors from that point to the disconnects. 240.21

 

[TrickleCharge]

Please see attached. From the transformer to the gutter they will be running conduit with secondary conductors and this is <10'.

 

[mcnut]

Tap a tap..

Tap a tap..

240.21

Conductors supplied under the provisions of 240.21(A) through (H)shall not supply another conductor except through an overcurrent​

protective device meeting the requirements of 240.4.

 

[TrickleCharge]

COnfused at your response mcnut....tap conductors and secondary conductors are two different things. My question deals with having mutliple overcurrent devives on the secondary side that come from this proposed "buss gutter." This gutter is rated at 400A which is above the total connected load ( i think its around 350 amps).

 

[jim dungar]

COnfused at your response mcnut....tap conductors and secondary conductors are two different things. My question deals with having mutliple overcurrent devives on the secondary side that come from this proposed "buss gutter." This gutter is rated at 400A which is above the total connected load ( i think its around 350 amps).

If the conductors that feed your individual disconnects go all the way back to the transformer lugs/pads, your installation might be compliant.

The problem is the single conductor run from the transformer to the wireway.

 

[bob]

COnfused at your response mcnut....tap conductors and secondary conductors are two different things.

That is not exactly true. Transformer secondary conductors are tapped conductors and are subject to 240.21.

 

[david luchini]

That is not exactly true. Transformer secondary conductors are tapped conductors and are subject to 240.21.

I think TrickleCharge has this right. Tap Conductors and Transformer Secondary Conductors are not the same thing. A Tap Conductor has overcurrent protection ahead of its point of supply that exceeds the value for similar conductors, while a Transformer Secondary Conductor has NO overcurrent protection ahead of its point of supply. 240.21 deals with Tap Conductors in parts (A), (B), (E) and (F). 240.21 deals with other than Tap Conductors in parts (C), (D), (G) and (H).

My question deals with having mutliple overcurrent devives on the secondary side that come from this proposed "buss gutter." This gutter is rated at 400A which is above the total connected load ( i think its around 350 amps).

In addition to the conductors supplying other conductors, as others have pointed out from 240.21, the total overcurrent protection equals 850A, so the 400A conductors and buss are not properly protected either.

 

[steve66]

I don't understand why an engineer wouldn't just use a panelboard?

Is there a really good reason why fuses are needed instead of circuit breakers? Even so, use a fused panelboard.

I don't consider large conductors to a buss, and smaller conductors to a fused disconnect code compliant.

I do consider conductors running to a Main Lug Only panel compliant, if the panel doesn't need a Main Breaker per 430. If 430 requires a main breaker, its easy to provide one in a panel anyway.

 

[bob]

Cooper Bussman seems to look at differently

http://www.cooperindustries.com/con..._Lib_Transformer_Secondary_Tap_Conductors.pdf

 

[david luchini]

Cooper Bussman seems to look at differently

Cooper Bussman isn't the NEC. Interestingly, they change the words "Transformer Secondary Conductors" from the Code to "Transformer Tap Conductors" for their discussion. In any event, Transformer Secondary Conductors don't meet the definition of Tap Conductors found in 240.2.

 

[jim dungar]

Cooper Bussman isn't the NEC. Interestingly, they change the words "Transformer Secondary Conductors" from the Code to "Transformer Tap Conductors" for their discussion. In any event, Transformer Secondary Conductors don't meet the definition of Tap Conductors found in 240.2.

And their summary says they are 'considered' as tap conductors.

 

[RB1]

If the secondary conductors have a rating not less than the rating of the copper bars in the gutter, those conductors are OK. However, the conductors from the bussed gutter to the breaker enclosures violate the general requirements of 240.21 that prohibit conductors supplied under the provisions of 240.21(C)(2) from supplying another conductor except through an overcurrent protective device. In that sense, the copper bars are both devices and conductors.

 

[TrickleCharge]

Im with Steve66. EE come up with stuff sometimes that just dont make any sense. I think the panelboard would have been ideal OR multiple secondary connections in the XFMR, but i think anything more than 2-3 makes it hard to have that many conductors in the XFMR. I just dont see the advantage of this design, I have been doing this for over 15 years and have never encountered this. But moreson why I like my Job because I learn something new everyday! Thanks for everyone's input

 

[meternerd]

As a POCO, I see this done all the time. Comes from our transformer secondary, to a bussed gutter, then to multiple meter sockets, each containing a service disconnect. Transformers are only fused on the primary side. Why is this any different?