Xfrmr Secondary Conductors

Status
Not open for further replies.
A

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
225AF WITH 110AT breaker feeding 75 kva xfrm(277/480v primary). Secondary of xfrmr feeds two panels, both 125A main breaker, right next to each other. The feeder to those panels has a tap. The primary conductors are not my concern, the secondary are.

They sized the secondary conductors to be 4 #1’s. That seems incorrect.

Thanks.
 
horsegoer said:
225AF WITH 110AT breaker feeding 75 kva xfrm(277/480v primary). Secondary of xfrmr feeds two panels, both 125A main breaker, right next to each other. The feeder to those panels has a tap. The primary conductors are not my concern, the secondary are.

They sized the secondary conductors to be 4 #1’s. That seems incorrect.

Thanks.
Click to expand...
#1 ampacity is 130 Amps. They terminate on a 125 A CB. As long as there are two sets of conductors, one going to each PB, I don't see an issue.
 
horsegoer said:
i thought because of the ta

they are tapping one set to 2 two sets to feed both panels .
Click to expand...
You're saying there is one set of conductors connected at the transformer secondary that runs to a box or trough, where a splice is made to feed both panels? That wouldn't be Code compliant.
 
Transformer secondary conductors are just that, they are not feeder conductors. Different rules on transformer secondaries
 
tom baker said:
Transformer secondary conductors are just that, they are not feeder conductors. Different rules on transformer secondaries
Click to expand...
There are times I wish that 240.21(C) was not in the same section as the 'tap rules'. But 'ease of use' is rarely a reason the NEC gets changed.
 
david luchini said:
You're saying there is one set of conductors connected at the transformer secondary that runs to a box or trough, where a splice is made to feed both panels? That wouldn't be Code compliant.
Click to expand...
well that’s the ways they show it on the single line drawing . if that’s the case you can’t splice one set of secondary to feed two panels ?
 
horsegoer said:
well that’s the ways they show it on the single line drawing . if that’s the case you can’t splice one set of secondary to feed two panels ?
Click to expand...
But you can run two sets of secondary conductors from the transformer, with one set going to each panel, as long as you comply with one of the rules in 240.21(C).
 
david luchini said:
But transformer secondary conductors ARE feeder conductors (or maybe in some rare cases, branch circuit conductors.)
Click to expand...
While they may meet the definition of feeder conductors, you have to know and understand that they are a special case, and use the term transformer secondary conductors to apply the code. If you just call them feeder conductors, you won't get to the rules in 240.21(C) that cover the overcurrent protection of those conductors.
 
david luchini said:
Sure you would. 240.21 applies to all feeder conductors.
Click to expand...
If you call them feeders you will stop at 240.21(B) Feeder Taps, and not get to 240.21(C) (C) Transformer Secondary Conductors.
If the code user thinks they are feeders they will look only at (B) when then need to be looking at (C).
 
don_resqcapt19 said:
If you call them feeders you will stop at 240.21(B) Feeder Taps, and not get to 240.21(C) (C) Transformer Secondary Conductors.
If the code user thinks they are feeders they will look only at (B) when then need to be looking at (C).
Click to expand...
They're not feeder "taps", so 240.21(B) wouldn't apply. So move on to 240.21(C).
 
Status
Not open for further replies.
Top