bifurcated dry type transformer - sort of

[mshields]

I've got a 150kVA transformer and on the secondary, it's been proposed to me that we come off the transformer with a single feeder to a nearby wireway. Tap off that wireway with 2 200A circuit breakers.

The primary is protected with 200A fuses which could be a problem with inrush but this part is existing so it ought to be ok it's worked til now. Regardless of that I'm wondering about the secondary feeder and OCP's. Does the NEC address this kind of installation. I know that the secondary cables are protected by an application of the tap rule, do they therefore need to be rated 125% of the FLA of the transformer? Where you come off the wireway, isn't that a tap of a tap which of itself would not be allowed right?

I think at a minimum I need two distinct feeders comming off a double lug on the secondary of the transformer.

Thoughts?

Thanks,

Mike

 

[augie47]

240.21(C) is your best reference.
It will make a differecne if the transformer is two-wire, delta, or other.{(see 240.21(C)(1)}
Double lugs with two feeds is by far the most common method I see.

 

[dkidd]

There is a good article at http://www.iaei.org/magazine/2002/03/feeder-and-transformer-secondary-tap-conductors/

Figure 3 illustrates what you are describing.

 

[mshields]

thanks very much

thanks very much

thanks