Transformer Arrangement

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bphgravity

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I have a 30 kVA Delta/Wye step-up transformer (208 to 480) being tapped from an 800A feeder outside of a building. The taps consist of #6 and terminate into a 60A disconnect with 60A fuses. The 480V secondary is also #6 run approx. 650 feet away and terminates into a 60A disconnect and fused at 30A.

The HO is bonded to the frame on the secondary. There is no grounding electrode connection. The load is a motor load 28A.

There are a few other minor issues. However, the engineer has approved this installation and asking for it to be approved.

Anyone see any problems or code violations?
 
Re: Transformer Arrangement

Bryan

From your description, the 60 amp fuses are on the source, 208 side, and the 30 amp fuses are on the load, 480 side, is that correct?

If so, how is secondary conductor protection provided? 240.21 requires secondary conductor protection much closer than 650'.

If the installation is or could be premises wiring, it seems there are grounding issues also. At some point this could be a separately derived system, and you have little grounding at the secondary side.

I can't be sure without additional info, but it seems to have problems in a couple of areas.

I am anxious to hear more about the installation.

Jim T
 
Re: Transformer Arrangement

Yes Don, I have requested them to connect to the building steel.

My main concern is the circuit and OCD sizing. If the load is 28A at the secondary, doesn't that mean a load of 65A on the primary. How can #6 and 60A fuses be sized correctly?

What requirement requires an outside secondary to have protection closer than 650' away?
 
Re: Transformer Arrangement

Bryan
I missed the point it was "outside" of the building. It appeares you meet all of the requirements of 240.21.C4.
 
Re: Transformer Arrangement

If this unit is outside, why have the GEC terminated to building steel? How about ground rods. Is the motor load outside of the building?
Take a look at 240.21(C)(3), for the load side tap of the transformer.

Bryan is the motor load the only load from this transformer?

Take a look at 240.21(B)(5) for the taps to the feeder on the primary side of the transformer.

Bryan - what is the 800 amp feeder doing outside the building? Just curious...
 
Re: Transformer Arrangement

The main structure is a multi-unit retail center. The building has an 800A main. The 800A feeder is run into a trough on the back of the building. Each unit disconnect/meter is tapped from this main feeder. The original plans called for the lift station to be run off the house panel. The problem is that the building is served with 208Y/120 and the lift station requires 480Y/277.

So, hence the arrangement. #6 tap the main feeder terminate into a 60A disco with 60A fuses. This disco serves the 30kVA transformer. The secondary runs underground over to the lift station 650 feet away and terminates at a disconnect there fused at 30A, the approx. load of the lift station.

I just don't think the conductor sizing or OCD sizing is going to be adequate?
 
Re: Transformer Arrangement

I don't know the code well enough to make a judgment. Mostly because I work for a utility however the fuse seems to be sized to both protect the trasformer and the wire but not serve the load at full capacity. I would put in #4 wire on the 208 side with an 80 A fuse then go to #6 and my 30 on the secondary. Assuming the 30 passed my motor starting current.
 
Re: Transformer Arrangement

Bryan
You did not say in the origional post that you had concerns with the wire size and fuse. It apears to me that you meet the code requirements with the installation. If the motor pulls 28 amps
and you have it fuse at 30 amps I share your concern. The fuse may be a TD fuse and may allow the motor to start. Do you think the voltage drop is a problem? I caculate a 15 volt drop or 3.2%.
 
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