xfmr

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paul renshaw

paul renshaw

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Cordova, Maryland
When I took the cover off of a xfmr I was asked to look at I noticed the following. It is 37.5 KVA 1ph 480v pri 120/240 sec Hv amps 78 LV amps 156 amps. The feeder is on a 100 amp breaker with #2 conductors and the secondary is also #2 wire, and the main breaker in the secondary panel is 200 amps. Is this compliant? It seems to me that #2 is too small for the secondary amps capacity of the xfmr. There also was no GEC run to it either. There also was a piece of # 8 run through EMT with a romex connector on each end as the ground lead for the telephone system. Does that ground wire need to be bonded on both ends of the raceway like a GEC in a metal raceway? They also had four conductors under one single barrel lug, which I am sure violates the listing of the lug.
 
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Primary protection at 100 amps and secondary protection at 200 amps are both appropriate. But you are right in saying a #2 secondary conductor is too small.
 
That would be a 60 KVA rated transformer. A #2 primary conductor would be OK if, and only if, the primary protection is no higher than 125 amps (i.e., the next higher standard size from the 115 amp rating of the conductors). But it would be a waste of some of the unit's capacity. I would size the primary protection at 150 amps, or even 175 amps (i.e., to allow for inrush currents), and size the primary conductors accordingly.
 
Sorry, should have clarified, the 45kva is 3ph 120/208 wye secondary with 480v primary. The secondary conductors are #2 and go to a 150amp main breaker panel. The nameplate says HVamps 54, LV amps 125.
 
Sorry. I misread your second post. For a 45KVA with a 120/208 volt secondary, I would have chosen a 150 or 175 amp OCPD for the secondary. Once again, a #2 is inadequate for this installation.
 
Also, I just realized the panel that the 45kva xfmr secondary conductors terminate in is about 50' away. Does there need to be overcurrent protection at the xfmr since it is over 25'? The main breaker in the panel is a 150 amp breaker. Wouldn't this violate 240.21?
 
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Paul,
Yes, in general the conductors must be protected at their source. See 240.21(C) for the exact requirements.
Don
 
Thanks guys, that's what I thought, but I always like other opinions if I am not 100% sure. These people are gonna hate me when I turn in this list of violations...and this job has already passed inspection.
 
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