To disconnect or not to disconnect

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Jerkyboys

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I have an electrical question if you could help. In a commercial building...we’re bringing in another 480 feed off a transformer into the building. It will come into the building into a trough, then piped out of the trough for about 10 feet then head back outside to eventually feed a rooftop unit. I know it’s a crazy setup but my question is “do we absolutely have to have a disconnect in the building before we head back outside?” Long story short...the way it is...it would be pretty difficult to mount a disconnect.
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There are two separate issues here. First, the transformer's secondary windings and the conductors leaving the secondary terminations must both be protected against overcurrent. If the conductors are outside the building, then you can run them an unlimited distance before hitting an OCPD. Conductors that are below the slab are still considered "outside." But yours are run inside. So you need to install an OCPD somewhere between the transformer and the side of the building (that could be on the inside wall). Secondly, any power going into a building must have a means of being disconnected. That disconnect device need not include overcurrent protection. But if it does, it could serve both purposes. It does not matter that the power is not used inside the building, but merely passes through. If a firefighter wants to spray water around without risking spraying live electrical equipment, they have to be able to turn off all power.
 
you are bringing in a feed to the supply a rooftop unit for the building,you would first determine if the additional feeder is compliant
 
Good point, David. 225.30 and 230.2 both say only one source of power per building, and this would likely not meet any of the exceptions.
 
230.2 Number of Services. A building or other structure served shall be supplied by only one service unless permitted in 230.2(A) through (D). For the purpose of 230.40, Exception No. 2 only, underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service.

If it meets the above (underground, grouped disconnects, etc) would it no be compliant ?
 
augie47 said:
If it meets the above (underground, grouped disconnects, etc) would it no be compliant ?
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The OP is trying to avoid having to install a disconnect for the new service. So this would not fit within that exception.
 
charlie b said:
The OP is trying to avoid having to install a disconnect for the new service. So this would not fit within that exception.
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As I read it, they are trying to avoid having to install the disconnect before it enters the trough that passes into and then out of the building. They have to have the disconnect and ocpd _somewhere_, but as noted the distance can be quite long _outside_ of the building.

If there were some way to make the trough _officially_ outside of the building (eg. sufficient thickness of concrete), how does this change things?
 
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