14 kAIC Available Fault Current in Service upgrade, 120/240V, 1PH to 120Y/208, 3PH

[Paul the BIG Finn]

The project adds additional air conditioning in a relatively small commercial building. The size of the required air conditioning units requires 3-phase power and an increase in service size from 400A, 120/240V, 1PH, 3W to 600A 120/208V, 3PH, 4W. The utility informs us the new available fault current is 14 kAIC, while the original panelboards are rated 10 kAIC. Not wanting to incur the expense and time required to replace 5 panelboards we are looking for methods to reduce the available fault current.

The only solution I can find is a 75 kVA, 208V-120Y/208V transformer to feed a new distribution panel supplying the existing panelboards with 120/208V, 1PH, 3W power. We plan to connect the first panel AB, the 2nd BC and third CA to balance the load. Is there a better solution available?

There is one other problem. There is a small 120/240V emergency generator supplying a 60A, 120/240V, 1PH, 3W paneboard through an ATS. There are no 240V emergency power loads. If we lower the low voltage start to below 198V will there be a problem supplying the utility side of the ATS with 120/208V, 1PH, 3W power?

I'd appreciate any thoughts.

 

[ron]

Be sure to calculate the fault current at each of the panelboards in question to be sure the 14kA rating is needed.

The 14kA given by the utility is usually at the secondary terminals of their transformer or at the meter. They don't take into account any downstream impedance like feeders.

 

[iwire]

The only solution I can find is a 75 kVA, 208V-120Y/208V transformer to feed a new distribution panel supplying the existing panelboards with 120/208V, 1PH, 3W power. We plan to connect the firswt panel AB, the 2nd BC and third CA to balance the load. Is there a better solution available?

Will a single 75 kVA meet the NEC load requirements for the existing five panels?

There is one other problem. There is a small 120/240V emergency generator supplying a 60A, 120/240V, 1PH, 3W paneboard through an ATS. There are no 240V emergency power loads. If we lower the low voltage start to below 198V will there be a problem supplying the utility side of the ATS with 120/208V, 1PH, 3W power?

From a code perspective that may be a listing violation to supply a 120/240 ATS with 208/120.

 

[ron]

From a code perspective that may be a listing violation to supply a 120/240 ATS with 208/120.

I'm not worried about the listing because it is being used at a lower value than the 240V rating, but how the sensing of voltage occurs, that might be an issue. Hopefully it senses L-N and not L-L.

 

[iwire]

I'm not worried about the listing because it is being used at a lower value than the 240V rating, but how the sensing of voltage occurs, that might be an issue. Hopefully it senses L-N and not L-L.

I am worried about the listing in so much as it tells us what the sensing circuit is designed for.

If it is not designed for 208 IMO it would be correct to fail it based on that.

Perhaps the perimeters could be changed but we can't tell.

 

[dkidd]

I'd appreciate any thoughts.

I would look at seeing if the existing panelboard breakers can be series rated with a properly selected feeder OCPD.