malachi constant
Senior Member
- Location
- Minneapolis
Hi all,
I think I have this worked out, but would appreciate some feedback.
1. Existing service to a community center. 1200A 480V 3p 4w. 1200A main fused switch. Service is located indoors on a mezzanine.
2. Owner wants to purchase a generator and transfer switch to backfeed entire building.
3. To avoid relocation of utility metering and having to buy a service entrance rated transfer switch we are planning to intercept the switchgear on the load side of the man switch.
4. The transfer switch can be conveniently located on the main floor in an empty storage room directly below the switchear. This is on an exterior wall and the generator feed can come right into it, while the normal/utility and load feeds come from directly above.
5. We have had a contractor with relevant experience look at plans and photos, ditto a custom switchgear manufacturer who will be supplying the lug connectors. We also ran it by the local electrical inspector. All are OK with it. We will need a PE to certify that the installation meets UL standards and have been advised by the contractor and manufacturer that meeting UL standards will not be an issue.
6. This morning we had a switchgear manufacturer out on site to shut down the service and take some measurements.
7. We determined this morning that the switchboard was physically too small to contain 1200A worth of feeder to each bus (four parallel 350s to each phase, times four phases, time two outgoing/incoming connections).
8. We know the historical max load is only roughly 200kVA, which at 480V works out to 240A (300A if applying 125% factor).
9. Due to physical restrictions (note in #7 above) we have decided to reduce the main fuses to 600A, and connect the intercepted bus bars to the transfer switch using a 600A feeder (two parallel 350s to each phase).
10. We will now provide a 600A transfer switch.
I think this is pretty air tight. Think I have all my bases covered. See any red flags?
I think I have this worked out, but would appreciate some feedback.
1. Existing service to a community center. 1200A 480V 3p 4w. 1200A main fused switch. Service is located indoors on a mezzanine.
2. Owner wants to purchase a generator and transfer switch to backfeed entire building.
3. To avoid relocation of utility metering and having to buy a service entrance rated transfer switch we are planning to intercept the switchgear on the load side of the man switch.
4. The transfer switch can be conveniently located on the main floor in an empty storage room directly below the switchear. This is on an exterior wall and the generator feed can come right into it, while the normal/utility and load feeds come from directly above.
5. We have had a contractor with relevant experience look at plans and photos, ditto a custom switchgear manufacturer who will be supplying the lug connectors. We also ran it by the local electrical inspector. All are OK with it. We will need a PE to certify that the installation meets UL standards and have been advised by the contractor and manufacturer that meeting UL standards will not be an issue.
6. This morning we had a switchgear manufacturer out on site to shut down the service and take some measurements.
7. We determined this morning that the switchboard was physically too small to contain 1200A worth of feeder to each bus (four parallel 350s to each phase, times four phases, time two outgoing/incoming connections).
8. We know the historical max load is only roughly 200kVA, which at 480V works out to 240A (300A if applying 125% factor).
9. Due to physical restrictions (note in #7 above) we have decided to reduce the main fuses to 600A, and connect the intercepted bus bars to the transfer switch using a 600A feeder (two parallel 350s to each phase).
10. We will now provide a 600A transfer switch.
I think this is pretty air tight. Think I have all my bases covered. See any red flags?
