Power Feeder
Power Feeder
(OP)
I have a dispute going with our design engineer over the location and feeder sizing for a new 6.9 kV 1200 amp switchgear. The gear will be feeding 10 loads which will run almost continuously and represent 80% of the bus sizing. He wants to locate the gear in the main power distribution center and I want to locate the gear near the loads.
The rub comes when we calculate the feeders size. We are both using 500mcm XHHW2 in a ductbank. I've derated the conductors by 40% and say we should be installing 5 - 500mcm cables per phase. He says we should derate the conductors by 80% and should be using 14 - 500 mcm cables per phase. Who’s right?
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The rub comes when we calculate the feeders size. We are both using 500mcm XHHW2 in a ductbank. I've derated the conductors by 40% and say we should be installing 5 - 500mcm cables per phase. He says we should derate the conductors by 80% and should be using 14 - 500 mcm cables per phase. Who’s right?
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RE: Power Feeder
For a feeder this large, it would be advisable to run detailed ampacity calculations using the Neher-McGrath method. This will take into account the duct bank configuration, conduit material, thermal characteristics of the concrete and/or soil, etc.
If you don't have the means of doing this calculation, you can probably get one of the large cable manufacturers to do it for you. I've gotten Okonite to run these calcs in the past at no cost.
RE: Power Feeder
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Power Feeder
ScottyUK – I’ll be feeding the new switchgear from an existing 6.9kV switchgear. There will not be a transformer in the circuit. The cable distance between the two switchgear units is approximately 600’ and the cost in wire could be considerable. Especially at today’s copper prices.