Panel main/feeder coordination
Panel main/feeder coordination
(OP)
If a panel has molded case circuit breakers for both the main and feeders, they are technically not coordinated for a short-circuit fault (looking at a TCC). However, feeders always trip first. This happens at my house panel. Never once has my main tripped for a short-circuit even though it does not have an intentional "delay." Is there a technical reason for this?






RE: Panel main/feeder coordination
RE: Panel main/feeder coordination
Bill
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"Why not the best?"
Jimmy Carter
RE: Panel main/feeder coordination
1) If your feeder CBs are 15A, and your main is (say) 100A; you will have good coordination with both overloads and short-circuits.
2) If your feeder CBs are 15A, and your main is (say) 30A; you may have decent coordination with overloads but short-circuit coordination will be poor (ie likely non-existent).
Fuses are generally easier to coordinate, even down to a ratio of 2:1. Circuit-breakers are a bit tricky, and you really need to review the respective TCCs.
GPTech is correct, in that most short-circuits are downstream from the feeder CB, and therefore the added impedance limits the fault-current to less than the instantaneous pickup of the main CB. Therefore, the feeder CB usually trips first.
RE: Panel main/feeder coordination
If your house has a 200 A Main breaker, then a >2000 A fault would trip it.
RE: Panel main/feeder coordination
Bill
--------------------
"Why not the best?"
Jimmy Carter