Tie Breaker Rating

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Anonymous Poster #1	Tie Breaker Rating 04/27/2026 4:48 AM
	Main-Tie-Main: Transformer rating (2 Nos) - Normally rated to supply both Bus A and Bus B. Bus tie - Normally open, so normally the transformer is only 50% loaded. The bus tie breaker is normally open. Only in case of Failure of one transformer, the tie breaker will be closed, so the current flow through the bus tie is not always 100% capacity of the transformer. Should I still go with same Incoming breaker rating (100% rating) for the bus tie breaker?
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rwilliams Guru Join Date: Jul 2016 Posts: 1367 Good Answers: 105	#1 Re: Tie Breaker Rating 04/28/2026 12:07 AM
	Yes, unless you have some method to ensure that later on someone doesn’t put all the load on one or the other load bus. Or mismatch the load so that one bus has more than 50% of the load. Plus, having the same breaker in 3 positions gives you some flexibility in the case of a failure, or to accomplish maintenance.
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beancycle Active Contributor Join Date: Apr 2026 Posts: 12	#2 Re: Tie Breaker Rating 04/28/2026 2:49 AM
	Yeah you still size it for full load because if one transformer drops out that tie gonna carry everything so you don’t want it undersized because it’s normally open
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