Asking About Branch Breaker

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hien.nguyenquoc Power-User Join Date: Sep 2009 Location: BH, Vietnam Posts: 435 Good Answers: 1	Asking About Branch Breaker 05/24/2011 3:24 AM
	Considering yourself working with an uncomfortable customer. We need to install the branch panel which is about 200Amp after the main panel (500amp). So, the main incoming breaker for the branch one would be around 200amp. Moreover, we also need to have a branch one inside the main panel. But, the customer says it is not necessary because he will connect the branch panel directly to the main 500amp breaker? How to persuade him that we are bringing him the safety by doing that? Of we jsut satisfy him temporarily by following what he said? We are electrical engineers so we should not let him lead. But how? __________________ Anything that can go wrong, will go wrong
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Tornado Guru Join Date: May 2009 Location: Richland, WA, USA Posts: 21017 Good Answers: 795	#1 Re: Asking about branch breaker 05/24/2011 4:47 AM
	I'm not sure, but I think there are cases (with certain restrictions) in which the U.S. NEC (National Electrical Code) allows a feeder to be "downstream protected" by a smaller circuit breaker or fuses. Other codes might not allow this. __________________ In vino veritas; in cervisia carmen; in aqua E. coli.
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#2 Re: Asking about branch breaker 05/24/2011 5:15 AM
	Sorry but is this another of your hypothetical questions? So long as the feed to the sub panel breaker can withstand the 500A feeder fault current I can't see a problem. __________________ The reports of my death are greatly exaggerated.
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hien.nguyenquoc Power-User Join Date: Sep 2009 Location: BH, Vietnam Posts: 435 Good Answers: 1	#3 In reply to #2 Re: Asking about branch breaker 05/24/2011 5:37 AM
	Sorry for not being clear, I am thinking of the issue that the main incoming breaker of the branch panel has problem. So we need to switch off the power to this panel to replace it. So, if this customer connect directly the branch panel to the main incoming 500amp breaker. We need to switch this off... It means that the other loads now sharing with this main 500amp breaker is also off. It will bring him inconvenience. This is only the upper part of the iceberg. I have faced the more ridiculous issues. __________________ Anything that can go wrong, will go wrong
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TonyS Guru Join Date: Aug 2010 Location: Resting under the Major Oak Posts: 4347 Good Answers: 181	#4 In reply to #3 Re: Asking about branch breaker 05/24/2011 6:13 AM
	If you hypothetical customer connects the 200A breaker to the main bus then in the event of a problem the whole bus has to be isolated. Connected to the sub 500A breaker the main bus can stay live. It's swings and roundabouts as to where you connect in to a system. Just accept one fact, you will never be in the right! GE System4 switchgear is great, I changed a 630A switch in less than 5 minutes without switching off the main bus. __________________ The reports of my death are greatly exaggerated.
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90.ivan Participant Join Date: May 2011 Posts: 4	#5 In reply to #3 Re: Asking about branch breaker 05/24/2011 9:40 AM
	Just, not only for normal issue, when a fault happens in any load of branch panel, it can prodruce that main incoming switch off, and all loads will be off.
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#6 In reply to #3 Re: Asking about branch breaker 05/26/2011 8:04 AM
	It is always preferable to feed any branch panel with a seperate outgoing feeder - properly sized, rather than grouping it to a higher sized feeder.
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hien.nguyenquoc Power-User Join Date: Sep 2009 Location: BH, Vietnam Posts: 435 Good Answers: 1	#7 In reply to #6 Re: Asking about branch breaker 05/26/2011 8:14 AM
	Yes, we are electrical engineers... we know it and we will apply it since it is like our blood. But how to explain to the other to understand to follow is the other issue. My God insists on connecting the main breaker of the branch panel to the main bus bar of the main panel. LOL __________________ Anything that can go wrong, will go wrong
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