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Discussion Starter · #1 ·
Short circuit on a 20A lighting circuit and it shut down the whole building!!
What would have caused this to happen? Why did none of the other breakers in the series trip?
Guessing the trip settings on the existing main were dialed down way too low?

Needless to say, my guys had a stressful morning/:biggrin:
 

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Phase to phase, or to ground? Spiked the CT's in the main sw. gear? But at the least I'd get the distribution, and main breaker's tested. What kind of building management system, or energy efficiency (load shed) scheme do they have?
 

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Discussion Starter · #3 ·
Not certain, it’s an older building. I don’t believe they have any type of management system. I am flying over Friday to take a look. The short was to ground...
 

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perhaps under normal circumstances the main breaker is already running close to the edge, and the lighting circuit short was just the straw that broke the camels back or so to speak !
so check current pull on your main.
 

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I agree a coordinated study may not have been done and the setting was too low on the main.

I took out a 400 amp breaker and a 7 pole contactor with a short on a 20 amp circuit at an IBM plant in ny
 

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I agree a coordinated study may not have been done and the setting was too low on the main.

I took out a 400 amp breaker and a 7 pole contactor with a short on a 20 amp circuit at an IBM plant in ny
LOL at an IBM facility!?! That's priceless, they were known for running a ridiculously tight ship and letting you know about it constantly. I wonder how many of their engineers had eyes on this and it still made it past the goalie...
 

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Short circuit on a 20A lighting circuit and it shut down the whole building!!
What would have caused this to happen? Why did none of the other breakers in the series trip?
Guessing the trip settings on the existing main were dialed down way too low?

Needless to say, my guys had a stressful morning/:biggrin:
They certainly have a coordination issue.
My conversations begin with something like:
"I want this event to be my responsibility but, this simple lighting short has exposed a deficiency in your circuit breaker coordination all the way to the main breaker. This will keep happening until it gets resolved"
Would you like us to commission a coordination study and present you with the remediation plan or do you have an engineer that can help you with it?
 

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But why wouldn’t the branch circuit breaker trip first? Or the breaker feeding the lighting panel?

I’m not entirely sure the mechanics of why, I was probably not paying attention at that point of my apprenticeship but I do know that a 20A phase to phase short has the potential to drop an entire building GFI.
 
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