Life Safety Coordination

Location
Fl
Occupation
E
Per NEC, do all breakers in this life safety circuit need selectivity, or only need selectivity between the main swgr breaker and all downstream breakers. Right now I have overlap between feeder ls and ls main

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Does the exception to 700.32 apply to your installation.
Exception:
Selective coordination shall not be required between two overcurrent devices located in series if no loads are connected in parallel with the downstream device.
I just re-read your comment. If this is life safety as in Article 517, the rules in Article 700 do not apply.
 
The overlap between Feeder LS and LS main is acceptable. If you have overcurrent devices in series with no other loads in parallel, they do not have to coordinate. An easy way to keep it straight is to look at what would lose power if an overcurrent device were to open. Any other overcurrent devices that result in the same loads losing power are not required to coordinate.
 
The overlap between Feeder LS and LS main is acceptable. If you have overcurrent devices in series with no other loads in parallel, they do not have to coordinate. An easy way to keep it straight is to look at what would lose power if an overcurrent device were to open. Any other overcurrent devices that result in the same loads losing power are not required to coordinate.
what about - iF a fault happened at panel ls, if LS main and Feeder LS arent coordinated feeder LS would trip and activate the gen unnecessarily. Should that be a concern?
 
Per NEC, do all breakers in this life safety circuit need selectivity, or only need selectivity between the main swgr breaker and all downstream breakers. Right now I have overlap between feeder ls and ls main

View attachment 2579785
Out of curiosity, how do you know you have an overlap? The only way to know is to provide the coordination study.
 
As Don said, unless the Engineer is using unconventional confusing nomenclature, LS would mean Life Safety which is only used in high end medical. Article 700 circuits are referred to as emergency, not Life Safety.
 
what about - iF a fault happened at panel ls, if LS main and Feeder LS arent coordinated feeder LS would trip and activate the gen unnecessarily. Should that be a concern?
No. The generator starting is not part of the coordination criteria.

In Wisconsin we were required to have full selective coordination all the way up to the generator but only past the first breaker on the normal service. So your Feeder LS and LS main would need coordination but Feeder LS and SWGR Main do not. LS Main needs to stay closed or else there is no need for the generator.
 
Personally, I would never put a main breaker after an ATS. If it trips, they whole system is out, and the generator isn't going to help.

I see no way that this complies.
 
The only conditions that would trip that main breaker in a properly coordinated system are an overload or a fault in the panelboard.
 
Are the circuits supplied by this system Article 700 or Article 701 circuits? If not, there is no requirement for selective coordination.
Yeah.
Industry slang gets in the way, again.
Life Safety is a term for hospitals and Article 517.
Emergency is the term used in Articles 700 and 701.
Backup would usually be Article 701 or 702.
 
from my limited experience (1 year internship) it has been a common setup
Agree, it seems common, but that doesn't make it a good idea.

If one single branch breaker fails to trip, that main will trip, or you are just left with a dead short until something burns in two.

Even if a branch breaker just takes too long to trip, there is a good chance it will take out the main breaker and the entire system.

I suppose there is also a chance a bad branch breaker could take out the normal power main, and then the generator starts and the ATS switches, and it also takes out the emergency side main, but that's much less likely.
 
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