circuit breaker coordination
- Thread starter rob1kva
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- Illinois
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- retired electrician
Re: circuit breaker coordination
For the most part the NEC does not require OCPD coordination.
Don
For the most part the NEC does not require OCPD coordination.
Don
ron
Senior Member
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- New York, 40.7514,-73.9925
Re: circuit breaker coordination
Are you looking for the concepts or the code requirements?
Selective coordination is required for grouped elevators, hospitals and Article 700 and 701 loads (as of NEC 2005).
The concept of selective coordination is that the overcurrent protective device closest, and upstream, of a fault or overload trips before devices further upstream to localize a problem.
It is biased toward fuses vs breakers, but here's a good overview http://www.bussman.com/library/docs/spd05/spd05-s06-pp89-105.pdf
Are you looking for the concepts or the code requirements?
Selective coordination is required for grouped elevators, hospitals and Article 700 and 701 loads (as of NEC 2005).
The concept of selective coordination is that the overcurrent protective device closest, and upstream, of a fault or overload trips before devices further upstream to localize a problem.
It is biased toward fuses vs breakers, but here's a good overview http://www.bussman.com/library/docs/spd05/spd05-s06-pp89-105.pdf
ryan_618
Senior Member
- Location
- Salt Lake City, Utah
Re: circuit breaker coordination
There is also 240.12, although it is quite vague.
Edited for spelling
[ February 21, 2006, 12:15 PM: Message edited by: ryan_618 ]
There is also 240.12, although it is quite vague.
Edited for spelling
[ February 21, 2006, 12:15 PM: Message edited by: ryan_618 ]
bdarnell
Senior Member
- Location
- Indianapolis, IN
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- Retired Engineer
Re: circuit breaker coordination
While you are on the Cooper site, download this PDF also. It's got some good info on SC calcs as well as coordination.
http://www.bussman.com/library/docs/EPR_Booklet.pdf
While you are on the Cooper site, download this PDF also. It's got some good info on SC calcs as well as coordination.
http://www.bussman.com/library/docs/EPR_Booklet.pdf
Re: circuit breaker coordination
This is a very brief overview on how I have always looked at it "coordination":
The coordination of the common TM breaker is a bit difficult at best. Naturally overload protection is a no brainer but short circuit coordination is the gray area. When you think about it the mag calibration is essentially 110x the rating of the breaker commonly +-20%. The small resi breakers are more apt to be in the 6-7X range.
But when one considers that most faults are arcing faults what is the current magnitude? Yes, the breaker with the lowest mag. pick-up will most likely pick it up IF the current reaches a point high enough to trip the breaker. The real trick comes with a bolted fault where all breakers is series see the same fault. If that magnitude is high enough it may be pot luck which one will trip.
How many times has there been a bolted fault in a branch circuit of a residential panel that takes out the main? It's common.
With electronic breakers there are pick-up and time delay features that can be adjusted with the hope of allowing a breaker to take a deep breath and with the hope that the down stream breaker will do its thing. Better yet, some breakers have the ability to communicate regarding fault conditions.
Then there is ground fault coordination that is often more important. Main breakers with ground fault often trip before a branch breaker w/o GF even sees the fault. If you think about it main breakers that require ground fault have a maximum GF pick-up which is adjustable from about 250- 1000a. Keep in mind that there also may be a time delay adjustment of 100-500ms. Going back to the instantaneous mag. calibration of a common TM breaker the question would be how do they fit in with the main breaker as well as the other feeders?
It must be rememberer that the best layed plans of mice and men may not work as anticipated because all events aren't like we would anticipate them to be.
This is a very brief overview on how I have always looked at it "coordination":
The coordination of the common TM breaker is a bit difficult at best. Naturally overload protection is a no brainer but short circuit coordination is the gray area. When you think about it the mag calibration is essentially 110x the rating of the breaker commonly +-20%. The small resi breakers are more apt to be in the 6-7X range.
But when one considers that most faults are arcing faults what is the current magnitude? Yes, the breaker with the lowest mag. pick-up will most likely pick it up IF the current reaches a point high enough to trip the breaker. The real trick comes with a bolted fault where all breakers is series see the same fault. If that magnitude is high enough it may be pot luck which one will trip.
How many times has there been a bolted fault in a branch circuit of a residential panel that takes out the main? It's common.
With electronic breakers there are pick-up and time delay features that can be adjusted with the hope of allowing a breaker to take a deep breath and with the hope that the down stream breaker will do its thing. Better yet, some breakers have the ability to communicate regarding fault conditions.
Then there is ground fault coordination that is often more important. Main breakers with ground fault often trip before a branch breaker w/o GF even sees the fault. If you think about it main breakers that require ground fault have a maximum GF pick-up which is adjustable from about 250- 1000a. Keep in mind that there also may be a time delay adjustment of 100-500ms. Going back to the instantaneous mag. calibration of a common TM breaker the question would be how do they fit in with the main breaker as well as the other feeders?
It must be rememberer that the best layed plans of mice and men may not work as anticipated because all events aren't like we would anticipate them to be.
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