Short-circuit study - Selective coordination vs. series rated
Short-circuit study - Selective coordination vs. series rated
(OP)
When performing a short-circuit study, can someone explain the difference between selective coordination vs. series rated?






RE: Short-circuit study - Selective coordination vs. series rated
As a way to avoid buying more expensive breakers with high interrupting ratings, it is possible to rely on a upstream breaker, normally larger, to "help" interrupt the high magnitude faults IF THESE BREAKERS HAVE BEEN TESTED IN COMBINATION and are UL listed for "Series Rating".
Selective coordination refers to the concept that in case of a fault, the breaker closest to the fault should trip to interrupt the fault, thereby limiting the outage to the smallest portion of the system as possible.
If as system is designed to rely on series rating for safely interrupting a fault, it is impossible to have a fully selective system, since the upstream breaker must open to protect the downstream breaker.
So basically, if you can save money by relying on series rating, but you give up any notion of selective coordination if you do so.
RE: Short-circuit study - Selective coordination vs. series rated
Selective Coordination
http://polk-burnett.apogee.net/pd/dsefc.asp
http://ww
Series rated
htt
Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon
Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376
RE: Short-circuit study - Selective coordination vs. series rated
Fuses, when selected per certain tables, will provide selective coordination, but then you have all of the disadvantages of fuses.
With circuit breakers, full selective coordination is difficult to achieve when using Thermal-Magnetic trip units. In many cases the trip curves of breakers that would form a series rated combination are identical to the trip curves of breaker that would form a fully rated combination. You can't tell a fully rated combination from a series rated combination by trip performance alone.
RE: Short-circuit study - Selective coordination vs. series rated
If low voltage power circuit breakers are used and properly applied, full selectivity can generally be achieved.
RE: Short-circuit study - Selective coordination vs. series rated