Breaking capacity
Breaking capacity
(OP)
A switchboard got this data: Ik(peak): 100kA
Ik(rms): 40kA
Which one of these values should be used for calculating the minimum breaking capacity for a breaker in a cabinet placed X ft. from the switchboard?
AntonX
Ik(rms): 40kA
Which one of these values should be used for calculating the minimum breaking capacity for a breaker in a cabinet placed X ft. from the switchboard?
AntonX






RE: Breaking capacity
The breaker duty shall be checked for both symmetrical rms and asymmetrical peak values. Compare the calculated values to its rating. Asymmetrical peak depends on the X/R ratio too.
Rafiq Bulsara
http://www.srengineersct.com
RE: Breaking capacity
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RE: Breaking capacity
These values are allready calculated for this switchboard.
By calculating new SCC (for the cabinet placement) based on the cable length and dimension and switcboard data I get:
Ik(peak): 25kA
Ik(rms): 15kA
These are the values for the new breaker in the cabinet.
The supplier of the breaker asked for only one value - Ik.
Then I'm not sure if we can use a 20 kA breaker :)
AntonX
RE: Breaking capacity
You need to confirm that with the vendor. The standards assume a certain X/R ratio, you can adjust the rated asymmetrical rating based on the actual X/R ratios.
Also look up momentary duty and interrupting duties.
Rafiq Bulsara
http://www.srengineersct.com
RE: Breaking capacity
The tables are prepared by the switchboard maker.
RE: Breaking capacity
Bill
--------------------
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Jimmy Carter
RE: Breaking capacity
It depends on the type of breaker. For MCCBs 1/2 cycle momentary duty applies, that is the asymmetric peak. Its interrupting capacity must be equal to or greater than asymm peak.
Rafiq Bulsara
http://www.srengineersct.com