Determining Short Circuit rating of MV fused switch
Determining Short Circuit rating of MV fused switch
(OP)
I wanted to know how the overall all short circuit rating of a MV fused switch was determined when both the switch and fuses had different SC current ratings.
Most MV switches that I have come across have a listed 25kA Short Circuit Rating with a 40kA momentary or C&L rating. When these switches are fused I typically see the fuses having a 50kA rating with a 80kA momentary rating or something higher.
My question comes to how these ratings are applied against the avaliable short ciruict current avaliable at the switch. For the "Equipment Evaluation" to ensure that the switch is is rated properly do you use the short circuit values of the switch itself or the fuses?
For example lets say that the avaliable short circuit current available at the switch is 35kA Interrupting and maybe say 55kA Momentary. Would the switch fail since the 35kA and 55kA short circuit values are higher than the switches short circuit and momentary values respectively, or would the switch pass since the short circuit values fall below the fuses short circuit and momentary values inside the switch?
I am familiar with applying interrupting and momentary ratings to MV breaker but and not quite sure with an MV switch that has both a switch and fuse rating.






RE: Determining Short Circuit rating of MV fused switch
RE: Determining Short Circuit rating of MV fused switch
RE: Determining Short Circuit rating of MV fused switch
I guess a similar example would be in the case of a Westinghouse DSL breaker where the fuse limitor increases the interrupting rating of the breaker and is therefore combination rated with the breaker. This works by having the fuse interrupt for high fault levels in order to prevent the breaker from opening. This would be similar with the MV switch except the switch does not interrupt faults so the fuse would just be protecting the thermal rating of the switch?
RE: Determining Short Circuit rating of MV fused switch
RE: Determining Short Circuit rating of MV fused switch