70e

[jimbo123]

We have a mcc with a 500amp. main at 480volt 65ka. According to the esp the main breaker needs to have a detailed af analysis because based on its clearing time of 2cycles and the available bolted fault current of 65ka exceeding 100ka cycles. What does to do about work being done in the rest of the mcc ? Can we continue to work at 2*[company policy] in the rest of the mcc until we deenergize and loto ?.
I do not believe anyone will calculate any af protection .

 

[jim dungar]

We have a mcc with a 500amp. main at 480volt 65ka. According to the esp the main breaker needs to have a detailed af analysis because based on its clearing time of 2cycles and the available bolted fault current of 65ka exceeding 100ka cycles. What does to do about work being done in the rest of the mcc ? Can we continue to work at 2*[company policy] in the rest of the mcc until we deenergize and loto ?.
I do not believe anyone will calculate any af protection .

It depends on the construction of the MCC. It has to do with the separation of the cross bussing from the incoming line conductors. Some people consider the entire MCC to have the same AF values as the main lugs, while others will calculate the AF values based on the opening time of the integral main device.

 

[zog]

We have a mcc with a 500amp. main at 480volt 65ka. According to the esp the main breaker needs to have a detailed af analysis because based on its clearing time of 2cycles and the available bolted fault current of 65ka exceeding 100ka cycles. What does to do about work being done in the rest of the mcc ? Can we continue to work at 2*[company policy] in the rest of the mcc until we deenergize and loto ?.
I do not believe anyone will calculate any af protection .

Is 65kA your actual available fault current or is that really just the AIC rating of the breaker?

Your plant needs to stop guessing and do an actual arc flash analysis. What sort of "work" is being done in this MCC? Why not de-energize?

 

[jimbo123]

We will work de energized when work comes up in mcc. The cb was listed on label as @ 480volts 65ka . Did not know if that kept anyone from going into mcc, since we have to go into mcc to verify presance of voltage when loto of any bucket. Does main and tie cb both 65ka eleminate work in mcc?
We have been trying to get company to afa but didn,t get anywhere.

 

[zog]

We will work de energized when work comes up in mcc. The cb was listed on label as @ 480volts 65ka . Did not know if that kept anyone from going into mcc, since we have to go into mcc to verify presance of voltage when loto of any bucket. Does main and tie cb both 65ka eleminate work in mcc?
We have been trying to get company to afa but didn,t get anywhere.

The 65k AIC rating of the breaker does not tell you much, you need to know the actual fault current and clearing time to determine if the tables can be applied (I think that is what you are asking). If your system exceeds the limits in the notes of the tables you are required to do an arc flash study.

 

[RoberteFuhr]

I agree with what Zog stated. You need to do a detailed AF analysis which will require the actual bolted fault current and upstream protective device settings. The interrupting time of the upstream protective device is very important as this will affect the AF energy calculations more than the bolted fault current will.

 

[zog]

And be careful of that 2 cycle assumption, most breakers are either 3 or 5 cycle, unless they don't have an INST trip, then youare looking at 30 cycles for ST or hundreds of cycles for LT.