Breaker ka rating ?

[puckman]

I thought i posted this question already, can't seem to find it.

We have 3 sq. d mhp36800 breakers listed up to 600 volts. When used at 480v 60hz they are rated for 65ka , don't know the fault clearing time. These are main breakers used in a mcc. Two are used for mains and 1 as a tie breaker.
We believe we can not work in the mcc because these cb are above the rating listed in the task tables. None of the electrical equipment has had a AF Hazard study.
Can workers switch these cb on or off ? Is the rest of the mcc off limits because of the rating of the main cb SCC ?

 

[ron]

65kAIC is the rating. That is not the amount of short circuit current available to see if the note in the 70E table apply.
Unfortunately, you need at least a short circuit and coordination study to be done to determine the clearing time and available fault current to see if you can use the 70E tables.

 

[puckman]

I thought the kaic rating of the circuit breaker was listed on the breaker label itself .
I believe qo cb have a label of 10ka and 10kaic rating.
Are you saying cb don;t list how much scc they are able to clear unless you do a cord. study?

Thanks again

 

[ron]

The 70E tables are based on what is available, not the rating of the device. In addition the table required you to know the clearing time of the upstream device. You are correct the device AIC rating is printed on the manufacturers label on the device.

The clearing time is only a result of a coordination study.

 

[zog]

I think I see the problem here, Some companies decide not to calulate, or teach thier electricians how to calulate the availble fault current and instead tell them to look at the AIC rating on the breaker instead, easy shortcut some companies take to see if they can use the tables or not but they forget about the clearing time requirements of the tables.

The tables require you knowing the available fault current and the clearing time of the OCPD. An AIC rating is a rating of that breaker, not the same thing.

Your company really nees to do an arc flash analysis. Or you could remotely operate that breaker from 250' away and be sure you are safe.

 

[puckman]

Our companys eeswp says to used the task listed in the tables 130.7[c][9], wear our ppe @ 2*at all times when doing ee work. Set up our boundaries and we are compliant with Osha and 70e.

The work policy says all afa and hazard category rating is based on sc capacities and fault clearing times that are commonly found in industrial work places and are identified as notes at the bottom of appendix. It does go on to say these HRC ratings would not be valid for work done on electrical systems with fault clearing times and sc capacities that exceed the information contained in these notes, and a Qp or ee must ensure that when the tables are used the electrical system is within the parameters of the tables.

This statement does'nt sound like the company knows if we are in the parameters or not and we have to find this information before we do the work.

No electrical worker was shown how to ensure the system is within the parameters of the tables. Most though the KA rating is what was ment in the notes.

Is there a way to do electrical work without an AfA ?

Getting confused.