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ARC FLASH IN LOW VOLTAGE MAIN BOARD

Former Community Member
Former Community Member
Hi eveyone ! 


I was wondering if there is a conservative table out there that tells which PPE you should use depending on the voltage, normal current, and shortcircuit perhaps of the place you are working.. 


Specially this is because of a new installation, which will have a main circuit breaker of 2000A, in 400V with a three phase shortcircuit fault of aprox 30KA at the point of the main CB.


When we energise for the first time, what type of PPE should we use ? I have been reading and depends on the cal/m2 but perhaps there was a rapid conservative table or experience of yours to tell what type of PPE we should use 


Also, the main circuit breaker is inside the gabinet, and has no dead front to cover the cooper busbars, they are covered in the front with transparent acrylic (6mm depth), in order to prevent to touch them. So to turn on the MCB we have to do it with the gabinet open
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    I don’t know of any “ready reckoner” tables for this, although there is software that will do the calculation. You will need the fault current of the supply, the clearance time and the distance between the operator and the device for the calculation. Once you have the arc flash energy (usually in cal/cm2, you can start working out your PPE. As a base, it should be all cotton (including undergarments), which you would supplement by adding additional layers to get your rating. 


    We (a DNO) wear arc flash trousers, cotton shirts and cotton undergarments as a minimum, then add to that as necessary. Don’t forget to consider hearing protection too. We have simplified to four ratings where basic (class 1) is as above, to class 4, where you shouldn’t actually be there. The preference these days is remote operation so you can stand in a safe location. 


    Regards,


    Alan. 


    Edit: We have two classes of PPE: one for below 8 cal/cm2, and one for 8 to 25 cal/cm2. For values above 25 cal/cm2, you shouldn’t be there when operations are carried out. Most plant these days is operated either by telecontrol, or temporary lanyards rigged up to the operating handles as a first choice. Obviously in some cases this is not achievable.
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    I don’t know of any “ready reckoner” tables for this, although there is software that will do the calculation. You will need the fault current of the supply, the clearance time and the distance between the operator and the device for the calculation. Once you have the arc flash energy (usually in cal/cm2, you can start working out your PPE. As a base, it should be all cotton (including undergarments), which you would supplement by adding additional layers to get your rating. 


    We (a DNO) wear arc flash trousers, cotton shirts and cotton undergarments as a minimum, then add to that as necessary. Don’t forget to consider hearing protection too. We have simplified to four ratings where basic (class 1) is as above, to class 4, where you shouldn’t actually be there. The preference these days is remote operation so you can stand in a safe location. 


    Regards,


    Alan. 


    Edit: We have two classes of PPE: one for below 8 cal/cm2, and one for 8 to 25 cal/cm2. For values above 25 cal/cm2, you shouldn’t be there when operations are carried out. Most plant these days is operated either by telecontrol, or temporary lanyards rigged up to the operating handles as a first choice. Obviously in some cases this is not achievable.
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