ARC FLASH IN LOW VOLTAGE MAIN BOARD

Calculation of incident energy for a specific configuration is problematic , and there is no EN or BSI standard way of doing it at present, which means officially you have little audit trail to say if visor and cotton overalls are more than enough, or at the other extreme if a double brick wall and a bunker is inadequate (common sense suggest somewhere in between).

For installations in the US, the IEEE publication 1584 (last revised 2018) attempts to assist, by providing formulae that are empirical fits to a number of published experiments involving instrumented tests of deliberate arcs as various parameters change.

While you need to pay to read the standard itself there is an Excel spreadsheet calculator that anyone who is happy to provide an Email to open a free account can download.

Having downloaded the spreadsheet, and (as I have IEEE access through work) also read the standard, I must say that I am almost none the wiser as to what actual figures would be applied  to your situation if you were to be using this standard, though there are a number of points worth noting, arcs in enclosures tend to be reflected, so the energy incidence is higher at the open face, than the same distance from an arc free to expand. The corollary of this of course is that it is much better to be to the side of the enclosure, than in the line of fire. The other odd one is that with some 'current limiting' fuses, the arc energy actually drops with increasing PSSC as the disconnection time is faster which is not intuitive.

As others have said, the best place to be is not there at all - it seems an odd design where the act of switching on requires the only containment to be fully open - I'd expect some sort of inner shield with a cut out around the breaker.

M.

Calculation of incident energy for a specific configuration is problematic , and there is no EN or BSI standard way of doing it at present, which means officially you have little audit trail to say if visor and cotton overalls are more than enough, or at the other extreme if a double brick wall and a bunker is inadequate (common sense suggest somewhere in between).

For installations in the US, the IEEE publication 1584 (last revised 2018) attempts to assist, by providing formulae that are empirical fits to a number of published experiments involving instrumented tests of deliberate arcs as various parameters change.

While you need to pay to read the standard itself there is an Excel spreadsheet calculator that anyone who is happy to provide an Email to open a free account can download.

Having downloaded the spreadsheet, and (as I have IEEE access through work) also read the standard, I must say that I am almost none the wiser as to what actual figures would be applied  to your situation if you were to be using this standard, though there are a number of points worth noting, arcs in enclosures tend to be reflected, so the energy incidence is higher at the open face, than the same distance from an arc free to expand. The corollary of this of course is that it is much better to be to the side of the enclosure, than in the line of fire. The other odd one is that with some 'current limiting' fuses, the arc energy actually drops with increasing PSSC as the disconnection time is faster which is not intuitive.

As others have said, the best place to be is not there at all - it seems an odd design where the act of switching on requires the only containment to be fully open - I'd expect some sort of inner shield with a cut out around the breaker.

M.