Bus Bar Ampere Rating from Existing Switchboard Data

Those are good approximations of course, not to be relied upon. If the board/data sheet doesn't have a rating on it then it probably doesn't comply with switchboard standards in all sorts of ways, not just the current rating (e.g. IEC60439-1 or now IEC 61439-2).

In my opinion you are right. In IEC 60439-1/1999-2004 Table 9 for 2 copper bars of100*5 the rated current is 1600 A. Tested for 1250 to 1600 A the temperature rise could be 23-25 K then ambient max. 45-47 K. [70 K rated temp. Table 2].

However, no calculation way is actually indicated here.

You cannot determine ampere rating from bus size since it also depends on structure of switchgear and movement of air for cooling. What you will get is a range of amps. If you do not know the rating you must use the lowest value given, not the nominal one and go with that. The amount if any of insulation on the bus bar will inhibit cooling. The other consideration is the type of insulation, which could have a temperature limit. If the manufacturer is still in business, they will give you the values. The other possibility is to look up old catalogs from the manufacturer for the time period when the switchgear was manufactured.

Thanks to all for the valuable answers:

Regards

Subhash

If no other info available, I would guess the rating is the same as the incoming breaker. THis would put you on the safe side...

temperature rise alone does not do it.

The forces during short circuit are big and bus bar bracing need to be considered.