Cu Busbars of Rectangular Section In Air

Hello again, Ron Nombri

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Correct Data:

Say Single Bar per Phase; Bar Width = 12.5mm

Minimum Phase Centers = 25mm ???

Thickness = 2.5mm

Current Capacity = 190A

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What this is saying that your rating for copper busbars 12.2mm wide x 2.5 mm thick, has a rating of 190 Amps, when the centres of those 3 phases busbars are 25 mm centre to centre.

Now because the busbar is 2.5mm thick, it is 1.25 mm from the outer face to the busbar centre line, thus in practice, there will be a gap of 25mm - 1.25mm - 1.25mm = 22.5mm actual gap between the outside "width side" surfaces of the adjacent busbars.

I do not know your operating temperature, but that will, of course, have a large bearing on the actual busbar maximum current.

Busbar chambers must be carefully designed, more as the Short Circuit rating increases.

In large installations, under short circuit conditions, there may be thousands of tons of force exerted on the busbars, because of the extreme magnetic fields.

I have seen large busways and associated switchboards destroyed, because the designers forgot to allow for the combined effect of a short circuit, combined with a simultaneous lightning strike.

If you are designing a busbar chamber, or switchboard, please derate for higher ambient temperature, ensure plenty of strong insulating fixings of the busbars, allow for explosion venting away from persons and/or equipment, and trust you don't get a direct or near hit, with a lightning strike.

I see your location is Papua New Guinea, which is a lightning factory, on many days per year.

Trust you feel assisted.

Kind Regards....