Measuring Copper Bus Bars to Estimate Ampacity

[FaradayFF]

Hi Guys,
If you didn't have ampacity data on an existing bus bar system, would taking measurements of the bus bars be a reasonable approach to try to estimate ampacity? There are tables available that give you max. continuous ampacity based on the physical dimensions of the bus.
Am I on the right track here?
Thanks,
EE

 

[jim dungar]

Bus bars in UL listed equipment may have been sized based on heat transfer not current density.

For other applications a common rule of thumb has been 1000A/square inch.

 

[ggunn]

Bus bars in UL listed equipment may have been sized based on heat transfer not current density.

For other applications a common rule of thumb has been 1000A/square inch.

Of cross section?

 

[Hv&Lv]

Wow. Sort of hard to do…
size, thickness, proximity, skin effect, chimney effect, hardness…
Its hard to say with any certainty without taking ALL the variables in the calculations.
Most calculators or rules of thumb are for perfect scenarios.

 

[jim dungar]

Of cross section?

Yes.

 

[electrofelon]

Bus bars in UL listed equipment may have been sized based on heat transfer not current density.

For other applications a common rule of thumb has been 1000A/square inch.

FWIW, the NEC mentions that figure in 366.23. I believe it is the only reference to NEC makes to bus bar ampacity.

 

[jim dungar]

FWIW, the NEC mentions that figure in 366.23. I believe it is the only reference to NEC makes to bus bar ampacity.

But that is for when you are building your own bus bar assemblies. I don't know of any OEM that uses it.