Thermal Dynamics?

[Doug S.]

I just read the MWBC= more heat or Less heat? thread and was thinking...

Conduit fill is calculated (to some extent) with heating in mind, however, Isn't the conduit (in most cases, ex EMT) a far better conductor of heat than the air? With that, no doubt simple, thinking wouldn't you want to fill a smaller conduit up?

Maybe some of you can help me get the cobb-webs out.

Thanks,
Doug S.

 

[PetrosA]

Metal does conduct the heat, but the design of EMT and most other pipes isn't exactly the best design for a radiator of heat, so what happens is that the ambient temperature increases in the dead air space inside the conduit which increases resistance in the conductors and at some point can begin to break down the insulation on the wires. Since the pipe isn't getting rid of the heat faster than the wires are producing it, overheating can occur. Others will certainly explain this better than I

 

[Smart $]

... With that, no doubt simple, thinking wouldn't you want to fill a smaller conduit up?

...

Sure... if we could manage to keep each and every conductor against the wall of the conduit. :grin:

 

[ItsHot]

Aerial cable

Aerial cable

Keep in mind why aerial conductor is permitted to be small.