Xfmr temp rise & conductors
Xfmr temp rise & conductors
(OP)
What is the impact to conductors and lugs when terminated to an encapsulated dry-type transformer in a high-ambient environment? Must the transformer be derated to prevent temperature rise from exceeding the temperature/current rating of the conductors and lugs? I'd hate to spec xfmr and cabling 3x too large, but I'd hate even more to burn it all up.






RE: Xfmr temp rise & conductors
I'd get manufacturer's installation instructions for the transformer and follow their guidelines/requirements. The installation instructions should deal with the extra heat coming from the transformer.
If you have to de-rate the conductors, you can start from the 90 deg C ampacity.
Normally the primary conductors end up being oversized anyway because the primary breaker or fuse has to be sized to handle the transformer inrush.
RE: Xfmr temp rise & conductors
ONLY if the conductor has a 90 deg C ampacity for the conditions. If, for instance, type THW is used which does not have a 90 deg C rating your derating would have to start with the 70 deg C ampacity.
RE: Xfmr temp rise & conductors
RE: Xfmr temp rise & conductors
Does this mean I have to derate the transformer to 20% in order to keep the enclosure temp to 80C? I can't imagine manufacturers would sell enclosed transformers with 115C or 150C rise if this were the case. Is there something I'm missing?
RE: Xfmr temp rise & conductors
RE: Xfmr temp rise & conductors
You can get high-temperature wire. It can be run some distance away from the transformer and then spliced onto normal building wire. This is routinely done around burner fronts on boilers.
Can you find another location for the transformer?
RE: Xfmr temp rise & conductors
Am I worried over nothing, will the cables wick away the heat fast enough that it's not an issue? I don't mind derating cabling, but it's difficult to derate a 90C cable for 128C ambient conditions. What's the proper way to terminate to a NEMA 4 transformer?
RE: Xfmr temp rise & conductors
Not sure about your termination issues -- I'd think you would want a bit of liquidtight flex, though.
Here's some cable you can use to get yourself outside the hot area:
http:
Let us know what you decide on!
Good on ya,
Goober Dave
RE: Xfmr temp rise & conductors
RE: Xfmr temp rise & conductors
RE: Xfmr temp rise & conductors