cable overheating
cable overheating
(OP)
Greetings,
We have a problem of overheating cable/conduit here. We have 3 sets of wire coming from the swithcgear on the control room. The 4" conduit that is penetrating the flooring is overheating. Cables are installed one conduit for each phase? Is the conduit acting as a CT that is it is overheating?Or there are other rason behind this.
Thanks.
We have a problem of overheating cable/conduit here. We have 3 sets of wire coming from the swithcgear on the control room. The 4" conduit that is penetrating the flooring is overheating. Cables are installed one conduit for each phase? Is the conduit acting as a CT that is it is overheating?Or there are other rason behind this.
Thanks.






RE: cable overheating
Is each phase in a separate conduit?
If answer to both of these question is yes, the conduit may be getting hot due to induced current from the magnetic field created by the cable. The solution is to put all three phases in each conduit to minimize the net flux.
RE: cable overheating
Keith Cress
kcress - http://www.flaminsystems.com
RE: cable overheating
I would suggest using 9 smaller cables, 3 inside each of your 4" conduits with each conduit having all three phases inside. This should minimize the heating issue and you'll still be able to use your 4" conduit.
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If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: cable overheating
I worked at a cotton mill once where the maintenance electrical staff wired a 1200A ILine panel without distributing the phases properly. The hot conduits were found when one of the electricians took a break by sitting on the 3" LB's fed from the main switchgear before they entered the ground approx 75' from the panel. On inspection of the ILine panel, the phase conductor insulation had melted away by about a foot. It was a "miracle" nothing shorted out.
If you hired an electrical contractor to perform the installation, I would recommend hiring a different contractor.
RE: cable overheating
Bill
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"Why not the best?"
Jimmy Carter
RE: cable overheating
RE: cable overheating
RE: cable overheating
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: cable overheating
Aren't these induced currents and eddy currents that you spoke of magnetic flux currents as opposed to actual electrical currents.
Wouldn't it be the same as if you wrapped a coil of wire around a core, with the current in the wire causing an electrical flux to circulate in the core?
Just trying to understand.
RE: cable overheating
RE: cable overheating
Proof the currents are "electrical currents" is the Joule heating generated by these currents.
Here is a link to a paper from TI on the subject:
http://focus.ti.com/lit/ml/slup197/slup197.pdf
Here is the Wiki on eddy currents (I didn't read it closely so the standard wiki warning applies):
http://en.wikipedia.org/wiki/Eddy_current
Finally, these eddy currents are so fundamental to electrical installations that the NEC includes an entry specifically related to this problem and states it is a problem associated with ferrous metal and induction. The solution to the problem is not rocket science - just distribute the phases per the NEC mandate.
RE: cable overheating
RE: cable overheating