# Hot Conduit



## cdnelectrician (Mar 14, 2008)

I was reading another thread that reminded me of an issue I had a couple of years ago. I wired up 2 AHU's in a basement mechanical room of a building. I believe the motors were 30HP, 575 volts. I ran #8 T-90 in 3/4" conduit to feed them (as called for on the prints). Job was inspected and passed. I got a call from the building maintenance man about the 2 conduits being very warm to the touch. So I went to have a look, checked the draw on both motors and they were well within value, the O/L's were set properly and were not tripping, fuses were also of proper size.

I know I should probably know the answer to this but I'm drawing a blank why was this happening? The conduits were actually quite warm to the touch. The ambient temperature in the room was around room temp so that was not an issue. I have never seen this happen before.


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## MDShunk (Jan 7, 2007)

What's the chance that these motors were passing some fault current on the pipe, sufficient to heat the pipe, but below the value of the breaker (and not enough to make the measured amp draw seem unusual)?


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## cdnelectrician (Mar 14, 2008)

MDShunk said:


> What's the chance that these motors were passing some fault current on the pipe, sufficient to heat the pipe, but below the value of the breaker?


Sorry, I forgot to add that I meggered the motors and feeds from the starters and checked the winding resistance with a DMM. The motors were both brand new as well as the conduit and starters.

This is why I was a little confused.


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## RIVETER (Sep 26, 2009)

That was a couple of years ago. Are they still running okay?


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## cdnelectrician (Mar 14, 2008)

RIVETER said:


> That was a couple of years ago. Are they still running okay?


As far as I know they are, I worked for that company for about 6 months after I did the install and then got laid off due to lack of work. Never did get another call about it before I left!


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## RIVETER (Sep 26, 2009)

cdnelectrician said:


> As far as I know they are, I worked for that company for about 6 months after I did the install and then got laid off due to lack of work. Never did get another call about it before I left!


There are a lot of wierd things that can happen. Today we re- routed a welding cable because we suspected it of inducing current through a pivot pin of a welding gun and heating it up. Sometimes it is trial and error.


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## cdnelectrician (Mar 14, 2008)

RIVETER said:


> There are a lot of wierd things that can happen. Today we re- routed a welding cable because we suspected it of inducing current through a pivot pin of a welding gun and heating it up. Sometimes it is trial and error.


 
Yea! It was certainly a weird occurence thats for sure! It bugs me from time to time because I always love to know WHY and HOW when it comes to these things. Thats why I miss service soo much sometimes (aside from the hours and paperwork).


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## John Valdes (May 17, 2007)

Are these motors on drives? Does each motor have it's own conduit or are you feeding multiple motors from one conduit.
This is not a mystery. There is an answer. If you could be a bit more specific, we may just come to a conclusion.


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## sparky105 (Sep 29, 2009)

was the condiut feeding the motors run above the motors through the top of the pecker head maybe you had a chimmeny effect .. heat rising ?


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## cdnelectrician (Mar 14, 2008)

sparky105 said:


> was the condiut feeding the motors run above the motors through the top of the pecker head maybe you had a chimmeny effect .. heat rising ?


 
The motors were not on drives, I am aware of the problems that can arise from having multiple outputs from drives in the same conduit.

The chimney effect MAY be possible, but I doubt it...I ran liquid tight from the motor (inside the AHU) and then through a hole I holesawed into one of the AHU's panels into the back of a 4x4 box. From the 4x4 box I ran a short piece of liquid tight coupled to the 3/4 EMT (for vibration) that went to the starter(s).

I also ran a ground in the EMT from the source.


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