Induction Heating

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marissa2

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The code tells us that under normal conditions that you cannot run a single conductor in a metal raceway because of eddy currents being induced in the metal raceway will cause it to become hot. I can live with this requirement and I understand why it can happen with only one conductor, but what I would like to know is what does the current have to be to generate enough of a field to heat the raceway. We tried this today with a 10 foot length of ? in EMT with a single #12 conductor with 11 amps of current which ran for several hours and didn?t heat the pipe at all. The EMT was grounded at one end. I have never tryed this before but we had some time today to set it up and let it run.
Lou
 
It may be the devil on my shoulder, but I've been itching to try that myself!
happydevil.gif


I wonder if the results would have been different if the conduit were ungrounded?

I'm very interested to hear replies on this. :)
 
I remember about 25 or so years ago a guy running a parallel feeder. He ganged the phases together, A in one pipe B in another and C in another. I don't remember all the details but it got quite warm in a hurry. I think it was like 600 Amp feeder @ 480 V.
 
I would guess that you ran the test in open air where the conduit could dissipate any heat that was being generated in it. If so you may consider insulating the conduit so the any heat that is generated will be stored and addition heat will add to it causing the temperature to rise to a level where it could be detected.
What I do know is that heating by induction is considered when designing terminations. You may find plain steel terminals in lower ampacity breakers, stainless steel which looks like plain steel which is nonmagnetic, and aluminum and copper terminals. Subsituting steel screws and adding steel washers when making terminations can cause heating at the termination even though these fasteners may not be used to condict current directly but to simply secure a connection.
 
marissa2 said:
We tried this today with a 10 foot length of ? in EMT with a single #12 conductor with 11 amps of current which ran for several hours and didn’t heat the pipe at all.
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Lou, try this: parallel two lengths of EMT between two metal boxes, and run one conductor of your test circuit through each EMT.

Now you'll have a loop of metal, sort of like the "secondary" of a soldering gun, which actually is a one-turn transformer secondary winding.
 
Thanks for th help, it was in the open air and we did question the current level ourselfs, but this is wat you get when you try to do something they tell you not to do. If we have time we will try it again but with insulation on the pipe.
Lou
 
While you're trying interesting stuff, connect both ends of a new spool of THHN to 120 volts and pass a piece of EMT in and out of the core.
 
mdshunk said:
While you're trying interesting stuff, connect both ends of a new spool of THHN to 120 volts and pass a piece of EMT in and out of the core.
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won't that make a magnet?
 
mdshunk
We did do taht also but with two rolls (not full) of MTW 16 AWG and it did make a great magnet but it didn't damage the wire maybe because there was enough resistance to limit the current, and when we placed a piece of EMT in the core it was interesting to watch the current change becaues what we made was a large inductor. When doing this the pipe did get warm.
Lou
 
We tryed it again this time with some HVAC pipe insulation on the EMT with 14 amps of current and the pipe did get warm. The second pipe without insulation remained at room temperature. Thanks again for the help.
Lou
 
W/O being insulated the EMT simply dissipated the heat which resulted is no noticeable warmth.
By insulating the EMT the heat was not able to escape and was retained by the EMT which was then added to by additional heat that was generated which resulted in noticeable warmth.
 
marissa2 said:
We tried it again this time with some HVAC pipe insulation on the EMT with 14 amps of current and the pipe did get warm. The second pipe without insulation remained at room temperature. Thanks again for the help.
Lou
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I wonder how much of the temperature rise was a function of inductance and how much was just good old fashioned current?

Maybe you could run a test with the return in the conduit and see how much of a difference it makes.
 
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