Conduit heats up

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As suggested earlier, the next thing to do is beg, borrow, or steal a cl/amp probe to check around that conduit for an imbalance.
 
Bikeindy, here is a question I haven't seen asked yet, nor have you told us so here goes- what is the typical current readings of each conductor in your conduits while the heating is happening? Do you own an amprobe? Maybe somebody got there before you and mixed up the lights so that one circuit gets overloaded and other circuits do not . I have run across that same thing more times than I have posted here at this website.
 
From the posts, I see either of two things.
1. the circuit is loaded and is creating heat. This is normal, and sometimes the person who is investigating is not that fimilar with the fact that a loaded circuit will create quite the amount of heat.

2. There is a fault somewhere and the effective ground fault current path is not effective. That is where the clamp-on meter will be a good help in determining if this is so.
 
OK,

You said you have a and b phase going down one pipe,and a and c phase

going down the other pipe, and then said the neutral was #10 for a,b,c

(network) this will produce heat.
 
bikeindy said:
. . . the travelers and switch legs are in one of the conduits . . . in conduit # 2 there are two 20 Amp circuits power feed and switch legs
Click to expand...

I am not certain I know the difference between "traveler" and "switchleg" and "power feed," and I would greatly benefit from a sketch, if anyone can create one. But I think the most likely cause is that this set of circuits is wired wrong, in terms of which wires are in which conduit.

I believe the right answer was given by LarryFine and Benaround. Current traveling down one conductor in a conduit must be allowed to return via another conductor in the same conduit. Having two phases (from a three phase system) and one neutral in the same conduit, and having no other wires associated with the same circuit, will not get the job done. You need to rearrange the wires in the two conduits such that all the wires associated with one switch are in the same conduit, and all the wires associated with the other switch are in the other conduit.
 
tonyi said:
One easy test should be to just clamp a probe on the pipe and see if its carrying any current.
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How do you measure current in the conduit, without at the same time measuring the current in the wires contained by the conduit? The probe will see a magnetic field that is the sum of all fields created by all conductors that are within the clamp.
 
travlers and sw.legs and power feed

travlers and sw.legs and power feed

switch legs to my understanding are the black or phase wires coming from the light,power feed I would assume is the hot feeding the switch or switches and travelers are the other wires on the switch
 
boboelectric said:
I had the same problem trying to switch mh fixtures on 3ways. Ended up using the 3ways to control a contactor.

Bob O.84,Pa.
Click to expand...

And that solved it?

Ok for all those who asked the about the amp probe. yes I have one no thats not the problem. the lights are only pulling 17.5 Amps per switch. and the are on #12 THHN which is rated for 25 Amps.

I will see if the owner wants me to give the contactors a try cuz it will cost him big$
 
bikeindy said:
the lights are only pulling 17.5 Amps per switch.
Click to expand...

That'll do it. That much current on #12 will cause heat; running four wires so loaded in one conduit will heat up the conduit.
 
"hot"

"hot"

agree.... in addition, I think we are all somewhat trained that heat = bad when it comes to electrical circuits, but, its important to remember that the lowest temperature rating of the componets in this circuit is probably 40C, or 140oF.....if they are operating at that level the radiated heat to the touch is indeed going to be hot.
 
I'm not so sure that direct heating of the wires is a sufficient explanation of the hot conduits here. The original poster described a junction box with two conduits feeding to a box with switches, with other conduits bringing the conductors to and from the junction box. The conduits between the junction box and the switch box are much warmer than the other conduits.

I wouldn't ignore direct heating of the wires as the probable cause of the warm or hot conduits, its just that I would want to understand why one length of conduit (the one that happens to be arranged in a loop) is warmer than another length of conduit, presumably carrying similar current in similar conductors.

Conductors operating normally at near their full rating will get quite warm. When a conductor is operated at its thermal ampacity, then it will heat up to the temperature rating of the insulation. For 90C conductors, this thermal ampacity is calculated at almost the boiling point of water; not particularly cool! Note: the ampacity numbers in table 310.16 are based upon certain _conservative_ assumptions about how quickly the surroundings carry heat away.

At the same time, a 12ga conductor carrying 17.5A will self heat at about 0.5W per foot. Put 4 conductors in the conduit, and you have to dissipate about 2W per foot. This should be noticeable but not significantly hot unless the conduit is thermally insulated from the surrounding air.

I am still in the camp that is suspicious of inductive heating of this conduit pair. Try putting the amp-probe around the entire set of conductors going into a _single_ conduit. Placing the amp-probe around the conduit may also give a reading, but if there are induced currents in the conduit they will act to balance the currents in the wires contained, meaning that you will get a much smaller reading than the actual un-balanced current.

-Jon
 
bikeindy,

"cuz it will cost him big$"

If it cures the problem he will probablly be glad to pay it. If nothing

happens he may have a different story to tell all those people.

Trouble shooting (in my opinion) is the best part of normal electrical

work, Keep doing what your doing, researsh the problem until you feel

confident that you have the correct solution,then give it a try! Guess-

work will get you in hot water real quick, of course, none of us are right

all the time. good luck.
 
I am not replying in order to start any longer thread than need be necessary, but I am just going to report that which I have witnessed more than once. A 3/4" conduit carrying 3 or sometimes more circuits feeding banks of lay in flourescent lights, wherein each of the #12 conductors was loaded to very near the rating of the overcurrent device (20 amp). The conduits in those certain installations were entirely too hot to leave my hand on for any time at all. The 4" junction boxes and the 4" square blank covers were also heated up. Running another conduit, more wiring, and splitting up the banks of fixtures into smaller banks on more circuits corrected the heating problems. I am fully aware of the heating effects of unbalanced wiring in metal conduits, but more times than not, the situation I have described above is the problem that needs solving.
 
Check me here, but I think we're all on the same page. 17A on #12 is hot enough, and illegal for continuos use. Experience discribes normal capacities that heat conduit, but now raise that IR? by a factor of 2 when any neutral imbalance was not figured to carry current.

Jack that heat further still if the conductors are loosely spaced or isolated. Cancellation of the two magnetic fields is anticipated by NEC tables, or else higher reactance, X, and voltage drop occurs in the circuit. Toss in a high ambient section, some noise for skin effect, painted / insulating conduit, and induction heat between ferrous barriers, and a similar issue results from much smaller loads.
 
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