# Very hot 1 1/2" conduit



## 480sparky (Sep 20, 2007)

Without a temp reading, you're just guessing.

But modern building wire is rated 90°C, which is 194°F.... pretty hot to the touch.


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## MDShunk (Jan 7, 2007)

How hot is hot? Until I measured the temperature, I wouldn't get too excited.


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## jza (Oct 31, 2009)

Maybe the conductors weren't de-rated.


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## 480sparky (Sep 20, 2007)

60 to 120 amps, but no mention of wire size.


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## millerdrr (Jun 26, 2009)

480sparky said:


> 60 to 120 amps, but no mention of wire size.


He mentioned five contactors. Maybe...?

Fifteen hots, in inch and a quarter, assuming no MWBCs (505.21?),max filled, to ordinary hi bays...

Twelve guage THHN? 

Too many variables.:laughing:


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## nitro71 (Sep 17, 2009)

First thing I would do is make sure everying is installed to code. Check neutral sharing. Check loading. My head hurts so couldn't quite decipher the whole thing. Make sure it's wired correctly then put a amp probe on it. Take some temp readings.


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## micromind (Aug 11, 2007)

Being able to keep your hand on the pipe for 2-3 seconds seems like about 120˚F or so. If the wire is THHN, then even though it seems hot, it's actually well below its maximum operating temperature. If it's TW, I'd be a bit more concerned. 

The current readings seem normal to me. Yes, better balancing would cut down on the neutral current somewhat, but HID lights will always result in higher neutral current than you'd think. 

The 2-3 amps on the ground is somewhat normal, depending on the general area and layout of other systems. 

Loose connections are (were) the biggest issue I see here. By tightening, etc., you very likely prevented a catastrophe. 

Rob


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## brian john (Mar 11, 2007)

1. Temperature?
2. How many conductors?
3. What size conductors?
4. Load on each conductor?

Perform a zero sequence on all the conductors and the reading should be zero if not you have a phasing/neutral, induction issue.


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## jwjrw (Jan 14, 2010)

brian john said:


> 1. Temperature?
> 2. How many conductors?
> 3. What size conductors?
> 4. Load on each conductor?
> ...


 

Stupid question..:whistling2:
What is a zero sequence test?


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## McClary’s Electrical (Feb 21, 2009)

jdf said:


> I am a electrician currently working as a building maintenance supervisor and normally dont run into many electrical issues I have not seen before.
> 
> That being said just today I was doing a small job on the second floor of a hanger we maintain when I lent up against a 1 1/4 pipe and was very surprized to see that I could only keep my hand on it for 2 - 3 seconds because of the excess heat. I traced the Pipe into the ceiling and it did not take long to realize it fed into a 12 x 12 junction box that feeds around 30 or so 120 volt 400watt high bay lights.The pipe is about 50 feet or so in length. The conduit originates from another box with fan cover for cooling contactors. This box is located about 3 feet away from a 120 /208 volt 3 phase pannel by a 1 1/2 conduit. This pipe is just as hot as the other. Inside the contactor junction box I found 5 12o volt coil 3 phase contactors being controlled by 2 swiches out in the hanger area. There were numerous wires showing signs of over heating on both the contactors and a terminal block. I replaced all the wires and terminal blocks with new and tightened everything down because I noticed things were quite loose.I beleave the problem in the contactor box was to to poor wire tightening and not the heat. Anyway I felt the wires and althow they feel sligtly warm I find it hard to beleave they are wam enough to create this kind of heat on the pipe. The pipe fill codes are at a max but bang on and all looks ok. I tested for amp readings and this is where things got interesting. Red phase 120 amp- black phase 80 amp-blu phase 60 amp. The neutral had a 80amp reading.The ground is showing 2-3 amps.I know this is not normal especially the ground. Even if I try to balance the system Wich I have not done, does this not seem excesive on the neutral? I also want to mention that some of the feeders in these pipes are night lights and are continuously on and if I had to guess I bet the other lights are rairly shut off.
> 
> ...


 
Those measurements aren't that far from anything you might see.

If you're concerned about excessive neutral current, use this calculation:
√((Ia²+Ib²+Ic²)-(Ia*Ib)-(Ib*Ic)-(Ia*Ic)) 

to see if the unbalanced phases are overloading your neutral.


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## brian john (Mar 11, 2007)

jwjrw said:


> Stupid question..:whistling2:
> What is a zero sequence test?



There are no (OR FEW) stupid questions.


Zero sequence is where you take all the conductors of the circuit in your amp clamp and the reading should be zero "0" amps. That is the phase conductors and neutral all together. Any reading but zero and you have possible issues.

As for excessive neutral current take a reading of all the phase conductors without the neutral and the reading would be (or should be) the measured neutral current


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## RIVETER (Sep 26, 2009)

I was working in the rear of a liquor store where the compressors were fed. Conduit was very hot...I would say about 120 degrees to the touch. Two, or more circuits of the same phase were sharing the same neutral.


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## Skipp (May 23, 2010)

brian john said:


> There are no (OR FEW) stupid questions.
> 
> 
> Zero sequence is where you take all the conductors of the circuit in your amp clamp and the reading should be zero "0" amps. That is the phase conductors and neutral all together. Any reading but zero and you have possible issues.


 
O the West coast we call that "net current" if it's anything except zero.


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## uber stein (Aug 20, 2010)

brian john said:


> There are no (OR FEW) stupid questions.
> 
> 
> Zero sequence is where you take all the conductors of the circuit in your amp clamp and the reading should be zero "0" amps. That is the phase conductors and neutral all together. Any reading but zero and you have possible issues.
> ...


 What does it mean if there is other than zero reading? What does this test actually test for?


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## MDShunk (Jan 7, 2007)

uber stein said:


> What does it mean if there is other than zero reading? What does this test actually test for?


Neutrals crossed up between one or several full boats, for one. If too much neutral current, another circuit on that phase(s) you're dealing with have hijacked your neutral. If too little, you might have your neutral interconnected with another neutral in a box someplace. Just a couple for instances.


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## brian john (Mar 11, 2007)

Also grounds on the neutral so you have ground current.


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## RIVETER (Sep 26, 2009)

brian john said:


> Also grounds on the neutral so you have ground current.


But, that wouldn't necessarily heat things up.


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## brian john (Mar 11, 2007)

RIVETER said:


> But, that wouldn't necessarily heat things up.


But at this point we were not discussing heat. BUT enough current on EMT will result in heat.


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## jza (Oct 31, 2009)

Maybe it's a hot water pipe.


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## RIVETER (Sep 26, 2009)

brian john said:


> But at this point we were not discussing heat. BUT enough current on EMT will result in heat.


I thought this thread was about abnormal heating of the conduit.


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## brian john (Mar 11, 2007)

RIVETER said:


> I thought this thread was about abnormal heating of the conduit.


It is but we were discussing some trouble shooting techniques utilized to verify proper loading of circuits and well here we are.

GO TO BED


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## RIVETER (Sep 26, 2009)

brian john said:


> It is but we were discussing some trouble shooting techniques utilized to verify proper loading of circuits and well here we are.
> 
> GO TO BED


I am not quite ready for bed. The OP is asleep but I'll be up awhile.A couple of amps on the conduit won't heat it up. The problem is either an overload or a misuse of a neutral. The neutral IS tied to the ground somewhere other than the service and needs to be corrected.


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## Vintage Sounds (Oct 23, 2009)

What about induction heating? I think he said there were two hot pipes so maybe someone messed up and connected something using phase conductors from one pipe and neutral from the other, thus creating a big induction coil?


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## Bob Badger (Apr 19, 2009)

jdf said:


> Inside the contactor junction box I found *5* 120 volt coil *3 phase contactors*


That along with this



jdf said:


> The pipe fill codes are at a max


certainly suggests at least 15 current carrying conductors in the conduit, could be as many as 30 CCCs.

What wire size is being used?

Under the NEC 15 CCCs in one raceway would require a 50% deration meaning for 20 amp circuits the condutor size would have to be 10 AWG.

If the CCC count is 21 or greater you would have to use 8 AWG.


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## brian john (Mar 11, 2007)

Vintage Sounds said:


> What about induction heating? I think he said there were two hot pipes so maybe someone messed up and connected something using phase conductors from one pipe and neutral from the other, thus creating a big induction coil?


This was noted earlier in the post.


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## brian john (Mar 11, 2007)

RIVETER said:


> I am not quite ready for bed. The OP is asleep but I'll be up awhile.A couple of amps on the conduit won't heat it up. The problem is either an overload or a misuse of a neutral. The neutral IS tied to the ground somewhere other than the service and needs to be corrected.


I have seen as much as 285 amps on a main neutral ground bond...More than a few amps, I Think.


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## jwjrw (Jan 14, 2010)

brian john said:


> There are no (OR FEW) stupid questions.
> 
> 
> Zero sequence is where you take all the conductors of the circuit in your amp clamp and the reading should be zero "0" amps. That is the phase conductors and neutral all together. Any reading but zero and you have possible issues.
> ...


 

So you are sayingto put both the ungrounded(1 phase) and grounded conductors inside your clamp meter. If I read amps I have a potential issue? 

What would be a potential cause if I had voltage?


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## brian john (Mar 11, 2007)

jwjrw said:


> So you are sayingto put both the ungrounded(1 phase) and grounded conductors inside your clamp meter. If I read amps I have a potential issue?
> 
> What would be a potential cause if I had voltage?


If it is a MWBC you use all conductors ungrounded and grounded NOT THE EGC.
reading should be zero, if you do the ungrounded conductors only, the reading should be = the neutral current.


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## ichimo23 (Nov 30, 2009)

Vintage Sounds said:


> What about induction heating? I think he said there were two hot pipes so maybe someone messed up and connected something using phase conductors from one pipe and neutral from the other, thus creating a big induction coil?


 
If this was the case, wouldnt the conduit be (potentially) RED hot? Not sure, just asking.


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## Vintage Sounds (Oct 23, 2009)

ichimo23 said:


> If this was the case, wouldnt the conduit be (potentially) RED hot? Not sure, just asking.


I'm not really sure either because I've never seen it....it's just something I've heard can happen. Reminds me of an induction stove though.


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## brian john (Mar 11, 2007)

Vintage Sounds said:


> I'm not really sure either because I've never seen it....it's just something I've heard can happen. Reminds me of an induction stove though.


Depends on the current on the circuits involved, size of the conduit, parallel paths...................


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## Shorty Circuit (Jun 26, 2010)

jdf said:


> I am a electrician currently working as a building maintenance supervisor and normally dont run into many electrical issues I have not seen before.
> 
> That being said just today I was doing a small job on the second floor of a hanger we maintain when I lent up against a 1 1/4 pipe and was very surprized to see that I could only keep my hand on it for 2 - 3 seconds because of the excess heat. I traced the Pipe into the ceiling and it did not take long to realize it fed into a 12 x 12 junction box that feeds around 30 or so 120 volt 400watt high bay lights.The pipe is about 50 feet or so in length. The conduit originates from another box with fan cover for cooling contactors. This box is located about 3 feet away from a 120 /208 volt 3 phase pannel by a 1 1/2 conduit. This pipe is just as hot as the other. Inside the contactor junction box I found 5 12o volt coil 3 phase contactors being controlled by 2 swiches out in the hanger area. There were numerous wires showing signs of over heating on both the contactors and a terminal block. I replaced all the wires and terminal blocks with new and tightened everything down because I noticed things were quite loose.I beleave the problem in the contactor box was to to poor wire tightening and not the heat. Anyway I felt the wires and althow they feel sligtly warm I find it hard to beleave they are wam enough to create this kind of heat on the pipe. The pipe fill codes are at a max but bang on and all looks ok. I tested for amp readings and this is where things got interesting. Red phase 120 amp- black phase 80 amp-blu phase 60 amp. The neutral had a 80amp reading.The ground is showing 2-3 amps.I know this is not normal especially the ground. Even if I try to balance the system Wich I have not done, does this not seem excesive on the neutral? I also want to mention that some of the feeders in these pipes are night lights and are continuously on and if I had to guess I bet the other lights are rairly shut off.
> 
> ...


I'd check the L-L and L-N voltages on both the line side and the load side of the contactors and at the fixtures. I'd also thermoscan everything. Wires tend to loosen over time from vibrations. That is what annual PM is for even though I'll bet almost nobody does it anymore. The number of fixtures suggests about 12 kw of load but the readings only add up to 9.3 kva???? Might be you have fewer fixtures on these circuits than you thought. I'd check the contacts on the lighting contactors. If they are burned or pitted they may be arcing which would create a lot of heat. They might need replacement. I assume your readings are the totals of several circuits and that the load side of the contactors are not in parallel to try to increase their effecive current rating (that doesn't work but I've seen something like it tried with fuses.) Thermoscanning would be helpful.

The high neutral current is typical and nothing to be alarmed about. This shows the importance of using full size neutrals or larger on MWBCs and not relying on cancellation to reduce neutral current. (It also shows why zig-zag transformers only work in a lab, not in the real world.) Ground current seems high to me, I'd be concerned but that is not enough to heat the conduit even if there was a high impedence fault to ground right through it. (If this load was on a single phase 150 amp GFCI it would probably trip on ground fault.) Could there be a fault unrelated to the conduit heating problem in one or more of the fixtures? 

If there is an appreciable voltage drop from the voltage at the load side of the contactors to the fixtures that would suggest direct inductive heating of the conduit and boxes, the result of some sort of high frequency harmonic or parasitic waveform on the wires. It could come from an external source including an RF source.


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## jdf (Sep 11, 2010)

Thanks for all your suggestions.

I will get more detailed information for some of your questions as soon as I can.I realize my first posting was some what vague and apreciate all your suggestions.
I am running around dealing now with other problems related to our ICAF sprinkler system wich has taken first priority.
Thanks again,
JF


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## josh5879 (Sep 21, 2009)

I once had customer show me a pretty hot conduit strap (maybe 150F). The 1/2" EMT cooled down as it got farther away from the strap. 
I open the nearest outlet box, turns out the receptacle it was feeding had stranded wire connected under the screw and a couple strands were out of the bundle and were shorting to ground.(not enough to trip breaker) 
It seems the EMT wasn't grounded very well, therefore causing the current to travel through the pipe strap screw that was connected to a metal stud.


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## bobelectric (Feb 24, 2007)

Sounds like he wouldn't be the 'GO TO GUY' in an emergency situation! Meaning jfd


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## guest (Feb 21, 2009)

jdf said:


> *The conduit originates from another box with fan cover for cooling contactors.*


Which way is that fan blowing? If it is inward, it is possible that the heat from the contactors is getting blown up the pipe and that is what you're feeling. 

If possible, I would change the fan around to blow out of the contactor can (if it is currently blowing inward) and see what happens.


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## etb (Sep 8, 2010)

Skipp said:


> O the West coast we call that "net current" if it's anything except zero.


I agree. The real meaning of zero-sequence is any portion of voltage or current of the three phases that sums to non-zero. I.e. the neutral current is the zero sequence current. In a "normal" circuit zero-sequence current results from imbalance of the phases, or harmonics that are triplens (multiples of three). As others said, in an abnormal circuit it can be shared neutrals or ground fault. So if you clamp phases and neutral you're measuring net current, ground-fault current, or a meaningless value if circuits are interconnected; if you clamp just the phases, or only the neutral (in a normal circuit), that's zero-sequence. An interesting note is how modern VFDs intentionally output zero-sequence voltage in order to get full line voltage to the motor.


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## Mastertorturer (Jan 28, 2009)

Harmonics from HID Lighting causing a distortion of the Sine Wave and thus mutual heating of the current carrying conductors off the neutral.

http://www.istartupchina.com/files/No_Harmonics_Created.pdf

And

http://www.wisdompage.com/SEUhtmDOCS/SEU06.htm

And

http://en.wikipedia.org/wiki/Harmonics_(electrical_power)
Edit: Added links and cleaned my wording up.


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