anltechnical
New member
- Location
- USA
wires in conduit are not hot!!!
why would an electrical conduit get hot
- Thread starter anltechnical
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- Location
- Placerville, CA, USA
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- Retired PV System Designer
Non-zero net current flowing in the wires inside a ferromagnetic (iron, steel) conduit will cause inductive heating in the metal of the conduit. But that normally requires a pretty high current to be noticeable.
Also if the conduit is being used as an EGC, a high ground current (not normal) could be causing resistive heating.
Use a clamp-on ammeter to measure net current in wires and in wires plus conduit (put the clamp-on around the whole thing) and then figure out whether the problem is a missing neutral run or different phases and their returns being split over more than one conduit.
- Occupation
- Licensed Electrician
Wires in conduit can get hot. Wires in no conduit can get hot. That is why there are rules about wires in the NEC.
- Location
- Massachusetts
- Location
- Illinois
- Occupation
- retired electrician
Please define hot. The normal current flow in any conductor will produce heat. It is not too hot unless the conductors are at a temperature higher than their temperature rating. The lowest commonly used temperature rating for conductors is 140?F. That will be hot to the touch.
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spark master
Senior Member
- Location
- cyberspace
I've seen 80% loaded conductors cause a conduit to get warm. And it has been warm for years. 90 degree's F.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Note that the OP states that the wires are not hot but the conduit is hot. I am assuming that means that the wires are not as hot as the conduit and so it is not possible that they are the sole source of the conduit itself heating up.
Agreed.
I'd go for earth fault or more likely inductive heating from unbalanced current.
I have to agree with Don who has made an excellent point, please define what you mean as being hot. Quite often anything that is expected to be cool to the touch quite often is referee to as being hot should it be only warm to the touch. When referring to heat the temperature should be provided so there is no misunderstanding as it is relative. Wires that are loaded do give off heat.
The same thing happens with sound. When you expect something to be quiet and it's giving off sound often it's considered as being noisy. Db sound level should be provided when referring to noise.
The same thing happens with sound. When you expect something to be quiet and it's giving off sound often it's considered as being noisy. Db sound level should be provided when referring to noise.
But, in this case according to the OP, are not hot.
A reasonable inference, as has been previously stated, is the conductors are not the source or at least not the sole source.
junkhound
Senior Member
- Location
- Renton, WA
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- EE, power electronics specialty
+1 on all the previous comments about giving good data when you refer to any phenomenon, whether heat, electricity, or noise.
Do you mean the wires that are comong OUT of the conduit are not hot? How did you get inside the conduit to measure wire temp IN the conduit?
What did you measure 'hot' with? Hand, thermocouple, IR device? If by human skin measurement, it could be HF leakage current interpreted as 'heat', if thermocouple it could be EMI, if IR device it cold be pointing error.
Is there a VFD or inverter at the load end?
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renosteinke
Senior Member
- Location
- NE Arkansas
I observed the same thing when I took part in wiring one of those huge mail-order warehouses. I sure I could have circled the earth several times with all the wire I pulled.
The point is that, even without an 'load' to speak of, but with all the circuits powered up, SOME raceways were noticeably warmer than neighboring conduit. These pipes contained wires for a multitude of sensors, readers, and solenoids - everything went to the PLC cabinet.
Fast forward to today, where I daily deal with "wires" that stay rather cool (maybe 'only' 180 degrees F) while they make neighboring steel hot enough to glow and even melt.
The secret lays in the fluctuating magnetic field of the electricity flowing through the wires. It's not current, really - it's much more about frequency. Kick the frequency up to a few thousand cycles, and nearby steel starts getting hot.
This is the same principle used in the new "induction" ranges - where the pot gets hot, but the cooktop does not. (Well, not as hot as the pot does!)
The point is that, even without an 'load' to speak of, but with all the circuits powered up, SOME raceways were noticeably warmer than neighboring conduit. These pipes contained wires for a multitude of sensors, readers, and solenoids - everything went to the PLC cabinet.
Fast forward to today, where I daily deal with "wires" that stay rather cool (maybe 'only' 180 degrees F) while they make neighboring steel hot enough to glow and even melt.
The secret lays in the fluctuating magnetic field of the electricity flowing through the wires. It's not current, really - it's much more about frequency. Kick the frequency up to a few thousand cycles, and nearby steel starts getting hot.
This is the same principle used in the new "induction" ranges - where the pot gets hot, but the cooktop does not. (Well, not as hot as the pot does!)
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
It is about the hysteresis losses in the iron, which for a given time interval will be proportional to the current times the frequency.
Even at high frequency, if the currents are balanced and ideally in twisted pairs, there will be no inductive heating.
An inductive range uses a multi-turn coil around the core. Inductive heating in a conduit will be at most a single turn.a
kwired
Electron manager
- Location
- NE Nebraska
and in the conduit with properly installed conductors or "turns" there is equal number opposing polarity turns which cancel one another out. If every turn of the coil in the inductive range were to have an opposing polarity and same magnitude turn wrapped around the same core it would not transfer any significant amount of heat to the pot. There probably would be some inefficiencies and some heat, but not enough to be considered effective for the purpose of heating the pot as desired.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Wouldn't the bonding of the primary X/0 on a step up 3-phase common core transformer cause enough current in the grounding if the secondary is not balanced, but not heat the phase conductors?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I only seen a hot conduit once where a contractor had tried to pull isolated parallel phases in EMT like we do with PVC, he didn't know it would be a problem, but that was a long time ago.
kbsparky
Senior Member
- Location
- Delmarva, USA
I've seen instances where a load management system was installed with lots of single-wires going through the same nipple causing the conduit to get noticeably warm.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
First thing that came to my mind too. 3 phase installation requiring parallel conductors, but done by an amateur having one conduit holding all Phase A, one with Phase B, one with Phase C, instead of one of each phase in each conduit.
kwired
Electron manager
- Location
- NE Nebraska
was line side and load side of each circuit passing thru the same nipple? Even one common line conductor and several switched load conductors still has cancelling effect as the line conductor is carrying the same current as the sum of the load conductors.
kbsparky
Senior Member
- Location
- Delmarva, USA
There were 2 nipples:
One for "line"
The other one for "load"
Needless to say, those 2 foot sections of EMT were quite hot to the touch ...
One for "line"
The other one for "load"
Needless to say, those 2 foot sections of EMT were quite hot to the touch ...
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