conduits are very hot!

brad richmond

New member
I have a project for a client who is running (12) 1000 HID fixture in his current grow room, the panel is approx. 50ft. away from his remote ballasts. The ballasts are 240 volt and
use 4.5 amps. Panel is 120/208 volt, 3 PH, there is a 3/4" conduit with (8) # 12 conductors feeding (4) quad receptacles (120 volt devices) wired with 208 single phase. when I amp prop
the breakers they are about 17-19 amps, the breakers are slightly warm, however the branch conduit is almost to hot to touch. Is this a derating issue? the devices are not hot at all.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
That is a lot of amperage in that conduit that is creating hit. The wires in the conduit should be able to handle the heat however if you have 17-19 amps on a 20 amp cir. then someone has not allowed for continuous rating. I assume the lights are on for more than 3 hours so the max load should be 16 amps (80% of 20 amps).
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I have a project for a client who is running (12) 1000 HID fixture in his current grow room, the panel is approx. 50ft. away from his remote ballasts. The ballasts are 240 volt and
use 4.5 amps. Panel is 120/208 volt, 3 PH, there is a 3/4" conduit with (8) # 12 conductors feeding (4) quad receptacles (120 volt devices) wired with 208 single phase. when I amp prop
the breakers they are about 17-19 amps, the breakers are slightly warm, however the branch conduit is almost to hot to touch. Is this a derating issue? the devices are not hot at all.
Welcome to the forum!


Several things come to mind
I don't think you are derating your wires due to the count of CC conductors in the same conduit.
You claim you are using 120v devices - that is a serious code violation.
you may have issue with MWBC not having handle ties but we cannot asses this.

Do you have any pictures.
did you do this work?

Hey by the way your profile says 2012 code. Does NB have a special code that is unique to that city.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Welcome to the forum!


Several things come to mind
I don't think you are derating your wires due to the count of CC conductors in the same conduit.
You claim you are using 120v devices - that is a serious code violation.
you may have issue with MWBC not having handle ties but we cannot asses this.

Do you have any pictures.
did you do this work?

Hey by the way your profile says 2012 code. Does NB have a special code that is unique to that city.
The way interpretations are bounced around the NEC quoted could be 2012.06.23.1324.18.
 

kwired

Electron manager
Location
NE Nebraska
I have to agree the conductors are undersized even if there were only less then 3 in the raceway if they are drawing 17-19 amps for a continuous load.

That said if they were 10 AWG they are probably code compliant(though I didn't verify the math), but you would possibly still be surprised just how warm that raceway may still get, though it should be somewhat cooler then what you have now.

120 volt receptacles - is another code issue but has nothing to do with the question about the heating.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
While I echo many of the statements that have been made, I don't think the issue of the hot conduit has been answered. When I hear "hot conduit," I think "net magnetic field from the wires inside." This, for example, is why we are generally not allowed to run three phase circuits with separate conduits for each phase. Obviously you can't get an exact balance among the three phases when you are powering four 208V circuits. But are you as close as you can get to a balance? I mean are the four circuits connected as A-B, B-C, C-A, and A-B? Even that attempt at balancing load will leave you with a net magnetic field generated by the A and B phases. But if your four circuits are all connected to phases A&B, then you have a serious net magnetic field. The impact of that magnetic field is that it will cause current to flow along the surrounding conduit. That is what will cause the conduit to get hot.
 

fmtjfw

Senior Member
While I echo many of the statements that have been made, I don't think the issue of the hot conduit has been answered. When I hear "hot conduit," I think "net magnetic field from the wires inside." This, for example, is why we are generally not allowed to run three phase circuits with separate conduits for each phase. Obviously you can't get an exact balance among the three phases when you are powering four 208V circuits. But are you as close as you can get to a balance? I mean are the four circuits connected as A-B, B-C, C-A, and A-B? Even that attempt at balancing load will leave you with a net magnetic field generated by the A and B phases. But if your four circuits are all connected to phases A&B, then you have a serious net magnetic field. The impact of that magnetic field is that it will cause current to flow along the surrounding conduit. That is what will cause the conduit to get hot.
Would the net current in all conductors be 0? Why would the net magnetic field be not be 0? I don't understand how you would calculate the net magnetic field....
 
Would the net current in all conductors be 0? Why would the net magnetic field be not be 0? I don't understand how you would calculate the net magnetic field....
I agree, I thought a net magnetic field would only be created by current not coming back thru the same conduit. If all wires are in the same pipe it's zero. Unless I am missing something?
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Ok, So why do we reduce ampacity when we load up a conduit with more conductors.

And what is the net result when conductors are taxed for long and continuous loads or maxed or beyond the current carry capacity.

Are we still confused.

Why does conductors that are in free air can carry more current.
Why does high voltage lines sag when reaching their capacity.

Anyone , anyone ?

Bueler , Bueler.....................:eek:hmy:
 

kwired

Electron manager
Location
NE Nebraska
I agree, I thought a net magnetic field would only be created by current not coming back thru the same conduit. If all wires are in the same pipe it's zero. Unless I am missing something?
Same here, Charlie could you give us more info on what is causing this net magnetic field for those of us that seem to be missing something?
 

kwired

Electron manager
Location
NE Nebraska
Same here, Charlie could you give us more info on what is causing this net magnetic field for those of us that seem to be missing something?
A little more thinking about it and maybe I can see that for a wye system and circuits that do not utilize a neutral you may have some increased heating because of the 120 deg phase angle that you wouldn't have if the angle were 180 deg. But that heating wouldn't be as much as if you had only conductors of the same phase in the raceway.
 

GoldDigger

Moderator
Staff member
The phase angle does not make the three phase situation any different from the single phase three wire. If all of the circuit conductors are in the same raceway the net current will still be zero. You just may have to do a vector addition of three or four currents instead of two. (A GFCI/RCD can be built for three phase too.)
If you have only a single line to line load, the line currents will be in phase and opposite even though the voltages are 120 degrees out of phase.
 

kwired

Electron manager
Location
NE Nebraska
The phase angle does not make the three phase situation any different from the single phase three wire. If all of the circuit conductors are in the same raceway the net current will still be zero. You just may have to do a vector addition of three or four currents instead of two. (A GFCI/RCD can be built for three phase too.)
If you have only a single line to line load, the line currents will be in phase and opposite even though the voltages are 120 degrees out of phase.
Well I was thinking they should cancel even though the phase angle is different, after all if you clamp an amp meter around them the net measured is zero. What can be confusing is if you have all three phase conductors they are each 120 deg apart, but supply a single phase load from a three phase source what goes out on one conductor has to come back on the other - there is no where else to go (outside of a fault) so the differential has to be 180 degrees in that case. I believe one has to consider the peak voltage is still going to be 120 degrees differece between L1 and L2 from the source, but the current wave is what is makes the magnetic field, not the voltage wave, and current only has two points to flow between and the wave is either positive or negative at any one point at any one instant. They will be opposing at the same instant from L1 to L2 for a simple two wire circuit.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
So you guys are saying that balanced loads or Net Zero loads will not create any heating of conductors.

That using too small a conductor , too many conductors in a conduit, or the ballasts of these grow light privide no contribution to heating of the conduit.
 
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