EMS wiring

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Wross

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I am new to the forum. My company has recently began to provide high volt support for commercial EMS installations. Upon inspection of a recent install in which my Team installed 2 lighting control panels, I noticed 2 of the conduits were very warm. I immediately inspected the pipes for wire volume. They are 3/4 pipes with 16 THHN #12 conductors in each. I pulled 2 circuits out of each pipe and saw a reduction in temperature. My concern is that they are still warm. Each pipe now has 12 conductors. The panel is a 120/208 and all circuits in the panel are 20 amp lighting circuits. The pathways serve as a loop to bring the line to the LCP panel contactors and then back to the panel to splice into the load in a pull box next to the panel. There are no neutrals or grounds in the pipes - only line and return (sharing same pipes). There are no signs of a fault. Any ideas as to why we still have hot pipes? Thanks in advance for your input.
 
Wross said:
Any ideas as to why we still have hot pipes?
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Yeah, because the wires in them are carrying current. ;)

Unless you up sized the wires you have too many in the same conduit.

Depending on the specifics you are generally limited to only 9 current carrying conductors per pipe before you need to derate the ampacity of the wires.

In other words the 12 AWG is no longer good for 20amp circuits.


Also hot is not always bad, how hot is hot in your case?
 
Yes, he is correct 12 AWG is no longer good for 20amp circuits, you need to change it and I have faced dificulties earlier while using 12 AWG for 20 Amp circuits.
 
Wross said:
I am new to the forum. My company has recently began to provide high volt support for commercial EMS installations. Upon inspection of a recent install in which my Team installed 2 lighting control panels, I noticed 2 of the conduits were very warm. I immediately inspected the pipes for wire volume. They are 3/4 pipes with 16 THHN #12 conductors in each. I pulled 2 circuits out of each pipe and saw a reduction in temperature. My concern is that they are still warm. Each pipe now has 12 conductors. The panel is a 120/208 and all circuits in the panel are 20 amp lighting circuits. The pathways serve as a loop to bring the line to the LCP panel contactors and then back to the panel to splice into the load in a pull box next to the panel. There are no neutrals or grounds in the pipes - only line and return (sharing same pipes). There are no signs of a fault. Any ideas as to why we still have hot pipes? Thanks in advance for your input.
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In addition to what the others said about derating, there is one other thing that may be a possibility. Since you mention that the neutral is not present, what you have is a switch loop and that would require that that the line and load conductors be in the same raceway. I've seen a lot of this type of install where the line was run in one conduit and the load was taken out of a different raceway adjacent to the line conduit. This can lead to severe inductive heating and is a code violation.
 
texie said:
In addition to what the others said about derating, there is one other thing that may be a possibility. Since you mention that the neutral is not present, what you have is a switch loop and that would require that that the line and load conductors be in the same raceway. I've seen a lot of this type of install where the line was run in one conduit and the load was taken out of a different raceway adjacent to the line conduit. This can lead to severe inductive heating and is a code violation.
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A good indication of this, other than the fairly obvious one of identifying the two sides of the switch loop, is if the conduit is hotter than the wires in it. :)
 
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