Running wire in conduit near hot equipment surfaces

Status
Not open for further replies.
P

PhaseShift

Senior Member
During new construction I recently found that the contractor had run conduit near a piece of equipment that becomes extremely hot during operation. Temperature on inside of vessel reaches about 1000deg F so the outside temperature will be less where the conduit is.

What is the rule of thumb when conduit is run close to these hot surfaces? With THHN in conduit what is max temp rating it can be run near? What about if cable is tray cable?
 
PhaseShift said:
During new construction I recently found that the contractor had run conduit near a piece of equipment that becomes extremely hot during operation. Temperature on inside of vessel reaches about 1000deg F so the outside temperature will be less where the conduit is.

What is the rule of thumb when conduit is run close to these hot surfaces? With THHN in conduit what is max temp rating it can be run near? What about if cable is tray cable?
Click to expand...

Id get a temp reading of where the conduit is/planned to be, and adjust the THHN amperage for ambient temp.

~Matt
 
Cow said:
Don't forget that the 310.15(A)2 exception may apply.
Click to expand...

Is it saying, that if he calculated he needs to run #10 for a 30A circuit for example, but the temp adjustment says he needs to upsize to #8.
However, the length of wire running by the machine, say 6 feet, is smaller than the mentioned 10 feet, he can run #10 and its compliant?


I may have confused myself even more...

~Matt
 
I'd be more concerned with the heat from that equipment breaking down the insulation on the conductors more so than the derating issue. But that's just me....
 
mxslick said:
I'd be more concerned with the heat from that equipment breaking down the insulation on the conductors more so than the derating issue. But that's just me....
Click to expand...

I agree, It might take some very expensive wire to be used "safely" in this environment. We need to know how hot the pipe actually is
 
TOOL_5150 said:
Is it saying, that if he calculated he needs to run #10 for a 30A circuit for example, but the temp adjustment says he needs to upsize to #8.
However, the length of wire running by the machine, say 6 feet, is smaller than the mentioned 10 feet, he can run #10 and its compliant?


I may have confused myself even more...

~Matt
Click to expand...

Yes, but the 6' in your example would have to be 10% of the circuit length or less.
 
mxslick said:
I'd be more concerned with the heat from that equipment breaking down the insulation on the conductors more so than the derating issue. But that's just me....
Click to expand...

Yes this is what I was concerned with as well. The temperature on the outer surface of the vessel gets to around 300deg F. The conduit is run right near the outer surface of the vessel.
 
Add a Heat Shield

Add a Heat Shield

This happens in our power plants when a 750F steam line gets routed too close to a cable tray or conduit. We've installed aluminum plates as a heat shield between the pipe and the conduit or tray. We placed thermocouples to prove to ourselves and the client that it worked. It kept the tray and conduit within the 50C ambient used in our calculations. A cooling air space on both sides of the plate helped a lot.
 
PhaseShift said:
Yes this is what I was concerned with as well. The temperature on the outer surface of the vessel gets to around 300deg F. The conduit is run right near the outer surface of the vessel.
Click to expand...

THHN is good up to 194? F. Derating might not be an issue due to 310.15(A)(2)Ex as Cow mentioned. You could always use a conductor with a higher temperature rating.
 
Status
Not open for further replies.
Top