Thwn and high temperature

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thinfool

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I quoted a labor only figure to wire new kilns at a sawmill. I am reasonably sure that the owner is going to try to use his 'own forces' to do the work.
The plans are to wire the fans in the kiln with #12 thwn. The ambient operating temperature of the kilns will be in the 160-180f degree range.
Can thwn be used for this application?
If no, then what will happen if they do? Will the insulation break down in a fairly short period of time, leading to multple failures? (there are a total of 32 fans, all of which operate in within this temperature environment.
 
thinfool said:
The ambient operating temperature of the kilns will be in the 160-180f degree range.
Can thwn be used for this application?
If no, then what will happen if they do? Will the insulation break down in a fairly short period of time, leading to multple failures?
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I would say No you shouldn't use thwn for this application. Review Table 310.13 , this table lists the maximum operating temperatures for insulation.

THWN has a maximum operating temperature of 167*F,
but THWN-2 has a max temp. of 194*F

Most new wire has multiple ratings such as thhn/thwn/thw/thwn-2 ,etc.

I would review this table to find an insulation that fits your needs.


ibew441dc
 
There are insulations, such as on some MTW conductors, that have 105 C (221 F) rated insulation. That has to include both the environmental temperature and the added temperature due to conductor heating. They might be larger so larger conduit may be required.

I presume that someone is working to limit the temperature on the fan motors. This won't be the first time that someone has designed the wiring for a fan in a kiln.

I suspect that the motors will be located so that the connections will be within design limits. They might even have shaft extensions so the motor is outside the kiln heat.

It may be more economical to put junction boxes somewhere outside where the smaller wire would be connected to larger wire with better insulation inside the kiln.
 
Bob NH said:
I presume that someone is working to limit the temperature on the fan motors. This won't be the first time that someone has designed the wiring for a fan in a kiln.
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Not that I could tell. The only design criteria from the mfr seems to be to 'not' use any steel inside the kiln. So all conduit and fittings will be aluminum and straps will either be aluminum or stainless steel.

I suspect that the motors will be located so that the connections will be within design limits. They might even have shaft extensions so the motor is outside the kiln heat.
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This is not evident, the fans are directly mounted on the motor shafts. There will be =/- 10' of conduit and flex within the hi temp area for each motor. (32 total motors)


It may be more economical to put junction boxes somewhere outside where the smaller wire would be connected to larger wire with better insulation inside the kiln.
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I thought of that, but if they don't buy my services, they don't get my experience/expertise to avoid future problems.

Unfortunately, many customers think that the price they should pay is just for the physical installation with no consideration for the nuances and subtleties of a quality installation.
 
thinfool said:
Unfortunately, many customers think that the price they should pay is just for the physical installation with no consideration for the nuances and subtleties of a quality installation.
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Hear, hear! Truer words were never spoken!

You may be thin, but you're no fool.
 
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