# Temperature derating



## goose134 (Nov 12, 2007)

Here is the situation: We are running a rack of feeders down a hallway in an existing, old building. The rack runs about two inches above a steam pipe, which is pependicular to the rack. I didn't have a thermometer or anything, but I know it is hot. Here is the question: I know that the insulation has to be able to withstand the temperature at ANY point in the run. Am I reading it right to assume that I have to derate the entire run for this? A second question: Would insulation around the steam pipe mitigate the problem enough for me to at least keep the same size conduits? Any thoughts would be great.


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## RePhase277 (Feb 5, 2008)

goose134 said:


> Here is the situation: We are running a rack of feeders down a hallway in an existing, old building. The rack runs about two inches above a steam pipe, which is pependicular to the rack. I didn't have a thermometer or anything, but I know it is hot. Here is the question: I know that the insulation has to be able to withstand the temperature at ANY point in the run. Am I reading it right to assume that I have to derate the entire run for this? A second question: Would insulation around the steam pipe mitigate the problem enough for me to at least keep the same size conduits? Any thoughts would be great.


Yes, you derate to the highest temperature you encounter in the entire run. In order to answer the second question, you need to know just how hot it is now and how much you need to derate. Is it possible to run the feeders under the steam pipes? This will reduce the temperature a good deal as the heat from the pipes is rising.

InPhase277


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## goose134 (Nov 12, 2007)

Unfortunately, we cannot move these conduits. We had to shoehorn them in there as it was. I had a feeling it would be bad news. Any thoughts on insulating the steam pipe?


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## frenchelectrican (Mar 15, 2007)

Goose,
If the building owner say ok to insluated the steam pipes go for it but make sure you get a hold of HVAC contractor or plummer if your company dont allow you do that kind of task.


BTW.,, If you can tell me what PSIG steam pipe are we talking about because i have a chart with tempture with PSIG reading [ i used to be boiler operator for short while and i keep that book it will come handy for me.]

Any way with true steam pipe the tempture will be 212+ °F [ 100+°C]
or more the last steam pipe i was pretty close when i ran the busductwork i have to put a heat defletor on it due the 350 PSI steam pipe cranking out about 425°F[218°C] 

Merci, Marc


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## idoelectric (Jun 3, 2007)

Derating will not do any good for steam line underneath conduit. Derating is for ambient temperatures, not extreme heat in one place. and number of conductors. insulating steam pipe may help but risky. 1 lesser of 2 evils, find another route or risk insulation melting off inside of conduit and kaboom.


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## 480sparky (Sep 20, 2007)

idoelectric said:


> ...Derating is for ambient temperatures, not extreme heat in one place....


If the temperature above the pipes is, say, 55°C, then isn't that the ambient temperature? It's only if the ambient temperature in that location exceeds the temperature rating of the conductor that you risk melting it. That's why the correction factors below T310.16 only go (almost) as high as the rating of the insulation. Go any higher, and the insulation states to degrade. If it's so high that the insulation will melt, there shouldn't be anything near there anyway. But I doubt the temps are _that_ high.


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## idoelectric (Jun 3, 2007)

480 Sparky,

I get what you're saying and you're right, but I do believe that steam line is hotter than you think. Conduit is already crammed in with no real room given for proper insulation around steam line isn't something I would not want to chance without scoping another solution. Not knowing the size of steam pipe and size conduits and wire for application, it's anyone's guess.


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## goose134 (Nov 12, 2007)

The steam line is about 2" or so, and the conduits range from 2" to 4". There are 12 on the rack. I agree that the question of whether or not the cable insulation can withstand the temperature in that location is critical. Derated or not, if the insulation melts, it's going to blow. I think I'll see if I can get a reading on this Monday and see how hot this actually is.


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## goose134 (Nov 12, 2007)

Good news and bad news. Good news is that the pipe we are right under is actually a sprinkler pipe. Bad news is I'm an idiot for not realizing it. Now the derating is just a matter of finding the temperature around the conduit. The steam pipe is in the vicinity, just nowhere near as close as I initially thought. DUH!:jester:


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## Greg (Aug 1, 2007)

At least it make life easier.


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