Conductor temperature, wet locations

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wringda

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I have an application where conductors need to be installed in wet locations where the ambient temperature is up to 110 deg C. In table 310.13 the only insulation listed for this is mineral, metal sheathed up to 250 C.
Is there any other option, even by special permission?

Why is a wet location such a severe derating (type ZW insulation for example)?

Thanks
 
It's a downhole heating application - the cable is run vertically down a well to a heater at 100 ft depth, below the water table. 110 C would be the maximum temperature of the heater (at the bottom of the cable).
 
wringda said:
It's a downhole heating application. . .
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I don't have a clue as to the reason for heating to 110? C but I would think the manufacturer of the heater would be able to help in that regard. The manufacturer may have accessory cord that would be included in the manufacturer's instructions so it could be approved for the purpose or even be listed with the heater as an accessory. :)
 
From what I see downhole applications are not described in NEC. The cable selection likely needs to be based on engineering rather than strict interpretation of the code.
 
charlie said:
I don't have a clue as to the reason for heating to 110? C but I would think the manufacturer of the heater would be able to help in that regard. The manufacturer may have accessory cord that would be included in the manufacturer's instructions so it could be approved for the purpose or even be listed with the heater as an accessory. :)
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At 110? C you would not need to consdier wet location as water boils at 100? C, so it will no longer be wet.:D

Most likely you want the heater purchased with a 'cold lead' installed by the manufacturer so that your feed point for your feeder connection is rated at 75? C. (The 'cold lead' is the cable that is connected to the heater and it is designed to be long enought that the heat loss on the length of the cable allows the temperature to be lowered from the hot connection point at the ehater to the service connection.)
 
weressl said:
At 110? C you would not need to consider wet location as water boils at 100? C, so it will no longer be wet. . .:D
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HMMM . . . I suspect a 100 foot water column would raise the boiling point of water . . . ;) :smile:
 
charlie said:
HMMM . . . I suspect a 100 foot water column would raise the boiling point of water . . . ;) :smile:
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It would... but the entire 100 ft depth is likely not all water. The usual reason one has a 100 ft plus water well is the water table is not near the surface :D
 
Correct, 110 C is due to the water column at that depth.

For the 'cold lead', do we not still consider the worst case temperature on the cable surface - at the heater connection?

What is the maximum temperature for wet locations based on? The insulation would melt at the same temperature wet or dry...
Is it a level of water permeability that is acceptable as the temperature increases?
 
wringda said:
Correct, 110 C is due to the water column at that depth.

For the 'cold lead', do we not still consider the worst case temperature on the cable surface - at the heater connection?

What is the maximum temperature for wet locations based on? The insulation would melt at the same temperature wet or dry...
Is it a level of water permeability that is acceptable as the temperature increases?
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Would not the 'wetness' deter the melting??
 
wringda said:
Correct, 110 C is due to the water column at that depth.
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I have to wonder about that. I think the high temperature is more likely from the core-element-ends of the heater, which is passed on to the wire terminations... i.e. theconductor insulation would be heated from the inside out, whereas heating from the water has substantially lesser effect but still adds to the temperature rise of the conductor.

For the 'cold lead', do we not still consider the worst case temperature on the cable surface - at the heater connection?
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I'd be more concerned about the insulation temperature between conductors... but yes, most likely at the heater connection.

What is the maximum temperature for wet locations based on? The insulation would melt at the same temperature wet or dry...
Is it a level of water permeability that is acceptable as the temperature increases?
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Don't know myself. Would such permeation lead to premature breakdown of the insulating material, perhaps providing a fault path sooner than in a dry location.
 
brother said:
Would not the 'wetness' deter the melting??
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Not if the wetness is hot enough to degrade the cable/conductor insulation.

PS: AFAIK, thermoplastic insulations will degrade at temperatures lower than their melting, or even their "moldable" temperature point, if subjected to such for long periods of time. (Not certain about cross-linked poly... I'm referring to PVC and Nylon mostly). Thermoset insulation does not melt... I believe it just "chars".
 
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wringda said:
Correct, 110 C is due to the water column at that depth.
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Is the water column will be that high? Then there would be really no reason to go that deep, would there.....?

wringda said:
For the 'cold lead', do we not still consider the worst case temperature on the cable surface - at the heater connection?
Click to expand...

'Cold lead' is the connection between the heater and the feeder cable. It is a special high temperature cable that is designed to withstand the temerature at the heater connection and designed to be such a length that the resulting gradual heat loss will result in a 'normal' temperature at the 'other end' suitable for regular 75*C connection of the feeder.
 
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