Derating Cable for High Altitude / Elevation
Derating Cable for High Altitude / Elevation
(OP)
Where can I find some instructions on how and when to derate cable for high altitude applications? It does not seem to be mentioned in the NEC.
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Derating Cable for High Altitude / Elevation
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Derating Cable for High Altitude / ElevationDerating Cable for High Altitude / Elevation(OP)
Where can I find some instructions on how and when to derate cable for high altitude applications? It does not seem to be mentioned in the NEC.
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RE: Derating Cable for High Altitude / Elevation
RE: Derating Cable for High Altitude / Elevation
Transformers and switchgear get derated at high altitudes, but I have not seen it done for cables. It makes sense, the less dense air has less cooling capability, but how much?
RE: Derating Cable for High Altitude / Elevation
RE: Derating Cable for High Altitude / Elevation
1000m = 100%
3000m = 96%
6100m = 90%
This is the current derating for fuses, enclosed air disconnects, metal enclosed and metal clad switchgear. Basically, it accounts for the reduces cooling effect of the less dense air.
As already pointed out, the insulation strength does not depend on air pressure so it would not de-rate. But, any place relying on through air clearances should be derated as follows;
1000m = 100%
3000m = 80%
6100m = 56%
So, say you require 3/8" clearance minimum for 480V. At 6100m this would be very close to 3/4" required.
RE: Derating Cable for High Altitude / Elevation
RE: Derating Cable for High Altitude / Elevation
"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)