I have an industrial oven to wire and need some advice. The oven consists of 6 zones of electric heaters, 3 on each side, 262 amps @ 63VAC each zone. Power is supplied via a 50A fuse to a SCR to a 21KVA 480-63 single phase transformer, 20ft of wireway to the heater connection. Since there is no secondary overload protection, I have to use the primary overload times the voltage ratio (480/63) or 50 x 7.62 =382 amps. Ambient temp along the oven wall where the heater connections are is 50C. Manufacturer suggests SRML cable in 2/0 but I don't believe this is sufficient. I know how to use the derating tables, but have a couple of questions.
Silicon Rubber insulation is listed in 310.13 as type SA with a operating temp of 90 or 200C. Table 310.17 lists SA only under the 90C rating. Table 310.18 lists 200C conductors but does not include the SA insulation. What is the correct table to use for 200C SRML.
Also, how does any of the 200C rating ampacity tables actually help anyway. Are we not limited also by the temperature rating of the termination. Checking the Burndy catalog for compression fittings all I see is 90C rated lugs. Yet Burndy says that their tin plated comrpession fittings can be used up to 375F (190C), but they are not UL listed for this temp.
The heater connection is from the manufacturer and is Dossert Ground clamp with no temp listing. Althought it is all copper bronze and is very beefy. Local cable guys says he sees them all the time on industrial furnaces.
Any comments regarding ampacities, and terminations.
I can't reduce the 50A primary as on cold startup current can reach 320 amps for brief periods.
Silicon Rubber insulation is listed in 310.13 as type SA with a operating temp of 90 or 200C. Table 310.17 lists SA only under the 90C rating. Table 310.18 lists 200C conductors but does not include the SA insulation. What is the correct table to use for 200C SRML.
Also, how does any of the 200C rating ampacity tables actually help anyway. Are we not limited also by the temperature rating of the termination. Checking the Burndy catalog for compression fittings all I see is 90C rated lugs. Yet Burndy says that their tin plated comrpession fittings can be used up to 375F (190C), but they are not UL listed for this temp.
The heater connection is from the manufacturer and is Dossert Ground clamp with no temp listing. Althought it is all copper bronze and is very beefy. Local cable guys says he sees them all the time on industrial furnaces.
Any comments regarding ampacities, and terminations.
I can't reduce the 50A primary as on cold startup current can reach 320 amps for brief periods.
