Industrial heating oven

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Davebones

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North Of Tampa Fl
Have a oven for drying parts out of the paint shop . Nameplate is 460V 3 Phase ( 27 amps ) .Can we use a 30 amp disconnect and feed with #8 wire or does the disconnect need to be 60 amp fused down to 35 amps ??? I understand we have to have a 60 amp disconnect fused down . Boss thinks we only need a 30 amp disconnect !
 
Heat input on the nameplate is 20 KW . Nameplate shows FLA as 27 amps .According to 210.10 ,I would find 125% of 27 amps which comes out to 33.75 amps . Then according to 240.6a I would use a overcurrent device rated 35 amps . Thats what I am figuring out according to the code .
 
cadpoint said:
Heating Equipment is right in Article 665.
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665 is for "Induction and Dielectric" Heating Equipment.

I think you need to look at 422.10 and 422.11.

For the conductors you need to apply 125% of the 27A (per 422.10(A)).

For the OCPD you can go to 150% (not to exceed 45A) for 422.11(E) applies, or not to exceed 50A if 422.11(D).

(It doesn't say you have to go to 45 or 50, but not to exceed those, so a 35A OCPD would be OK. But you can use the larger breaker size without increasing your wire size, so why not use the larger breaker?)
 
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Davebones said:
This oven would be a continuous load . Up to 10 hrs at a time .
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Just to clarify..... is the entire load, all 20kw on for 3 hours or more continuously, or is the equipment in operation for 10 hours with the heat cycling ?
It will effect the term "continuous" in regard to the total load.
 
augie47 said:
Just to clarify..... is the entire load, all 20kw on for 3 hours or more continuously, or is the equipment in operation for 10 hours with the heat cycling ?
It will effect the term "continuous" in regard to the total load.
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While I agree that by definition a heat load that is cycling may not be considered continuous. With all the variables that would come into play I don't see how you could calculate the actual load and the duration. I would consider it continuous and size feeder/breaker accordingly.
 
One-eyed Jack said:
While I agree that by definition a heat load that is cycling may not be considered continuous. With all the variables that would come into play I don't see how you could calculate the actual load and the duration. I would consider it continuous and size feeder/breaker accordingly.
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I probably would also, but I'm not paying the install bill :)
In terms of Code requirements, if the OP can determine if any portion of the load cycles in such a manner that he does not have a 3 hour continuous load he can, if desired, take advantage of that fact.
It might not be the most desirable route to take in the overall picture, but I was addressing Code compliance.
 
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