Question on breaker size/ amp draw..

Wolf Creek Forge

Wolf Creek Forge

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Jul 4, 2012
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We have a question..We just wires a new building for a clean room..We are gonna put out new heat treat oven(thats suppose to ship soon). We have one 240v outlet..Its run with 10-2 wire from a 30 amp breaker..Now the oven only calls for 13 amps and 3100 watts..Will it be ok to run the oven off the 30 amp breaker?(wondering about ramp up, or does it even draw more at the start-up?) Considering the feeder wire is about 100' long to the building(into a breaker box)..According to the drop calculator with the feeder wire size (10awg/ UF) our loss is about 2.57%..Under the recommended 3% loss. The oven and a couple lights will be the most ever drawn at one time and then only occasional use of the oven of course.
 
You should be good with the 30a breaker. It will carry 24a continuously without tripping, which should be plenty for both the oven and lights. The oven won't draw too much more current on start up (I think.. depends on the heating elements.. but the 30a breaker should take care of this) significant inrush is associated mostly with motor starting. Source - Electrician
 
Agreed, you should have no problems.

Voltage drop affects motors more than it affects resistive devices like ovens. The oven may top out a few degrees lower than a shorter run of wire would give, but that should not matter for a normal HT job.
 
You might want to consider any additional
Load you will have if you use a smaller oven along
With your HT oven for tempering.
 
No. It will work just fine. The only down fall is potential damage to the equipment. The breaker should be the weekest link in the electrical circuit to assure it will be the first to fail. At 80% of 30A this gives you 24 amps. This gives you 11 amps of over current before the breaker registers the problem and trips. (not talking about a direct short) This means that the equipment could be damaged more so than if the system was sized correctly for the load.
The problem that you sometimes encounter is the manufacturer is able to get away with things that electricians following the NEC can not. In this situation we would need to use #12 awg wire and a 20 amp breaker. Were they may have been able to get away with #14 awg wire.
#14 is good for 15 amps at 60 degrees C. We could not use this because you can not install wire rated less than the breakers rating which in this case would be 20 amps to cover the 13 amp load.
Simply said that additional time caused by the gap in protection (11 amps) could mean that your ovens wiring or components could be damaged beyond repair before the breaker trips. The whole idea of sizing the overcurrent device as close as possible is to reduce the time between event and fail. You may only burn up a relay instead of the entire control cabinet, wire and components.
It will work fine but not optimum for protection of the equipment.
 
kvolle said:
No. It will work just fine. The only down fall is potential damage to the equipment. The breaker should be the weekest link in the electrical circuit to assure it will be the first to fail. At 80% of 30A this gives you 24 amps. This gives you 11 amps of over current before the breaker registers the problem and trips. (not talking about a direct short) This means that the equipment could be damaged more so than if the system was sized correctly for the load.
The problem that you sometimes encounter is the manufacturer is able to get away with things that electricians following the NEC can not. In this situation we would need to use #12 awg wire and a 20 amp breaker. Were they may have been able to get away with #14 awg wire.
#14 is good for 15 amps at 60 degrees C. We could not use this because you can not install wire rated less than the breakers rating which in this case would be 20 amps to cover the 13 amp load.
Simply said that additional time caused by the gap in protection (11 amps) could mean that your ovens wiring or components could be damaged beyond repair before the breaker trips. The whole idea of sizing the overcurrent device as close as possible is to reduce the time between event and fail. You may only burn up a relay instead of the entire control cabinet, wire and components.
It will work fine but not optimum for protection of the equipment.
Click to expand...

The ovens should already have built in fuses depending on the make and model though ?
 
Some very good info, thanks everyone..This kiln does have a control fuse(to protect the control box) according to what Ive read..
 
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