220 single phase protection

[kozmic1520]

Simple question.
I'm building a control panel for a powder coating oven. It will have 3 3,000 watt 220 volt heating elements. On the Oven building forums they seem to only put over current protection on one leg of the 220 feeding the elements. I am under the impression that...
The relay that powers the elements should be 2 pole.
Both legs of power should be protected (fuse or breaker) via a 2 pole breaker.

I am running 50 amp to a 2 pole, SS relay to power the 3 elements. I am running 3 circuits from the relay to 3 2 pole, 20 amp breakers and 14ga wire from the breakers to each element.

The group is telling me this is overkill and one fuse on the 220 to a single pole relay would be fine.
This will leave one leg hot all the time, and I believe it leaves one leg unprotected. Also this would require the wire to the elements to be sized for the full 50 amps Correct?

All of my background is in three phase controls and we wouldn't think of doing it any other way.

I hope it wasn't too confusing.

 

[itsmoked]

If you want to protect the individual elements then one fuse per element will do it. However, you should have two pole protection for the oven.

Typically you'd have SSRs that cycle the element(s) and those would only be one leg. Then you'd have a contactor that supplies the entire oven. This contactor would disconnect both legs. You'd use it with some sort of overtemp safety. Also a ON switch that confirms a 'human' wants this to all run. That would be a latching switch thru an overtemp sensor. When an overtemp occurs the main contactor is dropped. To have any heat a human should have to hit the "START" button which latches in that contactor via the overtemp switch AND the power switch. It all should be fed thru one two-pole breaker.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[kozmic1520]

Wouldn't you have to size the wire for the full available current all the way to the elements then? If I run 50 amp to the SSR and only run 14ga to the elements from the SSR wouldn't the non fused leg be unprotected?

Thanks.