Buck Boost Transformers for loads requiring neutrals

[X49]

I've been thinking of using a buck boost transformer to boost from 208V to 236V single phase for a 230V stove that requires a 120/240V 50A receptacle. GE recommends using these transformers for some of their appliances.

The obvious concern is that the appliance requires 120V for lighting and controls, and one of the legs will be around 136V. If only the 120V leg is used for lighting and controls there should be no problems.

This doesn't exactly seem proper to me, but it is apparently common practice. Anybody care to comment with regards to safety or code compliance?

 

[cranky108]

If I recall, the 208 is the voltage between two phases of a three phase 208/120 system. Won't it work on 208? or is the heat produced a little low? If you use the 208, and keep the 120 reference to ground the controls should work correctly.
However with what you are talking about will provide high voltage to the controls, which is concerning as many new stoves use solid state technology and they may not like this. However if that is not a problem, use 130 V light bulbs.

 

[stevenal]

I'm not following the math here. If you choose to use a boost transformer, it should be center tapped to provide the 120 (or 118). I would not assume all the 120 loads are on the same leg. Even if they are, the replacement stove plugged into that receptacle some time in the future may be wired different internally.


These appliances are routinely used on 208/120 V systems. The controls, lights, and 120 V receptacle (some stoves) all have proper voltage. The heating elements put out reduced heat and take longer to reach set point, but will otherwise operate fine.

 

[stevenal]

If you are considering using an auto to step up the 208 to 236 while using the same neutral, I'm getting 145 V on the higher leg. Way high.

 

[jghrist]

It should be no problem technically as long as the high voltage leg (I also get 145V) is not used. I'm not sure if putting 145V to neutral on one leg of a 125/250V receptacle would meet code, however.

 

[waross]

Given the tens of millions of apartment dwellers in the US and Canada who are unaware that their appliances are fed by 120/208 volts, don't waste any more time trying to solve a problem that isn't there.
If you must use the boost transformers, then add a 120:240 transformer inside the stove to supply the controls. You may have to "break out" the control circuits from the incoming neutral. Some elements use 120 volts on the lower settings. You don't want to feed those loads from the small control transformer.
Forget warranties.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

I would advise against altering the stove. The whole idea behind the standardized plugs and receptacles is to ensure the proper device receives the proper voltage and current. When the altered stove is one day plugged into 240 after being sold off on a Craig's list estate sale, there will be a problem.

Is there a place we can see this particular GE recommendation on line?

 

[X49]

All good points. I think I'll stick with 208V.