Control transformer for oven controls

P

pipe_bender

Senior Member
Location
Boston
Occupation
Electrician
Greetings gang I was helping out a friend who works for commercial food processing facility and they got several 'household' type ranges, the available receptacles in this place are 50 amp 240V no neutral off a hi-leg system a NEMA welder plug 6-50.
New 4-wire range receptacles could be run but its a complex run and expensive for occasional use.
My pal that is the millwright came up with this low cost under $200 'hack' he isolated the 120V loads (controls and a 40W light) and installed a 50VA 240 - 120 control transformer in each range to power these controls.
The ranges got welder cords, are tested and running fine.
They will only be used in this food processing plant.
I am wondering if there is any safety issue with the 120V transformer being so small? I thought an oven needed a neutral 70% of the circuit rating. Here is the transformer he used:
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Some ranges use combination cooking eyes that use 120 and 240 for temperature control. I think I have posted the connection diagrams before, but can’t find them at this moment. Newer units probably use electronic control of the elements, which may be what you have.
 
Thanks everyone for the feedback. its a pretty clever solution my friend discovered, he said the element controls are a 'infinite' switch that cycles on and off to control temp, and confirmed the neutral is only for the controls and the light.
 
pipe_bender said:
Thanks everyone for the feedback. its a pretty clever solution my friend discovered, he said the element controls are a 'infinite' switch that cycles on and off to control temp, and confirmed the neutral is only for the controls and the light.
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With today’s electronics, and LED drivers, manufacturers could do away with all 120 volt loads for ranges, same can be said about dryers. If an old fashion range is plugged in, your friends 50 va transformer would become toast rather quickly
 
hillbilly1 said:
With today’s electronics, and LED drivers, manufacturers could do away with all 120 volt loads for ranges, same can be said about dryers. If an old fashion range is plugged in, your friends 50 va transformer would become toast rather quickly
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They should manufacture all electric dryers & electric ranges to only need 240 volts supply so it would be cheaper to loose a #10 or 6 copper wire . Use 10/2 & 6/2 NM cable. For a dryer they could install a $10 240 to 120 volts 50 VA transformer to supply power to LED drum light & timer then use a 240 volt motor. Something similar on ranges. Very difficult & expensive to pull new wire from finished basements, from garage panels etc. Don't even want to give an estimate to rep!ace older 10/2 NM cable to a second floor dryer with 10/3 cable.
 
hillbilly1 said:
With today’s electronics, and LED drivers, manufacturers could do away with all 120 volt loads for ranges, same can be said about dryers.
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Interesting, I bet its the same 120V logic boards for gas and electric models, he said it was quick and easy.
hillbilly1 said:
If an old fashion range is plugged in, your friends 50 va transformer would become toast rather quickly
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Well to be clear the he modified the range itself, the control transformer got installed next to the logic board, hence the super small transformer, then all he did was install a welder cord (6-50).
No changes to the building wiring.
 
Eddie702 said:
I am sure it violates UL or some other nonsense but I won't tell. It makes more sense to do that than what the MFG does. Why don't they make ranges and dryers all straight 240/208 volt?
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Because it is $0.50 cheaper for the manufacturer to use that 120V and require the neutral.

What might fly is for the manufacturer to offer an option (for a significant price premium) that lets the electrician add the necessary transformer and convert the range into a straight 240/208V unit without violating the UL listing. Then existing circuits with 10-50 receptacles (neutral used for bonding) could be converted to 6-50 receptacles (no neutral, just an EGC) and the range would function correctly.
 
Eddie702 said:
I am sure it violates UL or some other nonsense but I won't tell. It makes more sense to do that than what the MFG does. Why don't they make ranges and dryers all straight 240/208 volt?
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Bosch does.
This ships with their dryer and splits the dryer receptacle into lesser amperage no neutral receptacles so their 240v washer and 240v dryer can be powered from one 240v outlet.

WTZPA20UC Laundry Accessory | BOSCH US

WTZPA20UC Laundry Accessory | BOSCH US
www.bosch-home.com www.bosch-home.com
 
Thats cool I wonder if Bosh makes the same adapter from a NEMA 10- or 6- style receptacle?
Converting a 10-50 to a 6-50 would be a slick solution to the age old problem of residential service panel becomes sub-panel and there is 3-wire 10- crows foot appliance outlets.
Eddie702 said:
I am sure it violates UL or some other nonsense but I won't tell. It makes more sense to do that than what the MFG does. Why don't they make ranges and dryers all straight 240/208 volt?
Click to expand...
Yeah you'd want it to be done by an appliance guy they seem to mix and match parts all the time I am not sure that UL and inspectors follow around appliance techs like they do electricians.
 
pipe_bender said:
Thats cool I wonder if Bosh makes the same adapter from a NEMA 10- or 6- style receptacle?
Converting a 10-50 to a 6-50 would be a slick solution to the age old problem of residential service panel becomes sub-panel and there is 3-wire 10- crows foot appliance outlets.

Yeah you'd want it to be done by an appliance guy they seem to mix and match parts all the time I am not sure that UL and inspectors follow around appliance techs like they do electricians.
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Insurance companies and lawyers.
 
pipe_bender said:
Thats cool I wonder if Bosh makes the same adapter from a NEMA 10- or 6- style receptacle?
Converting a 10-50 to a 6-50 would be a slick solution to the age old problem of residential service panel becomes sub-panel and there is 3-wire 10- crows foot appliance outlets.

Yeah you'd want it to be done by an appliance guy they seem to mix and match parts all the time I am not sure that UL and inspectors follow around appliance techs like they do electricians.
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The Bosch adapter has two pairs of fuses, one pair for each 15A outlet. That's what those little things in the back are for. They have the 4 prong and 3 prong dryer outlet versions. 6-15R is not allowed to be directly installed on a 30A circuit, so it would have to be fused.

I'm sure Bosch has them approved for use as appliance installation with their appliances. Spiderboxes routinely break out higher amperage outlets, such as 208Y/120V L21-30R into normal outlets and they have breakers. Spiderboxes wouldn't be legal for permanent installation though.
 
winnie said:
Because it is $0.50 cheaper for the manufacturer to use that 120V and require the neutral.

What might fly is for the manufacturer to offer an option (for a significant price premium) that lets the electrician add the necessary transformer and convert the range into a straight 240/208V unit without violating the UL listing. Then existing circuits with 10-50 receptacles (neutral used for bonding) could be converted to 6-50 receptacles (no neutral, just an EGC) and the range would function correctly.
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There's that and expectations to work in both 208/120 and 120/240 based services. You'll note that roof top package A/C units are generally dual tapped. 0-208-230/240 for the 24v control transformer. One way around the need to select 208 tap vs 240v tap is to use a N-120v transformer which is available on either services. Another way is to use a 90-264v rated SMPS, but I've had a number of wall adapters based on switch mode technology fail. Old school wall warts rarely fail without a sustained overload or overvoltage. If a USB phone charging adapter fails, you simply get another one. It's easily a $400-500 repair bill if the switching power supply integrated onto the appliance control board fails. If they're separate boards, there's the manufacturing issue of increased in $1-2 in manufacturing cost...

Heavier duty "upper voltage" voltage sensitive appliances like microwaves have an internal automatic voltage selector to choose 208 vs 240, require setup at the time of installation or have dedicated models.
 
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