208 Grill on 240 volt

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augie47

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Acquaintance just connected a 208 3 phase grill to a 240 system ignoring advice to install B-B transformers. In the real world what can they expect ?
 

GoldDigger

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Acquaintance just connected a 208 3 phase grill to a 240 system ignoring advice to install B-B transformers. In the real world what can they expect ?
More than rated current.
Higher stress on the heating elements even though the ultimate temperature will still be controlled by the thermostat.
If there is a significant time lag between the heating element temperature and the temperature at the thermostat you could get higher heating element temperatures leading to earlier breakdown.
In an oven where the thermostat senses the air temperature, the element temp could get well above design levels.
Is the grill thermostatically controlled in some way or just constantly on, as with an oven broiler?
 
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We worked on a storage shed for potatoes last fall. Building had not been used as such for years but had to be brought into service. 208v heaters with 240v applied.
Heaters drew more current as expected, almost to the .x amp. We made sure the feeders were sized accordingly. They worked for several years before the period of nonuse, I expect they will work for several more.

Not apples to apples, but I would expect operating temperature of the grill to be reached more quickly, with maybe more rapid cycling. More stress on the components if they are marginally sized. Life expectancy???
 
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Wouldn't the current be less? If its 208 @20amps then 240 would be 17.33 amps.

You have to use ohms law and figure the resistance of the heating elements at rated voltage. The resistance of the elements will not change when the higher voltage is applied, so use ohms law again to find the current at the higher voltage. Then again to find the wattage output at the increased voltage.
 

Carultch

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Massachusetts
Wouldn't the current be less? If its 208 @20amps then 240 would be 17.33 amps.

The nominal current would be less, if it were designed to work with 240 Volts as its supply. Because you select the resistance of the heating element to achieve the desired power. And that power would be the same, whether you design for 208V or 240V.

But because it is a device that is already designed for 208V, you cannot assume that power is unchanged when you connect it to 240V. It is more realistic to model resistance as being unchanged, and therefore there will be ~15% more current and ~33% more power.
 

Carultch

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Massachusetts
Thanks, I see the increase now. Not sure what I was thinking in my post above.

I remember I got this wrong on a Physics test in high school. We were given a question with a 60W and 100W lightbulb in series on a 120V circuit, and asked what the power used by each bulb would be. I didn't realize that the wattage ratings were only valid with a voltage drop of 120V, and thought the answer was 100W and 60W.
 

kwired

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I remember I got this wrong on a Physics test in high school. We were given a question with a 60W and 100W lightbulb in series on a 120V circuit, and asked what the power used by each bulb would be. I didn't realize that the wattage ratings were only valid with a voltage drop of 120V, and thought the answer was 100W and 60W.
That one could still be a little tricky as incandescent lamps are not a fixed resistance, the resistance of the filament will vary with temperature changes, that means if you are not applying full 120 volts the temp will not be as high and resistance may be lower then it is when operating at 120 volts.

A heating element may vary some in resistance as well with temperature changes but is closer to being fixed then an incandescent lamp.
 

kwired

Electron manager
Location
NE Nebraska
Acquaintance just connected a 208 3 phase grill to a 240 system ignoring advice to install B-B transformers. In the real world what can they expect ?
Can the heat elements be re-configured in any way or are they fixed?

If the three phase element is wye connected then there are three individual 120 volt elements - if possible to re configure you could connect them line to neutral on a 120/240 system - but you can not connect any lead to the high leg.

Of course all this is likely going to go beyond listing instructions but is a possible option.
 

infinity

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Although it's output will be higher it might last a long time without any problems. I've been running a 208 volt heater at 240 volts (actual voltage is about 248 volts) for years in my garage.
 

iwire

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Although it's output will be higher it might last a long time without any problems. I've been running a 208 volt heater at 240 volts (actual voltage is about 248 volts) for years in my garage.

This is a case where I would not do it for a customer or my own home.

To do so with full knowledge that the elements are going to be running much much hotter than they, the element mounting means, the terminals on the elements or the enclosure they are contained in are designed for is at best a poor choice and at worst a fire.
 

infinity

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This is a case where I would not do it for a customer or my own home.

To do so with full knowledge that the elements are going to be running much much hotter than they, the element mounting means, the terminals on the elements or the enclosure they are contained in are designed for is at best a poor choice and at worst a fire.

I completely agree and I'm not suggesting that anyone do this. Many of us live with technical code violations in our own houses. :D
 

templdl

Senior Member
Location
Wisconsin
I know a place that did this inadvertently with belt drive pizza oven. They bought used 208v units and the unknowingly applied them at 240 and wondered why then needed to replace the motor once a year.
I identified a good deal on a back boost transformer to buvkmthe voltage but was ignored. They continue to replace motors.
 

templdl

Senior Member
Location
Wisconsin
???
I'm assuming you meant "buck" boost transformer and can only guess you were saying "buck the" for the part in red.

Thanks, yes, buck boost, and bucking the voltage but they opted to continue replacing the motors. Instead of paying for the cost of the transformer they chose to play Russian roulette as to when the oven would break down during dinner hour and the days that it takes to get the oven back into operation.
Note that I watched my spelling this time for a change. ;)
 
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