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Old 01-01-2007, 12:40 PM   #1
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208V element running on 240V?


I currently heat metal finishing solutions the old fashioned way, natural gas burners, an immersion thermometer, and constant monitoring/tweaking dials.
Quality thermostaticaly controlled immersion heaters are very expensive, and difficult to find on ebay in the size, length, wattage density, temp range, and sheath material needed for each distinct solution/bath.
I have found a plentiful source of used heaters that fit all my requiremeents save one... they are 208V 1ph, while I only have 240V 1ph service.
Occasionally I run across suppliers that sell 208V/230V heaters, while the same venders also sell 208V only versions. I am guessing the wattage rating would be exceeded with the step up in voltage.
Is there some way to limit current so the elements don't burn up prematurely from the increased voltage? Or better yet, is it typically OK to use a simple element with an increase in supply voltage of 15%? The watt density is low (large surface area) at 35W/sq.in, so the theoretical output would go to 40W/sq.in. of the element's heated surface.
Thank you in advance to anyone who might be able to help. Happy New Years Too!


Last edited by cleefurd; 01-01-2007 at 12:51 PM.
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Old 01-01-2007, 01:37 PM   #2
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208V element running on 240V?


Only the mfg of an equipment can tell you the operating range for their equipment. Most things will work fine at +/- 5 % . This is typically the guarntee from a utility company. Some will work fine at +/- 10%.

It is not just the wattage of the elements in question. I am sure that there are also control circuits that are powered from the same system voltage.

If you cannot get the infomation that you want, and want to be sure to not damage the equipment you can buy a "buck boost" transformer, usually for less than 200 dollars, that will serve one machine. Follow the instructions and you will be able to buck your voltage from 240 to 208.

If you have several tanks to wire, you may be better off to get a larger transformer and buck an entire panel, then use that new panel to feed all of the tank circuits.

Installing this type of transormer does, by code, create a "seperately derived system" For this reason this is not really a DIY project. If you do not completely understand everything that I just posted, you should hire a qualified electrician to install the equipment for you.

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Old 01-01-2007, 01:56 PM   #3
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208V element running on 240V?


cleefurd,

While the increase in voltage is only 15.4 percent, the increase in power is 24.9 percent because with respect to the fixed resistance of the element, Power = Voltage squared divided by Resistance (Ohm's Law). Therefore, the 208V elements will likely fail on 240V and that failure may be spectacular (very dangerous).

As you mentioned there are no cheap controllers for 240V.

If you can specify how many BTU/Hr. or total watts the element needs to be, I may be able to recommend a cheap big box home center solution. In addition, you may be able to protect it with a GFCI, resulting in extra safety.

Happy New Year...

...Christopher
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Old 01-01-2007, 08:01 PM   #4
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208V element running on 240V?


... that I may be better off matching my components to the source, rather than the other way around. I think I'll just buy some 240V-1ph cartridge heaters, J-Type thermocouples, PID programmable temperature controllers w/ SSR outputs (solid state relay), and taylor my own precision immersion heaters. I am not to familiar with how, but necessity is the ...... .. ........., and someone has invented all the parts to craft perhaps an application specific marvel, now all I have to do .... is homework.
Thanks for the guidance, hate to scare you, but I'll probably be back, with a picture of either the remedy, or the quick-sand.
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