208V instant water heater on 240V

Guys,
I got this 9kw instant water heater from ebay and was told it was good for 240V/208V and in the book that came with it there is a table with a bunch of models inc. 208V 50A model and a 240V (208) that runs 9kw at 240 but 6.3kw at 208. The model numbers are not listed in this table which is kinda lame and the unit is German and I think out of production (altho it is 'new').
Since the label outside and the stamp inside both just say 208V my assumption is that this unit cannot take 240V but the vendor claims it will.
Does anyone have any thoughts on how one might figure this out without risking a fire or something?
The element resistance is 4.9 Ohms which by my math gives ~8830W which would suggest this unit cannot run 240 as that would be over 11kw.
Think I'm gonna send it back.
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I think that's your best move, Nick.
You probably aren't at risk of a fire, but I'd bet the element doesn't last long.
If nothing else - if you do wire it up, you'll probably be paranoid about it from the first power up.
Ship it back gets my vote.
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Electriccal voltage vaires though the day. Your 120 volt wiring runs from 105 to 130 maybe. Voltage in a wire is kind of like pressure in a water line. Make sure you have the right circuit breakers and wire size and you probably will be ok.
Nick wrote:

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It varies, but nowhere nearly that much. If it's down to 105, that's a *big* problem. Variation is typically not more than a volt or two.

No, he probably will not. The element is rated for 208V. He's going to be pushing a fifteen percent overvoltage through it, and it's probably going to burn out very soon.
Please confine your advice to subjects you know something about. Inaccurate electrical advice is dangerous.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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"No, he probably will not. The element is rated for 208V. He's going to be pushing a fifteen percent overvoltage through it, and it's probably going to burn out very soon. "
I seriously doubt that a 15% overvoltage in a heating element that is surrounded by water is going to burn it out. Just because the instant water heater is labeled for 208V, doesn't mean that's the max rating of the individual components, like the heating element. As an example, some SPA/Hot Tubs are sold as either 120V or 240V. They are identical except the power packs are slightly different. Both units have the exact same heating element. If you look at the label on the 120V SPA, that's what it will say, even though the heating element can take 240V. You can switch it to 240V by simply changing the power pack, leaving the heater element as is. In that case the heater then puts out 6KW, instead of 1.5KW when wired for 120V.
BTW, I'm not saying I'd used this Ebay water heater myself, only that IMO, it's likely it would in fact work.
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You may be missing the point. If you put two 120 volt elements in series you can operate them at 240 volts, but you can't take one 120 volt element and operate it at 240 volt (not for long) These water heater elements are designed to be under water and produce a certain amount of heat at a precise voltage. If you power it with more than the rated voltage, it will both get hotter and shorten the life of the element

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"You may be missing the point. If you put two 120 volt elements in series you can operate them at 240 volts, but you can't take one 120 volt element and operate it at 240 volt (not for long) These water heater elements are designed to be under water and produce a certain amount of heat at a precise voltage. If you power it with more than the rated voltage, it will both get hotter and shorten the life of the element "
I'm not missing anything. The example I gave covers it quite nicely and has nothing to do with putting two elements in parallel.
"These water heater elements are designed to be under water and produce a certain amount of heat at a precise voltage."
There's nothing "precise" about what is simoly a resistor surrounded by lots of cooling water. Sure there's some upper current limit, but we have no way of knowing what the actual rating on the heater element of the OP's unit is, only the rating on the plate of the device itself. And the upper limit is very likely a lot more than 15%.
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Just my opinion: Foreign products are precisely engineered. There is usually no room for error.Products engineered in the states are usually over designed. Probably because of all the lawsuits by morons that don't follow the directions and then want to sue when something goes wrong......Did I say that out loud? If your german made model does not call out for 240 then I would either contact the manufacturer, someone familiar with that model, or send it back.

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More Ebay junk !!!! Some people never learn !!!!
Send it back, waste more money on shipping, then close your ebay account. Next go to your local HD or plumbing supply and buy the proper heater. You wont get ripped off on shipping and handling there, and you wont risk a fire.
Mark
On Sat, 07 May 2005 00:12:31 GMT, Nick

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I second Mark's idea. In the USA residential heating products are generally wired for 240 volts, but if used in some commercial buildings where you may have 3 phase 208 volt services, they want you to know that the heater won't get as hot. In your case you're doing the reverse and the elements will overheat which will shorten their life.

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Measuring the resistance of the heating element when it is cold does not give a valid result for calculating power. The resistance will be higher as soon as the element heats up and conversely the power will go down.
As a sanity check on this statement, do the same thing with light bulb or with a toaster and compare your calculations with the wattage ratings of those devices.
Charlie

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Nick -
This thread is quickly turning into a pissing match about who has the most knowledge of heating elements underwater.
Soon, people are going to be called out for spelling and typo's.
You have a chance to save us all, if you act quickly!
Are you keepin it, or shipping it back?
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Nick wrote:

If you got a good price on the unit then consider using an auto transformer to buck the voltage down to 208. You have to way the cost of installing the auto transformer against the added cost of switching to a 240 volt unit. -- Tom H
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