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Old 01-24-2011, 07:56 AM   #1
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I relaced my water heater with a 240 volt like the one that was in there and come to find out i have 208 volt. What will happen and will this work?

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Old 01-24-2011, 09:02 AM   #2
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At least on the straight resistance side, the difference will be that the resistance elements produce 208/240 or about 13 percent less power than they would if you had 240 volts, so it will take longer to heat the water. As for the controls, best check to make sure they are rated to operate at 208 volts.

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Old 01-24-2011, 11:37 AM   #3
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Ayuh,... Call the Power Company, 'n find out Why you have Low Voltage....
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Old 01-24-2011, 11:49 AM   #4
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thats normally a 3 phase reading, is this a commercial building?
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Old 01-24-2011, 11:51 AM   #5
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It will work, but you may have problem with the breaker if the circuit is sized close to the operating amps, as you amps will increase.

Standard acceptable voltage diviation is +-5% 208+5%=218.4V compared to 240-5%=218.4V

The problem may be when the voltage drops below 208 Volts, say during the summer when there is a high demand.
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Old 01-24-2011, 12:36 PM   #6
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Jack, you misunderstand current versus voltage. The relationship between voltage and current is V/I = R, where V is the voltage, I is the current, and R is the resistance. Since resistance is essentially constant over the range of voltage commonly available, the ratio of voltage to current is constant. Therefore, if voltage drops from 240 to 208 for any reason, the current will also drop proportionately, current DOES NOT increase.

Therefore, if the water heater draws 20A at 240 volts, it will draw 17.3A at 208 volts, and a 20A breaker would be fine. The with low voltage is that the power is reduced, since power equals V X I, and if the voltage goes down and the amperage goes down, the power goes down as well.

As previously noted, 208 volts is typical of a three phase connection, not a split phase connection as is typical in the US. The OPS did not state what country he was in, so perhaps 208V is common in their country.
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Old 01-24-2011, 12:44 PM   #7
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Thanks for the correction, Daniel, forgetting that the resistance on a water heater is constant. Here is an article on voltages in the US you may find interesting.

"There is no universal standard here unfortunately.

The US electrical grid is composed of a lot of smaller grids that were connected together, but each individual power utility may or may not have the same voltage standards as their neighbor.

Even within a utility's service area, there are new services and old services (called "legacy") that cannot change until the connected users are demolished.

The only thing that is now relatively universal is that we are all 60Hz (with the exception of a few islands of 25Hz still in use).

So here are all of the 3 phase low voltage "standards" I am aware of:

120Y208 (4 wire); New standard for commercial and light industrial

208V Delta (3 wire); rare legacy

240V Delta (3 wire); mostly legacy but still some occasional new services

120/240V Delta with a center tap between A and C phases for 120V (4 wire "stinger leg"); still provided for small commercial users with >10%

120V 1 phase loads

440V Delta (3 wire); legacy

480V Delta (3 wire); mostly legacy but some new rural services are still done this way as Open Delta or Corner Grounded Delta

277Y480V (4 wire); new standard for industrial service

575V Delta (3 wire); rare legacy, but found in the South East in textile mills and the North West in some Lumber Mills.
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Old 01-24-2011, 08:33 PM   #8
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The current draw cannot be easily predicted because at 208 volts the heating elements will be at a lower temperature compared with 220 volts and the resistance will be a little less because of this.

But generally the current consumption at 208 volts will be a little less.

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Last edited by AllanJ; 01-24-2011 at 08:41 PM.
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