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Thread: 240V electric water heater on 120v circuit

  1. #1
    DIY Junior Member miscmail1560's Avatar
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    Default 240V electric water heater on 120v circuit

    I had to replace my electric hot water heater a few days ago because the dip tube was disintegrating. It was 14 years old, so I felt it was time for a replacement. The plumber came out and replaced it with a comparable 50-gal electric water heater. Later that evening, I discovered that we were not getting enough hot water. I called the plumber back out. He determined that the power input into the hot water heater was only 120V, not 240V. The original HWH was 240V, and it met our needs. My questions are:
    1. Are there any 50-gallon hot water heaters that are 120v?
    2. Can a 240v hot water heater run on 120v?

    I am selling this house soon, so I don't really care about long-term efficiency. I want to minimize my current expenditure, but I don't want to end up with something that will fail a house inspection.
    Any advice will be greatly appreciated.

  2. #2
    In the Trades Gary Swart's Avatar
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    You apparently had a 120v water heater, so the answer to #1 is yes. You now have a water heater that requires 240v, and as you have found it doesn't work too well. My advice is to run a 240v circuit. It's hard to say how difficult this would be, often when a water heater is in a basement and the breaker box is down there also, it's really quite simple. I'm surprised a plumber would not have recognized the problem when he did the installation. Perhaps you had a handyman instead of a plumber?

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    1) I SERIOUSLY doubt it!

    2) NO.

    I would check the circuit run to the heater. Tell us what size and type wire it is and what breaker it is on.

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    DIY Senior Member Mike Swearingen's Avatar
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    miscmail1560,
    If your water heater circuit is 240v, it should be with 10/2-with-ground wiring from a 30 amp double breaker.
    How did that plumber test the voltage? At the circuit wiring connection or at the elements?
    Did he completely fill the water heater before turning the power back on?
    Is the temperature set as high as the old heater?
    Mike

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    In the Trades Bob NH's Avatar
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    You can't use a 120 Volt circuit to get the required energy into a 240 Volt heater. I suspect that the plumber didn't get it hooked up correctly.

    Almost all standard heaters use two elements, each 4500 Watts, that are controlled so that only one is on at the same time. If the top temperature is low then the top element has priority. If the top temperature is OK then the control switch sends the power to the lower temperature control.

    You need someone who has knowledge and a meter to diagnose the problem. If the plumber knew what he was doing he would have done that and he would not have installed a 240 Volt heater on a 120 Volt circuit. A 120 Volt circuit will provide only 1/4 of the heating power of a 240 Volt circuit, which would cause you to have insufficient hot water.

    SOLUTION:
    If the wires are 10/2 with ground as should be the case with almost any heater, then they can be connected to a 30 Amp 2-pole breaker and connected to the heater. That should be done only by someone who knows what they are doing.

    The heating elements should be checked to be sure that the plumber didn't damage anything in the process. However, a professional plumber should know enough to put water in the heater before turning it on. If he accidently burned out an element by not putting water in first, he may be now blaming the problem on a "120 Volt circuit" to avoid admitting his error.
    Last edited by Bob NH; 11-26-2007 at 05:45 AM.

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    Plumber Cass's Avatar
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    Is the breaker going to the heater a 2 pole breaker (fat one) or is it a single pole breaker (skinney one)?

  7. #7
    Plumber jimbo's Avatar
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    You can run a 240 WH on 120 . You will get one fourth the power. If it is a 4500 watt heater, you will have 1125 watts, about the same as you coffee maker. It will take hours for it to heat the tank. Once it is hot, you have hot water available, but when you use it, it will take hours to heat back up again.

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by jimbo View Post
    You can run a 240 WH on 120 . You will get one fourth the power. If it is a 4500 watt heater, you will have 1125 watts, about the same as you coffee maker. It will take hours for it to heat the tank. Once it is hot, you have hot water available, but when you use it, it will take hours to heat back up again.
    But the bottom line is you will have an installation that is highly "code illegal".

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    In the Trades Bob NH's Avatar
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    A 2-wire + ground cable can be used for water heater if:
    1. It is 10/2 with ground, which is required to carry the Amps, and
    2. It is properly connected at the panel to a 30 Amp 2-pole breaker.

    If a new water heater was hooked up to 120 Volts by a plumber, and the problem was not explained to the homeowner so the homeowner could get the proper circuit connection made (assuming that the plumber couldn't/wouldn't do it), then the plumber is a dunce or a fraud.

    I still wonder if the plumber might not have screwed up the installation and done some damage, else there would be no reason not to tell the homeowner about the problem at the time of installation.

    Someone who is even marginally competent in electrical work, which a plumber who is installing electric water heaters should be, should know how to do the job correctly or at least identify the issue so the homeowner could get it done.

  10. #10
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Bob NH View Post
    Someone who is even marginally competent in electrical work, which a plumber who is installing electric water heaters should be, should know how to do the job correctly or at least identify the issue so the homeowner could get it done.
    Hear Hear!!

  11. #11
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Quote Originally Posted by Speedy Petey View Post
    But the bottom line is you will have an installation that is highly "code illegal".
    Why? If the current draw is within the ampacity of the circuit, I doubt NFPA would care about the WH's recovery time. (Disclaimer: I haven't looked in the Code to see if in fact they do care .)

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    Moderator & Master Plumber hj's Avatar
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    Default heater

    The first thing to check is whether the circuit is 120v because it was installed that way, or whether it has some defect preventing it from getting 240v. Once that is determined, then correcting the problem may be simple. There are no standard 120v 50 gallon heaters, they are special order models. When I turn on the circuit breaker, I check the speed of the meter's rotating plate. With 120v it would rotate slowly when the heater was activated.

  13. #13
    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by Mikey View Post
    Why? If the current draw is within the ampacity of the circuit, I doubt NFPA would care about the WH's recovery time. (Disclaimer: I haven't looked in the Code to see if in fact they do care .)
    110.3 Examination, Identification, Installation, and Use of Equipment
    (B) Installation and Use
    Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.


    Installing a 240v heater on a 120v circuit is most definitely NOT code legal. Nor is it a smart thing to do.

  14. #14
    DIY Junior Member miscmail1560's Avatar
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    Default The rest of the story

    First of all, I want to thank each of you for your input on this issue. I am thoroughly impressed with your willingness to share your ideas and thoughts about this with me.

    I have learned a lot about this issue since I started with this a few days ago. I will answer your questions, then will give you the final chapter.

    I sketched a couple of diagrams to show my setup. There is an old one, which shows the original installation, and a new one that shows how it is now after the electrician finished.

    There was a single pole 20A breaker for the hot water heater. The wire between that breaker and the HWH is 12 ga. The disconnect appears to be a dual pole switch.
    When the electrician finished, he had replaced the single pole switch with a dual pole switch that is rated at 20A.

    So, what happened.....

    First off, no one can determine why it was installed this way. My suspicion is that one set of contractors assumed that the heater would be gas, and another thought it would be electric. For some reason, they did not verify the voltage when they hooked up the hot water heater. Unfortunately the first owner did not notice a problem, nor did we.

    I had an electrician come out today to fix the wiring issue. I was fully prepared for the replacement of the wiring. He told me the setup, then stated that the amperage draw from the hot water heater would be below the maximum allowed for the 12 gauge wire. He shifted another breaker down the panel and put in a two pole breaker with a rating of 20 amps. This supplied 240v to the hot water heater, and the amperage in one leg measured 18.5 amps and 19 amps in the other. His assumption was that the hot water is not under continuous load, so there should not be a problem with the arrangement. He also did not find any other failure in the wiring.

    I obviously have a few concerns about this arrangement:
    1. I am concerned because the strong recommendation from you has been to use 10 gauge wire. Of course, my primary concern is that there could be a fire based on this setup. He said that 12 gauge can carry up to 25 amps without failure, so that makes me feel a little better.
    2. My other concern is that the amperages are high enough that we could trip the circuit breaker frequently. That could become extremely inconvenient.
    3. I am also concerned that this will be an issue when I sell the house. I certainly do not want a fire while I am here, but I also do not want to have a future tenant to have a fire. I don't need that on my conscience and I do not want the legal headaches that could be involved.
    Thank you all again for your valuable input on this. Your information helped me make the right decision to get an electrician involved. Having written my response, I am now concerned that I should have been more forceful in questioning the final solution.
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  15. #15

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    Basically, he lied to you when he said 12 can carry 25 amps. Technically, it can, but not in this installation. 20 amps the the max.

    I don't think you'll have a possibility of a fire in this installation, but I would still have used 10ga on a 30amp breaker. 4500 watts at 240 volts is 18.75 amps, which makes 12ga marginal.
    Just my 2 worth.

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