Wiring requirements for 4500W dual-element

Discussion in 'Water Heater Forum, Tanks' started by Tom Wiedmaier, May 25, 2015.

  1. Tom Wiedmaier

    Tom Wiedmaier New Member

    Joined:
    May 25, 2015
    Location:
    California
    I purchased my older home 2-years ago. We have been having some issues concerning running out of hot water. I purchase a tester to check the elements and the thermostats. All appears to test out OK. In the process, I read in several places online that 10-2 wiring with a double 30A breakers are needed for a heater with 4500 watt dual elements. My heater has 12-2 wiring with a double 20A breaker.

    So this is my question:
    Does having the lighter wiring create a danger? It seems that the 20A breaker should protect the 12-2 wiring from overheating. Won't the breaker "pop" before allowing the circuit to overload? Doesn't the 20A circuit simply limit how much current is available to the water heater. It may be asking for more but it just isn't available? Hypothetically, if a person had a 1A circuit feeding an appliance rated for 30A it would never receive more that 1 amp, the breaker would immediately trip. Currently my water heater functions without tripping the breaker. Is it a wrong assumption that it is operating within the capability of the 20A circuit?

    Thanks for any help,
    Tom
     
  2. Tom Wiedmaier

    Tom Wiedmaier New Member

    Joined:
    May 25, 2015
    Location:
    California
    I forgot to add this bit of information. The internal wiring connecting the thermostats and elements
    appears to be 12 gauge. I visually compared it to a piece of 12-2 that I had. I didn't measure it, I would
    assume that 10 gauge should be obviously larger. If this is the case, wouldn't upgrading the circuit to 30A
    actually create a possibility the the internal wiring could overheat?

    Thanks again,
    Tom
     
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  4. JerryR

    JerryR Active Member

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    Jul 27, 2011
    Location:
    Florida
    My current Local code requires #10 wire and 25 amp breaker

    A 4500 watt element draws 18.75 amps at 240 volts. Code requires wire sized at 125% of continuous load. 18.75 x 1.25= 23.5 Amps.

    My previous local county building dept allowed a 30 amp breaker w/#10 wire for a 4500 element WH. My current county building dept requires #10 with the breaker to be 25 amp.

    Yes, the wire size in the WH interior is usually #12. That is because it was UL approved as such due to short wire lengths and type of wire used.
     
    Last edited: May 26, 2015
  5. JerryR

    JerryR Active Member

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    Jul 27, 2011
    Location:
    Florida
    I answered the wiring question but not the question of running out of hot water.

    How large is the tank?
    Where do you live (how cold is the cold water)
    How long does it take to run out of hot water? # of showers, won't fill the tub? Etc.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    The CB is dumb...exceed its rating and it will open. The ultimate limiting factor. It will NOT throttle the current to the device, it's either on, or its off. The breaker relates to the wire size such that the wire can handle whatever the breaker can supply (when it is installed per code).
     
  7. JerryR

    JerryR Active Member

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    Jul 27, 2011
    Location:
    Florida
    The other issue using 12 ga wire is that you won't be getting full voltage at the elements when they are active. If you factor in the resistance of the#12 wire and the resistance of the heating element I would guess that the elements are only getting close to 220v when active. The rest is wasted energy warming up the #12 wire. Of course the longer the wire run the worse the voltage drop.
     
  8. WorthFlorida

    WorthFlorida The wife is still training me.

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    Retired
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    Orlando, Florida
    It doubtful that the 12 gauge wire is dropping the voltage at all. If it was you would feel heat off the wires that is feeding the water heater. Your 20 amp 220-240 volt breaker is really two 20 amp breakers in parallel. As above the maximum current draw is 18.75 amps, that is 9.375 amps per leg. Under the circuit breaker rating but you may not have a full 240 volt supply. It could be 220 volt, therefore, the current draw will be less that means lower power and less heat but you'll never notice the performance difference

    To be sure put a voltmeter in a wall outlet and measure the voltage, it be anywhere from 110 volt to 125 volt. Then place the voltmeter across the upper thermostat of the water heater. Usually the top two connections. Here you'll read your 220 (sort of speak) voltage. Anywhere from 208 to 240 voltage will be normal.

    Here is a diagram Your problem is one of the heating elements is bad or the one of the two thermostat is bad. Only one heating element is on at a time and the switch over from one element to the other is done by the upper thermostat.

    Lastly, your hot water demand is exceeding the capacity the water heater.

    https://www.google.com/search?q=electric water heater thermostat wiring diagram&espv=2&biw=1600&bih=775&tbm=isch&imgil=3gjOKIV8jcIZnM%3A%3Bxi2-0iV0CaZVLM%3Bhttp%253A%252F%252Fwaterheatertimer.org%252FHow-to-wire-water-heater-thermostats.html&source=iu&pf=m&fir=3gjOKIV8jcIZnM%3A%2Cxi2-0iV0CaZVLM%2C_&usg=__JFPn14v_ktr4-Sj1v8whQJYWa0M=&dpr=1&ved=0CD8Qyjc&ei=8A5lVfz9KKPksATQpYDAAQ#imgrc=3gjOKIV8jcIZnM%3A;xi2-0iV0CaZVLM;http%3A%2F%2Fwaterheatertimer.org%2Fimages%2FWater-heater-wiring-w-num10.jpg;http%3A%2F%2Fwaterheatertimer.org%2FHow-to-wire-water-heater-thermostats.html;952;1799


    Here is a more detailed diagram of a water heater wiring.
    https://www.google.com/search?q=electric water heater thermostat wiring diagram&espv=2&biw=1600&bih=775&tbm=isch&imgil=3gjOKIV8jcIZnM%3A%3Bxi2-0iV0CaZVLM%3Bhttp%253A%252F%252Fwaterheatertimer.org%252FHow-to-wire-water-heater-thermostats.html&source=iu&pf=m&fir=3gjOKIV8jcIZnM%3A%2Cxi2-0iV0CaZVLM%2C_&usg=__JFPn14v_ktr4-Sj1v8whQJYWa0M=&dpr=1&ved=0CD8Qyjc&ei=8A5lVfz9KKPksATQpYDAAQ#imgrc=0BDr-J5ULmCK3M%3A;xi2-0iV0CaZVLM;http%3A%2F%2Fwaterheatertimer.org%2Fimages%2Fwire%2520thermostats.jpg;http%3A%2F%2Fwaterheatertimer.org%2FHow-to-wire-water-heater-thermostats.html;480;503
     
    Last edited: May 27, 2015
  9. JerryR

    JerryR Active Member

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    Jul 27, 2011
    Location:
    Florida
    A couple of points

    A 20 amp double pole breaker is actually two 20 amp single pole breakers tied together and a 30 amp double poke is two 30 amp breakers tied together. Each leg carries full current. If you put an amp-probe on one leg you will measure full current.

    P/E = I
    Watts/Voltage = Current
    4500/240 = 18.75 amps

    I have seen 240 volt drop to 180 volt on 20 amp sole use circuit on a copier that was rated at 16 amps, once the copier was fired up. That circuit was wired with #12 but it was significant distance from breaker panel. That distance caused the voltage drop due to the resistance of the wire at the long run.

    Second.
    The upper thermostat is the "master" thermostat. When water in the top of the water heater gets cold it switches only one leg to the upper element. The other leg always has power.

    Once the upper thermostat senses that temperature setting has been reached it switches that leg to the lower thermostat. if the upper element burns out you will get COLD water all the time since the thermostat never senses it reached temp setting.

    If lower element burns out or the lower thermostat remains open then you get hot water for very limited time.
     
    Last edited: May 26, 2015
  10. WorthFlorida

    WorthFlorida The wife is still training me.

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    Orlando, Florida
    Hi JerryR, I mentioned that a voltage drop (assuming all connections are good) is probably not the problem since most homes the water heater and breaker panel are near each other. Even if the two are at opposite ends of the home it may only be fifty feet or wire.

    At this URL there is a nice chart and a voltage drop calculator further down the page. I plugged in numbers for a 50 ft 12 awg wire at 240 with 18 amp draw. The drop is less than 3 volts.
    http://www.powerstream.com/Wire_Size.htm
     
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    A poor crimp or wire nut connection could easily increase the resistance of the whole wiring system, but as has been said more than once...that amount of current will create heat somewhere, and it shouldn't be too hard to locate.
     
  12. hj

    hj Master Plumber

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    Cave Creek, Arizona
    If the water heater asked for "more current and it was not available" the circuit breaker would trip because of overload. The wiring INSIDE the heater had absolutely NO BEARING of the wire size to the heater. They are two completely different situations. You are operating at the limit of the wiring, but that also has NO BEARING on why you do not have sufficient hot water. I would question HOW you tested the heater's circuitry, because, to be simplistic, it takes more than a light bulb with two wires attached to it.
     
  13. ballvalve

    ballvalve General Engineering Contractor

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    Location:
    northfork, california
    Our code calls for 10g copper and a 30a breaker to the WH. Seems like too large a breaker to me. But If its a short run, the 12g and the 20a breaker obviously operates the unit. You very likely have one element, likely the lower one burnt out. Or your switch is not sending power alternately as called for to the elements. I have had elements that were internally missing an inch or so of themselves, but did not trip the breaker or cause any extra amp draw. Still can't figure that one out. Pretty much have to put a clamp on ammeter on the feed to the element to see if its pulling power, and use an ohmmeter to see if its shorted or intact internally. For an awfully small amount of $, one can change the switches and elements and forgo the testing if able to do so. I will venture that MANY plumbers and even electricians are hard pressed to correctly test a water heater. Much easier to just say it's 15 years old and it's gonna blow any minute now.

    I have a 30 gallon electric water heater, cheapest made, that I added monster anode to, and rewired to have both 4500 elements on at the same time - it heats a huge house with radiant heat. I laugh when I see these radiant guys selling flow thru 10,000 watt heaters for $1500+ . They have no place for the calcium that builds up on the elements to drop down into for later removal, and the specialized elements are 20x the cost of the dime store 4500w unit. And gas water heaters? really, we are in the dark ages with their design and efficiency. I suppose with the 'free' natural gas now available in the USA, its not an issue for the masses.
     
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
    Location:
    New England
    BTU's per $ of energy, gas almost always beats out electricity. Once you have it installed, the energy use costs easily favor gas, and usually can recoup the extra installation costs, even with the somewhat higher standby losses. The newest ones are required to be more efficient, which helps, too. You'll typically have faster recovery rates and higher first hour delivery with gas unless you've got a commercial electric WH and large elements. If you had to pay for running new gas service in, the price of energy may never recoup the savings verses using electricity, but it all depends. Right now, where available, NG is a bargain.
     
  15. ballvalve

    ballvalve General Engineering Contractor

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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    We are on LPG, so basically screwed. Close to Electric cost with all the hassle.
     
  16. Kayleigh Bohannan

    Kayleigh Bohannan New Member

    Joined:
    Jun 16, 2015
    Location:
    South Carolina
    If he is in California, his incoming water temperature is anywhere between 57 and 72 degrees (roughly). So to get a shower at 105 degrees (average shower temp), he will need anywhere between a 48 and 33 degree temp rise. At 2 gallons per minute (standard for a shower) he will need anywhere from 14.05 and 9.66 Kilowatts to obtain that (roughly). Tom, if you click here http://myheatworks.com/technology.php you will find a calculator that will tell you exactly what you need to keep your shower producing the exact amount of hot water you want/need without running out.

    With the new DOE regulations in effect since April 16, 2015, he is going to have to replace his tank anyway and he won't be able to get the same size tank. The new standard effectively prohibits 55 gallon or greater tank water heaters. Homeowners who want these large capacity units will have to invest double or triple in a heat pump driven design that meets DOE efficiency standards. This will also effect your wallets as these new energy efficient systems are larger (need more space, won't fit in old space). The Heatworks MODEL 1 is different. It is roughly the size of a football and meets all the new DOE requirements. It is a small tankless electric water heater with NO heating element, and, unlike any other tank or tankless unit, utilizes graphite electrodes instead. Short explanation, no scaling or plating, no super heated part waiting to fail (or not give you as much hot water as you need), and instant, safe and INFINITE hot water. In the interest of full disclosure, I do work for the company that invented the Heatworks MODEL 1 tankless water heater, however I would love to help any of you in the forum, especially Tom, figure out your water heater needs. There is more info about the Heatworks MODEL 1 at our website found at http://myheatworks.com if you click here http://myheatworks.com/technology.php it will take you to a page that calculates how many MODEL 1's you need for your demand and shows a ground water temp map so you can quickly figure out what you need. thanks!
     
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