Help with electric heater connection!!

Discussion in 'Electrical Forum discussion & Blog' started by the_bosun_mate, Nov 27, 2008.

  1. the_bosun_mate

    the_bosun_mate New Member

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    3
    I am installing a Dimplex EWA40c31 4000w/240v Surface mount electrical heater. In my service box I have a empty double 20amp circut breaker. Can I use the double 20AMP service breaker or do I have to upgrade to a double 30AMP breaker. The basic electricity book (its old) that I have, says that you can use 20AMPS up to 4800W??? also plan on using #10 wire any problems??
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If I remember right, a continuous load shouldn't exceed 80% of the breaker, so you'd need a 30A circuit (you're close, but over that). See what the pros say as they've got access to the code book, or know it for sure.
  3. Igor

    Igor New Member

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    Quite correct, and fixed electric heaters are considered to be a continuous load.

    The NEC is available online for free (although you have to register) viewing at the NFPA.org website. Article 424 covers Fixed Electric Space-Heating Equipment. 220.19(A)(1) & 220.20(A) deal with continuous loads. Try this link and see if it works: Online NEC
  4. leejosepho

    leejosepho DIY scratch-pad engineer

    With your #10 (30-amp) wire being plenty heavy enough and with your load being 80% of only 20.83 amps, I would at least try the 20-amp breaker before buying a 30 ... and I would check the breaker after an hour or so to see whether it is running hot ... and if it is, I would go ahead and get a 30 to avoid having to deal with a breaker possibly tripping whenever the voltage might be a bit low.
  5. Redwood

    Redwood Master Plumber

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    Redwood just shakes his head and wonders why some people post what they do...:confused:
  6. hj

    hj Moderator & Master Plumber Staff Member

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    heater

    What, and why, is the question being asked? You are apparently installing a new #10 circuit, so why would you then try to low ball and reuse the 20 amp breaker instead of installing the correct 30 amp one. We would have a real problem if you had #12 wire and wanted to upgrade to a 30 amp breaker, but that does not seem to be the case here.
  7. Redwood

    Redwood Master Plumber

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    It's funny but I don't really like to try things that may not work.:cool:
    For some reason the NEC says that the c/b must be a certain percentage under its full load rating...
    Could it be that is what makes it function reliably?:eek:
    The fact that it may not trip with slightly over its rated 20 amps is not worth considering!
    Do it right! Do it once! Don't be a hack!
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Please don't suggest people do things that don't meet code! If you choose to do it yourself, I hope you don't live near me! In this case, for probably less than $10, it's easy to do it right and never have any problems. Burning up a breaker could damage the bus bar and create other problems. Keep in mind also that if the voltage drops to 220VAC instead of 240, you're at 90%, and during a brownout, it could even get higher. They write the code for a reason...
  9. leejosepho

    leejosepho DIY scratch-pad engineer

    Has the thought of asking crossed your mind?

    In my own actual experience, and however limited that might be, resistance heaters do not always draw their stated wattage. So, it is at least possible the load in question is actually *not* more than 80% of 20 amps ... and that would mean everything might just be fine without having to spend the money for a 30-amp breaker that at least possibly *could* help guarantee a bit of overheating somewhere if the heater or thermostat might somehow malfunction. Lighter-gauge wire would definitely be a bad idea, but as far as I know, and please correct me here if I am wrong: A borderline breaker would at worst be a nuisance when it trips.
  10. jimbo

    jimbo Plumber

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    If the voltage drops, the fixed resistance of a heating element does not change, so the circuit current goes down....not up.
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
    New England
    My typing gets ahead of my brain sometimes...

    More used to electronic circuits that pull more current to do their thing when the voltage drops...

    Regardless, do it to code!
  12. leejosepho

    leejosepho DIY scratch-pad engineer

    Oops, I too was wrong about that ... and my guess about the heater possibly not running at its stated wattage was also bad. I have a 4000-watt heater I plan to install in my workshop, and I just went out and measured its resistance ... and that leaves me with these numbers in my own situation:

    240 volts
    13.2 ohms
    4363.64 watts
    18.18 amps (80% of 22.725)

    So yes, a 30-amp breaker is the way to go!
  13. Redwood

    Redwood Master Plumber

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    No Lee it hasn't!

    I'm heading down to McDees I'm Having a Big Hack Attack!
  14. jar546

    jar546 In the Trades

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    USA

    Ignor that post.

    In a nutshell without showing calculations, you will need:

    10awg copper wire, such as NM 10/2 with ground.
    25A double pole breaker.

    The rating for that heater is 4000W @ 240vac so 16.6A exceeds 80% of a 20A breaker. You must be upsized to the next larger breaker which is 25A as listed in the NEC.

    Do not place it in contact with combustibles or below a wall outlet.
  15. jwelectric

    jwelectric Electrical Contractor/Instructor

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    2,561
    Location:
    North Carolina
    I was installing a wall mounted electric heater in my house and the inspector told me that the breaker was too small.

    I stopped the inspector in the middle of the driveway and told him that the small breaker would only drive me crazy running back and forth resetting it.

    The inspector kept telling me that he was not going to sign off on my work until I changed everything and brought it up to code standards.

    I kept telling the inspector not to worry that I didn’t have nothing to do but run and reset the breaker each time it tripped.

    While we were sitting in the middle of the driveway arguing back and forth the fire truck couldn’t get in to put out the fire and my house burnt to the ground.

    Moral of this story is just don’t call the damn inspector as he will not budge and the fire trucks can’t get to the fire and you will lose your house.

    On a side note, I am so poor that I had to do the work myself and due to the lack of money I didn’t have any insurance on my house. Now we are a ward of the state and all of them law abiding fools have to support me and my family so maybe things worked out well after all.

    I vote to abolish all these codes and just let us do as we damn please. All in favor say aye!
    Last edited by a moderator: Nov 28, 2008
  16. leejosepho

    leejosepho DIY scratch-pad engineer

    Honest question: Would someone please explain how a weak or undersized breaker could start a fire?

    I do know heavily-loaded breakers can get hot, and I also know it usually takes a load quite a bit above their stated rating to actually trip them.

    Is that the combination that can cause a breaker to actually burn or to ignite something else?
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
    North Carolina
    You answered your own question didn't you?

    "I do know heavily-loaded breakers can get hot,"
  18. leejosepho

    leejosepho DIY scratch-pad engineer

    Well, I do not actually know, or I do not yet fully understand, so I ask.

    A typical breaker in good condition will actually carry a load greater than its stated capacity without tripping, but can a typical breaker in good condition actually carry such a load to the point of either catching fire or starting one?

    I would like to believe breaker manufacturers design and make the typical breaker so that it *will* trip before any overload it might be carrying can actually cause it to self-destruct or burn something else. Otherwise, it would be too convenient for a manufacturer to try to hide behind the NEC by saying a given breaker that either caught or caused a fire should not have been used in the first place. And of course, yes, there must be some kind of "code behind the code" that must be met in relation to stated ratings and actual trip levels.
    Last edited: Nov 28, 2008
  19. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,561
    Location:
    North Carolina
    A breaker that is overloaded to the point of causing excessive heat can most certainly start a fire.

    There are many reported cases where breakers of all manufacturers have failed to open and have started fires in many numerous ways.

    The heat can be transferred to the wooden studs or finished wall in the event of wood paneling and start a fire. The flash point of wood is around 575 degrees Fahrenheit.
    Should the breaker start arcing at the bus bar then it could easily start a fire.

    If the breaker is getting hot and the connections are all good and tight then the conductor itself is getting hot. Here there is more than just the wood to consider for starting a fire. Some common house dusts can have a flash point as low as 150 degrees Fahrenheit and can drop even lower if cooking oils or other oils have settled into the dust.

    Should the panel be installed in an area such as closets where things like garments and apparel or even paper and cardboard boxes are stored then the issue is even greater.

    In the event of a fault a breaker will let through its listed AIC current which for most residential panels will be 10,000 amps, before damage occurs to the device.
    Should the device fail temperatures can raise to as much as 32,000 degrees Fahrenheit in a matter of a fraction of a second. This would be more than enough to start a fire wouldn’t you think?

    The question should be will the breaker get that hot before tripping. Most breakers will carry for a period of 20 seconds six times their rating. In other words a 15 amp breaker will let through 90 amps for about 20 seconds. This equates to about 10,800 watts or about 36,700 BTUs. This is enough heat to easily start a fire.
    Couple this overloaded circuit breaker and a fault and we have spontaneous combustion of any ignitable material in the area.

    One thing to keep in mind is that current in any circuit be it AC or DC rises at an exponential rate. This rate divided into five time constants each will rise at a rate of 63.2% each time. This is also true for current flowing through the human body.

    So the simple answer to your question it is very possible for a circuit that is overloaded to start a fire. This is the reason for the codes and the requirement in most areas for the installer to first obtain a license before attempting an installation. It is also the reason for so many who know and understand the theory of current flow to be so hard on the Do-it-yourselfer trying his/her best to do something they know little or nothing about.

    Electricity is a lot more in depth than white to white and black to black. Electrical circuits are one of the few things in this world that can be installed completely incorrect and still work. Circuits can be installed in a manner that they are nothing short of a death trap yet they still function.
  20. jar546

    jar546 In the Trades

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    Just follow post #14 and you can't go wrong.
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