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10kw electric garage heater

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Ecbh
Ecbh Member Posts: 1
A customer purchased a Dyna-Glo 10kw electric garage heater with two stage power with max 240v at 41.66amps. The manual specifies a 50amp max breaker. Following NEC rules on a continuous load would require a 125% increase in infrastructure (80% rule), requiring a 52.075amp allowance. 

They have already installed 6/2 NM-B which is only rated for 55amps which they don’t make in Type CH breakers. This pushes it to a 60amp breaker which a 75*C rated wire would handle, but not 60*C (NM-B). 

Called manufacturer and they have not gotten the question before and waiting on response. Do I follow manual or NEC and try to plead the case for 50amp during inspection? Other suggestions?
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Comments

  • mattmia2
    mattmia2 Member Posts: 9,738
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    The NEC allows you to use the next higher standard size fuse or circuit breaker.
  • ChrisJ
    ChrisJ Member Posts: 15,774
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    I'm confused.
    I understand the 80% rule.

    However, the manufacturer of the appliance has already said to use a 50A breaker maximum.

    What's the problem?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    rick in Alaska
  • motoguy128
    motoguy128 Member Posts: 393
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    I’m thinking the circuit feeding it needs to follow the 80% rule as it’s running a longer distance to feed it, possiibly in a hot attic, etc.  but the mfg max fuse size must be followed due to small internal wiring used.  

    You run in to similar scenarios regularly with AC condensers.  FLA is really close to MFS.  
  • ChrisJ
    ChrisJ Member Posts: 15,774
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    That's pretty much the end of it.
    Don't over complicate things.


    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • ratio
    ratio Member Posts: 3,649
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    Size the breaker per the mfgr's nameplate. This is Code, no wiggle room, no 80%. Barring the nameplate specifing a wire size or an MCA, size the feeders per the NEC table for the permitted wiring method. 50 amp breaker & it sounds like the 6/2 will be fine.

    The theory is that the mfgr has done all the calcs for you already, having intimate knowledge of their product.

  • PC7060
    PC7060 Member Posts: 1,173
    edited December 2020
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    ChrisJ said:

    ....the manufacturer of the appliance has already said to use a 50A breaker maximum.
    What's the problem?

    What @ChrisJ said.
    Always follow Manufactures guidance on UL approved devices.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    50A breaker per manufacturer, 6awg copper is absolutely fine for a 42A load continuously. 

    I see where you are coming from, if you are in doubt, ask the inspector. This is really ni different than an electric range, or welder. Even though welders get their own NEC article. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    Remember that the specified breaker is to protect the appliance. If the manufacturer says 50 amps, 50 amps it is. Now... you may well want to (and might be well advised to) use a larger gauge wire to go from the breaker box to the appliance -- no harm in that. Particularly where it is a longer run and may be in a hot space (wire capacity is based on two factors: voltage drop at operating or breaker current, and temperature rise at the same current).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    @Ecbh

    You explained the problem perfectly. Check and see if this heater is UL listed.

    I agree follow the name plate with the breaker size and wire size.

    But it does not sound right to me. The #6 is ok for the load 41.6 am load x 1.25= 52 amps. And one would assume the 80% breaker rule should be followed. You probably can go to a 60 am breaker as you are allowed to size up if the wire and breaker size don't match up in some cases. Would have to look it up.

    Amp it out when it's wired as well and see what it draws. That breaker will be hot if it runs a lot.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    @Solid_Fuel_Man

    Ranges are usually not considered a continuous load unless it was a commercial kitchen. Welders only have to be wired to there name plate rating x the duty cycle of the welder. Everything in HVAC is considered a continuous load
  • mattmia2
    mattmia2 Member Posts: 9,738
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    Ranges do not have all the burners and bake elements on full simultaneously for very long unless you are trying to start a fire of another sort so they are allowed a demand factor.
  • ChrisJ
    ChrisJ Member Posts: 15,774
    edited December 2020
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    @Ecbh You explained the problem perfectly. Check and see if this heater is UL listed. I agree follow the name plate with the breaker size and wire size. But it does not sound right to me. The #6 is ok for the load 41.6 am load x 1.25= 52 amps. And one would assume the 80% breaker rule should be followed. You probably can go to a 60 am breaker as you are allowed to size up if the wire and breaker size don't match up in some cases. Would have to look it up. Amp it out when it's wired as well and see what it draws. That breaker will be hot if it runs a lot.
    The appliance says right in the instructions 50A or less.

    Why do you feel it's ok to go to a 60? 

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    Yes, I'm aware of 3 hours or more and the 80% rule for all electric heat. However, if the nameplate says max allowable overcurrent protection is 50A, then any inspector around here would only allow a 50A breaker. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • ratio
    ratio Member Posts: 3,649
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    If it's stamped max 50A, no inspector anywhere will allow a larger breaker on it. Nor will they allow a wire smaller than specified on the nameplate MCA, if it exists. If they know what they're doing, I suppose; & don't make a mistake or miss anything. That happens.

    Go through the calculations for every individual piece in the appliance, apply all the deratings, verify all the sizing, etc. etc. etc. & you'll come up with the number on the nameplate.

    Solid_Fuel_Man
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    6awg Romex (type NM-B) does not fall under the small conductor rule of only using the 60C colum. Therefore unless its buried in thermal insulation....but even in the 60C colum #6 copper in a cable, raceway, etc is good for 55A. You would be allowed to use the 75C column for derating purposes and it's good for 65A. 

    Obviously distance to the heater from the panel is a factor, but in the vast majority or residential dwellings wire distance isnt a factor so I omitted it for this thread. 

    50A breaker on a 6awg copper Romex is what is code compliant. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    ChrisJ
  • Matt_67
    Matt_67 Member Posts: 288
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    Seems like a 60 amp breaker and 50 amp fuses in a disconnect would meet both requirements.
  • mattmia2
    mattmia2 Member Posts: 9,738
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    So what i don't understand is the rating of the breaker itself. Can it handle over 80% continuously without degrading? Is that part of the acr rating?
  • ChrisJ
    ChrisJ Member Posts: 15,774
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    mattmia2 said:

    So what i don't understand is the rating of the breaker itself. Can it handle over 80% continuously without degrading? Is that part of the acr rating?

    Yes it can.
    But it may trip for no reason if the ambient is warm.

    That's why the 80% rule.

    I'm not an electrician, and I don't play one on tv.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • mattmia2
    mattmia2 Member Posts: 9,738
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    The lugs and the stab are the same for a range of ratings so I think that part is fine. my concern is the thermal element and the parts around it continuously being near the tripping temperature and that degrading the materials and the connections. The same thing applies to a fuse.
  • ChrisJ
    ChrisJ Member Posts: 15,774
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    mattmia2 said:

    The lugs and the stab are the same for a range of ratings so I think that part is fine. my concern is the thermal element and the parts around it continuously being near the tripping temperature and that degrading the materials and the connections. The same thing applies to a fuse.

    You would need to look up how modern magnetic circuit breakers work.

    That's beyond my knowledge.

    But I do know when an appliance says 50A or less circuit breaker, you use a 50A or less circuit breaker.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    A 50A breaker will not trip with 42A continuously. As a master sparky, I've seen many breakers (usually 20A) with 21+ amps on them, usually lighting. That get nice and warm, but dont trip. 

    I have several brands of thermal-magnetic breakers that I drilled the rivets out of. The bimetallic thermal part just bends until it releases an over center spring mechanism which holds the contacts closed. The magnetic part is a steel strip placed close to the current carrying element in the breaker. A bolted short creates huge lines of flux which draws the strip to release the same over center spring. 

    I've got several pictures of breakers well over loaded and not tripping. A nice linear load like a resistance heat is about as good as it gets. The wire size is what causes nuance tripping is too small of conductor or poor/loose connections at the breaker. This makes the lungs get hotter and then the bimetallic trips. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    ChrisJ
  • ratio
    ratio Member Posts: 3,649
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    It's my understanding that an HACR rated breaker may be run at 100% of it's rating. Nameplates often specify HACR breakers as well, so check & see if you are required to use one any way.
    mattmia2
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    Bottom line, folks -- the breaker must be sized to protect the fixed loads and wiring connected to it whichever is less, unless the fixed load itself has its own protection (e.g. a motor starter and controller). If the wiring requires a 50 amp breaker, but the fixed load requires less -- then less. If the wiring is sized for 100 amps but the fixed load requires 50, then 50.

    In your case, your fixed load asks for a 50 amp breaker. If your wiring can support 50 amps or more, then 50 amps it is.

    Now the size of the wiring is the greater of two: that required to take the amperage without overheating, and that required to take the amperage without excessive voltage drop. In most applications, you will find that the amperage governs, but in longer runs you may have to go to a larger wire size to keep the voltage drop within limits.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    @ChrisJ

    My post said to follow the MFG instructions as far as wire size and breaker size.

    But the code states that for any continuous load (and any HVAC equipment is always considered a continuous load) that a circuit breaker cannot be loaded to more than 80% of it's rating.

    So there MAY be an issue.

    That's why I asked if the equipment has UL approval. A lot of stuff coming in from overseas does not have UL approval. i don't know where this thing is made.

    Example:

    A customer bought a cord for a portable generator on Amazon.
    Looked like it was UL approved, said UL on it.

    But the UL was encircled by a triangle...it was a fraud. The correct UL symbol has a circle around it. it wasn't UL approved

    And their may be more to the story. We don't know if there are any controls or load shedding built into the equipment to cause it to draw less power (I doubt it).

    There are many instances in the code that allow going up on the circuit breaker size. One of them is #6 wire normally rated at 55 amps. In some instances the code will allow a 60 amp breaker because 55 amp breakers are not made. lots of electric ranges wire with #6 and a 60A breaker but they are not considered a Continuous load

    In this case without having more information the electrician has no choice but to follow the equip.ment mfg. nameplate.

    The code has different rules.

    Packaged equipment like this heater contains more than 1 load (heater element and fan etc, maybe a contactor or relay) in the case of multiple loads it is required of the mfg to size the wire MCA or minimum circuit amps and the breaker MOCP Maximum over current protection and put that information on the name plate.

    This hasn't always been true. Back in the 60s old rooftop units the nameplate didn't have this information only individual amperage's and the electrician had to figure it out. As you can imagine with multiple condenser fan motors indoor blower motor multiple compressors this cause a lot of issues and changes were made in the code

    This is different from a single motor or an electric baseboard heater. In those cases the electrician is responsible to size the wire and the breaker according to the amperage of the equipment but wire size and breaker size is not on the equipment name plate
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    This is the manual I found for this heater. DYNA GLO is made by GHB products. Sold on Amazon, Home Depot etc.

    If I have the correct manual (It's the only 10kw heater I found) it looks to me like it's calling for #6 wire and a 60 amp breaker
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    That's the way I read it too, @EBEBRATT-Ed

    Quite possible that while it is listed at a lower current draw in operation, being an electric resistance unit the initial draw -- before the elements heat up -- could be quite a bit higher.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    I believe it said that the "maximum" CB to be 60 amp.
    So the 50 amp would be fine to cover both bases, IMO.

    I think today most 2 pole CB's are HVACR rated.
    I think they are designed for the inrush current of motors, such as time delay fuses are.
    In the past they were special order, IIRC.
    Same I believe applies to "switching duty" where you use CB everyday to operate lights or loads. They too were special.
  • mattmia2
    mattmia2 Member Posts: 9,738
    edited December 2020
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    so i knew hacr was some additional standards that allowed the manufacturer of an appliance to know more of the characteristics of the breaker so they could specify a breaker for protection of that equipment but I didn't know exactly what that entailed. It appears from @ratio 's comment that one of those things is that it is rated for 100% continuous load. That is the piece we were missing.

  • ChrisJ
    ChrisJ Member Posts: 15,774
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    Page 8 of that manual has the warning to use 50a or less.



    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    Seems to me the manufacturer doesn't know what size breaker to use and has published conflicting information
  • ratio
    ratio Member Posts: 3,649
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    No, the mfgr has done lots of calculations, sized everything internal, applied all the deratings & diversity factors & sized the breaker for you.

    If it has a UL listing you'll be able to collect your insurance if it burns the house down with the noted breaker installed. If you exceed that breaker, you will not collect any insurance.

    Solid_Fuel_Man
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    In any event a smaller breaker is safer. The worst case is the breaker tripping. But in this case of 41 amps on a 50, I doubt if there would be any tripping.

    I have put 15 amp CB's on 20 amp (#12) circuits for added safety.
    For instance rewiring the attic of a 100 year old church.
    ratio
  • Matt_67
    Matt_67 Member Posts: 288
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    I don’t believe HACR breakers are 100% rated, I think it’s that the trip curve meets a certain requirement. It looks like the typical QO breaker is not even available with a 100% rating.

    I’m thinking @EBEBRATT-Ed has it right, poor info from the manufacturer.

    If you install a circuit with a continuous amp draw above the rating of the breaker I am certain the installer would have liability if something went wrong.



  • ChrisJ
    ChrisJ Member Posts: 15,774
    edited December 2020
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    JUGHNE said:
    In any event a smaller breaker is safer. The worst case is the breaker tripping. But in this case of 41 amps on a 50, I doubt if there would be any tripping. I have put 15 amp CB's on 20 amp (#12) circuits for added safety. For instance rewiring the attic of a 100 year old church.


    NM-B is rated for that extra temperature, no?
    And modern MC etc a well?

    I thought that's what the "B" was all about.

    IE running modern NM-B in a hot Attic at its standard rating 12-2 @20a was perfectly acceptable?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    Solid_Fuel_Man
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    IIUC, the NM-B was upgrading the conductor insulation to THHN from (maybe T or TW) lower grade temp.
    This was to compensate for attic insulation covering the cables and also the heat generated by light fixture J-boxes. People would put 3 100 watt bulbs in a 60 watt max fixture. Between the design of the fixture and the attic insulation cover the over lamping would cook the cable ends inside the J-box and a few inches away from it. Seen it several times and it was worse with old Romex with "R" type insulation (1950's) or K&T.

    If you go to the tables in the NEC, (AKA known as the book of exceptions), it looks as if you could put 12 THHN on a 30 amp breaker. But the footnotes and exceptions state that for residential use #12 copper cable will have no more than 20 AMP CB.
    You can study the NEC until you go blind, but eventually learn what will fly for standard installations.

    The circuits in the church I mentioned were under fused and lightly loaded because of being in very hot summer attic, over 6 current carrying wires in some of the conduits, some conduits covered in insulation and the exposed chain hung fixture wires being 16 gauge and 50 years old.
    Plus the building is irreplaceable.
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    To add a bit to @JUGHNE 's very careful and sensible underfusing of the circuits in the church -- something I applaud wildly over here! -- if working with an older structure, even a residence -- and here I'd say older being anything much before the mid 1960s -- never assume that just because the panel and some of the more visible wiring has been updated that all of it has. There may well be stretches of rubber and fabric 14 gauge wire -- or smaller -- hiding out there. Bottom line -- if you don't need 20 amps, say, and are not positive that the wiring is rated for that, end to end, what's the harm in going for 15 amps?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    Thanks Jamie, after amp clamping the loads on those church circuits, I could have went with 10 amp CB. But they are special order and this was a bolt in CB panel.

    I would feel better about the project if I could rewire the hanging fixtures and replace the sockets. But with the height involved, stationary pews below, and no helpers and me starting to feel old, it may not happen. :/
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,614
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    @ChrisJ
    The newer Romex NMB the wire inside is THHN rated for 90 deg C but the code only allows it to be used at 60 C.


    As far as the above breaker size the OP needs to go back to the MFG and get clarification.

    The table in the manual calls for a 60 but the note @ChrisJ found calls for a 50.

    We can debate this all day with no correct answer.

    For now the electrician should follow what's on the nameplate.

    Long term I think a 60 is correct. for continuous load the 80% rule follows

    As far a "Church attic wiring" that's a different issue not likely a continuous load. Under sizing the breakers for more protection is probably ok.

    This heater is different it draws 0 amps or 40 amps on high so the breaker sees 0 load or full lode in most cases
  • Jamie Hall
    Jamie Hall Member Posts: 23,428
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    JUGHNE said:

    Thanks Jamie, after amp clamping the loads on those church circuits, I could have went with 10 amp CB. But they are special order and this was a bolt in CB panel.

    I would feel better about the project if I could rewire the hanging fixtures and replace the sockets. But with the height involved, stationary pews below, and no helpers and me starting to feel old, it may not happen. :/

    When you get those done, you can come and help me do the ones I care for...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
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    I've gone so far as mounting to teo pole fused disconnects with 10 amp fast blow fuses for Extra Protection in old building wiring. This was after explaining to the owner that fuses are much faster than Breakers and we wanted to protect it as much as possible. 

    Old K&T can be very scary up there in the old steel pancake lighting boxes. 

    I've replaced it with THHN and soldered it to the original cloth wire in the attic. Where it wasn't brittle from the heat of the light fixture. 
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    mattmia2