Please Explain Small Gauges of Extension Cords

Discussion in 'Electrical Forum discussion & Blog' started by molo, Nov 7, 2012.

  1. molo

    molo Member

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    I know that a general rule is to not reduce the size of wire, so then why are extension cord sizes for appliances so small? Are they sized to the appliances demand?

    Thanks in Advance
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Are you talking about the supply cord that comes on an appliance or are you talking about the cord that has a male and female end cap? Table 400.5(A)(1) gives the ampacity of cords
  3. jimbo

    jimbo Plumber

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    Ampacity is always a concern. And especially when you say "appliance". Small 16 or 18 gauge general purpose extension cords are intended for a lamp, a TV, etc etc. and lengths are limited....6 to 12 feet usually. When you are talking about a device which is rated at 12 to 15 amps......refrigerator, air conditioner, microwave, etc. while a light duty cord may be "rated" for that, continous use will tend to overheat the cord, and especially the end fittings which are applied with light duty crimp manufacturing techniques. For such applications, you should get a cord rated for appliances, "heavy duty" , 12 amps, etc. And EVEN THOSE, I happen to use them for my 1500 watt oil filled portable radiators. I always cut off the manufactures end fittings, and replace with "heavy duty" cord ends. This always eliminates the "hot plug" which you experience on the factory ends.

    In terms of your question about wire size......the answer is distance ( length). For example, our 'rule of thumb' is 14 gauge wire in the wall for a 15 amp circuit. But that is based on the very long total length of wire in the wall. It IS ok to reduce to say 16 gauge for 6' on an extension cord. That gauge will carry the current without overheating the wires.
    Last edited: Nov 8, 2012
  4. hj

    hj Moderator & Master Plumber Staff Member

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    You buy the extension cord based on the length of the cord and the load you are going to plug into it. Often, the very lightest cords have a polarized two slot configuration which will not accept the plugs for the "heavier" devices which have a three prong plug.
  5. LLigetfa

    LLigetfa DIYer, not in the trades

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    The maker and the seller does not know what sort of appliance you will plug into an extension cord. They make different gauges in different lengths for a variety or uses. It is up to the buyer to know what to get but the buyers all too often use price as their main deciding factor. Makers and sellers know that and tend to make and stock more of the smaller gauge cords.
  6. molo

    molo Member

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    I am referring to things like space heaters. I had a 1,500 watt space heater plugged in yesterday and the plug and cord were getting quite warm!
  7. LLigetfa

    LLigetfa DIYer, not in the trades

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    So then this is the permanently attached appliance cord, not an extension cord? Why then are we talking about extension cords?

    If you had it plugged into a cheap extension cord, that could explain it.
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

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    1500/120= 12.5 Now add the 125% as mandated in 424 and we have 15.65 amps of current flowing through that cheap cord cap.

    In every class I teach I point out that a 1500 watt electric heater is a violation when plugged into a 15 amp general purpose receptacle, see 210.21 through 210.23 for more information.

    These heaters are a fire waiting to happen. If you must use one make sure that it is plugged into a 20 amp circuit and this will relieve the heat in the cord to some extent but I will not eliminate it altogether.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Basically, an attached cord to an appliance should work okay when plugged into a receptacle designed for the load. When adding an extension to the cord, that's where it gets critical to maintain at least the wire size of what is on the device, and better yet, use a heavier gauge one to account for the connections at either end. Also, an old, worn out extension cord should either be chucked or the end(s) replaced when things get loose. To get an approval, the cord that comes with it should be sufficient for the load of the device.
  10. jwelectric

    jwelectric Electrical Contractor/Instructor

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    The major problem is someone will go to Walmart and get a portable electric heater that is rated at 1500 watts but runs all the time as the thermostat on the unit never satisfies and the load if far to great for the 15 amp receptacle that it is plugged into. The receptacle slots start to heat and expand and then the heat is transferred to the blades of the male plug on the end of the cord.

    At some point the cord caps get so lose in the slots of the receptacle that we spread the blades of the male plug to make it grip tighter until the male plug starts to deform.

    Table 210.21(B)(2) tells us that the maximum cord connect load that can be plugged into a 15 amp receptacle is 12 amps. It doesn’t matter if the 15 amp receptacle is on a 15 or 20 amp circuit the largest cord connected load that can be plugged in is 12 times 120 or 1440 watts.

    There is two times that a circuit is to be rated at 125%.when talking about this type of a load. One is when the load is going to last for three hours or more and the second is found in 424 concerning electrical resistive heating elements.

    In most cases these heaters are set on high and never reach the temperature to satisfy the thermostat and run for several hours on end. There is no break to allow things to cool down and the heat keeps intensifying until something bad happens.
  11. jimbo

    jimbo Plumber

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    As to the space heater.....not surprised it caused the ends to heat up. Those are the weak points on small cords. Get a heavy duty cord rated as "appliance" or such, 14 ga min, 12 ga preferred. And then, REPLACE the end fittings as I pointed out before. I have been using portable heaters for years, using this procedure. I keep the extension cord length to 4~6 feet max. BTW I also replace the mfg installed plug on the heater with a heavy duty version.

    As pointed out, heaters have inherent potential dangers, but you can minimize. Rule #1....you don't SLEEP with a heater turned on!
  12. molo

    molo Member

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    I should clarify that I was referring to appliance cords not extension cords. I would be willing to bet that only 1 in 1,000 know that a 1,500 watt heater should not be plugged into a 15 amp circuit. If properly designed an electric space heater wouldn't be a hazard (there are probably some out there that are OK).
  13. jimbo

    jimbo Plumber

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    Most small room heaters are rated at 1500 watts, and the also all have a plug allowing use on a 15 amp receptacle.
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

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    This is true and there would be no problem if they came on for a few minutes and then shut off like you furnace but this heater is being used in NY where there is no power and it is running 24/7 which it was not designed to do therefore it does not hold up.

    They are not designed to heat a house. They are designed to be foot warmers and the time of operation is not continuous.
  15. jimbo

    jimbo Plumber

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    I believe that fire departments around the country would concur with your analysis. This whole thing is just one of those loopholes that allow Darwin's Laws to come into play!!!!
  16. LLigetfa

    LLigetfa DIYer, not in the trades

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    It is also being plugged into an extension cord that is probably undersized and probably has an injection molded end on it. Those cannot take the heat as well as a proper wall receptacle can.

    Often too, you find extension cords that are too long and they leave the extra coiled up. They can get quite warm.

    One time I found an extension cord under a raised floor in our computer room that fed a powerbar with far too many devices plugged into it. Some IT folk should not be allowed to plug things in and should stick to programming.
  17. hj

    hj Moderator & Master Plumber Staff Member

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    quote; this heater is being used in NY where there is no power and it is running 24/7

    If there is no power, how is it running at all, unless it is by a generator and its power is seldom regulated so the output voltage may not be 120 in which case the amperage of the heater could be higher than specified.
  18. DonL

    DonL Jack of all trades Master of one

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    I am sure what you have is Normal.

    The power cord is most likely rated at a high enough temperature that it is still over rated, because of its short length.

    The power cord is normally in a cool place, or you would not be running a heater.

    As long as the power cord is in free air and not under or against anything it should be fine.

    I am with jimbo on the cut off the cheap AC Plug connector and install a new / good one.


    I use many portable heaters and I always use them on the low wattage setting. I also have smoke detectors near them.

    I try not to leave them unattended , but sometimes I trust the smoke detectors when I am in another room.

    And I do run them on a properly rated Extension cord, when needed. (Handy for the chicken house)


    If you need more heat than what the low setting will provide , then you need a better / safer heating source.
  19. molo

    molo Member

    Messages:
    849
    Location:
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    Thanks for all of the responses to the question. We typically heat with a wood stove, but I plugged the heater in to take the chill off before bedtime. I was surprised at how hot it was, and started wondering why so many appliance cords are so small.
    It seems counter to the rule of not reducing wire size.
  20. jimbo

    jimbo Plumber

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    I think you are mixing up the electr. code for building wire, and the UL regulations on appliance listings.
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