Dryer 10/3 & Breaker Slightly Warm

Discussion in 'Electrical Forum discussion & Blog' started by pcarpe01, Jun 13, 2018.

  1. pcarpe01

    pcarpe01 New Member

    Jun 13, 2018
    Long Island, NY
    I noticed on a new cable run to my dryer that the cable gets slightly warm, along with the breaker after running for 30 minutes. The only reason I noticed it was that I was running additional cables to the panel, which were cold to the touch, but the cable for the dryer is slightly warmer. Slightly meaning, that if I touched the dryer cable only, I wouldn't have thought twice about it or realized that it was warm - if that makes sense. I noticed the breaker is also slightly warm. The cable is consistently warm throughout the run - no hot spots.

    The cable is new 10/3 NM with a 30 A breaker. It's a home run of about 20', there are no sharp bends/twists in the cable and the staples are not squashing the cable. I rechecked the connections and re-seated the breaker with the same results. the dryer is a Whirlpool, about 3 years old. The lint trap/line is clean.

    I was wondering if this is normal for the cable and breaker to become slightly warm due to continuous high current load? I just never noticed it before.
  2. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    This graph does not show #10 wire, but you can see the pattern, and add your own #10 line.

    Also note the temperature rises are in degrees C.
    Last edited: Jun 13, 2018
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    All wire has some internal resistance, and just like say the filament in a light bulb, run current through it, it gets warm. It's just that the difference between the light bulb and a power line is fairly large. As long as the wire is run properly, and you do not exceed the temperature rating of the insulation, it should be fine. This is one reason why sometimes it's a good idea to run a larger gauge wire than technically required. You're paying for that heat generated in the wire. In the scheme of things, it's not much, but it would be better if it were all being used in the dryer than in the supply line to it! But, the difference in cost between 10g and say 8g wire would probably never be recouped.

    Obviously, the dryer seems to be running on that 30A circuit, but many of them call for a 40A circuit...what does the installation manual for your dryer call for? On appliances that could be running more than 3-hours, I think the code requires it to be derated to 80%, so if the dryer draws just under 30A, it might really call for a 40A circuit to safely run it to keep the wire temperature down.

    20' of 10g wire drawing 30A will have a resistance of about .02-ohms, which would be using around 18W of power.
    20' of 8g wire drawing 30A will have a resistance of about .012-ohms, which would be using around 10.8W of power.
    Both of those are for the cable itself and does not take into account any resistance in the connectors or the breaker itself.

    At 30A and 240vac, a dryer would be using 7200W, so, lots more than used in the supply cable. FWIW, there are 15W soldering irons, but one of those would concentrate all of that at a small point verses over say your 20' of wire. This is one reason why you need to ensure the receptacles are not worn out and the connections are tight - the additional resistance in the contacts will generate heat...potentially enough to burn something up.
  5. Norcal01

    Norcal01 Member

    Aug 16, 2008
    A dryer should be drawing 24A max, not 30A.
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