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ebjet123's avatar
ebjet123
Explorer
May 10, 2019

30 amp to 15/20 amp adapters

I have seen many "dogbone" adapters that will plug into a 30 amp outlet allowing you to plug in any 110 cord or appliance. My concern is the circuit is rated for 30 amps. Unless you have a dead short downline, that 30 amp breaker is not going to trip leaving any 110 appliance vulnerable to damage or worse yet, a fire. I have not seen any 30 to 15 amp adapters with inline circuit breaker protection. Can you use this adapter then plug in a 110 GFCI adapter (that any big box store sells) between the 30 amp adapter and the appliance you are attempting to run thus having a "protected" circuit? Or will the male end of the GFCI be vulnerable because it is being fed 30 amps thus overloading that connection? It still is not the same as having a 15 amp breaker between the 30 amp adapter and the appliance you are plugging in as you would with a standard circuit panel box. Any thoughts?
  • WNJeffers's avatar
    WNJeffers
    Explorer
    May 10, 2019
    Circuit breakers are there to limit the total current carried over the wire in a circuit in order to protect the wire. That’s why they are matched to the wire size (gauge.)

    Unless an appliance is defective, it will pull no more current than it needs. For example, if a toaster is rated at 900 watts, it will only pull about 7.5 amps (900w/120v) whether the wiring to the outlet it is using is protected by a 15-amp breaker, a 20-amp breaker, or a 30-amp breaker.

    An appliance cord is matched to the amount of current the appliance will draw. A typical AWG 16 lamp cord will not carry a continuous load of 15 or 20 amps to match the capacity of the breaker on the outlet into which it is plugged. But in normal use, the lamp cord will carry only the 1 or 2 amps the bulb(s) in the lamp will draw, which is far below the cord's capacity.

    Wayne
  • fyrflie's avatar
    fyrflie
    Explorer III
    May 10, 2019
    As far as I know, a GFCI is not a circuit breaker and will not trip unless there is a ground fault. Therefore, it should not be used as overload protection on a circuit.

    You are correct in assuming that the smaller circuit will be exposed to additional power, but if you are supplying power to your rv, then any and all circuits will be protected by their appropriate circuit breakers in the electrical panel.

    The smaller cord will get warm/hot if overloaded, but if it fails, I.e. melts, then it should create a direct short and trip the 30 amp breaker.
  • D_E_Bishop's avatar
    D_E_Bishop
    Explorer
    May 14, 2019
    Kind of reading between the lines, you're not suggesting plugging a dogbone adapter into a 30 amp socket and then plugging in an extension cord with a 15 amp plug into the circuit to power your RV, Right? If you are going to do that you should use a 30 amp extension cord.

    So if your not plugging that cord into your RV, what are you going to plug into that 15 cord and why would you? Doing so would override the safety factors built into the NEC and any possible fire caused by over heating the cord your responsibility. It just doesn't seem logical or necessary and you seem to be fully aware you are doing something you should not do.

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