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RVnRobin's avatar
RVnRobin
Explorer
Jul 25, 2013

50A rigs and wire sizing

A post yesterday about a burnt neutral wire got me to wondering...
If;
A 50A rig has all 120v appliances and loads,
A 120v 10A load will measure the same amperage draw on both the hot side and the neutral side,
A properly wired 50A service will measure 240v from L1 to L2,
And L1 and L2 will each measure 120v to neutral,
50A load max on L1 and 50A max on L2,
The neutral is shared with both,
The load amps from each of the hot lines are additive on the neutral,
Potential load on the neutral wire could max out at 100A.

Question;
Why isn't the neutral wire at least a #2 as per the wire sizing charts?
Wouldn't cords need to be constructed with two #6 for each of the hot lines, one #2 for the neutral, and then the ground?
Is this why we see neutrals frequently have heat damage?

I'm not an electrician. I know rarely both L1 and L2 would run at max. But the amperage charts seem to be pretty clear about what "code" requires.
  • RVnRobin wrote:
    I hadn't thought of the effect of phase. Thanks for the info.
    So, is it my imagination or do we really see more burnt neutral wires than hot wires? And, why?


    It's not phase... Generally all power you are exposed to (at home, and in the RV) is single phase - 3 wire.

    L1 and L2 are simply 180 degrees apart on the waveform.
  • I hadn't thought of the effect of phase. Thanks for the info.
    So, is it my imagination or do we really see more burnt neutral wires than hot wires? And, why?
  • Wow-- 100% correct replies (initial post incorrect) to a 50 amp wiring question!
    Way to go!

    Now, can we get this thread closed before "electrically challanged" answers posted?
  • What they said- equal loads on each leg gives a neutral current of zero. This is why a 50 amp outlet *must* be 240 volts.
  • RVnRobin wrote:
    ..
    The load amps from each of the hot lines are additive on the neutral,


    Incorrect.

    The neutral always holds the delta between L1 and L2.

    L1 is supporting 40 amps.
    L2 is supporting 10 amps.
    N would then be supporting 30 amps.

    L1 is supporting 50 amps.
    L2 is supporting NOTHING.
    N would be supporting 50 amps.

    L1 is supporting 50 amps.
    L2 is supporting 50 amps.
    N would be supporting NOTHING.
  • If all the load were on one side the neutral current would equal the hot side current. If you then add any load to the other hot lead the neutral current goes down accordingly since that load is of the opposite phase of the other.
  • L1 and L2 are on different phases and the neutral load from the two is zero or very small.

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