unusual rv / house wiring extention cord?

Question

looking for comments, suggestions:

i want a heavy duty extension cord for my rv.
i want to run a small tankless water heater (which i was told at the store is 220 40amp and 8 gauge would work),
and an average home size arc or mig welder,
a 15amp space heater,
and another 15amps or so of other things.

the water heater and welder and maybe the space heater will not be used simultaniously.

i want a breaker at the main box leading to a stove/dryer outlet next to the box,
about 100' waterproof? flexible? cord with stove/dryer plug and outlet on each end -
which plugs into another stove/dryer plug at the rv, which powers a box in the rv. i want a main breaker on the box that will go off befor the breaker at the main box.

i was thinking of using something like a 8/4 cable with 2 wires for black for water heater and welder, one more black and one neutral for the rest.
and maybe the neutral could double as a ground for the other two?

yes i mean to have a subpanel in the rv. and it will be a massive extension cord with stove plugs

Answer 1

I'm a bit confused! This question really need be addressed in a real time conversation like messenger. Contact me if you like via my answers profile. What you are asking is both illegal and unsafe with exclamation on dangerous! An RV has to be grounded with a grounding conductor not the neutral PERIOD!!! The water heater needs to be GFI protected but the welder can not. And YOU CAN NOT use an 8/4 cable when supplying from residential. The extension cannot ever be supplied by more than one overcurrent device ie the 2 pole breaker for the water heater and the single pole breaker for the "rest".
What you need is a tempory power configuration like what is used in the electrical trade. It consists of a spider (junction) box and extension cord. If you don't know what that is then go to the local rental yard and ask t see it and where to purchase them. Just bring the check book and a very nice pen!

Answer 2

You say it's an RV? But your talking like you want to wire it permanently. The best thing to do would be run 6/3 to the RV and install a subpanel. Run the proper size breakers and cicuits there. What you are saying about 3 hot lines with one nuetral is not the way to go, even if you have a separate ground. Think of it this way, wire it like you would an outbuilding with a subpanel.

Answer 3

It is probably a violation of the electrical codes in your area for using a netural wire as a ground. Can't you just use another cord?