Selecting the cable gauge for each load depends on the
- load's nominal current
- cable length between the load and the breaker
- heat dissipation conditions (cable in free air, conduit, multiwires...)
- acceptable voltage drop under max load (10%, 5%, 3%...)
Also, since camper vans are habitable and mobile, both RV & Transportation regulations apply. Leading to requirements that can be quite different from the home building NEC code: stranded wire, high temp, resistance to oil / chemicals, strain relief, etc.
Quite
a head scratcher when trying to select the proper cable types.
Fortunately, Sea Blue Systems (and probably others) provides a handy calculator online:
It
also calculates the breaker size. A breaker's Ampere Interrupt Capacity
(AIC) is, maybe counter-intuitively, based on the cable size, not on
the loads. Indeed, a breaker's job is to protect the cabling, not the loads. Nobody wants to tear down a wall in a house, or gut a boat, to change the cables after a load went faulty.
So,
now, all we have to do is to come up with all the loads & circuit
branches for the build and input that into the calculator:
- Fan kitchen (5A 2 wires 20'x2 10% in Conduit) → #16/2, 10A breaker (7351)
- USB back (15A 2 wires 30'x2 10% in Conduit) → #12/2, 20A breaker (7353)
- Fridge 6Amax (10A 3 wires 15'x2 3% in Conduit) → #10/3, 10A
- ...
Followed by ordering the corresponding marine cable and breaker equipment from reputable manufacturers
(Carling, Bussmann...). No, the cheap car audio thermal breakers &
wiring on Amazon are not compliant and, therefore, not recommended.
Camper vans are a 'living space' application. 'Living' is the key word
here 😉
____________________________________
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