You need to have the correct size wire for the amperage and voltage that will run through the wire. Remember every wire should be protected by a fuse, limiting the amount of current through the wire.
To determine wire size I recommend using Blue Sea Systems calculator – http://circuitwizard.bluesea.com/
Wire size is based on the amount of current going through the wire and the length of the wire run. Remember you can always use a thicker gauge wire in place of a thinner gauge wire. This will save money when purchasing wire.
The most amount of wire that will be run throughout your Van will be for DC, and AC appliances. For 12 Volts DC a 12 AWG wire should handle everything. A 12 AWG wire will handle 10 Amperes over a 20 foot distance. I do not expect any runs over 20 feet, or current needs over 10 Amps. The highest current draw item is the water pumps at 7.5 amps.
For A/C outlets
I will use a 12 AWG extension cord for all AC outlets. US electrical codes max current for circuits utilizing 12 gauge wire is 20 Amps.
The only high current items in our van build are:
- Bosch water heater 1440 watts, 12 Amps
- Air conditioner 5000BTU, 7.5Amps
- Microwave 700 watt, 6 Amps
- Insta-pot 1000 Watts, 8.3 Amps
We may have a kitchen blender or other kitchen appliance, but they would not have a greater current draw than 15 amps. So, a 12 AWG wire size will be enough for all our AC needs.
AC Circuit Breakers
There are 4 AC circuit breakers in the system. One 30 amp, one 20 amp, and two 15 Amp.
The 20 Amp breaker will be dedicated to the Bosch Water heater, and the outlet at the rear garage. The rear outlet may be used if I need to run any power equipment – drills, circular saws etc. I do not expect to need this, but as I have mentioned before always design with options. The 20 Amp breaker may be needed for that outlet due to the surge current of some of those devices.
One of the 15 AMPS circuit breakers will be dedicated to the Air conditioner. The other 15 Amp breaker will run the other outlets in the van, including the microwave.
The 30 Amp breaker will be the master shut off. It will take the power from the Inverter. This breaker will be connected to the other breakers. The inverter is capable of providing 50 Amps of current. This breaker will limit that to 30 Amps.
Yes, it is possible that we could exceed 30 amps if we run multiple items all at the same time. This would throw the breaker and cause no harm. We would then know to turn something off.