• wire
  • wire runs are typically sized for critical vs noncritical applications. Factors include both the amount of current and the total length of the circuit (POS and NEG sides combined). See below.
  • stranded wire is used in mobile applications; solid wire is more susceptible to damage and loosening from vibration
• solid-copper wiring is used in DC applications, like the van's 12vdc. Copper-clad aluminum (CCA) is sometimes used in AC applications but is not appropriate for DC.¹⁾
• fuses
  • fuses exist to protect the wiring.
  • fuses are sized 20% over the wire's rating. Example: a wire that is rated for 40A would be fused at ≤48A.
  • fuses are placed as close to the source of the power as practical to protect the maximum amount of wire
  • fuses are typically placed on the POS leg

Current on any wire tends to cause voltage sag. The problem gets worse as current approaches the wire's rated capacity. Some applications are greatly affected by sag and require heavier wiring. Some applications are fine with some sag.

Critical applications require voltage sag of ≤3%. With 3% sag 14.4v at the source drops to 13.97v at the other end of the wires. Some critical applications might include:

• solar charge controller output to battery bank
• solar panel to solar charge controller
• battery bank to fuse panel
• power distribution runs from one side of the van to the other (bus to bus)
• DC-DC charging of the house bank from alternator
• sensitive electronics
• inverters running large loads

Noncritical applications can accept voltage sag of ≤10%. With 10% sag 14.4v at the source drops to 13.0v at the other end of the wires. Some noncritical applications might include:

• isolator charging of the house bank (details), especially when some solar is present
• MaxxFan control boards are sensitive to overvoltage and may prefer some sag

A well-respected chart showing critical and noncritical wiring selection is published by Blue Sea.