Why Do 7-Way 12 Volt Circuits have 12 Gauge Wire While When 10 Is Recommended

Question:

I have a clarifying question about the wire size for the trailer battery charge wire. From the product description: Black, Battery,12 Gauge. Advice from another etrailer post: The wire that runs from the vehicles battery to the 7-way trailer connector and then from the 7-way trailer connector to the trailer battery should be at least a 10 gauge. If you dont have any 10 gauge wire you can purchase part # 10-1-1 by the foot. Please note, you will need a circuit breaker part # 9510 on this charge line wire about 6inch away from the battery on the tow vehicle. The 7-way trailer connector can then be used to attach and disconnect the charge line between the tow vehicle and trailer. helpful expert reply by: Conner L This kit comes with 10 ga wire for the battery charge wire, and the part number listed in the expert response is for a 40 amp circuit breaker, but then all of the 7-pole sockets listed on your site choke down to 12 ga. at the plug harness. Why? 12 gauge wire is not rated for 40 amps. Will the 12 ga in the charge line create an issue? Can you help me wrap my head around what Im seeing as conflicting information?

asked by: Sean K

Expert Reply:

This is a really great question but 12 gauge wire ran in a very short length doesn't have nearly as much resistance as it does in longer lengths so while the 7-ways will have short runs of 12 gauge wire for the 12 volt accessory circuit you still would want to run the longer lengths of wire for this circuit in 10 gauge like part # 10-1-1. This is because the longer the wire the more the resistance increases.

expert reply by: Jameson C