Brake Wire

BruceMc wrote:

All that said, the point isn't necessarily just the wire size, but how its wired. You don't need 10 or 8 gauge wire to each brake, that's overkill. But you do need to consider both the total current on each lead and how it's balanced.

You are correct to a point.

Typical trailer wire runs are rather unballanced, wire from front of trailer is run down one side of the trailer to one side of the first axle.

Then a light ga wire is run through the axle tube to the opposite side.

Then the same side of the trailer that the wire was run on there is a short jumper to the next axle and that axle is the repeat of the first axle.

The result is the first magnet closest to the front of the trailer ends up getting more voltage which results in that brake being the strongest. The next brakes end up being less effective due to additional wire resistance. Typically you will always feel the trailer pulling you towards the side with the least amount of wire.

This effect is eliminated by using either a heavier ga wire to all brakes and or doing a "star" or "hub" wiring pattern where the wire run from front of trailer to a central point equal distance between axles and magnets. Then you run the same ga wire of equal lengths to each magnet. Now all magnets get the same voltage and will now have equal braking power.

Sometimes it is not possible to do that star or hub distribution and that is OK, upgrading the wire size several ga sizes can reduce the wire resistance enough that it is no longer an issue.

What I did was run two pairs of 10Ga wire to a weather tight box located on my drivers side near the first axle. From that box I ran very flexible 12Ga rubber cased SJ cord (typically used for outdoor extension cords) to each magnet (these cords employ many small strands of wire that makes then very flexible unlike THHN building wire). Since the 12Ga wire runs are short enough the resistance loss is low and all brakes work equally well.

The big key here is to use a far heavier ga wire than the minimum specs would require and you will end up with better overall brake operation.

The reasons I used the wire I did was I had boat loads of that wire leftover from other projects and I at one time worked for a small hardware distribution chain which would often get damaged goods returned from the stores. As an employee of that distribution chain I was able to buy the returns for scrap prices..