Thor Brake Issue - undersized wiring

[grtblu]

During the repair of a broken electric brake wire on my Thor/Crossroads 25 foot travel trailer I noticed that the feed wires (ground and blue brake wires) were #18 AWG. This seemed like much too small a wire gauge given that E Trailer recommends #10 wire. I did a diagram of the wiring and then calculated the resistance of each length from tongue to brakes. I then did a network calculation of the voltage drops and the currents that fed each brake magnet. I did this for #18 awg throughout and then another calculation with long feeds (+brake and ground) as #10 and the distribution wires at #12.
Given that the magnetic braking force is calculated as the current squared, I then compared the magnetic braking forces of the #18 wire (OEM) with my #12 and #10 modification. It turns out that the OEM #18 wiring only provides 72% of the braking force availabale with the larger wire. This is in my opinion a dangerous situation. My trailer is relatively light (slingshot brand), if heavier trailers are similarly wired this would be particularly dangerous.

[ducksface]

Did you take into account the actual brake size?
72% of ability may be 125% of required braking.

Your 'IF' only tantalizes. It's irresponsible to 'IF' the larger trailers.

You've only measured part of the whole system.
Maybe the brakes are oversized and erases your danger diagnosis.
We need brake surface area and all brake info to decide danger.

And
I'm not sure but do trailer manufacturers have to pass DOT requirements and are they fined TO DEATH if they don't?

Punchline:
Newbs need not be skeered of their brakes.

[DavidEM]

I did a theoretical calculation of the voltage drop using 8 amps to the brakes and #18 wire. 8 amps is from measuring the braking amperage required to lock the brakes on my 16' TT.

I assumed that the wire splits right behind the A frame and one leg goes to one side and one to the other. So from that split aft, the current is half or 4 amps for each side.

I calculated a .85 volt drop to the wheels. That isn't great, but it isn't a killer either. I would want to keep the total voltage drop down to 0.5 volts which will require about 14 gauge wire.

David

[MLP]

With your brake controller on full at 25 mph, does it lock the trailer tires? If it does, then the wiring and the shoes are just fine. Just back off the setting until the brakes do not lock up. Remember to test again in wet weather and set as to not lock them up when wet. I always used two setting with my fifth wheel for dry and wet conditions. I never regretted getting disk brakes for the fifth wheel. What a difference in stopping distance. The shoe brakes could never lock the wheels up in dry conditions.

[grtblu]

As it is easy to check your wiring size, if you are concerned about my comments, check yours. It would have been irresponsible of me not to mention my findings. My brakes are 10" by the way.

[grtblu]

I tried to find "standards" for travel trailers and failed. Might just be poor searching or maybe there are no standards for travel trailer brake wiring.

[Metalman]

In this case, I'd say the larger the gauge the better (up to a certain point). #18 is not particularly strong wire. #12 or #10 would be much stronger and less apt break under severe situations. The less the voltage drop the more efficient the circuit. I say, "size matters".

[ducksface]

Originally Posted by Metalman

In this case, I'd say the larger the gauge the better (up to a certain point). #18 is not particularly strong wire. #12 or #10 would be much stronger and less apt break under severe situations. The less the voltage drop the more efficient the circuit. I say, "size matters".

Size indeed does.
And if the op knew percentage of pad area SIZE vs required pad area SIZE vs voltage(SIZE)required to execute mandated stopping distance(SIZE)we'd have something to address about SIZE.

We do not have enough information to do anything except try to scare people about something HIGHLY regulated that requires no consumer thought, let alone fearful/doubtful thought.

Newbs:
The wiring size on your factory wiring requires no thought, no worries.

I suggest anyone post a reliable source telling of an instance of brake fail due to factory undersized wires and then the percentage of trailers to failures.