Brake Wire

[Busdriver]

Thinking about running new wire for my Trailer Brakes , just not sure what size wire I should use.? The wire the manufacturer used is very thin.

[Gdetrailer]

Vintage465 wrote:
12/2 jacketed brake wire is the proper conductor. I would not go less.

https://www.ebay.com/itm/352212792104?hash=item520184b328:g:USEAAOxyAs9SRbIh

$5.99 per 10ft plus $4.99 shipping, $11 for 10ft??

$1 per ft..

That is an insane price!

You can buy that same jacketed wire in the same 12 Ga at Amazon for $.79 per ft..

But 12ga is not an upgrade and if one is going to go through the hassle of changing the wire, one might as well go big and upgrade further.

Additionally, you do not need to use that plastic jacketed wire, an improvement and better wire is Neoprene jacketed "SJ" rated wire which uses a heavy neoprene rubber outside jacket and the inside wires also are jacketed in neoprene rubber. That advantage of SJ type cord is the wire strands are very fine and allows the cord to flex very easy.

Standard jacketed RV brake wire on the other hand uses large strands which are far less flexible and much more brittle and prone to breakage.

The more flexible SJ cord will hold up better in areas that the wire must flex a lot, like where they touch the axles!

Can get 2 wire 10ga SJ cord for around $1.15 per ft maybe a bit lower if you search around a bit.

Not everything must have "RV" on it to use, heck even 12Ga speaker wire or zip (lamp) cord can be used in a pinch..

Not every must be sourced from Ebay either, much better places that sell much better quality and prices.

[Vintage465]

12/2 jacketed brake wire is the proper conductor. I would not go less.

https://www.ebay.com/itm/352212792104?hash=item520184b328:g:USEAAOxyAs9SRbIh

[Sjm9911]

Gdetrailer wrote:

Sjm9911 wrote:
I get the principles and practices, i just figured the manafature has allready considered the drop into the specs. So its designed to work woth the guage it has and to upgrade it will not nessassarly equate better stopping.

The trailer manufacturer only goes by published minimum specs. Those specs are based on total current draw over the distance from the axle manufacturers.

Dexter Axle used to have a chart calling out the MINIMUM wire ga for certain distances for a certain quantity of brake magnets. Not sure if they still have that on their website.

Because the magnets are rated 3A draw at 12V,each axle can draw as much as 6A.

So a single Axle trailer typically is rather short you could get away with a minimum of 16 Ga which would handle the max current of two magnets.

Longer trailers with two axles means you have the potential for 12A at 12V and typically the minimum recommended wire is 14 Ga because of the current.

RV manufacturers let the wire selection go to the frame manufacturer that they buy from (RV manufacturers typically "farm out" the frame building to a third party). That frame manufacturer will typically use the minimum recommended wire ga from the axle manufacturer.

Using the minimum basically is to cover only the max amperage draw, not the best performance.

The brakes will work, just not as well as they would if you were to have less resistance in the wire run.

This gets very apparent with folks who have larger and heavier trailers like 8K-12K 30ft+ trailers. Many of those folks end up scrapping the drum brakes in favor of disc brakes using Electric over Hydraulic system.. Your talking a $1K overhaul of the brakes..

In low voltage world wire resistance is a major problem, with 12V a .1V loss can make the difference of a device working or not working.

The magnets strength is directly affected by how much current flows through it. The current is controlled by the resistance of the magnet and the voltage across the magnet.

If the resistance of the wire going to the magnet is increased, the voltage at the magnet is reduced which reduces the strength of the magnet.

The less strength the magnet has it will not grab the drum surface hard enough to mechanically push the brake shoes against the drum.

That all equals far less effective brakes.

So, in reality, reducing distance of wire and/or increasing the wire size can have a huge impact on improving your drum brakes braking power.

Since you can't shorten the wire length, increasing the wire size is the only way to go.

I have made this mod to two trailers, 20ft and 26ft both dual axle and both rated 7K GVWR, in both cases the wire upgrade resulted in better braking, enough that I was able to reduce the brake controller output considerably.

This explains it well. And probably why i had a smaller wire hooked up. Actually i was thinking about what i did, and forgot to consider other facters. Like other campers may have larger runs and more wheels and larger magnets. All in all that would lead to a generic more is better approach. So my first statment may be only good for me and my size unit. Thats for the detailed explanation.

[Sjm9911]

Mike134 wrote:

Sjm9911 wrote:
I will be the on the oposote side. Etrailor recomended 10/2 wire. Way to big and cumbersome to attache to the way smaller wires in the electric brakes. If i had to do it over 16 guage would be enough. I think my original stuff was that big or smaller.

And this is why I compare getting information from a forum the equivalent of asking the folks sitting along the campground bar what they think. Same odds of wrong or right answers

"I'm no expert but I play one online"

Safe travels

Right back at ya bud! Youn can always go elsewhere for your information.

[Sjm9911]

larry cad wrote:

Sjm9911 wrote:
I will be the on the oposote side. Etrailor recomended 10/2 wire. Way to big and cumbersome to attache to the way smaller wires in the electric brakes. If i had to do it over 16 guage would be enough. I think my original stuff was that big or smaller.

You cannot use a wire size that is the same as the wire size on the brakes. The trailer wire has to carry enough current (amps) to power all the brakes, not just one. Two trailer wheels takes less amps than a 4 wheel trailer. 6 wheel trailer takes more amps than a 4 wheel, and so on.

Most trailer wire harnesses use #10 wire which is rated at 30 amps.

On each individual electric brake magnet the amperage draw would be 3.0 to 3.2 max amps at 12 to 13 volts on 7-inch brake magnets and 3.2 to 4.0 max amps at 12 to 13 volts on 10 and 12-inch brake magnets.

The max amperage draw for the brake magnets on a single axle trailer (2 brakes) would be 6.3 to 6.8 max amps on a 7-inch brake system and 7.5 to 8.2 max amps on 10 and 12-inch brake system. The amps will be higher if using a tandem axle or triple axle trailer.

I never said to use a wire the same as the brake wires, just that 10 /2 was way overkill. I belive mine was a 18 guage wire run from the factory to the brakes on a dual axel. The magnets had much smaller wires. Maybe because my TT isnt that long or heavy and the brakes were smaller in size?

[time2roll]

50' of marine tinned duplex wire is $55 #10, $36 #12, $30 #14.

I would probably go #14 for 1 axles, #12 for 2 axels, #10 for 3 axels.

https://www.genuinedealz.com/collections/flat-duplex-dc-marine-wire

I have seen some go with a bus and run separate wires to each wheel.

For truly superior braking skip right on up to hydraulic disks 😉

[Lynnmor]

theoldwizard1 wrote:

larry cad wrote:
Most trailer wire harnesses use #10 wire which is rated at 30 amps.

That is for "continuou use" typical household wire. For a short time usage DC circuit less than 50' #10 can easily carry 50A.

Heating of wires and safety is just one factor. Voltage drop at the brake magnets is the issue here. Use a voltage drop calculator for 12 volt DC and you will see that 20% or more may be lost using typical wiring provided by trailer builders.

[theoldwizard1]

larry cad wrote:
Most trailer wire harnesses use #10 wire which is rated at 30 amps.

That is for "continuou use" typical household wire. For a short time usage DC circuit less than 50' #10 can easily carry 50A.

[Gdetrailer]

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..

[Gdetrailer]

Sjm9911 wrote:
I get the principles and practices, i just figured the manafature has allready considered the drop into the specs. So its designed to work woth the guage it has and to upgrade it will not nessassarly equate better stopping.

The trailer manufacturer only goes by published minimum specs. Those specs are based on total current draw over the distance from the axle manufacturers.

Dexter Axle used to have a chart calling out the MINIMUM wire ga for certain distances for a certain quantity of brake magnets. Not sure if they still have that on their website.

Because the magnets are rated 3A draw at 12V,each axle can draw as much as 6A.

So a single Axle trailer typically is rather short you could get away with a minimum of 16 Ga which would handle the max current of two magnets.

Longer trailers with two axles means you have the potential for 12A at 12V and typically the minimum recommended wire is 14 Ga because of the current.

RV manufacturers let the wire selection go to the frame manufacturer that they buy from (RV manufacturers typically "farm out" the frame building to a third party). That frame manufacturer will typically use the minimum recommended wire ga from the axle manufacturer.

Using the minimum basically is to cover only the max amperage draw, not the best performance.

The brakes will work, just not as well as they would if you were to have less resistance in the wire run.

This gets very apparent with folks who have larger and heavier trailers like 8K-12K 30ft+ trailers. Many of those folks end up scrapping the drum brakes in favor of disc brakes using Electric over Hydraulic system.. Your talking a $1K overhaul of the brakes..

In low voltage world wire resistance is a major problem, with 12V a .1V loss can make the difference of a device working or not working.

The magnets strength is directly affected by how much current flows through it. The current is controlled by the resistance of the magnet and the voltage across the magnet.

If the resistance of the wire going to the magnet is increased, the voltage at the magnet is reduced which reduces the strength of the magnet.

The less strength the magnet has it will not grab the drum surface hard enough to mechanically push the brake shoes against the drum.

That all equals far less effective brakes.

So, in reality, reducing distance of wire and/or increasing the wire size can have a huge impact on improving your drum brakes braking power.

Since you can't shorten the wire length, increasing the wire size is the only way to go.

I have made this mod to two trailers, 20ft and 26ft both dual axle and both rated 7K GVWR, in both cases the wire upgrade resulted in better braking, enough that I was able to reduce the brake controller output considerably.

[BruceMc]

When we had our 22' fifth wheel, the passenger front tire would always lock up but the others kept rolling... the problem wasn't necessarily the wire size, but how it was wired. The factory routed the wires along the right side of the trailer, then tapped off and ran across to the left side. The right front tire was first in the circuit.

I rebuilt the wiring using a variety of sizes. As Larry Cad stated, each brake pulls around 3 amps at full braking. 3 amps is easily carried by 16 gauge, which is the same size as provided on the brake puck. I wired each of the 4 brakes to an equal length 16 gauge pigtail. At the center of each axle, I joined the pigtails to equal lengths of 14 gauge, then ran those back to the right frame rail. Those, then were joined to a 12 gauge lead that ran to the 7 pin plug.
All connections were soldered, sealed with liquid tape, then protected with heat shrink.

The point of this exercise was to provide equal current and voltage to each brake. From that point forward, I never slid one wheel, but could lock all four up if desired. It was a vastly different towing experience.

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.

On the tow vehicle, you'll need an adequate size wire for the job. At 12-14 amps maximum for 4 brake trailers, 12 gauge (20 amp max) is all that is needed. In practice, you'll never pull 12-14 amps on a constant basis. I'd venture a guess that current during usual braking is commonly between 1 and, say 6 amps. Those who have current readouts on their brake controllers know the story.

[Mike134]

Sjm9911 wrote:
I will be the on the oposote side. Etrailor recomended 10/2 wire. Way to big and cumbersome to attache to the way smaller wires in the electric brakes. If i had to do it over 16 guage would be enough. I think my original stuff was that big or smaller.

And this is why I compare getting information from a forum the equivalent of asking the folks sitting along the campground bar what they think. Same odds of wrong or right answers

"I'm no expert but I play one online"

Safe travels

[larry_cad]

Sjm9911 wrote:
I will be the on the oposote side. Etrailor recomended 10/2 wire. Way to big and cumbersome to attache to the way smaller wires in the electric brakes. If i had to do it over 16 guage would be enough. I think my original stuff was that big or smaller.

You cannot use a wire size that is the same as the wire size on the brakes. The trailer wire has to carry enough current (amps) to power all the brakes, not just one. Two trailer wheels takes less amps than a 4 wheel trailer. 6 wheel trailer takes more amps than a 4 wheel, and so on.

Most trailer wire harnesses use #10 wire which is rated at 30 amps.

On each individual electric brake magnet the amperage draw would be 3.0 to 3.2 max amps at 12 to 13 volts on 7-inch brake magnets and 3.2 to 4.0 max amps at 12 to 13 volts on 10 and 12-inch brake magnets.

The max amperage draw for the brake magnets on a single axle trailer (2 brakes) would be 6.3 to 6.8 max amps on a 7-inch brake system and 7.5 to 8.2 max amps on 10 and 12-inch brake system. The amps will be higher if using a tandem axle or triple axle trailer.

[ktmrfs]

10 or 12 is more than adequate. when taking into account the coil resistance of each brake magnet and typical runs, drop is acceptable. with the factory skimpy wiring on our and a prodigy, full brake on the prodigy wouldn't lock up the brakes on dry pavement. After going to 12g and soldering the connections, including bypassing the typical side to side wiring in the axle, 6 or 7 will lock up the brakes at 60mph on dry pavement.