Main Breaker Nut/Washer Options

The default main breaker nuts are keps nuts. We use nylocks and nord-locks for our battery terminals.

Is it legal to use nylocks and nord-locks for the main breaker?
Is there a recommended nut/washer configuration for the main breaker that is better than the default keps nuts?

There is no particular rule that prevents using any particular nut/stud combination on the main breaker. I strongly suggest using the proper size/thread combination, but beyond that…

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We used nordlocks and 1/4-28 nylocks last year- worked great, felt confident that they wouldn’t come loose. We did stud->lug->nordlock->nylock.

The one thing that caught us at inspection is that the little rubber insulating cap doesn’t fit with the nylock on so you’ll have to tape over the top of the terminal a little bit.


Wrapping it well with electrical tape so it isn’t super easy to get to bare metal is the right way to do it. As someone who has inspected in years past, if the connection is well taped the cap isn’t necessarily needed in my personal opinion.

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Using the double nordlocks there is no reason to use a nylock nut.

What do you mean by double? We only use a single nordlock washer on top of the lug, as recommended by the technical guide.

Also we have nylocks handy, so why not use them?

all these top “recommended” cases do not have a washer (we can think of a lug essentially as a washer) involved. You can see that using nordlock washers in combination with another non-locking washer is not effective from the bottom case. Intuitively this is because the nordlock washer can only prevent rotation between the two thing’s it’s touching. So when a normal washer is placed below a nordlock washer, sure, the washer won’t rotate relative to the screw, but the nut can still rotate relative to the threaded studs. i think @IndySam is probably suggesting putting an additional nordlock below the lug (washer) to mitigate this effect, but i would be skeptical about the conductivity of the nordlock washer in this case.


Given that this is an electrical connection and possibly subject to heating, a nylon insert nut here would be considered an incorrect application. As we know though, if your battery connections heat up enough to soften nylon, you have much larger issues. imo nylocks are fine here.

@Winston89 you’re bang on in assessing that this is technically a disallowed application. I make that same argument for battery lugs here and in the thread continuing after. Nord Lock really needs to clean up these graphics because people love to misinterpret them, willingly or not. Idk if Aidan fully got that message from the previous thread.
I also diagram out the double nordlock situation and note its shortcomings there.

If the lugs are constrained rotationally by some other means, then a single wedge-lock washer is appropriate by the manufacturer documentation.


Most square lugs are constrained rotationally by the breaker body itself as well.

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Isn’t this case closer to “Stud bolts”? The not recommended case is where you put a nordlock on top of a regular washer.

but i don’t think the ones used in FRC are right? I’ve never set up a FRC breaker like that at least.

no, the difference is that in the washer case there is something touching the nordlock that isn’t rotationally constrained (the washer, or in this case the lug).

you can see in this video that the “no washers” rule is intended to be generalized to all the listed valid use cases, not just the “tapped holes” use case.


I mean a nordlock on each side of the lug like the through-hole example on the chart.

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how do you think that would effect the electrical performance of the connection?

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I wouldn’t do it like that for 2 reasons:

  1. The through-hole example is for clamping two pieces of material with two fasteners that can spin (nut and bolt). In our situation the stud can’t spin, and the goal is to clamp the lug against the breaker. I think our situation is more akin to the stud bolt example.
  2. Most of the electrical connection between the breaker and lug comes from direct contact with the metal pad at the base of the stud- putting a nord-lock there would significantly degrade the electrical connnection.

We use lugs similar to these (picture below). The geometry of the breaker constrains the lug from rotating due to the squareness of the lug (similar to the situation seen here, although there is some ability for movement.


Like @troy_dietz mentioned, there is a conversation in the other thread about the use of nord-locks on terminal lug connections.

The bigger question is: is this termination method (nylock+nord-lock) better or worse than the default keps nut setup? I think it’s better, or at the very least isn’t worse- we did not have to re-tighten our main breaker terminals at all last season, where in previous seasons we’ve had to do it at least once or twice because they’ve loosened. (yes, yes, sample size of one… take this with a grain of salt)


you are correct, my mind was on the battery connections.

We might try normal nut + a second low-profile nylock nut this year, but we have had really good luck with keeping the lugs from being subject to twisting and torquing down the supplied nut to spec. As a CSA, I do see far too many of these that are loose though.