I hear and see it stated quite frequently on the web to not use nylocs on batteries. Okay fine, can we examine this a bit..?
The nylocs I use are rated to 140C for the safe working range. This is 284F. The best marine UL1426 battery cable you will find is rated to 105C. There are still thousands and thousands of boats out on the water, built in the 70's & 80's, using 60C rated battery cable, sad but true.. If the nylocs will melt and cause a failure then I suppose we may all need at least 140C rated marine wire too?
Of course we can't just look at the safe working range if we want to see when an actual failure might occur. Where would that likely occur? Probably somewhere close to the melting point for the nylon...
The actual melting point is about 425 degrees... But for a seat of the pants look we can still use the safe working temp of 140C/284F..... Of course if you have soldered battery lugs you could have a solder that actually melts at between 360F and 425F, about the same as the nylon in a nyloc.
But wait we certainly can't forget about the plastic battery cases which are made of polypropylene. Polypropylene, or the battery case, actually melts at approx 100F BELOW where the nylon in the nyloc nut does.. We are seeing exactly that here in this case.. Oh my Gawd fellow netters we'd best get rid of those plastic battery cases. (wink)
Letís also look at the way the vast majority of inexpensive batteries for marine use ship to us? Many marine batteries, even today, and I install hundreds of them, still ship, believe it or not, with hex nuts but no locking washer. Yep you guessed it there is no lock washer to be found with many of the price-point brands. Heck there are still some brands shipping with wing nuts and no locking mechanism.
There are however a good number of premium battery battery makers, who actually do supply locking washers, they are Odyssey, Northstar, Firefly, Victron, Full River, Rolls, Lifeline, Mastervolt & just about every LiFePo4 prismatic cell manufacture I know of. All the batteries brands I just mentioned can deliver MASSIVE amounts of short circuit current into a dead short.
So, would using a nyloc be worse than what the factory shipped the battery with? Remember MOST marine batteries ship with wing nuts or regular nuts but NOTHING to "lock" them with....
Interesting question, and in this case, the nut was still well "locked" so I'd have to vote for the nyloc being better than nothing....
Why does this matter? Because before your nyloc can melt, the battery will have likely already begun to melt, as it did here. So even if you somehow exceeded the 284F, and the nyloc failed to perform its locking feature, we would still need to have a nut torque failure on top of all this. Course we had BOTH here but not due to the nyloc failing.
We would need two failure modes to have the actual failure of a nyloc. A melted nyloc and an improperly torqued nut to begin with. I propose that before this nyloc failed the battery case would have been so melted that the owner would have been alerted to something well before the nyloc became an issue.
The way most batteries ship, WITHOUT ANY LOCKING WASHERS, your failure mode is just ONE! Add a nyloc and you now need TWO failures before anything bad could happen.
I see thousands of battery posts every year with no locking mechanism. Do I carry piles of 5/16" and 3/8" lock washers and 5/16" and 3/8" nuts, you bet I do. I also however carry a lot of 5/16" and 3/8" Nylocs too. I go through multiple boxes of 100 each of lock washers and Nylocs 5/16" and 3/8" every year..
My personal preference here is to use a locking washer when ever I can, but when it won't fit, I have no issues using a properly torqued nyloc on a battery terminal.
How often do I see regular nuts, like most battery manufactures actually ship the product with, that lack a locking washer actually come loose? Pretty rarely... When I do there are often signs or evidence they were tightened by a pair of pliers, as is the case here..
When tightened with a wrench it is very rare to see a loose standard nut, even without a locking washer. The key words are "properly torqued"... This is the reason the ABYC & marine industry in general has moved away from wing nuts. People opted not to use a wing nut wrench and thought proper torque meant with thumb and finger. It is simply NOT possible to properly torque a wing nut with your thumb and fingers. It is also not advisable to torque standard nuts with a pair of cheap pliers.. Would you torque your lug nuts with pliers...........??
I can personally point to numerous instances of loose wing nuts, but not a single case where a nyloc came free because it melted and vibrated loose. In almost every case of a wing nut coming loose it was because the installer made the nuts "finger tight" which is a far cry from wrench tight..
I find it interesting to note that the ABYC safety standards specifically prohibits wing nuts above 6GA wire but they make no such prohibition for nyloc nuts.
My only point here is to suggest that I would rather see a nyloc used than the option of a regular nut with no lock washer or a wing nut with no lock washer. My first preference is for a nut and locking washer, second a nyloc and third a regular nut properly torqued. Unfortunately there are situations where a regular nut is all that will fit on the post and in this case proper torque is a must..
Just some points to ponder... Rant officially over.... (smile)