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Frayed wire strength?

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 ebdon 06 Jun 2022

Anyone got any idea how much a couple of frayed bits of wire on a nut will reduce its strength by? On a scale of say, total death to bomber.

 ScraggyGoat 06 Jun 2022
In reply to ebdon:

Not a lot, but after getting unexpectedly pricked like a needle by the broken strand while in extremis a few times it will seam like a false economy.  The only question is will you learn the lesson via your finger/palm, or via your lip….   Depending if you put wires in your mouth or not!

If you have one put on your winter rack and leave behind in preference when bailing.

Post edited at 19:33
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In reply to ebdon:

For £11.50 you can never need to find out

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In reply to ebdon:

If your wires are starting to fray, you might want to consider the state of the other wires; have they become work hardened?

Otherwise, you might expect it to derate linearly with fraction of wires broken.

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OP ebdon 06 Jun 2022
In reply to Longsufferingropeholder:

I bloody wish, it's a couple of black diamond micro wires that seem rarer than hens teeth!

 deacondeacon 06 Jun 2022
In reply to ebdon:

I had a frayed wire on Friday. When I fell on it, it snapped. I won't be climbing with frayed wires again 🙂

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OP ebdon 06 Jun 2022
In reply to ScraggyGoat:

Yes its surprising how often the one or two fraid bits find their way into my thumb. I think I shall be retiring them regardless as it's like climbing with a pin cushion currently

OP ebdon 06 Jun 2022
In reply to deacondeacon:

Ouch! A cautionary tail.

I have in fact ordered some replacements and shall relegate the offending articles to my pen pot at work whitch seems to have become a bit of a wire graveyard.

 CantClimbTom 06 Jun 2022
In reply to ebdon: 

It's tempting to estimate how many strands there are and then look at the proportion broken and factor down the strength that way, but that'd assume all remaining strands are in perfect health. Broken strands might have gone due to a combination of corrosion and mechanical stress, if so there might be some corrosion on the remaining ones. Failing that it might have taken a knock, if so are any other strands damaged. One way or the other the survivors aren't full strength.

For reference I found a couple of well used original wild country wired rocks size 2 in the bottom of a bag of non climbing stuff in the loft when looking for something and they're probably 25-30 years old. The wire isn't shiny! but none are broken so just age on it's own doesn't break strands.

​​​​​​Assuming they look otherwise good and there's only a couple of strands popped (and they're not spiking your fingers), you'll probably find that the wire isn't the weakest link unless they're big nuts perfectly placed. Replace them in due course... But no rush

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 henwardian 06 Jun 2022
In reply to ScraggyGoat:

> Not a lot, but after getting unexpectedly pricked like a needle by the broken strand while in extremis a few times it will seam like a false economy.  The only question is will you learn the lesson via your finger/palm, or via your lip….   Depending if you put wires in your mouth or not!

This.

I decided some time ago that I would just replace frayed wires for exactly this reason, just too many painfully stabbed fingers.

Other things worth bearing in mind are:

1) micronuts with the wires soldered into the heads tend to fray exactly where the wire meets the head and it's not obvious to see (and they don't have that much extra strength to spare), so inspect them regularly.

2) Check your cams where the solid metal part of the stem stops and the plastic cover starts, the broken wires there are completely hidden normally and I only discovered this particular cam foible when I was playing with a partners cam and discovered completely by accident that about half the strands were broken. Much to the surprise of my partner.

 henwardian 06 Jun 2022
In reply to deacondeacon:

> I had a frayed wire on Friday. When I fell on it, it snapped. I won't be climbing with frayed wires again 🙂

Wow, that's an interesting experience! What size/make was it? What was the nominal kN rating? How many strands were broken to start with? How big was the fall? Was it also rusty or otherwise worn or did it look fine except for the broken strands? Did the broken ends afterwards show any corrosion through the wire or other evidence of substandard strength?

 Ceiriog Chris 06 Jun 2022
In reply to deacondeacon:

> I had a frayed wire on Friday. When I fell on it, it snapped. I won't be climbing with frayed wires again 🙂

Interesting (although probably not for you at the time) , where did it fail ? was it the actual wire ?

 deacondeacon 06 Jun 2022
In reply to henwardian:

All I know is that it was a pretty small, non-soldered brassie. Don't know the size or kn but it was medium sized lol (ive chucked it now). There was 2 or 3 frayed pieces and when it snapped the wire slipped through the swage a little.

My other rope was through some threaded tat so I was fine.

It was a no-star route at the right hand end of Chee Tor. Can't remember the name.

In reply to ebdon:

Does this have anything to do with your search for first aid crib cards...?

OP ebdon 06 Jun 2022
In reply to captain paranoia:

I'm sort of hoping the one wont lead to a need for the other...

 kingholmesy 06 Jun 2022
In reply to ebdon:

I fell on one of my tiny micro wires last week, I think it was a DMM size 00 or possibly 0, and the wires snapped clean off where they enter the nut.  It was a pretty small fall (although I had quite a hard catch from my belayer) and I was very surprised it snapped.

That said, these wires are only rated for 2kn falls, which I think can quite easily be exceeded in a leader fall.

In the future I will only buy micro wires where the wire is soldered into the nut (rather than threaded through the nut), as I understand this allows a thicker (and therefore stronger) wire to be used for the same size nut.

 I would also throw away any micro wires where the wire is frayed - although I would be less concerned if there was a little fraying of a normal size wire as these are much thicker to start with.

 jkarran 06 Jun 2022
In reply to ebdon:

From memory, normal size nuts tend to be on 7x7 wire so 49 strands total. Each one is theoretically 2% ish of the total if they're loaded equally which is a big if.

Several of mine have the odd broken strand or two tucked back in. Your call ultimately.

Jk

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 TobyA 06 Jun 2022
In reply to kingholmesy:

This sounds very similar to accident that the BMC reported on maybe a decade or so ago?  I'm pretty certain it was Knight's Move (HVS 5a) at Burbage, and the micro wallnut was placed in the crux which is about the first bit of gear you place. From what I remember they worked out that with minimal amounts or rope out, the force on the piece exceeded the low breaking strength and the wire snapped. If it had been higher on a pitch with more rope out, it might have worked. 

Anyway, as a result I took my Walnut 0 and 00 off my rack and decided to only use soldered small nuts: RPs, Offsets, BD micro stoppers etc. I could have warned you in advance had you asked!

 beardy mike 07 Jun 2022
In reply to ebdon:

It's pretty simple to work out. Each strand broken is more or less directly proportional to the number of total strands. Most wire constructions used are 7x7 or 7x19 in climbing products. 7x19 would be used in microcams, 7x7 in most other things. 1 strand in 7x7 is 1/49 of total wire strength, 1 strand in a 7x19 is 1/133 of total strength. Bear in mind that the loop strength is nothing to do with the rated strength, but if you multiply your rated strength by your broken strand fraction you will be underestimating the remaining strength as generally the wire component is one of the stronger elements of the system.

Post edited at 10:03
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 beardy mike 07 Jun 2022
In reply to kingholmesy:

Dear lord, you're surprised that a 2kN nut snapped when pretty much the minimum load you'll see in a a fall is 3kN? Micronuts are marginal at best, they should be nested if at all possible to distribute load. If you are relying on a single 2kN micronut, you are well on your way to destination f'ed...

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 Moacs 07 Jun 2022
In reply to ebdon:

I would replace.  The factors that broke one strand have also been affecting the others, even if they haven't shown it visibly yet.

 PaulJepson 07 Jun 2022
In reply to kingholmesy:

Alloy micros (where the wire loops through) and brassies (silver soldered) have different applications really. Depends on the rock-type and the placement as to which is best. You've got to cluster the smaller alloy micros to expect them to take any more than bodyweight. 

I could be wrong but I think the general theory is-

Harder rock (e.g. granite) is better to use softer metals (e.g. brass) on. On softer rock the alloys can be better as they get a lot more surface-contact?

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 bpmclimb 07 Jun 2022
In reply to ebdon:

> Anyone got any idea how much a couple of frayed bits of wire on a nut will reduce its strength by? On a scale of say, total death to bomber.


The strength will be reduced by exactly 63.5%. Regardless of all other factors.

 TobyA 07 Jun 2022
In reply to PaulJepson:

> Harder rock (e.g. granite) is better to use softer metals (e.g. brass) on. On softer rock the alloys can be better as they get a lot more surface-contact?

That sounds like one of those classic climbing 'presumed truths' that there is actually no, or next to no, evidence for. Regardless of rock type I would just use whatever style micro nut has the greatest strength, and that's soldered ones. 

I googled and found the BMC report I mentioned earlier. Turns out it was 2003! So 19 years that we've known alloy micro wires are a bit rubbish. I'm surprised actually that DMM are still making the 0 and 00, when their own brass nuts of the same size are twice and 4 times as strong. 

 TobyA 07 Jun 2022
In reply to TobyA:

the link I mentioned above is: https://www.thebmc.co.uk/ae-microwire-failure 

 beardy mike 07 Jun 2022
In reply to TobyA:

I think the presumed wisdom is about rock failure rather than the wire failing. No point in the wire being strong enough if the nut pulls through the rock. Like you say, whether that's actually the case, I don't know.

OP ebdon 07 Jun 2022
In reply to beardy mike:

Interestingly the case in point with one of my frayed ones (a BD micro no.3) the placement did indeed rip rather than the nut snap. 2 wires have snapped at the head though (as I think is common with soldered ones) and I felt it give a fair bit of resistance. It was probably not far below my feet so not a mega fall, but far enough!

Fortunately backed up with several bomber pieces.

 beardy mike 07 Jun 2022
In reply to ebdon:

It's well possible that you've stretched the wire a bit too. Soldered joints are a point of stress due to flexure of the wire at the joint, but then so are hydraulically crimped ferrules. Where the stainless steel termination is pressed into the cable you have a stress raiser which coincides with a flex point and I have it on good authority that whole heads of cams come off sometimes due to that flex... not much you can do about it though other than watch your gear...

 kingholmesy 07 Jun 2022
In reply to TobyA:

Thanks. That’s a really useful link and explains clearly why you really don’t need to fall very far at all to snap a 2kn rated nut - my understanding of that article was you’re not that far off that sort of load just sat resting on the rope.

 jim jones 07 Jun 2022
In reply to ebdon: It’s been discussed many times on UKC. Best just to bin them, you’ll never know how many strands inside are broken until it’s fallen on. Aerospace standards dictate one broken strand in a cable = scrap and immediate replace. 

Post edited at 22:26
 Toerag 08 Jun 2022
In reply to kingholmesy:

> Thanks. That’s a really useful link and explains clearly why you really don’t need to fall very far at all to snap a 2kn rated nut - my understanding of that article was you’re not that far off that sort of load just sat resting on the rope.

Yep, Andy K wrote that bounce testing a bit of gear in etriers will generate 2kN easily.

In reply to ebdon:

> I bloody wish, it's a couple of black diamond micro wires that seem rarer than hens teeth!

A frayed wire on a micro wire? I wouldn't risk it. (not that I'd risk it on a 'normal wire)


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