ATC Belay Guide Devices- Strength of the large loop when in guide mode---Device contains a non-redundant, catastrophic failure point

Dave K wrote:

Despite the sarcastic answers, I'm sure everyone here had similar thoughts the first time they saw a guide-mode device. Maybe not about redundancy, but simply about trusting that small loop of aluminum. It doesn't look very solid. But it is more than enough to hold body weight.

Yeah, I only trust partial loops of aluminum with moving parts. The cross sectional area of a carabineer isn't all that different from that of the guide loop.

Your glasses?

Tamiban Gueterstan wrote:

No descender/belay device has a breaking strength stamped on it because the results would be meaningless and inactionable for the intended use. Pull a rope really hard through an ATC guide and it will slip before the device breaks. If you tie-off the rope through an ATC guide and the rope will break before any of the hardware. So for any standard use the rope breaks first, so what exactly are you supposed to stamp on the device? A paragraph about the testing parameters down to what rope was used and how it was tied off?

So what if you put 2 carabiners in the guide hole and pulled it until you broke the aluminum. Or a carabiner through the rope channel and one through the guide hole and you pull until you rip the aluminum apart. You can get a kN figure but what are you supposed to do with that figure? Are you planning on using the ATC guide as a rigging plate? Carabiners have a kN MBS because some people actually need to estimate how close they are to breaking a carabiner, climbers usually don't. When are you going to need to estimate when you're going to snap your ATC guide in half based on some measured load? If all you need is the reassurance that it's strong enough, trust that the manufacturer is reputable, not that they can print some specific number you think is arbitrarily high enough.

Well roughly yes. They are tested anyway to 7 or 8kN to check they don't destroy the rope and with the usual modern ropes in use you'd be lucky to get 3-4kN in guide mode before the rope swaps over and slips. Put thicker ropes in (10+mm) and you start seeing numbers like 8-10kN before the rope sheath cuts and the whole lot slips.

I've destruction tested a few devices over the years but that private information, only a few manufacturers actually give the strength of their devices.

Tamiban Gueterstan wrote:

No descender/belay device has a breaking strength stamped on it because the results would be meaningless and inactionable for the intended use. 

for recreational devices, this is true...but goes out the window when you enter the rope access or NFPA world of descending devices...

One that is rated.

yeah, any of those devices that are also rigging plates will be rated, my grivel scream (like a gigi but for skinny ropes) is rated to 30kn, their shuttle says 20kn on the website

Meaningless to you as you have stated passionately, but yeah, do that pull test to ease others concerns, please.

The Scream isn’t a rigging plate but has a rating?

You can lead a horse to water (or a noob to knowledge) but you can't make him drink.

Tamiban Gueterstan wrote:

I think it's basically true for rope access and rescue descenders as well. These will have a working load limit around 200kg, without a breaking strength. Any MBS printed on these devices will be for use as a pulley: MPD, Clutch, Maestro. Or the strength of the frame from anchor to becket. The Petzl ID, the most popular rope access descender in the world does not have an MBS, nor would one really make sense.

To be very technical... NFPA weirdly does have MBS for descent control devices but these are manufacturer standards, not printed on the device, not meant to be considered by the user, and not wildly known. For example, for NFPA-G gear, the descent control MBS is 22kN, and has nothing to do with the NFPA-G carabiner MBS of 40kN. This is not, as was never intended to be a universal minimum system strength. And so I stand by my comment that descent control devices do not have MBS with this caveat.

we're getting a little into the weeds here. the overall point i was trying to make is there indeed a subset of descending devices where the manufacturers include load ratings/limits (either MBS or WLL) on their devices because of the standards they are designed and certified to.