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What does it mean to cross load a carabiner? I know it's bad, and not to do it, but I don't really know what exactly it is.

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Even more dangerous than cross loading is nose hooking, a nose hooked biner can fail under body weight forces blackdiamondequipment.com/en-us/journal/climb//… –  crasic May 3 '12 at 20:47

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up vote 15 down vote accepted

A carabiner is designed to be loaded only along the long axis, near the spine (leftmost figure below). It will be weaker in any other direction of stress. Primary long-axis strength should be marked on the carabiner spine with an up-down arrow symbol, and is typically given in kilo-Newtons (one kN equals approximately 225 pounds of force).

Cross-loading is shown in the middle figure below. Strength in this orientation should be marked on the carabiner with a left-right arrow symbol.

The gate is a load-bearing member even when the carabiner is correctly loaded, therefore the "open gate" strength is much less, as should be marked with a symbol that looks like an open carabiner. Be aware that the inward gate strength is usually much less than the outward cross-load gate strength because only the locking sleeve holds the gate in place.

There is another weakness you need to be aware of: loading the carabiner at a point or direction away from the spine. This happens in "tri-axial" loading seen in the rightmost figure, or with a nose-hooked carabiner. This is or can be even weaker than the cross-loaded configuration.

enter image description here

Here is another instance of tri-axial loading (source). This is probably not as weak as a carabiner loaded the same way but upside down, because the offset-D has a shorter lever arm in this configuration, but it is still weak:

enter image description here

Likewise a carabiner loaded with multiple ropes, or a single rope with a bulky knot, even if loaded in the same and proper direction will be weaker on the strand(s) farther from the spine. (source)

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Nice illustrations of the point. Particularly the multiple strand load issues. –  Russell Steen May 2 '12 at 22:56
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It's worth noting that using a carabiner on your harness and looping the carabiner through 2 straps on the harness (instead of using the webbing loop that holds those 2 loops together) and connecting the other end to a piece of gear like an ATC or something will create the same tri-axial pull. This is a common mistake I see all the time even in veteran climbers. –  MaskedPlant May 24 '12 at 18:45
    
@MaskedPlant indeed; just a few days ago a corrected someone who was putting a carabiner through both points on the harness to belay rather than using the belay loop. –  Mr.Wizard May 25 '12 at 0:03

It represents a two major things. I'm not going to illustrate, but the core of it is:

  • Don't load carabiners across the gate or spine side of the carbiner (i.e. the side opposite the gate). This is pretty obvious, but happens sometimes when you make an anchor or whip out a quick draw and then load it without getting all the carabiners in-line with the force that will be put on them.

  • Don't load carabiners across an external edge. If your anchor runs over an rock ledge, this would manifest as having the power point carabiner half-over the edge.

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Ahh, ok, yea that's what I thought but I wasn't sure. I've seen it happen with people clip in. –  Patrick Scott Apr 23 '12 at 19:40

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