chh wrote:Then I don't see how the strength of the cord is of any importance.
I assume you DO think that it must meet
some minimal strength. You would balk if we went climbing and I belayed you off an equalette tied from dental floss, wouldn't you?
chh wrote:If there is any difference though in the quality of the placements, in this configuration, you put the loop on your strongest piece. I'm sure you know this already.
No, that is incorrect in a very important way.
You put it on the piece you think is strongest. That is more a function of placement than the MBS on the piece. I'd trust a well-placed 7kN piece over a poorly placed piece of...any rating. And you can be wrong about the strength and reliability of your placements. That's the main reason for placing multiple pieces for an anchor in the first place.
You've provided a number of reasons why the cord might not have to be 20kN strong, in some circumstances. None of them are reasons why it doesn't have to be 20kN strong.
Who says this all happens in the first fall? What if you have partial anchor failure due to one fall, resulting in one piece taking more of the load on another fall? It's in a second fall when the rope will be less shock-absorbing anyway.
A more likely situation would be that the angle between the arms is 90 degrees (or becomes 90 degrees when things stretch and tighten down a bit in a fall onto it). Then the load on each arm is about 70% of the load on the power point. Suppose the load on the power point is 10kN. Then the load on each arm is about 7kN. If the cord has a 10kN MBS and the clove hitch reduces its strength by half then each strand of cord with a clove hitch in it is 5kN strong. 5/7 is about 71%. So if 71% or more of the load in either arm of the equalette is on one of the clove-hitched pieces (which will ALWAYS happen once the length of cord from the power point to the clove hitch is sufficiently different), then the cord will fail. This doesn't seem like such an unlikely scenario.
I agree that none of this warrants carrying around 20kN cord. But it might warrant not using an equalette.
But I don't think that either. I think knudeNoggin is on to something, and my assumptions about strength reduction due to knots are wrong. I think that cord doesn't decrease in strength due to knots--even clove hitches--nearly as much as I have assumed.
I'll check into published cordelette tests and post again.