Connecting parallel cables in a ropes course

The standards for cable connections (EN 13411 series) define only "Eye-splices":

In ropes courses we have different applications, one is the connection of 2 cable ends.

Here the standard for ropes courses EN 15567 defines:

I wanted to test this application.
In a first test I did it like I see normally: 
Most of the builders do not grease the clamps. And they tighten only once. Only a minority uses a torque wrench.

So - i prepared a test piece with 9 Nm, ungreased, an let it rest for 15 hours.
The torque has dropped to 5-6 Nm.

The slipping load was 23 kN.

This is definitely not enough for a high load.

Then I retightened the clamps to 9 Nm. But the load was not really higher (26,7 kN):

So - I tried it with properly applied clamps:

Greased, tightened to 9 Nm.
The result was disappointing, again: Only 32 kN.
Still not enough for a high load.

The only way to reach a slipping force that would be appropriate is to increase the torque.
As I wrote before, the higher the torque the higher the load.
I increased from 9 Nm to 15 Nm (50 kN), to 18 Nm (67 kN), and finally to 20 Nm (70 kN), when the cable broke.

I wrote an email to the DIN (German Institute for Standardization) for clarification, to provide the data on which this recommended application is based on.

Until this is not clarified (maybe I made a mistake in my tests) I recommend:
Do not use this application (stated in the EN 15567-1) if you need high loads, like in long zip lines, heavy elements etc.

Rather use this application:

And follow the rules:

1. use grease on the screws
2. retighten as many times as necessary (maybe 3-4 times, until the torque does not change any more).
3. check for slippage (make a marking, check after the first loads and during inspection).

Use rather a higher torque than a lower. I recommend in this application 18-20 Nm.

Appendix: Data