If i get it right you talk about steel cables as secound saftey for the rigging?
The common rules in Germany are :
(old) : BGV C1
New : DGUV Vorschrift 17
The part you need wasnt changed and you may only find the old version.
The importand parts:
Every part you mount over persons have to be saved twice. ( your normal mount + your safety)
Ropes are not allowed / You have to use steel cables or chains (first & secound mount)
Maximum way in case you first mount fail is 0.2m
The parts you use must be suited for the load they have to carry in the worst case. ( Also think about dynamic force when your projector "fall" till the safety hold it.)
The safety Cable you use need to be checked every year.
If you want to be totaly save. Insurance Stuff and so on. Then let the tec guy in place mount it for you
Further Informations are written down in about 10 different DIN VDE ( like ISO) and are very complex.
DIN 56927
DIN EN 1492
BGI 810 -3
BGI 622
Germany =/
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