Everything hung overhead has weight, and every truss, clamp and motor has a rated limit. Get this wrong and the consequences are not a re-patch — they're a falling fixture. This is the part of the craft with zero tolerance for guessing.
SWL is not breaking load
SWL (Safe Working Load) or WLL (Working Load Limit) is the maximum you're allowed to apply in use. It already includes a safety factor below the point where the component fails. You design to the SWL, never above — and never assume the breaking load is your budget.
Distribute, bond, sign off
- Distributed vs. point load — a truss rated for a spread load can fail under the same weight concentrated at one spot.
- Safety bonds — every fixture needs a secondary suspension rated for its mass, in case the primary clamp fails.
- Span matters — a truss's capacity drops as the distance between support points grows.
- Competent sign-off — a qualified rigger checks the hang. Always.
Safety factors and dynamic loads
Where the safety factor goes: a chain hoist rated 1000kg WLL may have a minimum breaking load several times higher — the ratio is the safety factor, and it exists for shock loads, wear and the unknowns of a real load. You never eat into it deliberately.
Static vs dynamic: a motor lifting a load applies more force than the static weight while accelerating. Ground-supported towers, outdoor wind loading and moving performers all add dynamic forces a static weight sum never captures — which is why a qualified rigger, not a calculator, signs off the hang.