Knowing your working load from your breaking load

Steel ropeOne thing to keep in mind is the difference between WLL – Working Load Limits, (or otherwise known as SWL – Safe Working Limits) and BLL – Breaking Load Limits.  And one anomaly is the potential confusion between load specifications between chain and wire rope; and fibre rope.

Chains and wire rope work on WWL’s, while fibre rope (polypropylene, nylon, polyester, dyneema, manila, sash, braided etc.) have BLL’s as an indication of what loads they can cope with.

Just to make it clear, the WLL on chains and wire rope is 20% of the breaking load.  So a 1 tonne working load, will only snap at 5 tonne (giving the operator real piece of mind when lifting heavy loads within their working load limit.)

Unfortunately the fibre rope industry mentions breaking loads on their weight loads specifications.  So a 1 tonne breaking load really is the maximum the rope can cope with.  To give you  breathing space – you should ask for a fibre rope with a weight tolerance considerably less than the breaking load.

Then you have a safety factor on the weight loads you are asking your fibre rope to work with.  So your 4 wheel drive winch won’t snap at the 1 tonne breaking limit, when you should have – maybe 1.5 to 2 tonne breaking load.  Once you also factor in the ‘shock’ – sudden load shock – placed on your rope, it is even more important to factor in more than a breaking load limit on fibre rope.

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