6.5.4 Design Considerations

  1. Electric power operated hoists should be of adequate design taking into account the requirements of the relevant standards for the hoist, trolley, runway or slewing jib and electrics.

  2. The marked SWL should be suitable for the load being handled. At no time must the load applied to the hoist exceed the marked SWL and allowance must be made for any possible shock loading which may occur.

  3. The hoist should be fitted with an automatic brake capable of arresting the mechanism and sustaining the load. Such brakes are mechanically applied and electrically released so that in the event of power failure the brake is automatically applied.

  4. In the case of power operated chain hoists, it should be realised that the action of the chain passing over the pocketed wheel causes an oscillation in the loaded side of chain and on long falls this can cause the load to swing. Manufacturers therefore limit the recommended range of lift for which their models of hoist are suitable.

  5. The hoist should be fitted with positive hoist/lower limits to prevent inadvertent over-hoisting or lowering. Lack of over-lower limit on wire rope hoists can lead to the danger of the rope rewinding on the drum in the reverse direction, resulting in the reversal of control sense and non-function of the over-hoist limits. When it is necessary to restrict the hook movement to suit a particular process or duty, additional working limits must be fitted, hoist limits must not be used for this purpose.

  6. All operating push buttons should be:

    1. Shrouded to prevent accidental operation.

    2. Of the ‘hold to run’ type, i.e. motion stops when the button is released.

    3. Interlocked to prevent conflicting commands, i.e. only one button will operate at a time.

  7. In the case of power operated hoists with top hook suspension and on all bottom hooks, it is important that hooks and other devices provided for lifting should be of a type that reduces the risk of the load becoming displaced from the hook or other devices. This requirement can be met by the use of hooks with safety catches or by the use of ‘C’ hooks. Most hoist manufacturers fit hooks with safety catches as standard.