13. Safety Alerts National Grid
 >  (continued) Incident Loosening Wire Clamp

Recently, there was an incident where the winch wire slipped out of a temporarily installed wire clamp. The winch wire swung away and landed against an employee's hand causing injury to the upper phalanx of the right ring finger.
The photos below show the deployed clamp.

Tensile Test

To ensure that this application is safe to use, a tensile test took place. The purpose of this test was to determine whether this application would be strong enough under normal conditions. The tests were carried out on the basis that the setup should be able to withstand more than 5 tonnes of force. This is the maximum tensile force of our own winches.


  1. Cable with pressed pulling eyes. Result: 10460 kilograms;
  2. Cable (with welding point on end) with wire clamp mounted with torque spanner (instruction of manufacturer). Result: 7600 kilograms;
  3. Cable (with welding point on end) with wire clamp mounted with impact spanner (2800Nm). Result 8800 kilograms.

In practice, however, a splice point (as in the photo on the right) is not present when a
repair is carried out performed on a cable. The end is then held together with a piece of
tape. This situation was tested with the following results:

  1. Cable with wire clamp mounted with an impact spanner. The end of the cable taped in. 7300 kilograms;
  2. Cable with wire clamp mounted with impact spanner. In this setup, a piece of the tape ended up in the clamp (approx. 1.5 cm of tape inside the clamp). Result: 5000 kilograms.

Measures > What to do?

Actions – What to do?
Based on the tensile test, we can conclude that:

  1. The wire clamp works when properly mounted. However, if there is tape between the clamp during assembly, we see that this makes a significant difference. The tensile force then becomes 5000 kg depending on the amount of tape between the clamp. It is therefore possible that the clamp comes loose at a lower pull force;
  2. A pressed pulling eye offers the best result.

On this basis, the Board issues the following instruction:

  1. A pressed pulling eye should be deployed in the base;
  2. The winch wire must always be visually checked beforehand. If the winch wire is damaged, never start it;
  3. A wire clamp may only be used as a temporary solution to repair damage in order to complete one pull. It must be possible to prove that the wire clamp is properly secured and pre-loaded (properly mounted + no tape between the clamp + pre-loaded = start work).

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