Manual Crimping

Task
Installing connectors for No. 10 and No. 12 electrical wires

Problem
Although demand for crimping is highly variable, an electrician will frequently perform approximately 200 crimps per day. This requires high grip force and is often done in tight areas with limited access. Risk factors include high force, high repetition, and awkward postures of the upper extremities.

An electrician purchased an expensive new design advertised as "ergonomic", but he and his co-workers had doubts about the benefit of this crimper compared with the brand they were already using. Ira Janowitz of the University of California Ergonomics Program was asked to evaluate the new crimper on site at a construction site.

Intervention
A comparison was conducted of the standard crimper (A) and the new, "ergonomic" crimper (B). Samples of No. 10 and No. 12 wire were obtained and a Chatillon strain gauge was used to conduct measurements of the force required on the handles to make a crimp.

Cost
$187 (money saved by not purchasing each additional "ergonomic" crimper)

Observations
Posture: Upper extremity postures were more awkward with crimper B, due to the thickness of the "nose" of crimper B.

Tool weight and balance: Crimper B was heavier than the standard crimper, with more weight unbalanced toward the "nose".

Force: Mean crimp force results (in pounds) were as follows:

Wire Crimper A Crimper B
No. 12 85 98
No. 10 110 119

It is recognized that large numbers of tools may have to be sampled before any conclusions can be drawn, as there is considerable variability from one tool to the next, even within the same manufacturer and model. Unlike cutting tools, crimpers may require more force to use when new than when they have been "broken in".

Evaluation of Intervention
The risk factors of high force and awkward posture were both worse with the "ergonomic" crimper (B).

Semi-Quantitative Evaluation of Intervention

  • Reduction of Identified Risk Factor
  • No New Risk Factors Introduced
  • Productivity not Reduced
  • Low Cost
  • Total
  • 1/5
  • 3/5
  • 2/5
  • 1/5
  • 7/20

This evaluation of crimpers illustrates the following points:
1. Claims of “ergonomic design” need to be taken with a “grain of salt”.

2. Any tool evaluation must be a multi-factorial. In this case, even if the "ergonomic" crimper had required less force, the fact that its nose is thicker and heavier than that of the standard crimper makes it more difficult to use in tight spaces.

Of note is the fact that the forces required to produce a satisfactory crimp (85-119 pounds) is in the same range as the 1-repetition maximum grip force for males. This means that male electricians are functioning very close to their maximum in terms of the muscle and tendon forces in the forearm, wrist and hand. Many female electricians would not be able to exert these forces using only one hand. With a high repetition rate, this is likely to lead to high levels of fatigue and possible upper extremity cumulative trauma for males and females.

Recommendations
The force required is partly a function of the connector design and materials. For highly repetitive crimping jobs, it is recommended that employers and engineers re-evaluate their specifications for connectors in case a lighter gauge metal would be adequate.

Use powered crimpers for heavier gauge or high repetition jobs.

Job rotation, if other tasks offer recovery time from gripping.

Acknowledgements
Submitted by Ira Janowitz, UC Ergonomics Program