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Electrical resistance of a Cadmium coated Aluminum Connector

2004

Hi,

We use a large connector on one of our products. The shell of the connector is screwed to the case to provide an earth. We require that the electrical resistance between the shell of the connector and the case is very low (preferably less than 1.5 milli ohms).

The connector is aluminum which is coated with a nickel layer and then a cadmium layer with a chromate conversion layer. We have been unable to consistently achieve the required resistances, and have found that readings are erratic and unpredictable (for example the resistance will increase very quickly if we take multiple measurements and stay high). Other, very similar, connectors made from Aluminum with a nickel finish do not cause up any problems.

The case is Aluminum L93 with an alocromed finish. We have also tried an Aluminum 6082 case with alocromed finish with the same results.

I would welcome any theories as to what is causing the problem. Has anyone had similar experiences?

Many thanks

Dave

David Cuff
electronics mfgr - Birmingham, UK

Sounds like you have just re-discovered an engineering rule-of-thumb: Don't use a connector shell as a conductor. Use a pin in the connector for continuity and if you need the shielding provided by the connector shell, connect it to that newly assigned pin.

Tom Gallant
- Long Beach, California, USA
2004