Re: Votre avis fusibles (Commentaire ou Suggestion)
Envoyé par: lionel cormier (Adresse IP journalisée)
Date: 10/05/19 07:10
Conductive greases and anti-seize compounds have a suspended base metal powder. The suspended metal powder is a fraction of the area occupied by insulating grease, and so the grease still insulates the connection. The grease does not conduct.
The working theory of "conductive" grease is when pressure is applied, the grease squeezes out of the way. This leaves a fine metal powder that theoretically pierces oxides or fills voids. Using aluminum and copper blocks with various surface conditions, I've never been able to actually verify connection improvement from specialized conductive greases. In my tests, it appeared the grease simply carried most of the suspended powder away. Any remaining powder has never been enough to reliably reduce voltage drop across clamped connections. The change in voltage drop has always been indefinable, even with careful repeats of clamping pressure. I'd appreciate anyone having useful data sending me a copy.
The suspended powder creates a problem that does not exist with dielectric grease. The suspended metal must be fully compatible with the metals being clamped. This means conductive grease is application specific. If the metals being clamped are incompatible with the grease's suspended metal powder, the connection will eventually fail. This is what happened in our CATV system connectors. The connections were a mix of copper, aluminum, and steel. The cable shields were aluminum, the trunk center conductors cables were copper clad aluminum. Drop cables were aluminum shields and connectors, with copper clad steel centers. Our records showed a much higher incidence of corrosion failure using conductive grease. Corrosion failure rate dropped significantly, almost to zero, when we switched to pure dielectric grease.
In bolted or clamped connections, I have no opinion if conductive greases help or are necessary. I feel like they help, but I'm not sure if that is true. I use Noalox on clamped aluminum slip joints in antennas because it is generally less expensive than silicone dielectric greases and it appears to last longer. I NEVER use conductive greases on push fit electrical connectors, or if I am unsure of metal to grease compatibility.
Conductive greases should specifically match materials being clamped. Conductive greases should never be used in low pressure electrical connectors, or in connectors with multiple terminals. Conductive greases should only be used in connections that are well-isolated from connections with differing voltages, and never in high voltage connections. They never belong in RF or signal connectors, unless they are bolted connections and the material compatible grease does not bridge insulation.
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