On Thu, 21 Dec 2017 18:44:31 +0000, Mike Fleming
wrote:

In article , "Dave Plowman (News)"
writes:

In article ,
Mike Fleming wrote:
In article , "Dave Plowman (News)"
writes:

Got a switch story from my old car. The window switches control relays.
The exact same Lucas switch is used on other makes with no relays. On
mine, the switches need regular cleaning. In the high power use, not.

When switching relays, presumably it's breaking the supply to a
reactive load?

Yes - although with only about 100mA flowing, not enough of a spark to
keep them clean.

I was thinking of the high voltage arc as the field collapses causing
damage to the contacts.

The trick for the best switches is the wiping contact. Initial contact
and arc happens at one spot, then the blades slide across each other
and final contact is made at a clean spot. And the wiping action
ensures that oxidation is never a problem either. Those switches tend
to cost a bit more, though.

d

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