In article ,
The Other Mike wrote:
On Tue, 09 Jul 2019 14:11:38 +0100, "Dave Plowman (News)"
wrote:

In article ,
The Other Mike wrote:
Does A1/2 misidentification cause problems generally? is it common to
ignore polarity in systems with "unquenched" relay's?

Switching a 'live' is generally preferable to switching 'earths'

Really? On car EFI systems, most is ground switched. Gets rid of the need
for a high(er) current positive rail on the PCB - the ground layer
normally being pretty massive.

I agree the likes of injectors (and ignition coils?) are low side
driven, maybe an architecture that evolved from the early days when N
channel mosfets were (and are?) always more rugged?

Yes.

Switches such as oil pressure warning also switch to earth, but the
likes of lamps on modern vehicles still seem to be live switched from
a body control ecu or local canbus node with an earth to the bodyshell
at or close to the lamp

Quite - where you can happily share a ground, the car body make sense.
Reduces the wiring needed for the power side.

Back to the original 'industrial' scenario switching 'live' reduces
somewhat the possibility of a stray earth causing an unwanted
operation / indication, said stray earth possibly introduced by four
or eight legged wildlife exploring a control panel.

Never thought of that.

For controlling things switching both +ve and -ve together with
circuit integrity monitoring is the norm when you need assurance it's
going to work when required and avoid false operation.

--
*I'm not your type. I'm not inflatable.

Dave Plowman London SW
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