Where did the assignation come from originally?

I'm currently playing with a system that has a 24V DC control panel
and every relay has A1 connected to 0V.

Not really a problem currently, but a few years back I took out a
channel of a dedicated control unit when thoughtlessly adding a diode
quenched relay to a digital output through connecting A2 as per
drawing. i.e to the digital output of the controller.

The control panel wiring in that was 24V too, although the panel
builders had obviously not wired to the "as builts", which showed
every A1 grounded.

The damaged controller was got around with the aid of a software
Engineer back home who managed to nominate a spare i/o, but since then
I have been very wary of the consequences.

Does A1/2 misidentification cause problems generally? is it common to
ignore polarity in systems with "unquenched" relay's?

AB

On Sun, 07 Jul 2019 08:01:24 +0100, Archibald Tarquin Blenkinsopp
wrote:

Where did the assignation come from originally?

EN50005

BS5472


I'm currently playing with a system that has a 24V DC control panel
and every relay has A1 connected to 0V.

Not really a problem currently, but a few years back I took out a
channel of a dedicated control unit when thoughtlessly adding a diode
quenched relay to a digital output through connecting A2 as per
drawing. i.e to the digital output of the controller.

The control panel wiring in that was 24V too, although the panel
builders had obviously not wired to the "as builts", which showed
every A1 grounded.

The damaged controller was got around with the aid of a software
Engineer back home who managed to nominate a spare i/o, but since then
I have been very wary of the consequences.

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'

But it often depends on the earthing scheme, for instance you could have a 48v
positive earth with a switched negative and a 110v negative earth with a
switched positive
--

On Mon, 08 Jul 2019 09:57:15 +0100, The Other Mike
wrote:

On Sun, 07 Jul 2019 08:01:24 +0100, Archibald Tarquin Blenkinsopp
wrote:

Where did the assignation come from originally?

EN50005

BS5472


I'm currently playing with a system that has a 24V DC control panel
and every relay has A1 connected to 0V.

Not really a problem currently, but a few years back I took out a
channel of a dedicated control unit when thoughtlessly adding a diode
quenched relay to a digital output through connecting A2 as per
drawing. i.e to the digital output of the controller.

The control panel wiring in that was 24V too, although the panel
builders had obviously not wired to the "as builts", which showed
every A1 grounded.

The damaged controller was got around with the aid of a software
Engineer back home who managed to nominate a spare i/o, but since then
I have been very wary of the consequences.

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'

But it often depends on the earthing scheme, for instance you could have a 48v
positive earth with a switched negative and a 110v negative earth with a
switched positive

No idea if 0V was ground.

AC wouldn,t matter

AB
AB

Saol fada agus breac-shláinte chugat.

Unless of course you are a Brexit voting moron or
child molester

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 got a sweater for Christmas. I really wanted a screamer or a moaner*

Dave Plowman London SW
To e-mail, change noise into sound.

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?

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

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.

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.

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
To e-mail, change noise into sound.