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Are the set/reset coils on a 2 coil magnetic relay actually any different if the contacts are form C? The datasheet lists one as "operate" and the other as "reset", but in practice they both just switch the contact from one pin to the other, right?

For example with the pictured relay:

  • I could put the load across pins 11 and 12. A2 would turn it on and A1 would turn it off.
  • I could put the load across pins 11 and 14. A1 would turn it on and A2 would turn it off.

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Is either of these arrangements better? I am trying to lay out a small PCB and it makes my routing much easier to use the "reset" as the "on" and the "operate" as the "off".

Teo
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1 Answers1

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You are correct. Both cases exhibit the same behaviour and can be used interchangably.

The only way in which it would differ is if they were Form A/B relays, in which case it would matter which is which.

The naming convention for set/reset will be carried over for a mixture of convenience (e.g. common datasheets), and/or to relate the operation of coil to the corresponding selected contact based on which is labelled NO and which is NC.

I suppose the only difference might be the default state the relay is supplied in, but that probably can't be relied on anyway, so isn't really worth worrying about.

Tom Carpenter
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