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I am adding a socket mounted relay to a PCB and only need one set of contacts (SPDT).

Does it increase the reliability of the component to connect the both sets of contacts? Are there any other issues this creates? Common practice or bad practice?

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Note that I do not intend to exceed the rated current of a single contact.

Just thinking through the failure modes it seems that if a relay fails on or off mechanically it wouldn't make the situation any worse. And it would reduce the odds of failing electrically by 50% since one contact would be the first to make, and the same or different contact would be the last to break.

Thanks!

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    \$\begingroup\$ the answer would be dependent on the construction of the relay ... if one contact fails closed and still allows the other contact to transfer, then that would short all three pins together \$\endgroup\$
    – jsotola
    Sep 11, 2020 at 0:38
  • \$\begingroup\$ @jsotola, good thought! I didn't think about that. This relay has a single lever, but not sure of its rigidity. In my application only the NC or NO contacts will be used direct to the load, but for fancier control logic it could certainly be an issue. \$\endgroup\$
    – ericnutsch
    Sep 11, 2020 at 3:13

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With either two 'NC' or two 'NO' contacts connected in series (depending on the requirement being 'NC' or 'NO'), the contact life would increase substantially on account of 'double breaking' being employed.

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  • \$\begingroup\$ I like it! I think parallel would improve reliability too, but the double breaking is a better idea. And it statistically favors the off state of the relay which is a much much better idea. Thanks! \$\endgroup\$
    – ericnutsch
    Sep 11, 2020 at 3:22
  • \$\begingroup\$ Looks like the only down side is that I have to wire it for NC OR NO with no option to use the opposite logic in the field. \$\endgroup\$
    – ericnutsch
    Sep 11, 2020 at 3:27
  • \$\begingroup\$ Sorry, I undid the best answer. I want to see if anyone has any input specifically on the parallel setup first. Thanks! \$\endgroup\$
    – ericnutsch
    Sep 11, 2020 at 3:29
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    \$\begingroup\$ Hi @ericnutsch, But, in either case, you would get one contact for the opposite logic. Yes, waiting for more answers and choosing the best is the right thing to do. \$\endgroup\$
    – vu2nan
    Sep 11, 2020 at 3:36
  • \$\begingroup\$ Good point! I didn't think about the opposite still having one available. \$\endgroup\$
    – ericnutsch
    Sep 11, 2020 at 4:24

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