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I've heard several cases where individuals burned out their motor start windings on inductor start induction motors. In almost every case, they've had their switch assemblies positioned upside down or in an odd orientation. Is it possible for an mechanical relay to stay open or closed due to gravity? What else could cause the relay to fail to open or close?

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    \$\begingroup\$ Relays can fail for a lot of reasons such as low voltage, coil failure, corrosion, loose wires, dirt or other contamination, contact welding due to excess voltage or current, or mechanical wear. Even if you had specific information such as brand and model of relay, operating parameters, schematic, time in service etc., there is no way that a specific answer can be given. This is a vague conjecture question that invites only opinions as a response. It is off topic for this site and I will vote to close it. \$\endgroup\$
    – user80875
    Commented Aug 29, 2016 at 3:21
  • \$\begingroup\$ General information and informed hypothesis about common failure modes are plainly on topic here... \$\endgroup\$
    – Passerby
    Commented Aug 29, 2016 at 4:25
  • \$\begingroup\$ @charles specifically, the posted answer shows how it's not random speculation. They provide evidence. Just like that close reasons states. Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. I for one did not know relays were orientation sensitive, or that fluid filled relays existed. \$\endgroup\$
    – Passerby
    Commented Aug 29, 2016 at 4:29
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    \$\begingroup\$ If my question referred to a specific described instance of failure and I asked for others to provide their hunches as to the cause, then it would be off topic for the reason you gave and because asking for a diagnostics. Im my specific case, I asked if relays can fail based on their orientation and asked for broader reasons why they can fail which has a factual, possible and finite number of possibilities. How can this possibly invite opinions or beliefs? Do you expect someone to answer with "God can easily cause a relay to fail. In the bible it says...." \$\endgroup\$
    – user148298
    Commented Aug 29, 2016 at 4:55

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Operating position is frequently specified on motor starter relay installation guides, so it can matter. For many of them it doesn't- they are specified as "non-positional".

An educated guess as to the root cause- crap from the contacts as they wear falling into the wrong places as they age. Which would mean that, after a period of heavy use, flipping it over for shipping or whatever could cause problems even if it was mounted properly.

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Reading the datasheet and application information such as installation guides is the best approach.

Of course there are other reasons that a relay or contactor could stick closed or stay open, such as overloading, contact welding due to a short circuit, poor design of the relay or contact metallurgy etc.

Hg-displacement relays will stay closed if you flip them upside down, because they are filled with liquid.

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  • \$\begingroup\$ Thanks for the answer. I was shocked to find that many power tools have inductor start motors connected to relays that are sensitive to their orientation. To make it worse, most of the motors don't have thermal fuses. If the tool topples over, it can possibly cause a fire. \$\endgroup\$
    – user148298
    Commented Aug 29, 2016 at 5:13
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If a relay is near a switching flux field, it may turn on or off. If load is greater than the contacts Voltage/current rating. If contacts are orientated from arc debris fallout cannot fallout. If is a latching relay and your control does not turn it off.

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