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I have a device where I want to use relays to run some important equipment. I want to use monostable relays because if power is lost or if there is any sort of system failure I want the connected device to shut off. This means I'll probably be running the relays continuously or nearly continuously for up to a few hours. I'm concerned about coil heating or otherwise damaging the relay.

I've been looking at some datasheets like these G5Q Datasheet, G5LE Datasheet and I'm having trouble determining how long I can safely keep the relay engaged. I don't see anything indicating a max time or max duty cycle. Does this indicate I can simply leave the relays engaged indefinitely or is there a proper way to go about calculating this?

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    \$\begingroup\$ As long as you don't exceed any ratings, and it's not enclosed in a heat tight box.. you can run it forever. \$\endgroup\$
    – Trevor_G
    Oct 30 '17 at 22:09
  • \$\begingroup\$ I imagine that the nominal coil ratings given in the datasheet are for "infinite" use. It's when you go beyond the ratings that you must consider a limited use period. \$\endgroup\$
    – Bort
    Oct 31 '17 at 17:31
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The air temperature around the case of the relay should not exceed the published rating. The referenced data sheets show a maximum ambient temperature of 85C or 105C for one variation. There also derating curves for operation above 40C. That information shows how the relays are intended to be used. If the relays are in a confined space or in a space that has other heat producing items, you need to test or otherwise verify the air temperature around the relay.

The relays should be ok kept operated permanently unless they are in a very confined enclosure. It is unlikely that they would overheat unless the temperature outside their enclosure is also high.

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I think virtually all general-purpose relays can be kept operated permanently.

There are some pulse-activated latching relays that may have maximum pulse duration - but that information should be clearly shown in the datasheet.

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