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UK mains voltage is 230V (RMS) with a tolerance of -6% and +10%. That gives it an upper limit of 253V (RMS).

Lots of relays are rated up to 250V: e.g. the Omron G5Q series has a "rated insulation voltage" of 250V.

My assessment would be that these 250V relays are not safe to be used with UK mains, given that UK mains could go up to 253V. However, there seem to be an overwhelming number of relays rated to 250V, which makes me think that I am incorrect here.

Is a 250V rated relay safe to use on UK mains?

In this specific case I am looking to use this Omron G5Q relay in a position where its insulation acts as a reinforced safeguard. Its datasheet specifies it is rated as reinforced insulation up to 250V.

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For the G5Q series specifically (here's the datasheet), while all the load ratings are given at a representative voltage of 250 V, this is not the maximum rated switching voltage of the relay:
enter image description here

The dielectric strength ratings are also more than adequate:
enter image description here

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    \$\begingroup\$ If you look at page 5 of the datasheet though, it states a rated insulation voltage of 250V. It also only claims to act as reinforced insulation (which is what I happen to want in my application) for a rated voltage of only 250V. \$\endgroup\$
    – Rob Gilton
    Commented Jan 11 at 14:22
  • \$\begingroup\$ Also, this answer is just about the switching voltage, not the insulation voltage. \$\endgroup\$
    – Rob Gilton
    Commented Jan 11 at 14:29
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    \$\begingroup\$ @RobGilton - Hi, You commented: "this answer is just about the switching voltage, not the insulation voltage" But the question title says: "Is it safe to use 250V rated relays to switch UK mains voltages?" (my bold). It's reasonable that people might concentrate on the title and less about the insulation voltage (which is mentioned, but only in the question text). || If the insulation is the main focus of your question, perhaps rewrite the title to emphasise that? (It's a fine line whether changing the title could be considered as changing the question after receiving an answer :( ) \$\endgroup\$
    – SamGibson
    Commented Jan 11 at 16:08
  • \$\begingroup\$ @SamGibson, I guess you could read the title like that. However, for a relay to be safe to use to switch something, the insulation must be rated for being up to the job. It's part and parcel of it all. \$\endgroup\$
    – Rob Gilton
    Commented Jan 11 at 19:55
  • \$\begingroup\$ @RobGilton - "the insulation must be rated for being up to the job. It's part and parcel of it all" Understood, but the title currently doesn't mention that yet it does mention switching, which IMHO will focus people on the contact rating. I just suggest, to help you get answers that you want, you may want to change the title. Perhaps even change "to switch" to "with". || I would also suggest that you incorporate the details from your comment above referring to datasheet page 5, as that seems to be your specific concern. It's completely your choice, of course. \$\endgroup\$
    – SamGibson
    Commented Jan 11 at 20:25

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