I need to instal a receptacle in my 240VAC, 3 phase machine for a 12V, 1A adapter. Adapter is good for 120-240VAC input. I happen to have a 125V, 20A duplex receptacle on hand. Is it okay to use it because of low current or is there an insulation or gap requirement for 240V that 125V will not meet. Thanks.
Use a 12V/1A enclosed chassis mount (or DIN rail mount, for that matter) supply
Your problem here is that you are trying to apply a "wall wart" in an application (inside a control panel of some flavor) where you'd be provisioning a receptacle solely for the wall-wart's use. This is a waste of a receptacle, and also poses NEMA 5/NEMA 6 confusion hazards, so why not use something more fit for the job instead, such as a DIN rail mounted supply like the one shown below? (It's a CUI PDRC-24-12, BTW, and is fully cULus listed to UL508 for field application in industrial control equipment.)
Of course, more traditional enclosed chassis mount supplies will work, although they don't usually carry a full UL listing the way the supply I linked does.
Putting a 120V receptacle on a 240V circuit = future guy’s fried 120V appliance when he plugs it in without the knowledge that you have that it’s actually a 240V circuit with the wrong outlet type on it.
You need at least a NEMA 6-15R or 6-20R (looks like standard 120V outlets, except the blades are sideways so you can’t plug in 120V appliances.
Can't do that! The reason is keying
The whole point of having different receptacles for different voltages is to provide interlocking so the firestarting thing does not happen.
And it may seem all clever to do this while you're the only person tending the machine. But what's your sunset plan for this? How do you plan to assure nobody else does something stupid with it? Do you earnestly plan to tear it out if you sell the machine on Craigslist, or give it to your son, or die in a traffic accident and your estate clears it out? Honestly your best plan is to say a sentence or two of words for them that they won't remember. Maybe not you, but somebody is gonna get bit by a 120V socket fed 240V.
And when someone does that, they did everything right. It'd be your fault.
The simple fact is, they make correct receptacles for this. Just use them.
And if you just won't, then OK, solder two #12 wires (none white!) onto the wall-wart prongs, gob it up with a ton of electrical tape, and land the #12 wire on terminal blocks. At least that won't be mistaken for anything other than what it is.
However, I agree with ThreePhaseEel. 12V is an absolutely generic, common voltage and they make hundreds of thousands of different models of 12V power supply that input 230/240V (since that's standard house power on every continent except North America). Just get one of them - any of them - Amazon is awash in unapproved cheap Chinese ones, even this would be better than a suicide socket... many others are RU-Recognized (UL's component certification)... and a few are UL-Listed.