Electronic – Mains isolation is mandatory for UL/CE/CSA compliance and other certification

I can only give some ideas for CE marking: -

It seems likely you can self-certify for CE but you need to create a technical file/document that justifies that your product meets the relevant directives and that any testing you have done is applicable and results indicate an acceptable "pass".

At 24V, you are within the voltage limits of the "Low voltage directive" so this doesn't apply BUT you should specify that a power supply that is CE marked is used.

However, you may be subject to the EMC directive in which case you have to justify why the limited tests you may apply justify not conducting full EMC testing.

There are a bunch of other directives that probably won't apply but it is down to you to specify which ones do and which ones don't AND, in the technical document justify why your product meets those various directives.

You also need to draft up a certificate that states all this stuff. There are examples on the web and there are good guidelines: -

UK government website for CE marking

guide on CE marking

I just grabbed one socket at random on Farnell UK, and got this drawing datasheet. In it is this little bit of text:

ELECTRICAL:

• Contact Resistance: 10 milliohms Max
• Contact Rating: 3 Amps
• Capacitance: 1.0pF per MIL-STD-202, Method 305
• Insulation Resistance: 5000 Ohms Min @ 500 VDC Per MIL-STD-1344, Method 3003.1
• Dielectric Withstanding Voltage: 1000 Volts (RMS) Per MIL-STD-1344, Method 3001.1

So I would conclude from that two things:

1. Datasheets with the relevant information in them are available if you look, and
2. Yes, that one would be OK for mains at low currents.

Besides, you'll have a resistor there too, right, which would mean you'd end up with maybe 2V across the LED anyway?

By the way, MIL-STD-1344A Method 3001.1 states:

1. PURPOSE. The purpose of this test is to prove that a given electrical connector or coaxial contacts can operate safely at its rated voltage and withstand momentary overpotentials due to switching, surges, and other similar phenomena. The dielectric withstanding voltage shall be established as 75 percent of the minimum breakdown voltage of the connector or coaxial contacts. It is suggested that the operating voltage of the connector or coaxial contacts be established as one-third of the dielectric withstanding voltage.

From that I can tell that the maximum normal operating voltage of that socket would be 333V RMS.

For clarification on the insulation resistance, Method 3003.1 states:

1. PURPOSE. The purpose of this test is to establish the methods and procedures to be followed in determining the resistance offered by the insulation materials and the various seals of a connector or coaxial contacts to a direct current potential tending to produce a leakage of current through or on the surface of these members.

So it's intentionally making the insulation "break down" and testing the resistance during that catastrophic event.

Addendum: Don't sue me if I'm wrong.