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I want to replace a cheap all encapsulated socket digi timer switch by an industry timer switch made for installation work, like this:

industrial timer, photo and wiring diagram from manual

I want to put it into a case that can be connected to a regular wall socket using a Schuko to IEC C13 cable, and there will be a Schuko socket to connect the device that is to be turned on and off by the timer, e.g. a lamp or a Raspberry Pi:

my drawing of how I think the wiring should be

I'm confused about the distinction between L and N line in the diagram for the timer. Since it depends on which way you plug in the Schuko which of the two pins is actually N and L, I want to understand if this matters, or if I can go ahead with my plan.

Do I need to check with a one-contact test light, before plugging into the wall, or would accidentally switching N / L be ok. Or this is approach fundamentally flawed?

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  • \$\begingroup\$ In many cases the timer relay might have only a small current rating on its contacts eg:2A. In which case the common solution would be to add a larger relay or contactor. This would solve your problem by using a double pole relay. \$\endgroup\$
    – Kartman
    Dec 22, 2022 at 0:23

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The problem is the timer has a single pole relay contacts and you have a Schuko.

The Schuko plug can be plugged into mains socket in either orientation so there is no guarantee which wire is live and which wire is neutral.

If you only route one mains wire through the timer, you never know if the timer swiches the live or neutral.

The last thing you want is a device having live turned on while neutral is disconnected.

Any load that is not earthed may have Y caps from mains input to metal case and that may or may not be dangerous if you touch it. It will not feel pleasant and can be frightening if you don't expect a shock from just touching a device.

So it is not the intended operation.

If you must wire your own mains switch box, at least make sure you use a second relay which breaks both live and neutral wires if you have non-polarized sockets.

(Please note I am not an electrician or don't know what ways to build your device is legally allowed or not allowed. Or if you are legally even allowed to build such an electrical device in your country. Or if the installation requires use of extra insulation, ferrules, cable ties etc to make safe installation. You are resonsible).

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  • \$\begingroup\$ Thank you. It's actually a two channel timer; so if I "make sure" I always program both channels identically, I guess I could route both N and L through the relays. That would make it safer, I guess? Is that what you are saying about "use a second relay which breaks both live and neutral wires if you have non-polarized sockets"? The enclosure is ABS plastic, so there shouldn't be any risk of shock touching the box. \$\endgroup\$
    – 0__
    Dec 21, 2022 at 20:35
  • \$\begingroup\$ A second question: "The last thing you want is a device having live turned on while neutral is disconnected" ; why is this a problem? Can the connected device use any current in such situation (only live wire connected, neutral disconnected)? \$\endgroup\$
    – 0__
    Dec 21, 2022 at 20:54
  • \$\begingroup\$ A third question: If I short ground and neutral, shouldn't this imply that if I connect in the wrong orientation, I'm just throwing the main fuse of the electricity, preventing further damage? \$\endgroup\$
    – 0__
    Dec 21, 2022 at 20:56
  • \$\begingroup\$ If it is a two channel timer, you could program the two channels with same time, but, it is unsafe if you or anyone else forgets to set exact same on/off times for both channels. And I explained why it is a problem. You have a relay box that turns devices off, do you expect the device to be energized with live wire and disconnected neutral, or actually de-energized? Any leakage from live to user when neutral is disconnected will be a shocking experience. This happens via capacitors in e.g. two prong mobile phone chargers. And you can't short earth and one mains wire as 50/50 chance fuse blows. \$\endgroup\$
    – Justme
    Dec 21, 2022 at 21:06
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    \$\begingroup\$ It's very simple. The timer has a single pole relay. Use it to drive a double pole relay/contactor which cuts both neutral and live wires to load. Failing that, if the timer requires too complex external circuitry, change the timer to one that needs no complex external circuit. If there is any doubt at all how to do that or how to do it safely, then unfortunately you should not manufacture a mains operated electrical product, for safety and legal reasons. By making it you likely are legally held responsible if a badly built device causes problems such as fire or death (local laws apply). \$\endgroup\$
    – Justme
    Dec 21, 2022 at 23:24

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