I have this power supply:
I would like to wire an on/off switch on the AC side of the circuit. I have a 2 position toggle switch but am unsure on which wire to have the switch on?
What is the safest way to do this?
The switch will do it's job if placed on either the Live wire or the Neutral wire, but it is mandatory to place the switch on the Live wire as a safety measure especially if it's a device which will come in contact with your body.
The Earth wire (3rd pin)should go to the earth socket without any switch in between.
If you have trouble identifying the live wire then use an electrical tester with indicator lamp to figure out which socket is live. The switch should go to that wire.
nick1992:
I have a 2 position toggle switch
Make sure your switch is rated to handle mains voltage.
This is how your setup should look like.
It is reccomended switch both live and neutral wires. Use the two pole mains rated switch.
Bear in mind that a power supply such as that is for mounting inside equipment or otherwise cased.
Not safe for bench use as is.
Thank you for your help guys. I will install the switch on the live wire. This is not for bench use, it is going inside a project 
nick1992:
Thank you for your help guys. I will install the switch on the live wire. This is not for bench use, it is going inside a project
Make sure to identify the Live pin your wall socket with an electrical tester. Otherwise you may never know if the guy who wired your electrical socket made a mistake or not.
srnet:
Bear in mind that a power supply such as that is for mounting inside equipment or otherwise cased.
Cased but should also be ventilated.
jendalinda:
It is reccomended switch both live and neutral wires. Use the two pole mains rated switch.
That's usually done with only 2 pin sockets , OP is talking about a 3 pin socket which he could not plug in improperly even if he wanted to, but I guess you're right when looking from safety point of view. The guy who wired his mains socket could have made a mistake. You never know.
Noobian:
but it is mandatory to place the switch on the Live wire as a safety measure especially if it's a device which will come in contact with your body.
No it is not mandatory.
To comply with safety regulations a live and nutral must be capable of being swapped over without compromising the safety of the equipment.
So it might be good practice but it is definitely not mandatory.
Grumpy_Mike:
No it is not mandatory.To comply with safety regulations a live and nutral must be capable of being swapped over without compromising the safety of the equipment.
So it might be good practice but it is definitely not mandatory.
it is for noobs.
in a 3 pin socket?
Grumpy_Mike:
To comply with safety regulations a live and nutral must be capable of being swapped over without compromising the safety of the equipment.
I didn't know that, interesting.
Btw I grew up calling it "line" not "live".
kenwood120s:
I didn't know that, interesting.Btw I grew up calling it "line" not "live".
Yes it supprised me when I found out. I was working for a consumer electronics company and they had a compliance department with six specialist compliance engineeres. I had to get my products through them.
If you called it line then you must have grown up in the US. In the UK it was always live, red, nutral, black and Earth, green. The colours change as a result of going into the EU and a recognition that red green colourblind was common. It's now live brown, nutral blue and Earth yellow and green stripes.
I was once at a supermarket self checkout with a bottle of brandy. The supervisor, a child that looked about 12 approached me, a pensioner, to authorise the sale. I said to him jokingly, I don't have any ID but to prove my age I can tell you how to wire a three pin plug.
@ noobian - just because it is for beginners their is no need to lie and say something is mandatory when it is not. Do not make the mistake of simplifying to the extent of making it not true. This is a growing trend in education and is rubbish. In the UK we have to officially teach our kids that a day is the length of time it takes the earth to spin once on its axis. This is wrong. Why lie to them when a true definition is just as easy?
Grumpy_Mike:
@ noobian - just because it is for beginners their is no need to lie and say something is mandatory when it is not. Do not make the mistake of simplifying to the extent of making it not true. This is a growing trend in education and is rubbish. In the UK we have to officially teach our kids that a day is the length of time it takes the earth to spin once on its axis. This is wrong. Why lie to them when a true definition is just as easy?
It could save his life. I had bought a couple of 2 pin timer switches from kaufland and I didn't know they switched on the neutral side until I got the shock.
Besides where I live it is mandatory to the switch on the mains live wire for wall socket outlets, bulb sockets, mcbs etc if you want to get approval for the electrical circuitry in your house from the electricity supplier. They give you electric connection only after they inspect your home circuitry and gives an approval.
Grumpy_Mike:
If you called it line then you must have grown up in the US. In the UK it was always live
No, I'm a Brit. My late Dad always called it "line" and although he wasn't an electrician, he did his apprenticeship in radio and radar in the RAF in the early 30s, and served HM until after WW2.
Noobian:
Besides where I live it is mandatory to the switch on the mains live wire
Then when you asserted it as mandatory, you should have qualified that with "... in ".
Noobian:
Besides where I live it is mandatory to the switch on the mains live wire for wall socket outlets, bulb sockets, mcbs etc if you want to get approval for the electrical circuitry in your house from the electricity supplier. They give you electric connection only after they inspect your home circuitry and gives an approval.
Fine, but the question was very clearly about the UK.
As Grumpy_Mike points out there is a differance between 'regulations' and what is mandatory (as in a specific legal requirement) in the UK. In a lot of cases the DIYer is not obliged by law to follow 'regulations'.
Besides where I live it is mandatory to the switch on the mains live wire for wall socket outlets, bulb sockets, mcbs etc if you want to get approval
Domestic wiring codes are totally a different matter and are not related to mandatory safety requirements, as you found out when you disrespected mains equipment.
Grumpy_Mike:
In the UK we have to officially teach our kids that a day is the length of time it takes the earth to spin once on its axis. This is wrong.
Hm OK I had to consult The Oracle of Google on that, and I'm still happy to go with a day being how long it takes to spin once.
Grumpy_Mike:
as you found out when you disrespected mains equipment.
I didn't disrespect mains equipment. The manufacturer wired it wrong in the first place.
Noobian:
I didn't disrespect mains equipment. The manufacturer wired it wrong in the first place.
No they didn't they were entitled to wire it how they wanted.
You were working on live equipment, which was your stupidity. Then you assumed their was no live voltage on a wire and you did not check first, which was your stupidity.
I had bought a couple of 2 pin timer switches from kaufland and I didn't know they switched on the neutral side until I got the shock.
From that I assume you are in Germany. I love Germans, I have been on holiday many times to Germany. But I have worked with German companies and they don't always "get" the scope of regulations. They like a rule and apply it where it is not applicable. Looks like you are falling into that trap and mixing domestic installation rules with equipment safety rules.
kenwood120s:
Hm OK I had to consult The Oracle of Google on that, and I'm still happy to go with a day being how long it takes to spin once.
So you say because it is on the internet it is true?
The time for the Earth to spin once on its axis is known as a Sidereal day. Sidereal time. This is 23 h 56 min 4.1 s, this is not a solar day which is 24 Hours. It might not seem much but there is one fewer solar day per year than there are sidereal days. So in a year the Earth spins 364 * times on it's axis. We get that extra day due to the orbit round the Sun.
Imagine the Earth were not spinning at all, we would see one solar day per year as it orbits the Sun. But as it is spinning then it has to spin slightly more than once for the Sun to appear in the same part of the sky as yesterday.
The length of a day as understood by the vast majority of people is the time it takes the mean sun to appear at successive highest elevations in the sky.
*This is to simplify things slightly as it does not have an exact number of spins per orbit but is very close to a quarter out. This is why we have a leap year every four years, and odd rules saying when we miss out on having a leap year sometimes like in the year 2000.