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First off: I realize that my problem could be solved by simply using a few power strips with built in on/off switches, but I do not want to do that. I look at this project as being a learning opportunity.

For aesthetic reasons I have hidden most of my electronics (PC peripherals etc...) under my desk. However in doing this I have sacrificed ease of access. Since I do not want to have to continually plug/unplug my devices but also do not want to leave them constantly running, I would like to add a switch box (to the side of my desk) where the power cords for a variety of these devices each are connected to a switch.

There are two types of power supplies I would like to add a switch too: 1) 120V AC 2) 5-20V DC (what comes off of many of the AD/DC converters that come with my devices).

Note for each of these devices I am not dealing with particularly high currents (again think normal household electronics, speakers, monitors, laptop...)

If, for each of these devices I have just two wires (+) and (-/Neutral) is it safe to simply cut one of them and add a switch?

If not what would be the proper way of handling this? Do I need a different approach for High Voltage AC and Moderate Voltage DC power cords?

Thank you very much for your help!

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I would not perform surgury on line cords to install switches. I'd look at solving the more general problem of switched power at your desk. This probably won't be up to code, so don't let anyone official see this, and hiding it a bit is probably a good idea. You can mount a regular wall switch somewhere on the side of your desk in a metal electrical box. Get a line cord with wire ends or cut the female end off a extension cord and have that go into your switch. Coming out of that you have switched power which can go to a bunch of regular wall outlets mounted in more metal electrical boxes under or at the back of your desk. Now you can plug in whatever you want switched to these outlets without having to modify the equipment at all. When you upgrade equipment, just plug in the new stuff without having to modify it.

Having general switchable outlets attached to you desk could be useful for various things. Here in the office I have several switched outlet strips stuck to backsides and undersides of various desks. They come in quite handy. There are a lot of things you need to plug in when you work with electronics and computers.

Added:

As Photon pointed out, I should have mentioned that all these electric boxes should be grounded. That's why I said to make them metal. I meant to say to ground them but somehow forgot.

There will be three wires that come from the line cord that goes into the first box with the switch: Hot, neutral, and ground. Here in the US these are usually color coded black, white, and green, respectively, but don't rely on that. The neutrals of everything coming into and going out of a box should simply be connected. The ground should also be connected, but also to the box. There is usually a separate screw inside the box just for clamping a ground wire to it. The hot line is what gets switched in the first box. What comes out of that box therefore is the same neutral and ground that went in, but the hot is either connected or floating depending on whether the switch is on or off.

If you are paranoid or want to go further, you can use a DPST switch to switch both hot and neutral. Never switch ground. That must always be reliably connected straight thru and to every metal box.

If you're really paranoid, you can install a ground fault interruptor in the first box immediately to the incoming power. That shuts off the power if it sees a imballance between the hot and neutral currents. When all is working right, all the current that flows out on the hot line should come back on the neutral line. If something goes wrong, like your body is conduting between hot and a metal radiator pipe for example, then the hot and neutral currents won't ballance anymore and it shuts off power before you get too fried, hopefully, if all works right.

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  • \$\begingroup\$ This is a much better idea (more general and adaptable) than what I was planning and I will go with your solution. As this is largely a project for my own education could you comment as whether there is anything unsafe with my previous plan? \$\endgroup\$ – jds Jun 6 '12 at 19:05
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    \$\begingroup\$ Cutting a line cord and installing a switch in line can be a safety problem because it is difficult to seal up access to the high voltage wires when the switch isn't meant to do that. Lots of electrical tape and hot glue can help, but hot glue unadheres after a while and electrical tape can unwrap. \$\endgroup\$ – Olin Lathrop Jun 6 '12 at 19:16
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    \$\begingroup\$ You forgot to add: Be sure to connect the electrical box to the safety ground. \$\endgroup\$ – The Photon Jun 6 '12 at 19:31
  • \$\begingroup\$ @thephoton: Good catch, fixed. \$\endgroup\$ – Olin Lathrop Jun 7 '12 at 12:41
  • \$\begingroup\$ That was extremely helpful. You mention the possibility of adding a Ground Fault Interrupter (if I am really paranoid). What about adding a fuse instead/in addition to that? Would that be a good idea, redundant, or completely useless? \$\endgroup\$ – jds Jun 7 '12 at 21:26
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Adding a switch to a mains power cord is technically safe provided you are competent and you can be certain of breaking the phase lead or you switch both leads.

In mains systems with a polarised power plug you can guarantee which conductor is Phase if everything is correctly connected. If the plug is not polarised or is wired incorrectly, breaking neutral will disable the apparatus but will leave phase live in the device. In a double insulated appliance this will not usually matter but can.

You can use a two pole switch and break both leads. If one pole fails "on" the switch will still work but may be lethally dangerous.

Case study: A batch of 2 slice popup toasters was imported to this country with one pole of the 2 pole switch not "breaking" in some cases (mechanical trapping of contact). In 50% of these the phase lead was not broken. A nephew of mine suffered electric shock when he (stupidly*) picked up the "off" toaster by the center bar so that his fingers entered both slots and touched an element. He could easily have died. I identified the problem and provided a means of testing in seconds - capacitance to case from P or N is low when the switch is OK. a product recall resulted.

  • Sticking your fingers into an appliance while it is plugged in, so you can touch a surface which is sometimes live, is an invitation to Murphy to kill you.
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  • \$\begingroup\$ Switching only the neutral lead can be dangerous indeed, since it will in many cases mean that the downstream side of the neutral wire will in many cases only less than 10K away from "hot" (U.S. term). Someone unscrewing a light bulb from a multi-lamp fixture whose socket's threads are connected to neutral will be safe if either the hot wire is disconnected or the neutral wire is connected. But if the neutral wire is disconnected without disconnecting the hot wire, the threaded part of the bulb could be live while it's exposed. \$\endgroup\$ – supercat Jun 7 '12 at 15:19

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