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Old 28th April 2012, 09:23 PM   #1
diyAudio Member
Join Date: Nov 2011
Location: US
Default Simple Power Switch Question

I am powering an audio circuit I made. It uses 120V wall power. Is it safe to run 120V through the power switch or must I use a relay? Is it better to put the switch on the hot or neutral side?

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Old 28th April 2012, 11:13 PM   #2
sreten is online now sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK

You can't use relay without some form of permanent power.

Standard practise is a double pole switch, switching live and neutral.

rgds, sreten,
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 28th April 2012, 11:15 PM   #3
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Yeah, that would have been my next question with the relay. Thank you for your response.
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Old 28th April 2012, 11:46 PM   #4
tvrgeek is offline tvrgeek  United States
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Normally only the hot side. NEVER just on the neutral. This leaves the unit attached to neutral at all times. You must use a polarized plug of course. As you said 120V, I am making the big assumption this is North American single phase. If you are two phase, then by all means switch both. (reason to put a country in your profile)

You did not mention what you are building. It is amazing how many big companies do not understand inrush current and have switches way too small for the real load.

Because this question is very basic, please let us know a lot more about what you are doing so we can help you have positive results. (neither you nor the project are fried)
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Old 28th April 2012, 11:54 PM   #5
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Yes, 120 single phase. I am building an interface to record from my amplifier's speaker output. It works on a breadboard, I'm soldering it into a more permanent home and adding switches. My switch says 3A 125V. I will be near 125V but and my 3/16A fuse hasn't blown yet, so I'm not worried about current. Will that all be ok?
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Old 29th April 2012, 12:01 AM   #6
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Does it matter which order the fuse and switch and switch are in--they are directly in series. I can't think of a reason why this would be an issue, but I'm sure half the people on this site have way more experience than myself.
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Old 29th April 2012, 12:24 AM   #7
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Location: Portland, Oregon
If the fuse was on the side of the switch opposite the mains power, it would not protect you from an electric shock when touching the switch in the case of a switch failure.
Just a suggestion: I always use this power entry module in everything I build
It has the power cord connector, fuse holder, and switch all in one convenient package. It's even got a feature which makes it impossible to change fuses without disconnecting the power cord.

Last edited by ByronInPortland; 29th April 2012 at 12:26 AM.
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Old 29th April 2012, 12:27 AM   #8
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Good point. I got a 404 on the link.
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