Power switch for 240 AC builds - SPST or DPST?

[Unit7]

Hi!

Title says it all.

I had an electrician installing stuff at my place a long time ago. I recall that he mentioned since we have AC current in Sweden it isn't optimal to only switch one of the poles, leaving the other pole on all the time. I don't remember if he explained why. Not sure I would understand anyway. It was just a thing I recalled while doing the Hairball kits and most recently an LA2A p2p.

Any reason to replace those SPST switches?

Cheers
Paul

 

[druu]

Just noticed this topic in the Related Topic below:

http://groupdiy.com/index.php?topic=8016.0

 

[Unit7]

Just noticed this topic in the Related Topic below:

http://groupdiy.com/index.php?topic=8016.0

Thanks Druu! Blushing here because I missed that thread.
The link in that thread links to info suggesting using a double pole switch, for safety, which could be reason enough. But I thought perhaps there were more reasons, like... that having one hot lead on all the time could cause 'wear' on components, or that the circuit would be more vurnerable for peaks, thundestorms etc, even when powered off?

Excuse a noob, but I realize that I'm not 100% sure about the differences between EU and US standards. US is 110/120, 60Hz, but still AC... so no hot/cold poles, correct?
But I still got it in the back of my mind that a power transformer work differently on 120V and 240V, and that when having it wired for 240V there was a reason for switching both poles of the power...

Remember I'm a noob, and that english is not my mother tongue. Eventually I will have to find some swedish literature on the subject. I'm 50 soon... but I realize it's back to school...

 

[PRR]

> Any reason to replace those SPST switches?

Already installed and working happy?

Leave them alone. Find something else to work on.

I am starting to suspect that, all else equal, 2-pole switching is a good idea generally, for *new* work.

However, NEVER bet-your-life that ANY switch has "cut all the power". That is why we have plugs and wall-sockets. Pull the plug out of the wall, be sure it is the RIGHT plug, keep it in sight, now it is pretty safe to work in (after any internal capacitors drain).

> I still got it in the back of my mind that a power transformer work differently on {US} 120V and {EU} 240V

No. Just the voltage, and some really obscure and unimportant local variations in building grounding.

Either way, one side of the line is connected to Earth. There may be some convention for which side. You can NOT (always) be sure that the wall-outlet is wired according to the convention. (Schuko plugs are the same either way.)

In EU it is slightly more likely that your "230V" is really one leg of a 3-phase system. However residences and small offices only get one phase, so there is no reason you care.

The US *also* has a 240V service, delivered as two 120V legs out-of-phase. That is how power comes from the street to the building. This does not come into the studio, except as separate 120V circuits. It does supply large air-conditioners etc.

 

[Unit7]

Thanks PRR!

Yes, already installed and working.
Thanks for the lecture. Appreciate it.
Paul