electrical outlet switch

[newtron]

Why is there a switch for every electrical outlet here in the UK?  What purpose does the switch serve?  Is it a safety issue?  In the US, we don't have a switch for every electrical outlet.  Thanks in advance.

[tony1941]

Yes it is a safety issue, but also isn't it better to be able to switch off an apppliance at the wall rather than to have to unplug it in the case that it doesn't have its own switch? (one case that springs to mind is an electric soldering iron!!).  Not every socket here has a switch, it's possible to buy ones without, but for the extra cost, you may as well have the convenience.  The other point is that in the US you mostly use 115V, which tends to kill fewer people than our 230V (nominal, but it is often a bit over 240V in practice).

I can recommend reading the Institution of Electrical Engineers Wiring Regulations (16th Edition) which also have the status of a British Standard (BS7671). Available from any good bookseller, riveting stuff for bedtime.  (only joking, but I hold a certificate C&G 2381 of competence in them - really boring, but sometimes life-saving)  Over here, we engineers can't believe how loose the regulations seem to be in other parts of the world - something to do with Michael Faraday perhaps!

[Tim Baxter]

Yes but you need the e.m.f. (potential difference or voltage) to drive the current through the circuit.  So if the human body's conductivity is x ohms the Yanks' 110V will drive (V=IR) half the current through your body.  The deficit for the Yanks is that they need twice the cross sectional area of a conductor to cope with the doubled current required to Power a device.  Swings & roundabouts.

[Pinotage]

UK system has twice the volts of the US electricity supply, thus twice as much electricity leaks out when no appliance is plugged in. The off switch prevents this wastage of electricity.

[tony1941]

Yes, Pinotage, that's about right!.  Of course with a properly installed and maintained system, nothing significant is ever going to "leak" unless through, for example, a finger in contact with a conductor.  Hence the switch.  It's for safety, really.

[Tabby]

The US household electrical system is safer than the UK, hence it�s a good idea for a switch off any appliance before you pull the plug out of the socket in the UK.

Why is it safer? Well for a current to flow, you need a circuit. The UK uses the Live and Neutral terminal in the plug for a normal circuit. Neutral is actually the same potential as Earth (0 volts), so if you touch the Live terminal, and are standing on a solid floor, you are �experience� 230V.

In the States, it�s a little different. There are again, two terminals in the plug where the current normally flows, but neither is at �Earth� potential (so they are not called Live and Neutral).  The voltage measured across both terminals would be 110 Volts, but if you measured to voltage from one terminal to earth, it would be only 55 Volts. Why?
Think of it as having one terminal at +55 volts, and the other at �55 volts, so to earth (0 volts), you only see 55 volts from either terminal but you still get 110 volts if you measure across the two terminals. [Strictly speaking there is a little more to it, as the voltage at each terminal changes from +50V to �55V 60 times a second, but we will ignore this for now]

Most accidents with electricity happen between one terminal and earth. So if this happed in the UK you would be subjected to 230Volts, but in the US it would only be 55Volts, hence your body would only see � of the current compared to the UK. It is generally recognised that below 50Volts, the current your body experiences is unlikely to harm you. [Cars soon will start to appear that run on 42V, but they can go much higher than this, for this safety reason]

Hope this helps!!

[livingstone1]

What a load codswallop!!  Plugs in the US work in exactly the same way as they do here . Ie, Live, Neutral, and on many plugs an Earth blade also. All modern two blade plugs are polarised with a broad and narrow blade each to ensure the plug can only be inserted in the correct way. Plugs are much safer in the UK, as it is virtually impossible to be able to touch the live conductor on a standard BS1363 plug  as you put it in/out of the socket. Blades on US plugs are not sheathed in any way and are easy to touch. Good RCDs prevent any nasty shocks though.

[Tim Baxter]

I sympathise with tabby, it's highly p(l)ausable!

[badams]

I think Tabby may be confusing the US system with the safety system used on building sites, which do work on 55v either side of earth to get 110v - the transformer is centre tapped to achieve this. 

The original UK 13A plugs did not have shielded pins - this is a relatively new addition.  So on the original plugs, it was very easy to touch the live pin - and end up not "live" yourself".

The other reason for the switch is quite a practical one - every time you pull a plug out or in, you wear the spring contacts, so leaving the plug in and using the switch (which has hardened and/or silver plated contacts) helps to extend the life of the fitting.  Although most people know that you should pull the plug and not the cable, there are exceptions! - so switching off rather than unplugging may help reduce damage to cables!

Many early appliances did not have on/off switches (especially lamps etc.), so the switch was a matter of convenience as well as safety.