Why switch always placed on line not on neutral, 2 pin plug - Page 1
Forum section: electronics / beginners

author: JoeN
author_rank: Frequent Contributor
timestamp: March 29, 2016, 06:13:59 am
content: I am aping another guy's question, I know, this is the real question that cannot be fit into the subject box. His question made me remember this one that I have always wondered about.Many prongs on AC devices in the US are so poorly keyed, or sockets are so poorly keyed, or both, anyone can plug a device in backwards. If it was DC, hilarity would ensue. With AC, it works, but it may not work exactly like the designer intended. For example, a switch designed to be on the hot side is now on the ground side. While this still works, a light socket in this arrangement is hot even when it is off.I guess my question is, this seems to me to be an serious and non-trivial problem. I don't know if this is a problem outside the US. It seems that we in the US have the plugs and prongs that are poorly keyed, but other countries may do it better. Why do you think the arrangement in the US is so amateur? Should have it been done better?

author: ataradov
author_rank: Super Contributor
timestamp: March 29, 2016, 06:22:52 am
content: Quote from: JoeN on March 29, 2016, 06:13:59 amFor the same reason US has terrible cellular and Internet infrastructure - legacy and lots of it. Being first to adopt a technology is a good advantage, but is also dangerous if you don't plan for upgrades.And then you can totally overdo it, like UK did with their plugs.Also, plugs are polarized after some rated amperage. So anything non-polar is guaranteed to be low power.

author: Brumby
author_rank: Unknown
timestamp: March 29, 2016, 06:26:07 am
content: I think Australia's is a good design. New Zealand and China use it too.

author: MarvinTheMartian
author_rank: Frequent Contributor
timestamp: March 29, 2016, 07:08:22 am
content: Quote from: Brumby on March 29, 2016, 06:26:07 amExcept when you are trying to plug into a socket and you can't see what you're doing (too dark, behind some furniture) - that's were the new insulated prong standards are a much safer idea!

author: vk6zgo
author_rank: Super Contributor
timestamp: March 29, 2016, 07:14:47 am
content: Of course,properly engineered equipment should switch both sides!

author: Gyro
author_rank: Super Contributor
timestamp: March 29, 2016, 09:27:27 am
content: Quote from: ataradov on March 29, 2016, 06:22:52 amHaving experienced and observed the scary blue arcing problems with mains outlets in meeting rooms in the US, I'm more than happy with our 'overdone' plugs thanks.

author: Kjelt
author_rank: Super Contributor
timestamp: March 29, 2016, 09:44:07 am
content: In the Netherlands and Germany we have the same issue.It is a symmetrical mains plug system, you can plug in backwards without noticing it.For my audio equipment where the phase is sometimes important to be correct, I have placed red dot stickers on the sockets and plugs protected by clear nail polish.I wish we had an assymetrical mains plug system but no way that is ever going to change. Learn to live with it

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: March 29, 2016, 09:47:33 am
content: Quote from: ataradov on March 29, 2016, 06:22:52 amLike when the US realised that they had to ground the systems. They ended up sticking one leg into the ground to ground the transformer (AKA corner-grounded B phase) to protect equipment.I hate the European plugs as they don't feel secure in the socket. Our plugs look and feel somewhat over-engineered and bulky though.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 29, 2016, 09:48:02 am
content: Quote from: MarvinTheMartian on March 29, 2016, 07:08:22 am(At least on some sockets) the earth pin on the socket is slightly indented so you can fiddle around in the dark to get it in.

author: Gyro
author_rank: Super Contributor
timestamp: March 29, 2016, 10:04:15 am
content: Quote from: Kjelt on March 29, 2016, 09:44:07 amUnfortunately it's never going to change until there is the political will to do something about it! The BS1363 plug was introduced in 1947 (yes, it is that old!) following a government sanctioned study into future electrical safety. Itcanbe changed, it's a matter of biting the bullet and getting on with it. Strangely introducing new unified standards is something that the EU ought to be quite good at!

author: Alex Trofimov
author_rank: Contributor
timestamp: March 29, 2016, 10:41:19 am
content: In Russia I've never seen polarized wall sockets (but they should exist in theory...) So, it's a proper practice to switch both sides.UPD: It's a good practice in any case. :-)

author: Kjelt
author_rank: Super Contributor
timestamp: March 29, 2016, 10:49:13 am
content: Quote from: Gyro on March 29, 2016, 10:04:15 amI personally (no offense) find that plug let's say it friendly a bit over the top. It looks like it is made to handle 5kV and 100's of ampsThen what I sometimes encounter is that the fuse is also inside that plug, very weird and expensive.But I agree it does not have our problem.Is there also a version without groundpin? Is it the same dimension?BTW that is the only positive I can find on our system, an flat unearthed plug can be put in an earthed wallsocket, unfortunately the opposite that should not be possible is also possible an earthed plug in an un-earthed wallsocketThe whole theory behind this was that only rooms that have a potential electrical safety issue like stone floors, kitchen etc. have earthed sockets and for instance bedrooms have unearthed sockets. However that rule changed tens of years back and modern houses have earthed sockets everywhere , however DIY enthousiasts do often not know the rules making it unsafe in some situations.

author: Brutte
author_rank: Frequent Contributor
timestamp: March 29, 2016, 10:52:11 am
content: Why would you want to rely on the location of the neutral (N) wire in a design?From AC point of view opening the circuit can be made at any location to stop the current flow. From safety point of view, it is tempting to shield a device with that fixed neutral wire by using just two wires (live and neutral) for connection. However, you cannot combine both functions of neutral + protection (N+PE) in a device this way because in case of a N+PE wire failure and when the switch is closed (device is on), there would have been a mains voltage on the shield with current flowing through the circuit of the device. So single wire failure would have meant a lethal hazard.That is why we use live+neutral+protection (3 wires, L+N+PE) for safety.IMHO fixing neural pin in AC circuit does not give the advantage but complicates the design and installation procedure. It could have the advantage in DC circuit (no rectifying needed in devices that rely on polarity), but not in AC.

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: March 29, 2016, 11:09:28 am
content: Quote from: Kjelt on March 29, 2016, 10:49:13 amYou won't find one without an earth pin because of the mechanics of the wall socket. The earth pin is longer and the mechanism opens the neutral and live terminals when you plug in. Supposedly makes them "child-proof". And means you need a plastic earth pin for two-wire connections.

author: Gyro
author_rank: Super Contributor
timestamp: March 29, 2016, 11:37:26 am
content: Quote from: Kjelt on March 29, 2016, 10:49:13 amAs RGB255_0_0 says on the earth pin - the shuttering on the live and neutral is another useful safety feature - certainly compared to US ones (I know most European two pin ones are shuttered too).Plug fuses are actually very cheap (mass production), unlike DMM ones - 1.5kA interrupt, not 10kA DC. Yes the plugs may be a little bulky compared to 2-pin ones*, but pretty modern looking for a 1940s design, and much smaller than the previous 'round pin' 15A plugs introduced in the 1920s (which also has an earth pin by the way). If you really want small, the Chinese do a very small UNFUSED version.Our Trading standards officers have (thousands of) hours of fun chasing those!Edit: * Actually one advantage of the UK one is that the cable comes out at 90' (downwards) which makes them much more flush to the wall when inserted - a small but often overlooked point.

author: Monkeh
author_rank: Super Contributor
timestamp: March 29, 2016, 11:55:23 am
content: Quote from: Gyro on March 29, 2016, 11:37:26 am6kA AC.

author: Gyro
author_rank: Super Contributor
timestamp: March 29, 2016, 12:03:00 pm
content: Oops!(busted on the 6kA, I did mean AC though, as opposed the the 10kA DC meter fuse rating).

author: Nerull
author_rank: Frequent Contributor
timestamp: March 29, 2016, 12:23:29 pm
content: Quote from: JoeN on March 29, 2016, 06:13:59 amUnkeyed plugs are only to be used on devices where polarity doesn't matter, such as on double insulated devices with transformers - which can't be grounded anyway. If your sockets are so worn out that you can plug in a polarized plug backwards, replace your sockets.

author: tooki
author_rank: Super Contributor
timestamp: March 29, 2016, 12:43:13 pm
content: Quote from: JoeN on March 29, 2016, 06:13:59 amI find it curious that you think the US is unusually poor at plug polarization. For one thing, most devices in USA are polarized, and as Nerull said, if your outlets are allowing them in the wrong way around, they are seriously damaged.Anyway, all of continental Europe uses non-polarized ungrounded plugs, and much of Europe uses non-polarized grounded plugs! (France, Switzerland and Denmark are exceptions, in that their grounded plugs enforce polarity.) So if anything, the US is better at polarization than most of Europe (and Asia and many developing nations, which often don't even have grounding!). Of course, this doesn't mean the US plug doesn't have other shortcomings…If you ask me, the world is long overdue for plug standardization, with some sort of keying to prevent insertion into an outlet of the wrong voltage. But we all know that's never gonna happen.

author: Zbig
author_rank: Frequent Contributor
timestamp: March 29, 2016, 12:46:33 pm
content: Quote from: RGB255_0_0 on March 29, 2016, 09:47:33 amI hate to open whole new can of worms but you ARE European. There was no UK continent last time I checked

author: RGB255_0_0
author_rank: Frequent Contributor
timestamp: March 29, 2016, 12:54:00 pm
content: Quote from: Zbig on March 29, 2016, 12:46:33 pmMainlandEurope, then

author: Zbig
author_rank: Frequent Contributor
timestamp: March 29, 2016, 12:54:44 pm
content: Quote from: RGB255_0_0 on March 29, 2016, 12:54:00 pm

author: Monkeh
author_rank: Super Contributor
timestamp: March 29, 2016, 01:01:48 pm
content: Quote from: Zbig on March 29, 2016, 12:46:33 pmWe find it a bit embarrassing to admit we're related.