Questions about electricity

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Martin Y
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Re: Questions about electricity

Post by Martin Y » Wed Sep 15, 2021 10:31 am

My parents would diligently unplug the TV every night, but back in the days of valve TVs they were a bigger fire hazard than now. (Even I can vaguely remember the TV repair man getting new valves out of their little cardboard cartons, probably at the end of the '60s.) A colleague told me some early TVs were made for lower than UK mains voltage and had a resistive mains lead to drop the volts. All very well until somebody cut the cable shorter.

Anyway, somewhat in defence of UK mains plugs, I believed the idea with the post-war 13A plug was to save copper in house wiring. The system uses ring mains so current can go both ways around the loop to get to a plug, so you can use thinner gauge wire and still deliver enough current to any plug, and by putting fuses inside the plugs themselves you can have a 32 amp fuse protecting the ring and a 13A (or less) fuse protecting each appliance. Yes, each plug needs a substantial amount of copper but that too is helpful as a heatsink if there's a slightly weak connection. They used to have a design weakness that you could get a shock if you tried to lever the plug out with a table knife but for decades they've had plastic shrouds halfway up the live and neutral pins to prevent that. One aspect I do like is that they only go in one way around so you have a well defined live and neutral, with the fuses in the live supply, so if a fuse pops it doesn't just stop the appliance working, it disconnects the mains volts.

I'm not saying it's perfect and other systems have their benefits but, as so often, it depends on what sort of accident you intend to have. If you intend to step on a plug in the dark, the UK system sucks.

PS My parents' house still had its pre-war round pin sockets as well as later 13A ones, and those had on/off switches too. Don't know why. Maybe to save on fatiguing the socket by constantly unplugging stuff.

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dyqik
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Re: Questions about electricity

Post by dyqik » Wed Sep 15, 2021 3:22 pm

There are two big problems with US outlets and plugs. Firstly, the pins are sheet metal, and easy to bend when pulling out if the socket or lying around.

Secondly, the outlets are usually installed with ground pin at the bottom, so a piece of metal sliding down behind the plug contacts the live and neutral rather than the ground. I've blown up raspberry pi that way.

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Re: Questions about electricity

Post by monkey » Wed Sep 15, 2021 3:37 pm

dyqik wrote:
Wed Sep 15, 2021 3:22 pm
There are two big problems with US outlets and plugs. Firstly, the pins are sheet metal, and easy to bend when pulling out if the socket or lying around.

Secondly, the outlets are usually installed with ground pin at the bottom, so a piece of metal sliding down behind the plug contacts the live and neutral rather than the ground. I've blown up raspberry pi that way.
Yeah, but that gives them the "oh no! You're sticking a plug in my face!" look.

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tom p
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Re: Questions about electricity

Post by tom p » Wed Sep 15, 2021 4:20 pm

IvanV wrote:
Tue Sep 14, 2021 7:03 pm
So I have fairly often, for some reason or another not got a stiff plug in fully in one go, and then I'm groping around to try and finish the job off under a bed or behind a cupboard, and managed to touch a live pin. It is all very easy to say, switch the socket off before you do this. But if the switch is the far side of the poorly accessible plug, it can be difficult to operate the switch once the plug is in the socket.
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Re: Questions about electricity

Post by basementer » Wed Sep 15, 2021 5:14 pm

monkey wrote:
Wed Sep 15, 2021 3:37 pm
dyqik wrote:
Wed Sep 15, 2021 3:22 pm
There are two big problems with US outlets and plugs. Firstly, the pins are sheet metal, and easy to bend when pulling out if the socket or lying around.

Secondly, the outlets are usually installed with ground pin at the bottom, so a piece of metal sliding down behind the plug contacts the live and neutral rather than the ground. I've blown up raspberry pi that way.
Yeah, but that gives them the "oh no! You're sticking a plug in my face!" look.

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In Denmark, by contrast, the sockets are quite cheerful.
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Boustrophedon
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Re: Questions about electricity

Post by Boustrophedon » Wed Sep 15, 2021 6:28 pm

I have always thought that where there are two (or more) light switches controlling one light, that the switch should be mounted sideways, as it doesn't have a set on or off position.
Such switches are often found in pairs for upstairs and downstairs lights, mounting them sideways would put one above the other which would indicate which was which.

Ditto sockets, why do UK plugs have to have the wire come out parallel to the wall and not at right angles, straight out? Anyway in one flat the socket was so close to the floor and then a thick carpet and underlay had been fitted, that the wire simply did not allow the plug to go in the socket. So I turned the socket upside down. I would have preferred sideways but the receptacle didn't have threaded holes in those positions.
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Re: Questions about electricity

Post by Millennie Al » Thu Sep 16, 2021 12:27 am

Boustrophedon wrote:
Wed Sep 15, 2021 6:28 pm
why do UK plugs have to have the wire come out parallel to the wall and not at right angles, straight out?
To remove the incentive to pull on the cable wen unplugging it. The plugs require quite a lot of force to remove, and applying that via the cable would cause it to fail - especially on non-moulded plugs.
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Re: Questions about electricity

Post by Brightonian » Thu Sep 16, 2021 1:00 am

Millennie Al wrote:
Thu Sep 16, 2021 12:27 am
Boustrophedon wrote:
Wed Sep 15, 2021 6:28 pm
why do UK plugs have to have the wire come out parallel to the wall and not at right angles, straight out?
To remove the incentive to pull on the cable wen unplugging it. The plugs require quite a lot of force to remove, and applying that via the cable would cause it to fail - especially on non-moulded plugs.
Have to admit that, when in France, I often yank plugs out by pulling on the cable if they're just two-pin. (Edit: they're apparently called Europlugs - didn't know that.)

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Martin Y
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Re: Questions about electricity

Post by Martin Y » Thu Sep 16, 2021 9:25 am

One thing that's perhaps surprising about UK mains plugs (the rewireable ones rather than the one-piece injection moulded type) is how very rare it is to break one when unplugging it. It sometimes takes quite a bit of force to pull one out and you're pulling on the back of the plug which is only held together by one screw so, if they were shoddily made, you'd just pull the back off and leave the rest of the plug behind in the socket with exposed terminals. I guess that would be a good moment to have an off switch on the socket.

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Re: Questions about electricity

Post by tom p » Thu Sep 16, 2021 12:15 pm

Martin Y wrote:
Thu Sep 16, 2021 9:25 am
One thing that's perhaps surprising about UK mains plugs (the rewireable ones rather than the one-piece injection moulded type) is how very rare it is to break one when unplugging it. It sometimes takes quite a bit of force to pull one out and you're pulling on the back of the plug which is only held together by one screw so, if they were shoddily made, you'd just pull the back off and leave the rest of the plug behind in the socket with exposed terminals. I guess that would be a good moment to have an off switch on the socket.
As I found out to my cost once.
I have no idea why I was stupid enough to try and pull the exposed plug out rather than turn off the circuit first, but it sure as hell hurt my arm when I touched the live by accident.

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Re: Questions about electricity

Post by Boustrophedon » Thu Sep 16, 2021 12:49 pm

tom p wrote:
Thu Sep 16, 2021 12:15 pm
Martin Y wrote:
Thu Sep 16, 2021 9:25 am
One thing that's perhaps surprising about UK mains plugs (the rewireable ones rather than the one-piece injection moulded type) is how very rare it is to break one when unplugging it. It sometimes takes quite a bit of force to pull one out and you're pulling on the back of the plug which is only held together by one screw so, if they were shoddily made, you'd just pull the back off and leave the rest of the plug behind in the socket with exposed terminals. I guess that would be a good moment to have an off switch on the socket.
As I found out to my cost once.
I have no idea why I was stupid enough to try and pull the exposed plug out rather than turn off the circuit first, but it sure as hell hurt my arm when I touched the live by accident.
MK had a batch of their otherwise excellent plugs that had the pins inadequately riveted in, so that sometimes pulling the plug out left the live pin stuck in the socket. It led to a redesign.

If you have to wire a plug onto an appliance an MK plugs, with their terminal and nut arrangement are so much easier than the ones where you have to poke a wire through a little hole and tighten a screw onto it. They don't get so hot carrying high loads either.
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Re: Questions about electricity

Post by dyqik » Thu Sep 16, 2021 3:05 pm

Boustrophedon wrote:
Wed Sep 15, 2021 6:28 pm
Ditto sockets, why do UK plugs have to have the wire come out parallel to the wall and not at right angles, straight out? Anyway in one flat the socket was so close to the floor and then a thick carpet and underlay had been fitted, that the wire simply did not allow the plug to go in the socket. So I turned the socket upside down. I would have preferred sideways but the receptacle didn't have threaded holes in those positions.
The third problem with US plugs is that they come straight out from the wall, and often get crushed behind furniture and bent that way.

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Re: Questions about electricity

Post by monkey » Thu Sep 16, 2021 3:34 pm

dyqik wrote:
Thu Sep 16, 2021 3:05 pm
Boustrophedon wrote:
Wed Sep 15, 2021 6:28 pm
Ditto sockets, why do UK plugs have to have the wire come out parallel to the wall and not at right angles, straight out? Anyway in one flat the socket was so close to the floor and then a thick carpet and underlay had been fitted, that the wire simply did not allow the plug to go in the socket. So I turned the socket upside down. I would have preferred sideways but the receptacle didn't have threaded holes in those positions.
The third problem with US plugs is that they come straight out from the wall, and often get crushed behind furniture and bent that way.
Only mostly. I have a few things that have a low profile plug with the cable coming out sideways. Nothing high current though.

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