Internal wiring of USA v UK mains plug

Are you really saying no-one ever unplugs things withoutout turning them off first? I really doubt it.

NT

snipped-for-privacy@care2.com wrote in news:1183330881.790940.287160 @n2g2000hse.googlegroups.com:

Some equipment simply has no off switch..

Who cares? I unplug and plug in items that are turned on all the time, worst case you get a little spark, it doesn't cause any problems. It's not hot enough to pit the plug prongs or contacts.

may not seem so at first, but this will damage the contacts and lead to the formation of carbonised areas. And more noticeable stateside what with the limited 'actual' contact area between the US plugs and sockets - I would avoid plugging in or removing plugs of live equipment for reliability reasons.

-B

Its well known that repeated small sparks make a total mess of the contact surface. This was one of the problems of our olf round pin system half a century ago.

NT

You'd have to explain that. Most of the old round pin sockets were switched - unswitched was a short lived fashion with 13 amp stuff. At least in my experience.

The old round pin sockets were far more likely to be overloaded, though.

It is also well known that the properly designed flat blade has a nose which has sharp enough corners to be the spark point for any arcs. That means they will all begin or end along those edges, and along the "lead in" faces of the receptacle. This means that the swept surfaces that make up the "contact area" of the blades and socket terminals during use will always be in fine shape.

Our plugs are designed to handle tens of thousands of "hot insertions" like this. It has to handle some specific number at full rated current as well. It is part of the design spec for the outlet. This is also why the ground pin on 3 wire setups is slightly longer. It "makes" contact before the other "pins" (blades).

Round pin systems did not consistently have good contact arrangement, leading to frequent bad connections between plug & socket, producing the same type of damage as occurs with unswitched sockets.

NT

Flat plugs came about because of Thomas Edison. He hated Tesla and refused to use anything but direct current in his electrical systems. His electrical service company, which supplied New York City, started out as DC and the large spring loaded plugs were needed.

The originaly were made of two leaf springs, probably brass.

Geoff.

I'd say it depended on the quality of the fitting - given most plug/socket arrangements have round pins. Including the heavy duty BS4343 type.

The problem is transmittable, thus only one bad socket was needed for the problem to occur and spread to the others. So good sockets went down too.

The way it occurs is one bad contact occurs, the plug pins get damaged, and when damaged pins are inserted into a good socket, bad contact occurs due to copper oxide and a rough surface. So the good socket is damaged. Plug something else into it, that plug gets damaged etc.

Slow process, but have seen it happen. AFAIK its the only electrically transmissible disease :)

Nowt wrong with round pins. The problem is that some of the older sockets didnt implement contact springing, either at all or effectively. Sometimes the split plug pin was the only sprung part, which is no good at all on 15A 3 pin plugs.

NT

Conduit is used where there is a problem with critters (squirrels, rats, and the like) chewing on exposed wiring. I am upgrading the 100A service to 200A in my house, and running EMT in the attic and fishing flex down the walls to the switch and receptacle boxes for this reason.

Thomas