Reply to: Now why didn't I think of that?

[gingerjedi]

Knew it!

(Waited for Zeity to confirm though).

[Churchill]

Go and change the polarity on your fan cooler and it will be blowing air out its arse.

Some items can deal with polarity changing, some cannot.

On the polarity discussion above:

What a lot of twaddle.

Wot comes out of the wall is AC at 50Hz and 230V (allegedly).

The polarity of which reverses every 10ms.

So for 10ms, the Live pin is positive with respect to the Neutral pin.

Then for the next 10ms, the Live pin is negative wrt the Neutral pin.

Swapping the pins about does very little, other than giving you the possibility of getting a switched Neutral rather than a switched Live. (I last encountered a switched Neutral when trying to fix a tv in someone's house. The socket was wired up with bell wire. "We had a proper electrician to install the wiring, Mr, honest").

If you swap the Live & Neutral on a fan, it will still go round the way it did before. Coz it's still fed with AC.

Ditto with all the power supplies you may encounter.

None of it gives a rat's arse about which pin is Live or Neutral.

On the "swapping pins makes it go backwards" front, the only way you'd see that with AC is if the device uses a 3 phase motor and you swap two of the phases.

Which I have seen, on a CDC tape testing machine that I moved & then discovered that the socket I had to use had two of the phases swapped so that instead of the vacuum pump sucking, it blew.

Not a lot of use when it should be sucking tape down a vacuum chamber.

So much for your engineering qualification Minestrone!

[swamp]

While our 3 pin design is arguably the best one in practical and safety terms it's too chunky and this design is a very elegant solution.

I always thought the UK plug was a crap design. Very painful if you tread on one in bare feet.

[minestrone]

If polarity was such an issue, why does nearly everything I own use a wire like this that can be plugged in either way round?

http://www.powersuppliesonline.co.uk...36/default.htm

Go and change the polarity on your fan cooler and it will be blowing air out its arse.

Some items can deal with polarity changing, some cannot.

[blacjac]

If polarity was such an issue, why does nearly everything I own use a wire like this that can be plugged in either way round?

http://www.powersuppliesonline.co.uk...36/default.htm

[conned tractor]

As sad as I am I had a think about the polarity issue whilst being frogmarched around around the shops.

If the load was inductive or resistive, i.e. a motor or light, then it wouldn't matter as a circuit is made across the load - apart from the fact that you would be switching the negative side - which is not necessarily a good idea since the item under load would remain on the live side.

However, if it was for example a power supply (probably most complex electrical goods) then it would matter and hence would not work.

The polarity only refers to the live signal though which alternates between +325 and -325 Volts. The negative is connected to earth at the substation and will be around a few volts potentially different to the earth pin.

However, I should imagine it is also possible to monitor and switch the supply around in the psu box of a product like this. And again as minestone said they would be better to reduce the size of the power supply box.

[d000hg]

It's a very slick design, especially the way he has multi-plugs which accept the folded configuration - a 4-gang the size of a normal plug.

There are potential safety concerns but I can't see them being insurmountable, materials science has advanced a long way.

[Platypus]

Correct me if I'm wrong but AC current doesn't have 'polarity' so it wouldn't mater which way it was twisted.

That's what I was thinking too, and how come the Yanks don't have a polarity problem with their easily reversible plugs?

[minestrone]

The times I see something like that being useful is in a laptop bag but when the plug size is incidental to the power adapter it is attached to it is meaningless. Even the mac I have in the house has a box about 4 times the size of the plug. My laptop dell has a potenital murder weapon sized power adapter.

Looking under my desk I can see about 5 of these things.

[minestrone]

It was a joke - 'potential'.

Trying to think back to psu design. I think most of it should still work - any sparky types about. OK just foundthe following - possible but not necessarily safe.



Anyhow, I should imagine the plug doesn't necessarilt have permanent conection to a single pin but a contact is made upon the swivel action meaning that incorrect polarity would not happen. I would be more worryed about arcing contacts though. (Although I dont know the internal workings and am guessing).

And I dont think this would make it through any heat type or high current standards so low power only. Good idea for mobile equipment though.

Knew it was a joke, honest, I left the question there for the rest of the board.

I reversed the polarity when trying to fix my ZX Spectrum once and pfffxxstt was the noise I heard. No more jet set willy for me.

Can I just say the chap could have used a nail brush before the photo shoot. God knows where that lad has put his thumb judging by the colour of it. Instant job fail for me if he came to an interview.

[conned tractor]

True to an extent, it would depend on the materials used.

I learnt that lesson not so long ago. I wired up a home made bodge job heating vessel with a 2.4KW element - stolen from a cheap asda kettle. Now although most kettles are cordless, inside the kettle the element still has the prongs for the plug. So, knowing not to use a computer lead went about the house looking for a suitable 'kettle' type lead. Found one with a moulded plug rated at 10 amps and moulded connection at the kettle end at 13 amps (or the other way around). Thought this would do as it would only be carrying 10 amps-ish through the wire.

When the wire started to melt on the worksurface started to panic a bit but no real harm done.

Later found out that there is also a heat rating for such connectors and as an electronic engineer suffered at first to get my head round it. Apparantly, according to the sparky types, it is the conducted heat back through the cable that causes it to melt and not the actual current itself. Although obviously it helps to heat it.

[gingerjedi]

Correct me if I'm wrong but AC current doesn't have 'polarity' so it wouldn't mater which way it was twisted.

[TykeMerc]

And I dont think this would make it through any heat type or high current standards so low power only. Good idea for mobile equipment though.

True to an extent, it would depend on the materials used.

Of course for higher power applications the devices tend to come with bonded plugs and aren't generally that portable or small so using a current design plug wouldn't be a disadvantage.
I got a mains charger with a camera a couple of years ago that presents as USB so will take any USB charge lead and came with a couple of types of slot on connectors for different regions of the world, again an elegant solution for people who travel and of course it means the manufacturer only produces one universal charger so saving money, quite an elegant solution to what can be a pain in the nads.

[conned tractor]

If someone on here wants to go around their house and reverse the polarity of all the electical devices they have...

It was a joke - 'potential'.

Trying to think back to psu design. I think most of it should still work - any sparky types about. OK just foundthe following - possible but not necessarily safe.

"Reverse polarity" is the term used to describe a situation where electrical wires are connected to the wrong terminals of a receptacle. It can be hazardous if the "hot" side of your electrical system gets connected to certain types of lamps or equipment.

It's a common condition because it's an easy mistake to make when hooking up wires and because receptacles work fine even when the polarity is reversed. You generally don't know the condition exists unless you look for it."

Anyhow, I should imagine the plug doesn't necessarilt have permanent conection to a single pin but a contact is made upon the swivel action meaning that incorrect polarity would not happen. I would be more worryed about arcing contacts though. (Although I dont know the internal workings and am guessing).

And I dont think this would make it through any heat type or high current standards so low power only. Good idea for mobile equipment though.

[TykeMerc]

You're right Minestrone, that's why I hope he can get Standards approval. There will be some finer design issues that will have to be ironed out.

It would be easy enough to avoid the reversed polarity issue with either a break link if it was rotated the wrong way or an internal connector that only mates if the live is on the right or always connects live to the right. Finer points of design and not hard to engineer.

As you said the UK plug is the worlds safest, it's hard to dislodge and the sockets have a very simple but effective safety design. Assuming this new design meets the right safety standards at some point it could be a huge success.