MikeUK

Which is why many new sockets and all new appliances have two different size 'pins' to force you to set it up the 'right' way
The old same size 2 pins are being phased out


the switch controlled the current, it didn't make the unit 'safe'

Pizzawheel

Yes. Ideally you'd have a double pole breaker for the 240V split-phase supply. Otherwise you're recreating the old fused neutral system the UK had pre-war, if you were unlucky the neutral fuse would trip leaving the circuit live for whoever came to fix it...

Technically the switch is there to control the appliance and you should unplug anything before going inside, but since you can switch off the live feed at the switch bad habits do emerge- pull the same stunt on a split-phase 240V and you have a higher risk of some ouch.

Most appliances that care about polarity actually have one fatter pin, which is the neutral, if they are two pin configuration with no earth. Laptop supplies etc that just convert to DC don't care so they have two slimmer prongs.

Davita

Quote by Mike: I look at its in a simple transformer view (as thats what your getting)
UK earth's one side of the 240v transformer and ignores the centre tap
US earth's at the centre tap/point and uses either side or both lives. Unqoute.

I totally agree with your explanation.

The US 240VAC 3 wire system taps from both live wires, and doesn't connect to the centre tap. The phase-difference between the two 120VAC legs becomes the neutral. The third wire acts as ground.

What I find difficult to understand is how can UK Black and Decker drill still rotate when directly plugged to this source. I would have thought the neutral wire, internally connected to the return end of the stator windings within the motor, would be energised incorrectly.

MikeUK

If you look on a US pole mounted transformer you can see the three taps, outer two taps your 120v phases, centre tap (neutral) 0v usually earthed right there on the pole ?

If you plot two anti phase 120V sine waves against each other, its give a 240V sine wave
All the motor sees is a voltage potential
Most if not all wired domestic power tools are a two wire double insulated set up ?


I'm not sure you do understand my explanation

Mangaboy84

Single phase motors from the uk use a capacitor to phase shift the input and allow the motor to start spinning which then is kept going upto speed using the normal single phase supply.

Davita

That's exactly what I think Mangaboy...but members here say they've managed to use a UK drill on the USA 240VAC system and I cannot follow how that's done....but I'm willing to learn.

Mangaboy84

Thats why i edited my post to tweek the answer after reading back through the thread, plenty of experience with uk electrical systems but i really need to learn the US systems once i move over this year before starting work again

Davita

Thanks Mike...I did say I understood your explanation to the split-transformer analogy and I'm familiar with the pole-mounted transformer although, in my street in the Vancouver suburbs, they've put all that stuff in a box and wires are now underground.

However, I understand that although you achieve 240VAC the difference in the phase-angles of the sine waves on L1 and N1 will be 180deg out. This is OK on N.A. 240V motors as the windings can be assimilated but it's not the same on UK 240V wound-motors.
How can a UK wound motor work if the designed continuous winding Line to Neutral wire, creating the magnetic stator field, use sine waves opposing at 60hertz?

Pizzawheel

I think it's RivingtonPike that may have a number of workshop tools from the Ulk- if not he's been active in the debate.

rivingtonpike

I do indeed have a bunch of tools that I brought from the UK. I've got 220v in my garage already, but I also have a 3000w transformer which is heavy, but in the garage, who cares. I still use 2 drills, a leaf blower, hot air paint stripper, jig saw, dyson, B&D electric screwdriver. No idea if they run faster or not, but they all work fine. As things have worn out, of course we've bought Canadian versions, but I couldn't see the point of selling my stuff in the UK for peanuts and having to replace everything. Plus I seem to remember having rather bigger issues on my mind that selling a few power tools.

Davita

Thanks for that info Rivington but, just to clarify, do you use those inductive UK tools directly from the BC Hydro 240VAC supply or through your 3KW transformer?

rivingtonpike

Mainly from the BC Hydro 220v. The Dyson we use around the place from time to time so use the transformer

Davita

Thank you Rivington.
Then I'm clearly wrong in my theoretical thinking....and it is perfectly OK to plug a 240Vac UK motor into the N.A. 240Vac system with impunity...and it will go faster due to the increase in hertz.

MikeUK

From the engineers at my former work place when utilizing equipment from 50hz to 60hz
the motor spins faster and its cooling fan spins faster ~ usually not an issue as excess cooling offsets the speed


60hz to 50hz slower motor slower cooling ~ risk of overheat, on this one I'm resurrecting a Compressor with 1.7KW draw shortly I'll let you know how reliable it is ??? or If I need to replace the motor


as for the voltage consider only the potential difference across the motors poles and ignore any neutral/earth reference points

Davita

We all know that it isn't voltage that turns an electric motor..it's magnetism.

The UK 240VAC produces a single sine wave and a UK motor 'usually' has a single winding. The magnetic polarity changes with the frequency of the sine wave and the motor, once started, runs. A capacitor is the simple way to kick-start but I'm aware that there are other methods using more windings.

As the US 240VAC system uses 2 sine waves 180deg apart (that's why it doesn't need a neutral wire) I couldn't see how that can make a UK wound motor turn.....as the polarity will reverse every cycle.
However, I'm only thinking theoretically...so I bow to those who have practical information and have made the UK motors work directly from the N.A. 240VAC source without modification.

I just cannot comprehend how that works.