USA domestic power supplies

[Bob Minchin]

I'm being asked to supply a high power electrical device to run on a US domestic supply. Ideally I'd want 240v input (120v is too low)

In some place on the web I read about 120/208v being available - the higher voltage being used for cookers/dryer etc

These voltages being the the ratio of root3:1, seem like our UK 240/415v phase to neutral and phase to phase voltages.

Elsewhere I read about centre tapped transformers being used to provide the 120v which would make the higher voltage 240v.

Can anyone clarify please

TIA

Bob

[Scott M]

This is what I've always understood (and have a vague recollection of

240v driers etc from visits to the US.)

[Peter Crosland]

I have often seen air conditioning units in hotels that were 240V but can't tell you the technical details. Many electrical items used in the USA require approval by Underwriters Laboratories (UL) and there is a mass of State legislation about it. Just beware you don't fall foul of it.

[JimK]

/These voltages being the the ratio of root3:1, seem like our UK 240/415v phase to neutral and phase to phase voltages.

Elsewhere I read about centre tapped transformers being used to provide the 120v which would make the higher voltage 240v.

Can anyone clarify please

TIA

Bob /q

Odd you haven't had an answer? Especially as many on here regularly boast of living or often visiting 'over the pond'...

One must presume they aren't really DIYers just posers?

Jim K

[spuorgelgoog]

Try asking on

And giggle at the 'code violations'

Owain

[Matthias Czech]

Am 11.10.2014 um 11:25 schrieb Bob Minchin:

Maybe these links could explain, where you find the 208V and where the 240V.

[The Natural Philosopher]

From what I understand, houses get a split phase. a neutral and two opposite phase 120v, at 60hz.

Earth (ground) is tied to the neutral

So you can get a 4 wire supply. essentially +120v, -120v, 0v and ground.

Most sockets wre wired to one 'phase' and neutral, and no ground but its possible to run the two phases and a ground or two phases a neutral and a ground.

[Bob Minchin]

Thanks Mattias

That certainly explains the voltages.

Bob

[Brian Gaff]

You don't need to be an expert in their supply system to live there and switch things on and off.

Brian

[harryagain]

The US commonly uses "zig zag" connected trnasformers. Larger loads run on 240v and lighting etc on 120v. Commonly both are available in all houses.

[A.Lee]

Supply frequency will be a factor too. CBA to google it, but IIRC, USA Hz are 60.

[Tim Streater]

Suggest you get the people at the U S site to ask their electricty provider whether they have 240 at their house, and whether its actually

240 or 208.

They might need an electrician to come in and install a socket for it which will be different to the standard US socket. Check also what the Yanks expect for colour coding of the wires, the sparks had probably better connect the plug.

[Bob Minchin]

Thankfully my application rectifies the incoming supply so the only issue is the difference in ripple current rating of the capacitor bank.

Bob

[Bob Minchin]

I'll be just providing a box with screw terminals for power input. It will be the users problem to use the correct size and colour scheme for the flex and the plug.

Bob

[Tim Streater]

Roger that, Huston.

[Andrew Gabriel]

Domestic supply is derived from a single phase, giving 120-0-120. Most appliances and all lights run on 120V from one or other live leg. There will typically be a 120-0-120 socket in the kitchen for a stove so it can use 240V, and sometimes in the laundary room, but they are not provided throught the house. Aircon units are often hard-wired to a dedicated 120-0-120 feed from the panel (consumer unit).

You will only find 208V in commercial premises where there's a 3- phase supply. 3-phase isn't normally run down streets with just houses - you will see the 3-phase pass at the end of the street, and a different single phase is brought up each street, where it's locally transformed down to 120-0-120 for every few houses (it can only be carried a few hundred yards before 120V regulation goes to pot).

[ARW]

So just to clarify. The UK has a better electrical system than the US? Both in voltage and frequency?

[John Williamson]

Yes and no?

Low voltage is safer from a shock point of view, while it needs heavier cables to carry the same power.

Motors and transformers can be made smaller for the same power at 60Hz, but resistive losses are greater due to the lower voltage.

I'd call it a draw, personally.

The long distance transmission systems use more or less the same voltages, it's only low voltage at the point of use.

[Dave Plowman (News)]

Well, the US won't be concerned about vacuum cleaner power limits that trouble so many on here. ;-)

[ARW]

230V is classed as low voltage!