US Green Black White cable - how to wire up in UK?

[chairmaker]

Hi All

We just received a machine from the USA which says it's 240v on the case ('cos that's what we ordered) but has turned up with a cable with 3 wires coloured Green, Black and White

No problem thinks I, and e-mail the supplier to ask which is earth, live and neutral.

Reply comes back that there is no neutral, Green is earth and Black and White should both be connected to the live. This seems a strange arrangement to me as I always thought you had to make a circuit somewhere along the line and the neutral was part of that!

Does anyone have any experience of this type of wiring? I spoke to the engineer at the supplier, and he assured me that this is definitely right. But I don't believe him!

 

[Lectrician]

US has 240 volt between 2 'split' phases (both of these are live). There is a 'center' neutral, giving them 120 volt between either of the two 'phases' and the neutral.

They have a strange setup!

Connect your white and black either way around to the live and neutral.

You should also be aware that the US has a frequency of 60Hz, and we use 50Hz. What type of machine is it?? If it has motors, you may have a problem.

 

[ban-all-sheds]

Yes he's right. In the USA they have a split-phase 120-0-120V supply, so 240V appliances are wired across the two 120V phases.

I've always assumed that a 240V appliance would work just as well with a 240V single phase supply as a 120V split-phase, and vice-versa, but I've never needed to find out for sure, and I'd not advise connecting this thing up on the basis of my assumption.

HOWEVER - my reply is not entirely pointless - you have confirmed, have you, that this machine will work over here? If it has any motors, will they be OK with our 50Hz supply instead of the 60Hz one they were designed for?

 

[Lectrician]

A very crude picture to try to explain further:

 

[ban-all-sheds]

Damn - too slow!

 

[Lectrician]

LOL

 

[andy]

Damn - too slow!

your gettin too old for this...

 

[chairmaker]

Thank you very much gentlemen for your replies! No wonder the bloke in the States couldn't understand what I was on about, nor I he.

I did tell them that we were 50Hz and not 60Hz, and was at pains to say the machine needed to be set up for 240v at the time of order. My concern is that they won't have carefully noted the frequency issue.

Oh boy!

The machine in question is a bowl feeder which sorts nails poured into it, then winds 'em up the spiral into a pneumatic device which then fires them into furniture frames with a hand-held gun. Sure the pneumatics will be no problem. Probably best to wire it up and switch on with a stick whilst standing on a rubber mat I guess!

 

[breezer]

please do let us know what happens

 

[Big_Spark]

If it has motors it will likely not work as the motors will be dual phase not single phase, as such the motors will need a capacitor to start them rotating. On dual or three phase this is unecessary as the phases are out of phase and automatically create the necessary stepped field.

Personally I would be very careful about connecting it up without the help of a qualifed engineer with experience of machinery such as process control machinery, conveyor belts etc. Most evryday sparks will understand the implications of the differences but may lack the experience to want to get involved.

There could be serious warranty issues here and you need to remember that the supplier is not subject to British Law.

 

[mapj1]

Oh wow! well, they have sent you bi-phase 240V gear with a single phase cord for a start.
Black is normally first live, white is neutral, red or purple is second live, and green is earth.
In such installations the 3rd phase (blue) is so the called 'wild leg' as instead of the centre of the star being earthed it is the centre of one side of the delta.
This puts the blue hop at 180v and 90 degrees to the other two, which are really best thought of as the same phase but up and down, rather than 2 phases at 120 deg to each other as we would have here.
A right old dog's breakfast actually..
the only 3 phase machines that don't care are the ones requiring no neutral, and even then the insulation is not equally stressed on all sides.
Fortunately for you it doesn't matter, because the earth core carries no working current (you were assured ther is no neutral) you really will have a single phase deveice, albeit a confused one.
If its expecting only 2 phases and an earth, then feed it thru an RCD as suggested, black live, white neutral, green earth from 240V. The three phase issus should not affect you this time, but generally be very wary of imported gear from the US and Tiawan.
It is often better to order 1 phase 110 V gear and run it from a yellow brick style 110V transformer in the UK.
The 50Hz issue may mean it runs rather warm, and at 5/6 of nominal speed. You should probably at least PAT test it before using it in earnest if your application is commercial.

 

[AdamW]

Oh wow! well, they have sent you bi-phase 240V gear with a single phase cord for a start.
Black is normally first live, white is neutral, red or purple is second live, and green is earth.
In such installations the 3rd phase (blue) is so the called 'wild leg' as instead of the centre of the star being earthed it is the centre of one side of the delta.

Correct me if I am wrong, but I thought the US split-phase system had two phase conductors with opposite voltages (i.e. in antiphase, one conductor varying between 0 and 170, the other between 0 and -170), plus one conductor for earth? A neutral wouldn't be required in this set-up as you have a potential difference of 240V rms and balanced currents between the two live conductors.

EDIT: I re-read your post and I think I am actually agreeing with you. Where does the 3rd phase (wild leg) come into it though? I'm lost!

EDIT2: Sorry, I didn't mean one conductor varying between 0 and 170 etc, I meant both between -170 and +170, but in antiphase. Doh!

 

[Adam_151]

Neutral is required in the us, becuase not much of their stuff uses 240v, sockets and lights, etc use 120v and that uses one live and one neutral, and they just try and have both sides balenced, but of course it can never be perfect, so neutral is needed. It is only stuff like cookers and air conditioners that use 240v

 

[plugwash]

connected between two ends of a split phase supply (which is what is most common in the us) and connected to a single ended supplly shouldn't make any difference to motors.

the frequency issue will cause motors to run hotter though. What exactly is this equipment.

 

[plugwash]

Oh wow! well, they have sent you bi-phase 240V gear with a single phase cord for a start.
Black is normally first live, white is neutral, red or purple is second live, and green is earth.
In such installations the 3rd phase (blue) is so the called 'wild leg' as instead of the centre of the star being earthed it is the centre of one side of the delta.

Correct me if I am wrong, but I thought the US split-phase system had two phase conductors with opposite voltages (i.e. in antiphase, one conductor varying between 0 and 170, the other between 0 and -170), plus one conductor for earth? A neutral wouldn't be required in this set-up as you have a potential difference of 240V rms and balanced currents between the two live conductors.

EDIT: I re-read your post and I think I am actually agreeing with you. Where does the 3rd phase (wild leg) come into it though? I'm lost!

it seems he was describing a 3 phase delta supply with the ground/neutral point of the supplly transformer center tapped

so you have split phase between the two phase cores on either side of the neutral and three phase between the three phase cores.

afaict most domestic supplies in the us are just single phase center tapped (split phase).