I have some equipment that was purchased in the UK that came with the power cord missing the plug (has 3 wires exposed; Brown Live, Blue Neutral & Green/Yellow Ground). The equipment says it is 50/60Hz so that shouldn't be a problem. My question is how do I wire a US plug to this with only 3 wires when the US needs two Live wires and a ground? Do we just hook 120v to Brown Live and 120v to Blue Neutral and Ground to Ground or does that end up putting live back to ground on the equipment? This line in the manual has us concerned:

Ensure that the mains supply is single phase alternating current (ac) of the stated frequency (Hz), with neutral nominally at earth potential

Not sure if that quoted text is just for in the UK or ??

  • What make/model/type is this equipment? Also, what type of 240V US outlets do you have? (i.e. NEMA 6, NEMA 10, or NEMA 14?) Dec 3 '16 at 18:12
  • The outlet is NEMA 6, so I'm not concerned there. My issue is how do you attached a plug to UK equipment that has all 220v live on one line to a US 220v outlet that is split with 110v on two lines.
    – Doug
    Dec 3 '16 at 18:36
  • What sort of equipment is it? I'm rather wondering why it'd be so picky about its mains input, myself...but we may have to reverse engineer its mains input circuitry to figure this out. Dec 3 '16 at 19:02
  • A UK appliance wouldn't connect neutral to earth internally. So you're unlikely to produce a hazard of that sort (or blow a fuse). The fussy input specs may have something to do with filtering (@threephaseeel).what sort of appliance is it?
    – Chris H
    Dec 3 '16 at 19:12
  • 2
    A human safety question is whether the switch on the equipment is a single-pole or double-pole switch. Does it cut just the live wire, or both the live and neutral wires? If it only breaks one wire, and you hook it up to U.S. split phase power, you would still have live components inside the equipment. Dec 5 '16 at 4:24

You can't do it, it means exactly what it says.

The manufacturer wants "neutral" (EU blue) to be near the same voltage as ground/earth (green). They are specifically saying DON'T do what you're trying to do, connecting line (EU brown) and neutral (EU blue) to two phases of hot (US black/red).

Transformers are your friend

A step-up/step-down transformer will do what you want. It is an autotransformer that takes 120V hot and neutral, and gives 240V hot and neutral. Neutrals are at the same potential. These are packaged commercial products with the correct cords and receptacles for your market. They are heavy because they are full of copper and iron.

  • Does the manufacture really want that or is it just written that way because that is how it is in the UK. I keep seeing this comment while searching for an answer to this: "“Note that currently all new American buildings get in fact 230 volts split in two 115 between neutral and hot wire. Major appliances, such as ovens, are now connected to 230 volts. Americans who have European equipment, can connect it to these outlets"
    – Doug
    Dec 8 '16 at 3:44
  • 1
    That's not new. America has been wiring that way since about 1920. Both our countries have always had 240V, it's just America pegs neutral (and ground) at center and UK/EU peg neutral (and ground) at bottom. This allows America to split it into two safer 120V legs for smaller devices (in practice, damn near everything). This also means with a 240V connection, both legs are 120V away from neutral/ground. This particular manufacturer is not comfortable with a "neutral" that's 120V away from ground. no idea why. Dec 8 '16 at 5:29
  • And by the way, UK also implements the "center tap ground for safety" -- in construction worksites. This is a peculiar setup where the supply transformer is 110V hot-hot, but the ground is tapped to center. Neutral is not used. That reduces potential shock voltage to a mere 55 volts. They do not use NEMA 5 connectors. Dec 13 '16 at 5:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.