I am trying to figure out what's the best way to get electricity from my garage to the garden. In the garage, I have the normal 230 V outlets/lamps, and the power gets there via 1.5 or 2.5 mm^2 (still need to check) 3-wire (line, neutral, ground) cable. I was planning to connect another cable to it, lay it in the garden and connect to the lamps/water-proof outlets there. In the shop, I've discovered the dedicated cables for the outdoor use. But they also have a 4-wire cable. I wonder what the purpose of this cable may be. In the photo below I show it next to the normal 3-wire cable.

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Those cables have totally different applications. On the left, you have common household power cable in the modern EU (IEC) colors:

  • Ground: mandatory green/yellow
  • Neutral: mandatory blue (today; older installations use other colors)
  • Hot: by common practice, brown

The American equivalent is bare-white-black. These colors in 14-2 Romex (jacketed cable; 14 gauge; 2 conductors +ground) is used all over the place in every US home.

The right is for three-phase power, specifically "delta" power (which by definition does not have a neutral.) That is why there is no blue "neutral" in the bundle. This is bigger power, for heavier loads such as factory lighting or air conditioning in a large retail store.

It'd be an odd duck in residences — while three-phase "wye" power comes down your street (230 V to neutral, 400 V phase to phase), it's rare to pull all 3 phases into a home. Probably more common in a townhouse (mansion) or a 12-unit apartment block. Because of its notable lack of neutral, this cable would only be useful for running large motors or heating units, say to deliver 400 V delta to a large air conditioning unit of 5 kW capacity. Here are the IEC color codes:

  • Ground: mandatory green/yellow
  • Phase 1: Brown
  • Phase 2: Black
  • Phase 3: Gray

Black is no longer legal for neutrals in the UK, and unless the cable is pre-2004 old stock, it is certainly intended for 3-phase delta, since the colors are just right for it.

What I hear from Euro folks is this is how normal 3-and-earth is sold, and you are expected to re-mark one of the phase wires to be neutral (if you need neutral). I would re-mark the black, since you should take it "out of play" as it's not a valid neutral color anymore, so that'll reduce confusion.

Note: North American people can never re-mark or re-sleeve wires, *except in cables, they can re-mark a white (neutral) wire to be a phase/hot. In wiring where only certain wires are always-hot, the remarked white must be used for the always-hot.

  • Better answer than mine for this image! – keshlam Mar 20 '16 at 2:17
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    Here in NZ, if we need 3C or 3C+E cable, it is supplied with 3x phase colours. If we want two phases and a neutral, we sleeve one of the phases to a neutral. I wouldn't be surprised if the UK did the same. Three phase power is significantly more common and commercial/industrial usually uses plastic cable, not conduit. – Someone Somewhere Jul 18 at 7:06
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    @SomeoneSomewhere Interesting. In North America you're not allowed to do any remarking/resleeving, except neutral to phase... and then, only in cable. Yes, bringing 400 wye to every house was a good move, because you only need one industrial power standard for power tools up to 25hp, and any "garage" business can get that power. – Harper - Reinstate Monica Jul 18 at 17:01
  • Huh. We're allowed to do it both ways. I wonder why you're not? – Someone Somewhere Jul 19 at 6:38
  • We usually only bring single phase to most houses, but if you're running anything larger than about 5kW you should probably be worried about the 15kVA pole fuse anyway - above that is almost always 3P. If you think 400V gear stops at 25HP you're very wrong... we don't go to a higher voltage until much larger. I don't think there's much 690V stuff around; you normally go 400V straight to about 2kV I think. Haven't done any of that. – Someone Somewhere Jul 19 at 6:40

Four-wire is used for "two-way" circuits, and for cases where two circuits are running to the same place (independent control of a ceiling fan and its lights, for example). In the US color coding conventions, red is the "second hot" needed for these applications.

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