1-Phase, 3-Wire....Anyone ever had to tick the box?

[ADS]

Hi,

On the BS7671 forms under 'Number and Type of Live conductors'

it gives the option of 'ticking' 1-Phase, 3-wire.

Now, I know how this works, but I have never come across it......unless it's simply referring to the 110V supplies to the likes of construction sites etc.....

...second thoughts, they're only two wire.

I know they use a similar system of supply in the states.

I was just wondering if anyone else had come across it and in what situation it was being used - photos of the supply head etc would be a bonus as it's got my curiosity going

Thanks in advance

 

[Lurch]

I'm not sure you'd see one TBH, some industrial equipment is 2 phase, but I think that the supply origin will always be single or 3 phase and it's the internal wiring that will be fitted to suit.

 

[the doctor]

hi

it is where you have a biggish storage heater consumer unit and they butt another main fuse unit next to the original................so you have 2 main fuses and the one neutral block "one phase, three wire"

next? Guinness

alan

 

[Lurch]

Hmm, should have read the question....

 

[steptoe]

hiit is where you have a biggish storage heater consumer unit and they butt another main fuse unit next to the original................so you have 2 main fuses and the one neutral block "one phase, three wire"

next? Guinness

alan

+1

that would be similar to my take on it,

2 line conductors via 2 fuses but on the same phase.

possible landlords supply on a large block of flats or sheltered housing.

never seen any though,

have seen 2phase feeds though, I couldnt work out why to start with,

 

[the doctor]

+1have seen 2phase feeds though, I couldnt work out why to start with,

Hi Steptoe,

me too, that is also called 400V single phase( two phases and NO neutral. it is used in europe on some machinery there......

 

[ADS]

Hi,

My understanding was that it's splitting the phase.

Single phase supply to a transformer, center tapped (and earthed)

neutral on load side, giving three wire working.

230V between lines (in phase with each other) and 110/120V

line to neutral/earth.

I've just never come across it - although I've heard it has been

used in agricultural areas in this country.

Cheers

 

[steptoe]

Hi Steptoe,me too, that is also called 400V single phase( two phases and NO neutral. it is used in europe on some machinery there......

it was in netherlands I came across it, used to be fairly common there by what I was told.

seen it a few times in spain too, but not very often.

 

[Riggy]

Lots of split phase supplies round here, mostly farms/caravan parks. Overhead supply, pole transformer single phase, output is 480V centre tapped to earth. Two incoming fuses each 240V to neutral/earth.

 

[ADS]

Hi Riggy,

Yeh, I didn't think about it being supplied single-phase but

at a higher voltage.

The setup you describe is exactly the same then - 1 phase 3 wire,

but with higher voltages available.

 

[PBC_1966]

There are plenty of 1-phase 3-wire 240/480V distribution systems still in use here in rural Norfolk. They're common for those clusters of a couple of dozen homes and farms spread along a few hundred yards of country lane, where there wasn't enough demand to warrant running a full 3-phase HV feed to them. Most of the houses are only fed 240V from one outer and the neutral, but the farms often have the full 3-wire 240/480V supply available.

Those installations where a second fuse has just been put alongside the original for storage heating or similar heavy loads and linked to the same line conductor are not 1-ph 3-wire, since the incoming supply is still only 2-wire (although there's nothing to stop that 2-wire supply from being derived from 1-ph 3-wire system).

1-ph 3-wire at 120/240V is the norm for residential and light commercial single-phase services in North America.

 

[Evans Electric]

I've done some new housing with all electric heating and the Network did as The Quack said , single phase 25mm split/con X 100A supply with two 100A cut-outs one of them for the off-peak heating .

I just called it single phase 2 wire though.

 

[ADS]

Thanks PBC,

That's exactly the kind of explanation I was looking for -

if I get any work around your neck of the woods I'll know

what I'm looking at now

 

[kme]

The "twin heads from one cable", as PBC stated, is a 2 wire "summation" supply; where the incoming cable can carry the necessary load; or where two CU units are installed within a building, requiring seperate metering.

KME