2 phases and neutral

[E.E.I]

went to look at a job this evening and the supply into the building is 2 phase and neutral.

They property is a shop ground floor and a flat on the first floor, one phase for each unit, my guess this is the reason for the two phases, but why not bring in all 3?

I haven't come across this before

 

[The Ghost]

If you look on your certs there is an option for 2 phase. So it would be easier to bring two phases in as shop and flat have to be separately metered rather than bring in 2 single phases.

 

[Leesparkykent]

you will get 460V between phases being split phase. What work have you got to do there?

 

[snowhead]

From the customers point of view why pay for 3 when 2 will do.
From the suppliers point of view why waste money putting an extra phase in that will never be used, and may already be at the max in the area.

 

[E.E.I]

Yes valid points, first time ive seen it in person

 

[7029 dave]

you will get 460V between phases being split phase. What work have you got to do there?

Yep, but I have been told many times no such thing as split phase. 2 wire of 3phase= 230x2 =460v. lol

 

[E.E.I]

Customer wants to relocate DBS and add an extra one for a flat that's going to converted in the loft

 

[westward10]

Sure it is two phases and not single with two fuses from the head to supply the separate premises.

 

[E.E.I]

I haven't tested the voltage between phases but they are labelled L1 & L2 on the tails to the meter although this is just in marker pen!

 

[Lucien Nunes]

Some confusion here. Split-phase (230-0-230) does have 460V between lines. That is an old system, more or less obsolete in the UK, where larger LV installations were served from single-phase HV lines such as on farms. It was not used where 3-phase supplies were available. Two phases out of a 3-phase supply will have 400V between lines and this will be the case in an urban system where 3-phase distribution cables are laid in the road.

Re the installation mentioned in the OP, if the service cable is old (e.g. prewar) it was likely a 3-core cable installed for 3-wire DC mains. A small installation would have only one outer (line) and the neutral, hence a 2-core service cable, but a larger one would be supplied with both outers via a 3-core service cable (i.e. positive line, negative line and neutral). When changed over to 3-phase AC, the two lines of the existing serivce cables were connected to two of the three phases of the new distribution cables. I have this at my house, with two separate single phase supplies derived from the two lines. I cannot have the third phase without the 1930s service cable being replaced.

FWIW there was another historical system properly called '2-phase' that was neither split-phase (which is really just centre-tapped single-phase) nor two phases out of three. It used a 3 or 4 wire supply with the two lines at 90°, intended to give the advantage of a rotating field without power-zeroes in induction motors, but it lost out to the more versatile 3-phase system.

 

[dmxtothemax]

Is it really a split phase ?
Or just two phases from a three phase system ?
The difference will be the between phase voltage.
But it looks like it is supporting only single phase loads.

 

[Onur]

I think, line of a phase was splitted. (A Phase break)

 

[Toneyz]

Sure it is two phases and not single with two fuses from the head to supply the separate premises.

I thought the same ,never seen 2 phase supply always been single phase split with common neutral and 3 phase.

 

[Onur]

Probably. This even was like your say.