Running 2 phase in swa

[Lucien Nunes]

The supply is 2 phase from cut out fuses to meter, and meter to isolator. From isolator to DB is 4 core 35mm. 415v between phases.

If it's a 2 phase supply, the voltage between phases is 460 volts (480 in old money).

The implication from the OP is that he has two out of three lines of a 3-phase supply, hence the 400 / 415V between phases. This is not unheard of in areas that have 3-phase 4-wire street mains but 3-core service cables from the 3-wire DC days. We have it in our street; two lines, two cutouts and at one time, two meters, because when the area changed over to AC the distributors were relaid in 4-core but the service cables were not.

This is why I prefer to call 230-0-230 (460) by the name 'split phase' instead of two-phase, to avoid the ambiguity. What the OP appears to have, and what I have in my house, I call 'two-out-of-three phase' to indicate that they are 120° apart and there is a third phase in the supply network that is not present at the origin.

IMO and strictly speaking, 2-phase means a system where the phases are 90° apart, which was used in the early days of polyphase AC instead of 3-phase. Both systems offered a rotating field vector so induction motors were self-starting and had no torque-zeroes, but 3-phase was more economical of copper and became the preferred system. I believe that Croydon still has some 2-phase 90° distributors serving single-phase customers, using the old triple-concentric cables. They are fed from Scott-connected transformers in the substations to spread the load across a 3-phase HV supply.

FWIW my very first post on this forum about 15 years ago was on these definitions. Someone was saying that a single-phase welder with a 400V input was '2-phase' when what they meant was that it connected between two lines of a 3-phase supply to get the 400V and confusion reigned.

 

[stay away from the grove]

The implication from the OP is that he has two out of three lines of a 3-phase supply, hence the 400 / 415V between phases. This is not unheard of in areas that have 3-phase 4-wire street mains but 3-core service cables from the 3-wire DC days. We have it in our street; two lines, two cutouts and at one time, two meters, because when the area changed over to AC the distributors were relaid in 4-core but the service cables were not.

This is why I prefer to call 230-0-230 (460) by the name 'split phase' instead of two-phase, to avoid the ambiguity. What the OP appears to have, and what I have in my house, I call 'two-out-of-three phase' to indicate that they are 120° apart and there is a third phase in the supply network that is not present at the origin.

IMO and strictly speaking, 2-phase means a system where the phases are 90° apart, which was used in the early days of polyphase AC instead of 3-phase. Both systems offered a rotating field vector so induction motors were self-starting and had no torque-zeroes, but 3-phase was more economical of copper and became the preferred system. I believe that Croydon still has some 2-phase 90° distributors serving single-phase customers, using the old triple-concentric cables. They are fed from Scott-connected transformers in the substations to spread the load across a 3-phase HV supply.

FWIW my very first post on this forum about 15 years ago was on these definitions. Someone was saying that a single-phase welder with a 400V input was '2-phase' when what they meant was that it connected between two lines of a 3-phase supply to get the 400V and confusion reigned.

What you said is what the property has, 2 out of 3 lines entering the property. As an installation electrician I've never came across this before, therefore apologies for the wrong terminology. So from now on it's best to call this a 2 line supply?

 

[Lucien Nunes]

I'm just being pedantic, ignore me. Two phases out of a three phase supply. Or two-phase, no-one thinks about 'real' 2-phase any moreunless they work for the DNO in Croydon (if that's still in use).

 

[brianmoooore]

no-one thinks about 'real' 2-phase any moreunless they work for the DNO in Croydon

Or in my village and the surrounding area.