two phase power ?

[zardoz]

I have seen a welder for sale, describe as "two phase". Is there such a thing, or has he mis printed something ?

 

[gordon stephenson]

Don't really know.Not being too electrically minded, But seen/read somewhere that 2 phase uses 2 phases of a 3 phase system.

 

[500e]

GS is correct 2phase is between \ across 2 of the 3 phases, 440volt quite a few welders can run like this my dial arc is wired this way also the BOC oil filled stick welder we have.
Zar
Usus est magister optimus

 

[Stueeee]

In a three phase system, there is 415V between any two phases; the welder zardoz has seen will just have a standard transformer with a 415V primary winding.

 

[BrokenBiker]

i would be careful, my electrical tutor in college said that two phase could be an americanised term for our single phase, apparently he worked in Florida and it was quite common for them to call it 2 phase as it only used 2 cables (live and neutral)

 

[Psychosaffa]

My ancient 300A triangle stick welder is 2ph and neutral.

 

[Rig Pig]

My Oxford stick set is 415v 2ph

 

[voipio]

i would be careful, my electrical tutor in college said that two phase could be an americanised term for our single phase, apparently he worked in Florida and it was quite common for them to call it 2 phase as it only used 2 cables (live and neutral)

Single phase in the US is 120V, whilst two phase (180 degrees out of phase, compared to the UK 120 degrees) gives 240V between the two "live" conductors, one from each phase, and used for devices running higher power.

 

[ford34/2]

I know nowt about leccy, other than its dangerous,but our Woodworking shop in the 60s/70s had all single phase I think 480 volt supply, the saw bench 24" was a star delta start up , amps too heavy to start straight through, we had a ginormous welder we used to cut RSJs up with + arc welding.
Now the supply was what I believe from the original Pit supply and all the motors on the Machines were rewound to this spec-- but definitely it was NOT 415 3 phase. and defiantly not 240 volt single phase.

Stan

 

[julianthegypsy]

I have an old olympic/oxford oil filled which is allegedly three/single phase. To run on three phase it is actually wired across two phases if I remember correctly, with the third phase redundant. Then for single phase across any phase and neutral.

 

[ben8vgte]

My tig is twin phase, just use's 2 from a 3 phase supply. But it's now set to run on single

 

[zardoz]

Thanks for the replies everyone.

Does anyone know of a good place that explains this two phases of a three phase system malarky? In fact somewhere that explains electrickery full stop. I will hold up my hand and admit anything other than live neutral and earth has always puzzled me. (ie when you undo a ceiling rose and see half a dozen wires going left right and centre)

 

[Keith 66]

My BOC oil cooled welder is dual voltage it can run on 230 v single phase or you can alter the shunt on the junction box to use two phases to give 415v, I also have an ex CEGB ancient Romac spraying compressor that has a dual purpose single or two phase motor, (its currently set to single phase & will stay that way) The thinking was by boosting to 415v there was less voltage drop at long distance. I wouldnt like the idea of an unarmoured long wander lead at that voltage.

 

[hotrodder]

Does anyone know of a good place that explains this two phases of a three phase system malarky? In fact somewhere that explains electrickery full stop.

It's witchcraft but this kinda explains... http://www.epemag.net/electricity-generation6.html Link goes to pg 6 as most of the earlier stuff is about making the leccy. Explains star & delta and how 230V domestic is gotten from one phase & neutral of the 3 phase supply in the street

As said big 'ol transformer machines are generally dual or even multi voltage and they get advertised randomly as 3 phase or 2 phase because to feed them 415V and make them less greedy with the amperage draw you use two phases of a three phase supply instead of one phase and a neutral

 

[JimK]

Hi Zardoz, there is no such thing as a 2 phase welder. Always look at the machines rating plate and you see "Single Phase" for any voltage input. There are 3 phase welders but you can't just change the bridge connections or unlock and switch a switch to allow then to operate from a single phase supply.
Two conductors must equal single phase.
Another example is when a 3 phase motor is running and one Fuse Cartidge blows, it will continue to run and it is said to be single phasing. If you are operating a 415 volt Single Phase welder from a 3 phase socket outlet, then you are using 2 of the phases to get 415v but your welder is not 2 phase.
In some North eastern areas of the US, more than 100 years ago they had 2 phase motors, these required 4 conductors to operate and they are all long gone, redundant, and if you had a 3 phase supply you still could not run these without connecting two specially wound transformers and connecting them the "Scott Tee Way".

Jim.

 

[Sidewinder]

Correct Jim, but it is not the way that manufacturers describe their kit unfortunately!

A "single" phase set running on 400 (it is now 400 in the UK, NOT 415/440) could well be described by the manufacturer as 2 phase.

You "can" get "split" phase supplies in the UK, which are 2 off 230V phases, 180 degrees apart rather than the normal 120 degrees.
These are rated @ 480V though, and whilst unusual are still available to this day, more so in rural areas, and need special consideration for the electrical install side.

 

[JimK]

Hi Sidewinder, I think the manufactures do state on the rating plate that the welder is Single Phase or 3 phase. Some years ago the Australian and New Zealand Electrical Standards changed to 400/230v Nominal Volts, but nothing much in our distribution system changed. I live in the rural with only a single phase supply and have a line voltage of 252v. It sounds the same here as you have, about a split phase transformer. Just a way of getting more energy through smaller conductors. Very rare here, but split phase is still single phase, it's just a transformer that has two secondary windings of 230v/240v which are series connected in phase to get 460v/480v and that connection point (the centre tap) becomes the neutral point for either side. Phase angles don't come into the discussion.

I am responding to this original question

This is the question Zardoz asked:
"I have seen a welder for sale, describe as "two phase". Is there such a thing, or has he mis printed something ?"

You may have a similar situation in the UK as we have here in Australia. People know it is a 3 phase 415v plug and it connects into a 3 phase 415v socket outlet, now if they know that the welder operates from only two of the actives then some people think the welder is two phase and some other think beause it has a 3 phase plug it must be 3 phase.
Like I have said look on the manufacturers plate, it will say Volts, Amps, Hertz etc and also Phase: single or 3 phase.

Jim

 

[Sidewinder]

Hi Sidewinder, I think the manufactures do state on the rating plate that the welder is Single Phase or 3 phase. Some years ago the Australian and New Zealand Electrical Standards changed to 400/230v Nominal Volts, but nothing much in our distribution system changed. I live in the rural with only a single phase supply and have a line voltage of 252v. It sounds the same here as you have, about a split phase transformer. Just a way of getting more energy through smaller conductors. Very rare here, but split phase is still single phase, it's just a transformer that has two secondary windings of 230v/240v which are series connected in phase to get 460v/480v and that connection point (the centre tap) becomes the neutral point for either side. Phase angles don't come into the discussion.
Jim

Yes Jim, I think that my description was a little misunderstood.
Not manufacturers, really, but sellers of the kit would be a better description!
The secondary phase angle between the supplies will be dependent upon the transformer internal design.
I know, one site that I have worked at where the suppliers engineer has stated that because of the transformer design the phase shift creates a supply where the p-p is 180 degrees rather than 120 deg.
Very odd!

Where I have my unit I have conventional 230/400 TP-N-E thank goodness!

 

[brightspark]

a few outlying farms round our way with overhead supplies have 440v single phase. ive come across about half a dozen in my lifetime on milking parlour and granary motors old brooks crompton and parkinson .