3 phase revisited ..sort of

I find it hard to believe that you have 3 phase at your home. I know of a few residences that do have 3 phase but they were VERY special situations and the owner PAID big time to get the service. 3 phase would be 4 wires coming in from the pole not 3. Unless of course your somewhere that the utility does not bring in an neutral from the transformer.

An 3 phase welder should have had 4 wires, 3 hots and a ground.

With an load like the welder or an motor connecting any of the incoming lines to any load will work. In the case of the motor worst case it would run backwards to your application.

| An 3 phase welder should have had 4 wires, 3 hots and a ground.

How would a 3 phase welder put all three phases at the welding rod? The only way I could see this happening is if it is really converting everything to DC. Or else it is not drawing current on all three.

I was once thinking about how to make an arc lamp with the light source being as small a point as possible, as bright as possible, and powered with three phase well balanced. The only thing that seems plausible is

3 arc rods at 120 degree angles.

well I did say there are three cables(well one large cable that opens into three before they are hooked up to the breakers etc.)coming from the service.the ground for the house is of course going to an outside pole in the ground.but the three wires are live..I can guarantee that..so what phase would that be?

and the welder is hooked up to the three live cables and works fine..btw it's an Esab LHF 400 welding machine.and the loaner was specific that there is no ground hook up just three positives,but there are four wires;there 2 blacks, a brown and a blue, the blue is not hooked up thanks

i assume you mean 110 to ground and 180 to ground measurement as you should be measuring 220 (more or less) from point to point. some tpye of 3 phase service have what is called a "wild phase" or "wild leg". an article with drawings can be seen here

the electricians in some areas call the point at which equipment chassis and electrical panels are ties together "bond".

your borrowed welder may be in fine shape and perfectly safe but if it was me i would look for a grounding lug somewhere on the case and wire it to "bond" (safety ground) using a cable of sufficient size to trip a breaker in case the transformer in the welder shorts to chassis.

the welder is hooked up already so I guess I need to know if

you should have something like this installed by a qualified electrician.

here it is

or here yup, looks like is a DC only welder.

4 wire with the ground left dangling :) maybe it's in Mexico?

lol try caribbean. what I'll try to do is take a pic of the hook up and post it on my ftp.. will try and do it tomorrow..

why would you say it's a dc only welder?

|>> | An 3 phase welder should have had 4 wires, 3 hots and a ground. |>>

|>> How would a 3 phase welder put all three phases at the welding rod? |>> The only way I could see this happening is if it is really converting |>> everything to DC. Or else it is not drawing current on all three. |>>

|>> I was once thinking about how to make an arc lamp with the light source |>> being as small a point as possible, as bright as possible, and powered |>> with three phase well balanced. The only thing that seems plausible is |>> 3 arc rods at 120 degree angles. |>>

|>

|> here it is

|>

|> or here

|>

|> yup, looks like is a DC only welder. |>

|> 4 wire with the ground left dangling :) maybe it's in Mexico?

It's simply a DC welder. The word "only" tells ho it behaves. It gives output as DC. And it is 3-phase. So at 50 Hz, that means you'll see the DC pulsing at 300 Hz. But it won't reach zero crossing due to the DC rectification from 3-phase. And it looks like a substantial welder on that esab.co.uk site ... 35 kW.

3-phase is a plus when you are doing such a high amperage. But you do have to recitify it to DC to get it all coming in through one rod.

Also, this will put some hefty harmonics on the power line. Since it is listed as 380 volts, it's obviously getting it's power without using the neutral wire (e.g. phase to phase). But an upstream transformer wired in star (wye in the US) configuration (as they almost always are in the UK) could have 2 to 3 times the current going through its common point for the three secondary windings. If it is a small transformer dedicated to this circuit, it needs to be double rated. If it is a big transformer for much more load, it is likely to be no problem.

|>

for some odd reason i chose welding as an elective in collage. it was kind of fun and i learned to use oxy-acetalyne, arc, MIG, and TIG. the ARC welders had a slector for AC output, DC+ or DC -

as i recall the DC polarity affects the depth of the weld (or something like that) the details are getting a little hazy. as far as i remember the ARC units were all single phase.

at 400 amps out this unit must have 6 awsome diodes in its rectifier circuit assuming its a bridge rectifier.... maybe it only has 3 ?

>

it kind of reminds me of the lady welder who only worked one day a week. she later went on to become an actress. perhaps you have heard of her... Tuesday Weld ?

On Wed, 3 Nov 2004 02:54:51 -0500, reqluq put forth the notion that...

There is no three phase system that gives you 110, 110, and 180. If you have a residential service with three wires coming in, you almost certainly have a standard 120/240 single phase service, which will not run three phase equipment without a phase converter. Something about this story doesn't add up.

| at 400 amps out this unit must have 6 awsome diodes in its rectifier circuit | assuming its a bridge rectifier.... maybe it only has 3 ?

It could have many in parallel. Or it could have thyristors that are being controlled by a circuit that knows when to make them switch. The do make AC to DC conversion up to the scale of electrical grid interconnects.

On Wed, 3 Nov 2004 19:50:09 -0800 Checkmate wrote: | | On Wed, 3 Nov 2004 02:54:51 -0500, reqluq put forth the notion that... | | |> Hi I was just browsing through the oct phase discussion. |> I borrowed a welding machine to do some welding duh,and the loaner said it |> is three phase,so he explained to me how to hook it up,saying that there is |> no ground just the three positives so I hooked up the three to the three |> different(three phase system?) cables entering the house from the service |> ,and of course it works fine..how can it work without a ground?(laymans |> response if possible please). |> and....they say that two of the lines coming in from the road service is 110 |> and the third is 180,does it matter which of the three welder lines is |> hooked up where?the welder is hooked up already so I guess I need to know if |> there is a *correct* way to hook the three up,for effeciency sake. |> thanks |> req | | There is no three phase system that gives you 110, 110, and 180. If you | have a residential service with three wires coming in, you almost | certainly have a standard 120/240 single phase service, which will not | run three phase equipment without a phase converter. Something about | this story doesn't add up.

The OP appears to be in UK, so 220 single phase, or 380/220 star three phase.

But, back to the USA. You could have three phase delta center tapped with the B phase (often called "stinger" or "wild" leg) having sqrt(3) times the voltage relative to ground than the other two phases. If the voltage is 110 for the A and C phases, then B will be 190, which may be what was meant when 180 was typed in. Nominally in the US it would be 120 and 208 with 240 between phases.

nope caribbean.with 110v normally.

I'll be sure to get the pics up tomorrow//today that is

In Britain, flexible cables are normally blue for neutral, brown for the first phase and black for the other phases. This is about to change to brown, black and grey (no, I'm not joking) under European harmonisation. Earth (ground) has to be green and yellow striped. Could this be a European welder, or could somebody at some time have connected some European three phase flex to it?

Is there a rating plate on the welder? I'd be surprised if there wasn't. What does it say?

It wouldn't

That's correct, most welders, at least the larger ones, tend to use a d.c. arc, with the work positive, and the electrode rod negative. a.c. arcs are used mainly on smaller, home type welders. Three phase welders tend to be things that are iether fixed in place, of moved around on wheels. a.c. welders tend to be something that you pick up and carry around.

Someone else thought of this; I have seen a design for an arc lamp which worked in this way. Whether it was ever built, I don't know. Most arc lamps also work on d.c. I have used many of them for film projection, though sadly they are becoming very rare now. There have been low intensity a.c. arcs, but they are much less common, and give an inferior light. I think just about all high intensity lamps are d.c.; the carbons are different, the negative is almost always copper coated, and smaller than the positive which has a different core material; in some cases the negative is uncored. The positive is sometimes coppered, sometimes not, depending on the design of the lamp, and how the current is fed into it. In some designs the positive rotates, and is held in water-cooled silver jaws. Cinemas used either motor-generator sets, or rectifiers, normally three phase, to supply the d.c. for their arcs.

herein lies the beast..hehe an electricians nightmare?or dream come true maybe ..depends on the perspective

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