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Topic Title: Welders: 400 volt single phase
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Created On: 25 July 2012 09:39 PM
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 25 July 2012 09:39 PM
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circle143

Posts: 213
Joined: 19 July 2007

Good evening all,

I have been asked to install a 400v single phase welder. The welder is to be supplied from an existing three phase board. A similar welder that was installed some time ago is connected into two separate MCBs in the distribution board - is this correct? Or is it possible to get two pole MCBs for 400v single phase equipment?




Thanks
 25 July 2012 09:46 PM
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slittle

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I'd be looking for a double pole MCB if it was my job.

They are available to fit most boards.

Stu
 25 July 2012 09:49 PM
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circle143

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Thanks for the quick reply
 25 July 2012 10:26 PM
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jamieblatant

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So it's not single phase welder then

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 25 July 2012 10:59 PM
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slittle

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Nope, I suspect it wants 400 volts and the only way that it's going to get it is across two phases

Stu
 25 July 2012 11:16 PM
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ebee

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Couldn`t you use a three phase MCB on two phases.

The equipment would see 400 (415) as a single phase anyway if it was derived from two actual phases of a three phase supply or if it was two phases 180 degree out of phase. It don`t care.

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Ebee (M I S P N)

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 26 July 2012 09:33 AM
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AJJewsbury

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Single phase, connected across two lines. 17th Ed terminology is a slight improvement in that respect.
- Andy.
 26 July 2012 09:35 AM
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rougediablo

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Originally posted by: slittle

Nope, I suspect it wants 400 volts and the only way that it's going to get it is across two phases

Stu


Agreed.

In a previous life I was involved in the sales/installtion/servicing of a range of industrial welding equipment. Most of the larger oil cooled arc welders & AC/DC TIG's were like this. If they are connected by a BS4343 socket just connect across two phases & the earth as normal. Same if wired directly into a 3ph isolator. Some machines also have an input connector which you have to select the correct input voltage for the supply.

I was for ever getting called out to supposedly faulty equipment which turned out to have been wired across a phase & neutral rather than across 2 phases!

One of the dangers of letting hairy a***d welders loose on electrics!
 26 July 2012 10:54 AM
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broadgage

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Make very certain that the welder ONLY requires two phases, it may need a neutral as well.

Conventional arc welders are in effect a large step down transformer.
Some designs connect the primary between phase and neutral for the lower output settings, and between two phases for full output.

I have seen one such connected to 2 phases, without a neutral.
It worked fine, but only on full or higher output settings.
On being switched to the reduced or lower output settings, nothing would happen.

I would use a 2 pole MCB if available, if not use a 3 pole one with one pole unused.
 26 July 2012 10:55 AM
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OMS

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Originally posted by: AJJewsbury

Single phase, connected across two lines. 17th Ed terminology is a slight improvement in that respect.

- Andy.


Wouldn't the phase angle have to be zero, Andy

It's two phase 3 wire without the N being distributed (Fig 3.3) - ?

Regards

OMS

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 26 July 2012 11:05 AM
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AJJewsbury

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It's two phase 3 wire without the N being distributed (Fig 3.3) - ?

The supply might be, yes, but I'd still argue the load is single phase... (sorry I should have quoted the context).
- Andy.
 26 July 2012 11:09 AM
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OMS

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OK - I can follow that Andy

regards

OMS

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Failure is always an option
 26 July 2012 11:52 AM
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jcm256

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I have this at quarries where the quarry regulations allow portable equipment (welder) provided protected by RCD. Attempting to comply (bluff) you could find on inspection two phases connected through a single phase double pole RCD, don't work on button (wonder why) or on trial (just to confirm once again RCD live probe to neutral earth combined don't work. However hopefully now superseded, bought one myself £50 at B & Q reduced because the mask was missing from the box. Carry it like a handbag with welding power more powerful and better than the big old-fashioned oil cooled stick welder. (The small none transformer inverter stick welder is a great invention).
 26 July 2012 06:48 PM
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circle143

Posts: 213
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The welder does not require a neutral - and I will try and get a double pole mcb, otherwise I will use 2 poles of a 3 phase mcb.

Thanks for the responses.
 26 July 2012 06:52 PM
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perspicacious

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I put my MIG welder away last week until I find some PPE.......

I didn't properly assess the risk of getting under my 6 x 4 x 1/2 steel bench top to weld it to one of the steel staunchions. I'd got the safety goggles, welding mask, gloves, trousers over the rigger boots and thought that was enough. *
I hadn't counted on some weld splatter hitting the underside of the top and landing in my ear........ Don't laugh

Regards

BOD

* In addition to my usual work clothes before anyone suggests otherwise
 26 July 2012 06:58 PM
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OMS

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I hadn't counted on some weld splatter hitting the underside of the top and landing in my ear........ Don't laugh


Ouch - still it clears out those stray ear hairs that men of a certain age get BOD - so it's an ill wind I guess

and that's one hell of a bench I might add !!

regards

OMS

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Failure is always an option
 26 July 2012 07:02 PM
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perspicacious

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It was a road plate that I "picked up"

Yes, I had to visit the Drs but when she looked in, she didn't find anything there

Regards

BOD
 26 July 2012 07:30 PM
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OMS

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It was a road plate that I "picked up"


Not on your own you didn't - or if you did, I've a wide belt you can borrow

That's just what you want to hear from the MedicO - all clear

ear defenders or a balaclava helmet or both - but wait till it's cooler eh -

Best regards

OMS

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Failure is always an option
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