Hi,

In an installation there are 6no. Eurarc 420 welders supplied from dedicated 40Amp single phase RCBO's housed within a dedicated distribution baord. The welders can be operated as either single or three phase via a selector switch. The current arrangement is single phase with ABB 32A plug/socket connections. The rated max load in single phase is 93Amps. The users of the welders only use up to 3.25mm electrodes which the manufacturer tells me that using these types of electrodes would only use max of 35Amps.

The RCBO's are 30mA C type and keep tripping out once welding commences. It will be a big job not to mind expensive to change out to hard wired connections via isolators and MCB's so I was proposing to change the RCBO's to D or even K type as the issue may just be in-rush current but I suspect that there may be a problem with earth leakage.

Anybody any thoughts???

John.

I have very limited knowledge in this area, however two things spring to mind:

1) why do you want or need RCD protection on these welders?

2) the single phase selector switch may be switching to connect between two lives phases giving 415 volts single phase, not a phase to neutral giving 230 volts, either way if they are supplied by three phase RCBO's when you switch to single phase you will not have the RCBO in balance as one or two phases will become unused.

Not being a expert in this field I would expect to open up the board and see a line of three phase type D MCB's in place.

Also when switching to single phase is the total load anything like balanced or do they go to the same phase/ phases?

Andy

Thanks Andy,

1. RCD protection is required because they are on a 32A plug/socket connection, therefore portable and requiring RCD protection.

2. I am not 100% on whether the selector switch switches between phase/phae or phase/neutral. The manufacturer stated that single phase RCBO's would work once the user did not use electrodes over 3.25mm, so I suspect that they are operated in phase/neutral at 230Volts. The welders were previously used in the previous workshop as single phase. [I am assuming this as they came with single phase commando sockets on the final connections].

There are six welders with 2 welders per phase (protected by single phase RCBO's) to balance the load over three phases at the distribution board.

I'd carry out a risk assessment and then get rid of the rcbos and replace them with D curve MCBS (subject to max zs etc).

AFAIK , there is no requirement for rcbo protection on 32A sockets and you can I'm sure also argue that the welding guys are instructed persons which would further help your case.

Stu

I have read the original question again, the three phase is a red herring, three phase is not connected is it!

Hard wire and do away with the C type RCBO in favour of a fuse or D type MCB would be the thought that springs to mind, the folks in the workshop would prefer a MCB than having to replace a fuse.

Andy

You could call it a red herring Andy....

The welder has the facility to be operated in three phase arrangement if set up this way but the welders are set up for single phase.

I would agree that the obvious solution is to remove the RCBO's and install MCB's and hard wire. I was trying to offer a solution without having to replace any of the socket/plugs or wiring as it will cost a good few quid. I am not an expert either in welders but I assume that due to the nature of electric arc welding that residual earth currents occur and this is why the RCD is tripping out. I am going to try out installing a K or D MCB with seperate RCD on one welder and see which one trips. If it is the RCD then the problem is earth fault, if it is the MCB then it could be just in-rush current which the C type can not accommodate.

I think Stu is right, a read of the regs book may result in getting rid of the RCBO's and keeping the 32A sockets.

Andy

543.7.1.1 and 543.7.1.2

Regards

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E & OE

It may be a combination of the inrush current tripping the MCB part of the RCBO and/or the harmonics and wide band noise spikes being detected by the amplifier in the RCBO. I would say you have no chance of using an RCBO on a welder circuit without nuisance tripping and not much chance with an ordinary RCD.

I would go further and say the welders might trip RCBOs elsewhre on the installation.

That said I have an old stick welder I use once in a blue moon on a 13A socket in my workshop and that has never tripped the RCD protecting the sockets.

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John Peckham

http://www.astutetechnicalservices.co.uk/

As far as I'm aware, these particular welders have a maximum current draw of 122.5A not 93A.

I have connected up a few welders in the last year, 2 & 3 phase. The manufacturers instructions always said to wire through an RCD and use D type breakers. None have tripped yet.

Thanks for the info lads.

Thanks itsmoked.

I did speak to the manufacturer and he said that 40A Single Phase RCBO's would work but they didn't.

The only solution I can see is changing the RCBO's to D Type MCB's. The single phase load on the welder nameplate definitley says 95Amps single phase.

FYI, I have attached the spec of the welder. I will have a read of the regs and hopefully I can get away with just replacing the RCBO's for D rated MCB's.....

Still unsure though if the manufacturer said single phase RCBO's should work but didn't.There must be many installations where welder are operated from plug/socket connections and have RCD protection....

This link is on Power forum 13/11/09 for the connection of three phase motors to RCD and may also be relevant for the connection of two phase or three phase welder. If you use it let us all know if it works OK.

http://www.voltimum.co.uk/news...for-motors.html

regards
jcm

I take it you have done a ramp test on the rcd to check its not faulty.

I suspect that the 122A is on the secondary side of the transformer in the welder. could be wrong

i've got a welder to wire up for someone in his garage - it says 23a on the tin - was going to use commando plug, 32 a rotary sw, then to a c type breaker in the dual rcd cu - any probs with that?

I've done a few welder supplies, industrial/commercial, normally steel trunking/conduit/swa supply so no need for an RCD to protect the cable. Plus the other requirements that preclude te need for this.

I will try to use a D if the Z is low enough, else a C, normally they will run off 32A so yes use a commando & rotary isolator, however, I normally go for the all in one interlocked with a 30mA rcd built in, as my clients insurer insists on RCD's on ALL s.o.! Don't ask...

Remember the DNO's frown on welders from what I can gather as they can induce a LOT of flicker, so depending on use, load, incoming network configuration, integrity of supplly etc. you may find issues!

A little off topic but, a little tale...

I saw the local DNO guys out late one wet windy winters night outside my house. They were there for ages about 4 vans.
One of the neighbours had reported flicker on their lights I found out later.
We were all fed by overheads at the time, (not bunched) so they were looking for O/H shorts (I found out later).

When I went back into my garage to carry on welding my car with my MIG set they saw the arc and there were several shouts and a few seconds later, 4 DNO linesmen appeared in my garage door!
A quick chat and there was laughter all round!

Quick round of tea & coffee later to warm up and they left for home!

The set runs happily off a 13A 3 pin plug, but the inrush etc. caused a lot of flicker, contactor switched transformer.

They have since changed the network configuration, we are now fed via underground from another supply seperate to all our neighbours!

Shame I don't do any welding at home now really...

HTH.
Paul

What about portable welders for use outdoors ?

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Empty barrels make the most noise.

I use a portable welder and wouldn't want to use it without RCD protection.
It is all too easy to chop through a cable when dealing with large pieces of metal and other work is going on too.
My thoughts on the original poster's problem is that perhaps the actual welding is causing large currents to flow in earthed metalwork somewhere which is feeding back into the CPC.
Whether a large current flowing through the CPC would cause an RCBO or RCD to trip very much depends on the circuit.
For instance a shorted neutral~earth somewhere else could cause the tripping.