Tripping RCD when using welding equipment.

[BigJonesy]

Hi all, this is an odd one but I just want to check out that my suspicions are correct. I've been asked to look at the electrics at a garage unit, but the only thing that is tripping the RCD is this particular industrial welding equipment. To my mind, this suggests that the equipment is faulty and probably needs PAT testing. Would you think the same thing? I could obviously get there and do a ramp test etc. but I think that would be a waste of time as the only time it trips is with this particular equipment. It's 3 phase, using B type MCBs too. They don't trip, just the RCD. Otherwise I'd have said change the breakers to C type. I could be wrong of course and would appreciate your opinions. Thanks.

 

[Engineer54]

Id be inclined not to use a 30mA RCD on 3 phase industrial welding kit, not unless the manufacturers stipulate the requirement!!

I would certainly change that type B for a type C or D MCB, the present RCD (faulty or not) maybe tripping out before the TYPE B MCB has a chance ...lol!!!

 

[BigJonesy]

Id be inclined not to use a 30mA RCD on 3 phase industrial welding kit, not unless the manufacturers stipulate the requirement!!

I would certainly change that type B for a type C or D MCB, the present RCD (faulty or not) maybe tripping out before the TYPE B MCB has a chance ...lol!!!

Thanks very much Engineer54. Would you change the MBC as a start point to see whether that cures it? Also, are you thinking it's unlikely to be faulty equipment? It's always great to run ideas past someone. This is a great forum.

 

[IQ Electrical]

The key question is 'when did the tripping start?' If the unit has functioned perfectly for the last 5 years and has only just started tripping the RCD then there is more than likely a fault on the input side of the welder.
If the MCBs do not trip then changing the type will make no difference to this problem as the RCD will not be tripping on overcurrent anyway.

 

[Engineer54]

I'm not saying the welding equipment is not faulty, that can only be ascertained by testing and inspection, against manufacturers data. I've personally never seen industrial welding machines sitting on a Type B MCB. lol!!!

 

[david john cook]

as a welder normally has a high in rush current a type d breaker would be better ,i would think .

 

[BigJonesy]

The key question is 'when did the tripping start?' If the unit has functioned perfectly for the last 5 years and has only just started tripping the RCD then there is more than likely a fault on the input side of the welder.
If the MCBs do not trip then changing the type will make no difference to this problem as the RCD will not be tripping on overcurrent anyway.

Now, this is the problem. The welding equipment was purchased very recently and is second-hand (or pre-owned as people seem to insist on calling things these days). Subsequently, they don't know whether it was faulty when they bought it. This is what leads me to believe that it may well be faulty. Thanks for the tip re: the MCBs, as that just confirms my initial thoughts. However, I would have said they need to be type C at least. But as it seems to be some kind of an earth fault, then the MCB issue may be one for the future, once this particular situation is resolved. Would you take the route that I first thought then, and get them to have the equipment tested? Thanks.

 

[BigJonesy]

as a welder normally has a high in rush current a type d breaker would be better ,i would think .

Thanks David, I'm fairly sure that this is probably the case too. I just wonder why the RCD is tripping though.

 

[Engineer54]

Get hold of the manufacturers data in the first instance and conduct any inspection and testing to that data. Not forgetting to test the 30 mA RCD, if it is required by the manufacturer. Other than that we are all flying in the wind, ...so to speak...lol!!

 

[IQ Electrical]

Now, this is the problem. The welding equipment was purchased very recently and is second-hand (or pre-owned as people seem to insist on calling things these days). Subsequently, they don't know whether it was faulty when they bought it. This is what leads me to believe that it may well be faulty. Thanks for the tip re: the MCBs, as that just confirms my initial thoughts. However, I would have said they need to be type C at least. But as it seems to be some kind of an earth fault, then the MCB issue may be one for the future, once this particular situation is resolved. Would you take the route that I first thought then, and get them to have the equipment tested? Thanks.

By rights, the equipment should have been 'tested' before it was used, especially given the tough conditions that many welders etc. are used in.

The MCBs should be a type 'C' or even 'D' to allow for the high inrush associated with a welder but that is a separate issue, I agree with E54 that RCds and welders are not an ideal marriage because of flicker, noise, harmonics etc.

Assuming the welder tests as it should, is there actually a requirement for RCD protection?

 

[Knobhead]

I’ve never installed RCD’s on welding plant, more trouble than they’re worth.

Out of interest is the RCD tripping on switch on or on striking the arc.
It would help to know the make and type of welding plant.

 

[barnzi]

Is it an immersed transformer unit? If any water has got in to the 'former oil, there will be leakage to earth from the windings. But, yes. PAT that beast first.

 

[Knobhead]

Would it be a Murex or Lincoln unit? I used to repair both types. Both would normally be 2 phase for the main plant, the 3[SUP]rd[/SUP] phase for wire feed if fitted. (There would be a socket on the back of the main unit for the wire feed to plug in to, it would also connect the welding current. Murex used an intermediate choke to regulate the current output, so between the primary and the secondary output there’s two levels insulation.
Smaller Lincoln units I’m a bit iffy on. The ones I worked on were DC immersed arc so not your normal run of the mill things. The one thing I do know is they were built like the proverbial “s*** house”

It’s important to know at what point the unit trips at. It gives a clue as to where the fault is.

 

[Knobhead]

Give me the make and model No. and I should be able to help.

I’m not knocking you but unless you know how welding plant works, a PAT test is likely to lead you up the garden path.

 

[thekingiam]

just a quick question are you using welder pluged into a socket or directly into cu ?
ie dedicated circuit?