RCD Tripping

[GrahamGKD]

My RCD in the house started tripping out the other day when I was doing some plasma cutting. I assumed it was the plasma m/c and sent that back to be checked but then realised I was getting the same problem with my Portamig plugged into the 32A socket I use for the plasma. I have thoroughly cleaned the socket and did a whole load more MIGing this morning without problem but I just went and took a shower and it tripped again. Could it be that the RCD has become over sensitive when under high load? This is a bit of a worry as we don't have the 17th edition split consumer unit - just one RCD for the whole lot, including the freezer. Options I can think of are to replace the RCD in the house or fit a more sensitive RCD in the consumer unit in my workshop? I guess I could isolate the workshop when not in use to see if I get any further trips in the house with the workshop isolated? Could an earth loop (e.g. SWA to workshop armour used as an earth conductor as well as one of the cores inside) cause this kind of problem - I can't see how it would?
I’d appreciate some help on this one please.
Cheers,
Graham.

 

[tigler]

If it's not tripping the actual circuit trip then it would indicate some sort of earth issue.

 

[GrahamGKD]

If it's not tripping the actual circuit trip then it would indicate some sort of earth issue.

Yes, I understand the RCD senses an imbalance in current between live and neutral - if I'm reading it right ours trips at 30 mA. No MCBs have tripped - there is no evidence of current overload.
Graham.

 

[Biscayne]

Hi Graham, don’t know if your place is wired the same as mine but I had a similar problem a while ago. I have a TT earthing system, where only a live and neutral enter the house and the earth is supplied by via a spike in the ground. The RCB would trip for no obvious reason.

I tried removing fuses selectively but the tripping still occurred. Then I realised that in domestic installations only the live conductor is isolated by the fuse/mcb, so, circuit by circuit, I removed the fuse and disconnected the neutral from the commoning block in the consumer unit. Eventually it became clear that the cooker was causing the problem, even though it was switched off!

I can only assume that the leakage was considerably less than 30 mA most of the time but something external was causing it to surge. So I put a voltmeter across neutral to earth. There would occasionally be a voltage difference which I assume was being caused by someone else on the same phase running some faulty equipment. Before I could investigate further, the problem stopped but I took a megger to the cooker and replaced a ring that had a slight leakage.

Perhaps an experienced electrician would like to comment on your workshop earthing arrangement but I have a separate earth spike for my garage and only bring live and neutral through an RCB.
Hope this helps

Steve

 

[hareng]

Wouldnt mind some help, i have same problem with a split consumer unit though.

Numerous RCD and independant wiring to sockets etc.
If compressor 3hp starts up and i manually switch, it trips the 20A RCD. Likewise another 20A RCD to lathe with 1 1/2hp motor will blow the 13A fuse 1 in 5 startups, and buy 13A fuses by the bag of 100.
Worst of all is the Butters 160A MIG, 2nd setting will throw the RCD on 2nd run almost every time if not the first. No way can i get it on to the 3rd power setting and same with all the other welders past and present.

Had a sparky install consumer unit and found a problem with the German Bosch fridge, 1 yr old at time.
Did have at other house light bulbs blowing and tripping consumer unit out, but never a smaller welder.

 

[GrahamGKD]

Thanks for that Steve. My earth is strapped back to the armour of the incoming supply (TN-S?) and the house earth is exported to the workshop by a 10mm cable. Understand what you are saying about the MCBs not isolating the neutral - I can isolate live and neutral to the whole workshop, however, with the main switch on the workshop consumer unit.
Graham.

 

[GrahamGKD]

Wouldnt mind some help, i have same problem with a split consumer unit though.

Numerous RCD and independant wiring to sockets etc.
If compressor 3hp starts up and i manually switch, it trips the 20A RCD. Likewise another 20A RCD to lathe with 1 1/2hp motor will blow the 13A fuse 1 in 5 startups, and buy 13A fuses by the bag of 100.
Worst of all is the Butters 160A MIG, 2nd setting will throw the RCD on 2nd run almost every time if not the first. No way can i get it on to the 3rd power setting and same with all the other welders past and present.

Had a sparky install consumer unit and found a problem with the German Bosch fridge, 1 yr old at time.
Did have at other house light bulbs blowing and tripping consumer unit out, but never a smaller welder.

Do you mean RCD or MCB - unless I am misunderstanding you your problem is more to do with current overload? Sounds like you need to install some 20A sockets for your bigger demand stuff? Also you can get slower tripping MCBs?
Graham.

 

[tigler]

My understanding of RCD's is that they detect the balance of current in the live and neutral conductors, so if any current is diverted to another circuit, like a person accidentally touching live and therefore leaking to earth , the device trips off.
Now, large induction motors and transformers, such as used in compressor, welders etc, have a large start up current which has a phase shift, this, I think, could cause an momentary imbalance from live to neutral.
Also, RCD's are known to nuisance trip on appliances that have a certain amount of earth leakage as normal, like water heaters.
So possibly it may require an additional consumer unit with a special RCD and anti surge MCD's to provide power to non standard loads that were not envisaged for use in a domestic property ?

 

[madkayaker]

its not unusual for RCD's to trip if things have transformers in as they can be leaky to earth and perfectly safe. my normal number 1 suspect is fridges and freezers especially if it trips at night. If it get more frequent get a sparkey to test the house

 

[brightspark]

as said transformers cause problems . namely in tv and computers each item gives off about 1.5ma leakage . when it reaches 15 ma and just as a given item u put the kettle on or the cooker the extra leakage will knock the trip . the trip maybee 30 ma but will trip at a lot less . the best thing would be to do is have the wiring tested with a 500v megger for earth leakage and also test for leakage with a clamp on milliameter that will tell u how much leakage there is of each item if u unplug one thing at a time .other than that its just guess work which is no use atall

 

[GrahamGKD]

Thanks for the suggestions guys - re. the transformer suggestion, there is nothing new in the house apart from a new printer - I could unplug that and see if we get any further problems with it disconnected. So far the trips have all happened when plasma cutting, MIGing or using the electric shower (by no means every time though) - all of which are big power users. Would it be worth me replacing the RCD first, as a relatively cheap and simple thing to try - do they get flakey at all with age?
Graham.

 

[the snooper]

if your rcd runs everything but only trips when using gear that demands high current could it be a bad connection developing ?

 

[brightspark]

Thanks for the suggestions guys - re. the transformer suggestion, there is nothing new in the house apart from a new printer - I could unplug that and see if we get any further problems with it disconnected. So far the trips have all happened when plasma cutting, MIGing or using the electric shower (by no means every time though) - all of which are big power users. Would it be worth me replacing the RCD first, as a relatively cheap and simple thing to try - do they get flakey at all with age?
Graham.

its not the power loading that trips them its leakage to earth either through apliances or damp behind sockets ect . only using an insulation tester on the full house and garage will identify where the problem is.its not a volex rcd is it or an old mem or an old crabtree is it there crap . wylex and hager square d and merlin are good makes people are flogging them new on ebay for next to nothing

 

[the snooper]

newer equipment like your printer and lcd tvs and so on dont have an earth so you can rule them out no earth leakage there

 

[GrahamGKD]

Brightspark, It's an old GE RCD. Yes, I understand the part about it being a leakage to earth which trips them - just seems odd that it has only happened when switching on / using big loads? When it first happened with the Plasma the thing wouldn't reset until I had unplugged the plasma m/c (hence the reason I thought that was the problem and sent it back for testing). This happened about three times in 10 minutes or so of cutting??

Damp behind a socket caught us out once while we were away - very smelly kitchen and freezer by the time we got back from a 3 week trip!! That one has since been well and truly fixed but in any case it is very dry and warm down here at the moment!

Snooper, Good point about the newer appliances not having an earth but I'm not sure how that relates to the phase shift thing in transformers which has been mentioned? If it were a loose connection how would that cause a leakage to earth?

Thank you both for the suggestions.

Graham.

 

[madkayaker]

we could drivel on for pages and the only way to definatly know is to test the circuits. An RCD should trip between 50% and 100% of its rated value so if yours is tripping at 50% (i.e. 15mA) it is working within its design tolerance and is safe but if your mig is preducing 15mA leakage it is also within safe levels but the RCD would trip. Also there could be leakage from else were like florescent lighting and the extra leakage from transformer etc is pushing it over the edge Or it could be an insulation resistance break drown and the large current being drawn is resulting in a larger leakage current. Or are you sure its a RCD and RCBO or RCCD the last two do have overload characteristics (itr is unusual to use as main switch unless its a flat sharing a supplely or that type of thing) a photo of the device will alow possitive identification

 

[brightspark]

it would be worth checking the conections in your distribution board where the rcd is. it has been known to make rcd trip

 

[the snooper]

Snooper, Good point about the newer appliances not having an earth but I'm not sure how that relates to the phase shift thing in transformers which has been mentioned? If it were a loose connection how would that cause a leakage to earth?

Thank you both for the suggestions.

Graham.

live and neutral imbalance but im no expert

 

[madkayaker]

Imagen a old fashion set of scales (or crown court statute) what goes into the circuit on the live must return on the neutral or it has ******esd off to earth on its own path. when the inblanage is great enough the transformer within the RCD generates nought current to operate the trip

 

[the snooper]

so in that case it must go to earth to complete the circuit to power the transformer that causes the trip.
with a bad connection there would be no circuit to the transformer and hense no trip