Electricians - advice please
Discussion
Hi folks, I wonder if any electricians out there can throw a bit of light on a problem I have ?
My workshop has a feed from the house, taken from the RCD side of the consumer unit with a 16a breaker. The cable looks the correct size rating (4mm-32amp) and AFAIK it was installed by the previous owner who was the village electrician (when we bought he told me he'd rewired the house). Strangely enough once in the workshop the feed goes through another smaller RCD unit, which I suspect was fitted prior to the main house consumer unit. The supply is for lighting and 13a sockets.
Problem - when I use my arc welder, a small 140amp unit powered from a 13a socket, it trips the house RCD. Not all the time, but around 50% I'd guess and it doesn't seem to make any difference what power setting I'm on, it will trip on 2mm rods. If I use my MIG welder, also a 130a unit on a 13a socket, it's fine and has never tripped the RCD even on the full power setting. The air compressor is fine as well, but I don't know the power consumption off hand.
I've tried all sorts to get round this, I even bought a new arc welder this year thinking the old one was past it (20+yrs old) but the new one is the same. There's never any big load on in the workshop or house at the same time as the welder, at most a couple of fluorescent lights. I could replace the plug-in 16a RCD breaker with a 20a one as there's capacity on the RCD side (it says up to 100a) but I'm not sure if that would do any good.
Any ideas ?
My workshop has a feed from the house, taken from the RCD side of the consumer unit with a 16a breaker. The cable looks the correct size rating (4mm-32amp) and AFAIK it was installed by the previous owner who was the village electrician (when we bought he told me he'd rewired the house). Strangely enough once in the workshop the feed goes through another smaller RCD unit, which I suspect was fitted prior to the main house consumer unit. The supply is for lighting and 13a sockets.
Problem - when I use my arc welder, a small 140amp unit powered from a 13a socket, it trips the house RCD. Not all the time, but around 50% I'd guess and it doesn't seem to make any difference what power setting I'm on, it will trip on 2mm rods. If I use my MIG welder, also a 130a unit on a 13a socket, it's fine and has never tripped the RCD even on the full power setting. The air compressor is fine as well, but I don't know the power consumption off hand.
I've tried all sorts to get round this, I even bought a new arc welder this year thinking the old one was past it (20+yrs old) but the new one is the same. There's never any big load on in the workshop or house at the same time as the welder, at most a couple of fluorescent lights. I could replace the plug-in 16a RCD breaker with a 20a one as there's capacity on the RCD side (it says up to 100a) but I'm not sure if that would do any good.
Any ideas ?
Simpo Two said:
Quite how you get 140 amps out of a 13 amp socket I'm not sure, but it reminds me of my old cooker. When the thermostat switched back on it would trip the whole house - something to do with spikes.
Very very low voltage. As said, it'll be to do with the initial draw, but im not a aparkey so dont know more. Can you not get a bigger RCD in the house? Might not be the safest thing to do, but should solve the problem.
There is another solution, but you should remember that external sockets should be RCD protected. Assuming no faults anywhere, move the shed MCB to the other side of the consumer unit that is not RCD protected. You will still have the protection from the MCB. Not ideal but an alternative.
Arc welders use a lot of current striking the arc,especially on a single phase supply.
Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
Edited by netherfield on Tuesday 2nd November 15:46
Phew, thanks guys, I didn't expect replies so quickly.
Ok, today I was finishing off a small project and the RCD tripped as soon as I switched on the welder. Not welding, just switching it on. It was connected with an electrode & the earth lead in place but no chance to start welding. (there is a cooling fan inside the welder if that makes any difference ?). I reset the RCD inside the house as this is the only one that trips, back into the workshop, switched on again and no more problems while I finished off the welding. That's really why it's got me beat, there's no consistency that I can see.
Thanks for the comments guys, especially the explanations. I might see about getting it run in 6mm cable next summer to see if that makes any difference, worth thinking about anyway.
Ok, today I was finishing off a small project and the RCD tripped as soon as I switched on the welder. Not welding, just switching it on. It was connected with an electrode & the earth lead in place but no chance to start welding. (there is a cooling fan inside the welder if that makes any difference ?). I reset the RCD inside the house as this is the only one that trips, back into the workshop, switched on again and no more problems while I finished off the welding. That's really why it's got me beat, there's no consistency that I can see.
duff-man said:
Does the RCD Trip on startup or during welding? Also what "type" rating is the 16A in the house? (A,B,C,D)
It's never tripped while an arc is operating. It has tripped when I first strike an arc and also (less frequently) when I first switch on the set. I'm not an electrician so without some more hints I can't tell what "type rating" the 16A breaker is - it just says NSB16A on the breaker.Melchett said:
There is another solution, but you should remember that external sockets should be RCD protected. Assuming no faults anywhere, move the shed MCB to the other side of the consumer unit that is not RCD protected. You will still have the protection from the MCB. Not ideal but an alternative.
That thought did occur to me as there are 2 spare breakers, but I saw it as last resort. I'm not sure on the legality of running a power supply cable outside the house without RCD between the house & the workshop, about 10-15M of underground cabling. Although if I'm honest I've had set-ups like that in the past, relying just on the "fuse box" in older houses.mk1fan said:
Should the mcb in the house consumer unit be 32amp not 16amp?
Having two RCD's can't be good either.
The cable is 32A rating but I'm only using 13A sockets which is why I've never considered changing it. I think there's 2 units because the workshop is an old outbuilding which used to house the CH boiler and from the looks of it is much older than the house wiring & MCU. I'm guessing the house (1950s) didn't have RCD on the original fuse box & just ran a supply outside then when the boiler was installed the sparky put a breaker & RCD inside the workshop. I could easily bypass the workshop one but that's never tripped, always the house one. I wish it would, I wouldn't get earache going in the house in overalls to flick it back on !Having two RCD's can't be good either.
netherfield said:
Arc welders use a lot of current striking the arc,especially on a single phase supply.
Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
That sounds ominous but I think I understand your comment about the voltage drop from my feeble electronics theory. I did wonder if Alan (previous owner) had used 4mm cabling instead of normal ring-main stuff to compensate for current drop over the length. And now you've got me thinking in that direction I think I can see why the mig is more reliable.Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
Thanks for the comments guys, especially the explanations. I might see about getting it run in 6mm cable next summer to see if that makes any difference, worth thinking about anyway.
b2hbm said:
Phew, thanks guys, I didn't expect replies so quickly.
Ok, today I was finishing off a small project and the RCD tripped as soon as I switched on the welder. Not welding, just switching it on. It was connected with an electrode & the earth lead in place but no chance to start welding. (there is a cooling fan inside the welder if that makes any difference ?). I reset the RCD inside the house as this is the only one that trips, back into the workshop, switched on again and no more problems while I finished off the welding. That's really why it's got me beat, there's no consistency that I can see.
Thanks for the comments guys, especially the explanations. I might see about getting it run in 6mm cable next summer to see if that makes any difference, worth thinking about anyway.
For the sake of another £1 per metre,I'd think about doing it in 10mmOk, today I was finishing off a small project and the RCD tripped as soon as I switched on the welder. Not welding, just switching it on. It was connected with an electrode & the earth lead in place but no chance to start welding. (there is a cooling fan inside the welder if that makes any difference ?). I reset the RCD inside the house as this is the only one that trips, back into the workshop, switched on again and no more problems while I finished off the welding. That's really why it's got me beat, there's no consistency that I can see.
duff-man said:
Does the RCD Trip on startup or during welding? Also what "type" rating is the 16A in the house? (A,B,C,D)
It's never tripped while an arc is operating. It has tripped when I first strike an arc and also (less frequently) when I first switch on the set. I'm not an electrician so without some more hints I can't tell what "type rating" the 16A breaker is - it just says NSB16A on the breaker.Melchett said:
There is another solution, but you should remember that external sockets should be RCD protected. Assuming no faults anywhere, move the shed MCB to the other side of the consumer unit that is not RCD protected. You will still have the protection from the MCB. Not ideal but an alternative.
That thought did occur to me as there are 2 spare breakers, but I saw it as last resort. I'm not sure on the legality of running a power supply cable outside the house without RCD between the house & the workshop, about 10-15M of underground cabling. Although if I'm honest I've had set-ups like that in the past, relying just on the "fuse box" in older houses.mk1fan said:
Should the mcb in the house consumer unit be 32amp not 16amp?
Having two RCD's can't be good either.
The cable is 32A rating but I'm only using 13A sockets which is why I've never considered changing it. I think there's 2 units because the workshop is an old outbuilding which used to house the CH boiler and from the looks of it is much older than the house wiring & MCU. I'm guessing the house (1950s) didn't have RCD on the original fuse box & just ran a supply outside then when the boiler was installed the sparky put a breaker & RCD inside the workshop. I could easily bypass the workshop one but that's never tripped, always the house one. I wish it would, I wouldn't get earache going in the house in overalls to flick it back on !Having two RCD's can't be good either.
netherfield said:
Arc welders use a lot of current striking the arc,especially on a single phase supply.
Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
That sounds ominous but I think I understand your comment about the voltage drop from my feeble electronics theory. I did wonder if Alan (previous owner) had used 4mm cabling instead of normal ring-main stuff to compensate for current drop over the length. And now you've got me thinking in that direction I think I can see why the mig is more reliable.Being a 4mm cable I think you will get a lot of volt drop whilst striking up,so basically when the volts drop the current increases.
Mig sets don't need that initial kick to get them working,you should be able to weld up to 300+ amp on a 13a plug with Mig.
Two phase supply is always better for arc welding.
Thanks for the comments guys, especially the explanations. I might see about getting it run in 6mm cable next summer to see if that makes any difference, worth thinking about anyway.
Unfortunately welders are prone to earth faults, which is the type of fault that trips the RCD.
The reason the the in-house RCD may be tripping instead of the garage RCD is because the household unit is covering far more wiring and possibly several cumulative small faults, with the welder tipping it over the edge. Or it could be better (quicker) to act, or the garage RCD could be faulty. It's actually bad practise (and against regs) and nonsensical to have 2 RCD's in line* so I don't give much for this "electrician" [*unless the upstream one is a special timed delay device]
It may be possible to put the garage on an individual RCD-breaker - not with the household RCD - to minimise inconvenience, this in itself *may* alleviate the tripping. If you wanted this breaker at the shed end you'd probably need to run armoured cable.
The reason the the in-house RCD may be tripping instead of the garage RCD is because the household unit is covering far more wiring and possibly several cumulative small faults, with the welder tipping it over the edge. Or it could be better (quicker) to act, or the garage RCD could be faulty. It's actually bad practise (and against regs) and nonsensical to have 2 RCD's in line* so I don't give much for this "electrician" [*unless the upstream one is a special timed delay device]
It may be possible to put the garage on an individual RCD-breaker - not with the household RCD - to minimise inconvenience, this in itself *may* alleviate the tripping. If you wanted this breaker at the shed end you'd probably need to run armoured cable.
hairyben said:
Unfortunately welders are prone to earth faults, which is the type of fault that trips the RCD.
The reason the the in-house RCD may be tripping instead of the garage RCD is because the household unit is covering far more wiring and possibly several cumulative small faults, with the welder tipping it over the edge. Or it could be better (quicker) to act, or the garage RCD could be faulty. It's actually bad practise (and against regs) and nonsensical to have 2 RCD's in line* so I don't give much for this "electrician" [*unless the upstream one is a special timed delay device]
It may be possible to put the garage on an individual RCD-breaker - not with the household RCD - to minimise inconvenience, this in itself *may* alleviate the tripping. If you wanted this breaker at the shed end you'd probably need to run armoured cable.
Thanks for the info, the more folks that say "TADTS", the less of an idiot I feel and even if it doesn't fix the problem I'm learning a bit more about it. The reason the the in-house RCD may be tripping instead of the garage RCD is because the household unit is covering far more wiring and possibly several cumulative small faults, with the welder tipping it over the edge. Or it could be better (quicker) to act, or the garage RCD could be faulty. It's actually bad practise (and against regs) and nonsensical to have 2 RCD's in line* so I don't give much for this "electrician" [*unless the upstream one is a special timed delay device]
It may be possible to put the garage on an individual RCD-breaker - not with the household RCD - to minimise inconvenience, this in itself *may* alleviate the tripping. If you wanted this breaker at the shed end you'd probably need to run armoured cable.
I did wonder about the 2 RCDs because it seemed illogical but I didn't realise it is against regs. I just assumed the house one tripped because it's modern and the first in the supply line but perhaps the workshop one is broken - never thought about it if I'm honest. The previous owner was the village electrician though, for the first couple of years here we had people turning up in our yard asking for "some wiring that needs doing" and one bloke was really put out when I said he'd moved away !
The current cable isn't armoured as far as I can see. It just looks normal twin/earth at the workshop end but I think that is a good idea, especially if it allows us to have a single RCD at the workshop. Then even if it trips I won't be trekking back through the house to the MCU.
Something to get planned in for next year, there's no desperate hurry & I don't really want anyone digging up the garden over winter to bury the cable. But a higher rated armoured cable sounds the right way to go and now you've mentioned it I'm wondering why it wasn't armoured the first time round.
Edited by b2hbm on Wednesday 3rd November 22:15
Few different points here. The most important point (not yet mentioned) is that all domestic work should either be carried out by a Part P competent person (who will then notify local Building Control) or you should notify Building Control yourself and see what hoops they want you to jump through in order to get sign off. This is a legal requirement (though obviously that won't actually stop somebody from doing stuff anyway!)
That said, this is what I would expect a competent person to tell you:
The situation you describe could be defined as a distribution circuit. If a mechanical method of protection can be provided for your cable, there is no need for an RCD at the main Consumer Unit. Such mechanical protection can be provided by the use of Steel Wire Armoured cable, buried to sufficient depth (not defined, though around 70cm usually does the trick) and covered with "Electric Cable Below" tape (and lots of soil!).
Required conductor size is dependent on many factors, and a definitive answer can only be provided by an on-site visit. That said, Reference Method D (direct in ground etc.) suggests that 6mm will give you 46A and 10mm 60A.
As above, the MCB at the originating consumer unit would not need to be RCD protected if SWA cable is used. This will prevent the nuisance tripping you are currently experiencing. 40A or 32A MCBs might be considered appropriate.
The installation at the workshop end then could then be considered a separate installation, which would require its own isolating switch, 30mA RCD and individual MCBs as required e.g. 32A for ring final (circuits), 6A for lights. If you wanted to go one step further, you could have two RCDs (or use individual RCBOs), one for sockets & one for lights, to prevent the lights going out should the sockets trip for some reason.
Hope this is useful.
(no responsibility can be taken for any consequences deriving from the above thoughts)
That said, this is what I would expect a competent person to tell you:
The situation you describe could be defined as a distribution circuit. If a mechanical method of protection can be provided for your cable, there is no need for an RCD at the main Consumer Unit. Such mechanical protection can be provided by the use of Steel Wire Armoured cable, buried to sufficient depth (not defined, though around 70cm usually does the trick) and covered with "Electric Cable Below" tape (and lots of soil!).
Required conductor size is dependent on many factors, and a definitive answer can only be provided by an on-site visit. That said, Reference Method D (direct in ground etc.) suggests that 6mm will give you 46A and 10mm 60A.
As above, the MCB at the originating consumer unit would not need to be RCD protected if SWA cable is used. This will prevent the nuisance tripping you are currently experiencing. 40A or 32A MCBs might be considered appropriate.
The installation at the workshop end then could then be considered a separate installation, which would require its own isolating switch, 30mA RCD and individual MCBs as required e.g. 32A for ring final (circuits), 6A for lights. If you wanted to go one step further, you could have two RCDs (or use individual RCBOs), one for sockets & one for lights, to prevent the lights going out should the sockets trip for some reason.
Hope this is useful.
(no responsibility can be taken for any consequences deriving from the above thoughts)
As Above.. but rather than using a garage consumer unit with an RCD and MCBs why not use a main switch and RCBO's, at least if it all trips whilst welding, the lights will stay on. just use type c for the socket/dedicated welder circuit so it will have the inductive load from the welding plant.
Thanks for the info guys, I really appreciate it.
D50cyx - before I posted I thought I'd be caught by the latest legislation, so your comments just confirm it. I've got to confess I hate things like that, I'd far sooner just get the job sorted but I think this time I'm stuck with it.
But I'm only a DIY guy and although I'm quite brave at replacing sockets/switches and wouldn't worry too much about putting in a new 13a socket, when it comes to designing a system (which I think this needs) I have to admit it's beyond my knowledge. And no matter how much reading I've done over the years, electricity is one of those areas I just "don't get" so designing isn't on for me.
So I've printed out all the ideas and I really must thank everyone who's chipped in to this thread because when I get around to talking to someone I will at least have an idea if I'm being sold a pup. Thanks guys.
(And if I find out what an "RCBO" is, then I'll have a new buzzword to drop in !
)
D50cyx - before I posted I thought I'd be caught by the latest legislation, so your comments just confirm it. I've got to confess I hate things like that, I'd far sooner just get the job sorted but I think this time I'm stuck with it.
But I'm only a DIY guy and although I'm quite brave at replacing sockets/switches and wouldn't worry too much about putting in a new 13a socket, when it comes to designing a system (which I think this needs) I have to admit it's beyond my knowledge. And no matter how much reading I've done over the years, electricity is one of those areas I just "don't get" so designing isn't on for me.
So I've printed out all the ideas and I really must thank everyone who's chipped in to this thread because when I get around to talking to someone I will at least have an idea if I'm being sold a pup. Thanks guys.
(And if I find out what an "RCBO" is, then I'll have a new buzzword to drop in !
)You're welcome.
The legislation is a pain but, having gone through the course, I do believe that it is there for a purpose. Namely to cover the one-in-a-million situation where something does go wrong and you want that circuit to cut out before it does any serious damage. If the cable is too small, or the breaker too big, or anything else isn't quite as it ought to be, there is a distinct possibility that insufficient current will flow to trip the safety device(s) and someone will get a nasty shock. Or die.
An RCBO is a "Residual Current Breaker with Overload", and essentially combines the functionality of an RCD with an MCB. They reduce nuisance tripping as only the circuit at fault trips, but they are more expensive.
The legislation is a pain but, having gone through the course, I do believe that it is there for a purpose. Namely to cover the one-in-a-million situation where something does go wrong and you want that circuit to cut out before it does any serious damage. If the cable is too small, or the breaker too big, or anything else isn't quite as it ought to be, there is a distinct possibility that insufficient current will flow to trip the safety device(s) and someone will get a nasty shock. Or die.
An RCBO is a "Residual Current Breaker with Overload", and essentially combines the functionality of an RCD with an MCB. They reduce nuisance tripping as only the circuit at fault trips, but they are more expensive.
mk1fan said:
Make sure you're sitting down when you check the prices of the RCBO's - or get the work done before the regs change next year and they become compulsary.
If that happens they'll become cheaper, pre 17th ed RCBO's were around £50 for the cheapest, due to increased sales volumes they're less than half that now.mk1fan said:
Still expensive compared to a £5 mcb.
Cheap if it saves you being charged £500 by emergency call-out scammers-r-us cos the s##tty dual-RCD board knocked half the house out and the poor client didn't know what was what, only that the freezer was melting, heating not working, couldn't make dinner etc.Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff