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Topic Title: Neighbours RCD Tripping?
Topic Summary: Power Tool trips their RCD (so i'm told!)
Created On: 03 December 2012 09:00 PM
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 03 December 2012 09:00 PM
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74jools

Posts: 408
Joined: 02 March 2008

A customer of mine phoned me to say that when he uses his electric chainsaw it trips his neighbours RCD?
I have been round to the property today, and while using his saw, nothing happened?
I'm not saying I don't believe him, but just trying to get my head around why it may be happening.
His property has a CU with a 30mA RCD as a Main Switch. Supply is TNS with no bonding.
Neighbours CU is a split load CU (installed by myself some 5 or 6 years ago) it has 30mA RCD to Sockets (16th edition), it too has a TNS supply with bonding in place for water and oil service.
Have only checked RCD operation to both boards so far, any ideas on series of tests or why this is happening?

Regards
Julian
 03 December 2012 09:24 PM
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slittle

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Possibly a high resistance neutral somewhere. Try high current loop tests (L-N & L-E) obviously before the RCD's and see if there are any clues.

Obviously they will differ as it's TNS but it might give you a clue.


Is it only the chainsaw that does it or would another large inductive load cause the same effect.

I'm wondering (as I type) whether it's an interference issue that the neighbour's RCD is seeing.


Stu
 03 December 2012 09:29 PM
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74jools

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I asked that question, and only seems to be with the Chainsaw. Sods law it wouldn't prove the point this afternoon.
CU's are in joining Garages, but I checked that he wasn't using neighbours electric! lol

Julian
 03 December 2012 10:45 PM
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Zs

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Julian, I love these.

Will now sow some seeds of thought on which the truly time-rich, and seriously clever, may expand if we are lucky.

How old are the supply heads? Are the properties joined, i.e. semi detached or terraced?

I'm wondering about it being one of the older properties where one supply was piggy-backed from the other throught the wall? Norm knows most about those and I think back to not believing him when I first read that.

I have heard of power tools tripping RCDs many times. Usually because they are stored in damp vans and garages, so that bit doesn't surprise me. But for it to be next door indicates (to me) either something shared in terms of the supply to the two properties, or a supply neutral issue on one of the phases perhaps? If next door is on a different phase from your chain saw man and if chain saw man and all the neighbours on the same phase as he, have a neutral issue......and so on.

Any lamps blowing in every third house on the street...or in every first and second?

Is chain saw man on RCD? Maybe swap his with the neighbour's one and see if the same RCD trips wherever it is located? i.e if it is the softest RCD of the three, where does it go off.......I'm rambling. I blame the commuter madness.

Of course, he hasn't declared that he is nicking the circuit through a 10mm hole into next door's garage has he?

Don't forget to tell us what it is.

Zs
 04 December 2012 07:10 AM
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MrP

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Julian
I had a similar head scratching moment with an RCD being tripped out by the use of neighbor's equipment
The offending device was an MEM electronic 32A RCBO.
The set was housing association sheltered housing small block of 4units two ground two first.
A new installation, new intake. Job tested perfect
After changing the affected RCBO and no change still tripping even got the MEM rep out
After changing the electronic RCBO to non electronic problem solved, what the actual problem was who knows

Hope this helps good luck

MrP home in 15days Inchallah
 04 December 2012 08:23 AM
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potential

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IME tripping of a neighbour's RCD is nearly always caused by a shared service introducing a voltage into the house that is affected by the tripping..
Water pipes and gas are the most obvious candidates.
 04 December 2012 09:15 AM
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AJJewsbury

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IME tripping of a neighbour's RCD is nearly always caused by a shared service introducing a voltage into the house that is affected by the tripping..
Water pipes and gas are the most obvious candidates.

Wouldn't there need to be pre-existing a N-PE fault (possibly of some significant resistance) in the neighbour's installation for changes in the PE voltage to be seen by the RCD? (presuming it's a modern RCD or current operated ELCB, rather than a voltage-operated ELCB).

Isn't the chain-saw double insulated?

- Andy.
 04 December 2012 10:33 AM
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OMS

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I'd go with that one Andy - the chainsaw doesn't have to have an earth fault - just load - and the starting load will be high so high amps x high resistance equals high volts on the neutral and off the RCD goes via the N-E fault.

I used to cause the same problem in my neighbours with a cement mixer - after 3 attempts she finally accepted there was a problem in her house - local electrician eventually found the fault after a few attempts - but I suspect he wasn't really looking based on the advice of the neighbour who's basically some guy who knows something about electrics - not a proper electrician of course

Regards

OMS

-------------------------
Failure is always an option
 04 December 2012 10:43 AM
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MrP

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The fault I described above was an inductive load used by a neighbor that took out the device
The incoming supplies where very close and the field wiring adjacent. The all field wiring tested ok
Changing the electronic device (RCBO) to box standard did the trick reason why and there is a reason for everything your guess is as good as mine but it worked
I don't think will do any harm to give it a go

Good luck buddy

MrP 15days
 04 December 2012 11:16 AM
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Patnik

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Have you tried running the chainsaw through a PAT tester to check for leakage current? Might be a good way to find out if it really is the chainsaw or some weird coincidence.
 04 December 2012 12:11 PM
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MrP

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I like that Idea
Running a chain saw through a pat tester

Devastation

Calibrate that then
MrP
 04 December 2012 12:39 PM
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Patnik

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Originally posted by: MrP

I like that Idea

Running a chain saw through a pat tester



Devastation



Calibrate that then

MrP


Maybe I could of phrased that better - there again maybe I've sprung a leak in my subconcious
 04 December 2012 01:43 PM
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daveparry1

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The pa tester won't show anything as it will be looking for leakage between LN-E and as the chainsaw is class 2 double insulated (i'm assuming that as many of them are) there will be no earth cable,

Dave.
 04 December 2012 02:22 PM
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Patnik

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Originally posted by: daveparry1

The pa tester won't show anything as it will be looking for leakage between LN-E and as the chainsaw is class 2 double insulated (i'm assuming that as many of them are) there will be no earth cable,



Dave.


If it is class 2 you need to connect your croc clip to an exposed metal part to offer an earth path to any current that has breached the insulation for the test to have any meaning - obviously not the chain itself though

I wonder what was being sawn at the time?

Nik
 04 December 2012 05:39 PM
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74jools

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Originally posted by: OMS

I'd go with that one Andy - the chainsaw doesn't have to have an earth fault - just load - and the starting load will be high so high amps x high resistance equals high volts on the neutral and off the RCD goes via the N-E fault.



I used to cause the same problem in my neighbours with a cement mixer - after 3 attempts she finally accepted there was a problem in her house - local electrician eventually found the fault after a few attempts - but I suspect he wasn't really looking based on the advice of the neighbour who's basically some guy who knows something about electrics - not a proper electrician of course



Regards



OMS


I'm confused! Are you saying a N - E fault on the Neighbours installation? If so why doesn't their RCD trip anyway?
To answer an Andy's question, both have up to date 61008 RCD's.

Julian
 04 December 2012 05:44 PM
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spinlondon

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Your customer has a socket-outlet connected to their neighbours supply, and the chainsaw had a leakage to earth which has cleared.
 04 December 2012 05:51 PM
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OMS

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Originally posted by: 74jools

Originally posted by: OMS

I'd go with that one Andy - the chainsaw doesn't have to have an earth fault - just load - and the starting load will be high so high amps x high resistance equals high volts on the neutral and off the RCD goes via the N-E fault.

I used to cause the same problem in my neighbours with a cement mixer - after 3 attempts she finally accepted there was a problem in her house - local electrician eventually found the fault after a few attempts - but I suspect he wasn't really looking based on the advice of the neighbour who's basically some guy who knows something about electrics - not a proper electrician of course

Regards

OMS



I'm confused! Are you saying a N - E fault on the Neighbours installation?

Andy and I are saying exactly that -

If so why doesn't their RCD trip anyway?

High impedance N-E fault and insufficient load in the system

To answer an Andy's question, both have up to date 61008 RCD's.

so you've tested both and both are working - if it's the chainsaw why isn't the clients RCD operating (coupled with the fact it's probably double insulated)


Julian


Regards

OMS

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Failure is always an option
 04 December 2012 06:06 PM
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OMS

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Supply is TNS with no bonding.


NE fault of a few hundred ohms in the installation (but to true earth, not the Met one),N & E happen to be similar voltages and nothing happens normally. However, as the large neutral current of the chainsaw starting under load, causes the L voltage to drop, and the N voltage to rise up to meet it, perhaps by a few volts if at the end of a long feeder. Suddenly N and E are not so close together, and the current that should return from the RCD N coil skives off via terrra firma earth, and lo the RCD sees an imbalance - and trips

Try a N_E insulation resistance test in your client neighbour

Regards

OMS

-------------------------
Failure is always an option
 04 December 2012 10:56 PM
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AJJewsbury

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NE fault of a few hundred ohms in the installation

Bear in mind that the fault might not be in the fixed installation - it could equally be in an appliance or extension lead (especially the surge protection types).
- Andy.
 05 December 2012 09:39 AM
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broadgage

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Agree, the neigbours installation or some appliance connected to the installation, has a high resistance fault between earth and neutral.

Due to the small difference in voltage between the earth and neutral wires, this fault might pass pass say 5ma and not trip the RCD.
The substantial starting current demanded by the power tool will cause voltage rise in the neutral and therefore increase the voltage between earth and neutral. The fault might now pass say 30ma and trip the RCD.

Such faults can be challenging to locate, remembering that they may be in portable appliances that are not used all the time.
For example a washing machine may have a neutral to earth fault only at certain points in the cycle. Or a cooking appliance may have a neutral to earth fault only on one part of the cooker, and then only when hot or cold.
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