Fault on RCD Trip

[Riggy]

Riggy,I will do a part 4, I have been a bit busy, with pc problems!

For now, it is possible for upstream disturbances to trip an RCD. This can be due to an imbalance on the incoming wiring caused by loads and or faults on the DNO network

Excellent, I couldn't believe you would leave us all in suspense!

 

[Riggy]

that is why the RCD trips,an imbalance in the N will trip the RCD when it is trying to feed 400v from a different phase.

regardless of where the fault is, the current is omnipresent on all of the neutral cable.

headbang

I'm certain you know what you mean, but I'm not getting it, sorry!

Hopefully Sidewinder's 4th instalment will crack it!

 

[kme]

Some of you may have seen the "RCD handbook" PDF, which I sent out to a few peeps who requested it.

If Admin is happy, I could upload it to the site, and you can have a look at your leisure.

Some of the myths & facts regarding what they will/ can/ won`t do may be dispelled??

Admin? (aka how do I do it?)

 

[Sidewinder]

kme,

Do you mean the BEAMA (British Electrotechnical and Allied Manufacturers Association) handbook?

Here?

http://www.beama.org.uk/en/publications/guidance-documents.cfm/rcd-handbook

HTH

 

[Manator]

Very good handbook and lists a few reasons why or how upstream faults can trip a RCD.

 

[sparkytim]

Yes I have seen this before but could not remember what it was called.

Thanks for putting link up.

I have come across several instances of EXTERNAL events causing RCDs to trip.

One example was due to faulty overhead supply connections, another caused by a Neighbour drilling into his supply cable!

Internally also I have had the Double pole switched socket cause as mentioned in the document.

Great things RCDs but can be a right pain when problems occur.

 

[kme]

That`s the `ammer. I`ve got it on a CD-ROM. Didn`t know it was available online.......

Thanks matey

 

[Lee321]

out of date terminology but principle wise its good

 

[Sidewinder]

lostit,

This is the 2k3 version, the 2k10 version will be out soon.

The electrical principles however have not changed since the days of Ampere, Volta & Faraday et al.!

 

[Lee321]

hence the later of my sentence

 

[binky]

By eck this has turned into a saga:^O.

 

[Andy™]

im just waiting for this drawing that shows how current can magically disappear from a circuit to create this imbalance

 

[steptoe]

[quote name='Andy

 

[Riggy]

kme,Do you mean the BEAMA (British Electrotechnical and Allied Manufacturers Association) handbook?

Here?

http://www.beama.org.uk/en/publications/guidance-documents.cfm/rcd-handbook

HTH

Interesting document but I'm not sure of the relevance in this particular case.

I'm struggling to see how Lawnmower Man could cause a significant transient surge, even if we assume that the OP's property has several miles of twin and earth to create sufficient Neutral to Earth capacitance!

Or have I missed the point AGAIN?

 

[green-hornet]

RCD's can be effected by Line side upstream faults, the most common being

Loose connections, mains bourne disturbance, site machinery/ plant, installed services and lightning strikes.

A combination of supply network transient overvoltages and capacitance to earth within the installtion can also cause unwanted nuisance tripping.

This I would agree is rare but possible, and is a known fault or inconveniance with RCD's.

All supplies are distributed as three phase which is why when you have a power cut on a particular phase some houses in your street will still have power.

Any imbalances on these phases along with a shared neutral can cause this tripping, I would suspect that whilst this is possible to only effect one property I would think there may be another reason why this is happening.

All I do know is that from my reading into the data and supply characteristics I find that it is possible to have this fault.

 

[Lee321]

while this thread grows and grows alot of people are still not grasping what is going on with words

a diagram will do wonders

or even can we invite a manufacturer of rcd's chime in?

 

[davetheglitz]

Don't know how I've missed this post - some interesting points!

Not sure if this approach has been covered - and it's something I have a hard job to wrap my brain around - but I reckon it's all down to transients.

As far as I can see these faults always seem to be associated with motors. As these are brush type motors I can imagine that current is being interrupted at the commutator resulting in some high frequency transient voltages - much like an ignition system on a car (points = commutator, coil = motor windings).

Assuming the motor is double insulated and there is no earth fault, then the neighbours RCD may have an instantaneous difference in current between live and neutral (storage via the motor winding inductance?) - but over a cycle it may even out - i.e. fault not there long enough to trip the RCD - and symmetrical.

As the earthing is PME it is possible that some of the transient may find it's way through the RCD coils to appear on the Line and Neutral.

At the OP's house neutral terminal the transient now has two paths to an appliance. One via the neutral winding of the RCD - the other via the cpc. The transient on the neutral would be attenuated due to the induction of the winding. However the transient at the CPC - assuming a high impedance path to either live or neutral via cable capacitance or appliance resistance - would not be attenuated, and would also be phase shifted to the neutral current due to the induction. So now there is a possibility of a differential and non symmetrical current existing - maybe enough to trip the RCD.

Am I barking up the wrong tree here?

Perhaps it's worth checking if the strimmer suppressor capacitor is fitted- or whether there is any radio interference from it?

 

[Sidewinder]

I'll try to find some time over the weekend to finish my installments if anyone wants.

Working tomorrow and some of Sunday though.

Let me know if anyone wants me to try to carry on, I'll have to re-read the thread and think again about the posts and the issues.

A bit under pressure at the moment.

Paul

 

[Riggy]

I'll try to find some time over the weekend to finish my installments if anyone wants.Working tomorrow and some of Sunday though.

Let me know if anyone wants me to try to carry on, I'll have to re-read the thread and think again about the posts and the issues.

A bit under pressure at the moment.

Paul

Yes please!

 

[kenwood33]

I have an update for everyone as follows:

On Friday evening our DNO cam out who is EDF Energy. The guys went into the box outside our property. They said there was nothing wrong and to remember 3.2 which is what they found (apparently thats ok). They came into the property and tested the socket and this tripped the RCD at 30, first they tried 10, then 20, then 30 and bang on target it goes off. The guys at EDF have no answer and are scratching their heads too. They have no suggestions of what we do next except buy our neighbour a petrol mower which is not very helpful. So we are no further forward and our electrics still keep going off!!. We cannot ask our house builder electrician to come out again as he has refused and is not willing to help us because he has the biggest contract for providing electricals in ALL the new houses this company builds so does not want to rock the boat, but he provided our electricals in our house in the first place.