Does anyone know what RCD fault he is talking about

[King84]

Hi
Basically I have visited a youtube link of another electrician and he is talking about how many electricians find RCD fault very hard to resolve and he mentioned it takes less than 3 minutes using the method he mentioned but not completely hence its really puzzling me so if anyone could explain this.

(If you got Dual RCD board, You can disconnect some of the rn which is obviously neutral and you have to disconnect them from one of the circuits and you gotto be careful as if its got load on it then it could still be 230V on it so just energise the circuit and put in connectors and make sure you try and draw out the load so you get that out and with in 3 minutes you can find an RCD problem)

This was very hard to grasp even upon question he didnt reply but still bothers me as we go standard by IR on circuits to find RCD fault but like how this could find out in 3 minutes with very weirdly explained method if anyone more experienced knows what this means, I really appreciate
cheers

 

[IAmSparkytus!]

post the link on here and it might give people a better idea of what you’re talking about?

 

[littlespark]

Without seeing the vid, it sounds like the “test” is disconnecting neutrals, turning the power on, then touching the (now live) neutrals against the bar until the rcd trips.

Effective, but dangerous.

 

[ipf]

I thought RCD's were supposed to be safety devices.
Messing about with live returns ain't the way to sort out problems with them.
Could be 3 minutes sorting problem but a hell of a lot longer in the grave.

 

[pc1966]

A common "confusing" fault is a N-E short in a board with single or dual RCD. Here the N normally has little voltage w.r.t. E (kind of the definition of neutral) and that is especially true with TN-C-S as they are common at the cut-out point.

The confusing thing is you can get the RCD tripping due to a high current on a circuit that is not faulted, simply because it generates enough N-E voltage due to the N impedance and current flowing. So another circuit that has the N-E short allows a diversion of current and the RCD sees it and trips.

Sparky comes along, home owners says "when I hoover this thing trips", sparky assumes the fault is on the sockets but finds the IR test OK. Actually it was the lights that were faults, but it was the hoover motor's inrush current that was enough to cause a fraction of a volt N-E and so divert 30+mA on the light's N fault and trip the RCD.

 

[Vortigern]

Of course you could always switch off all the MCB and switch on one by one and you can narrow down which circuit is (apparently See post above) causing the trip. A lot less dangerous.

 

[ipf]

Of course you could always switch off all the MCB and switch on one by one and you can narrow down which circuit is (apparently See post above) causing the trip. A lot less dangerous.

Yes, it seems to me he'll only find the cable (circuit) in question....not what is actually causing the RCD to trip.
Unless I'm missing something.

 

[nicebutdim]

Is no one going to answer the question and explain the unknown method of testing, shown on an unknown video, from an unknown youtuber?

Maybe the OP might provide a link to the video, if they get a chance.

 

[Lucien Nunes]

I can't make any sense of that either and I don't think there's a single guaranteed way to find any kind of fault that would cause an RCD trip. But I do agree that a lot of people make heavy going of finding some types of faults because they don't think carefully enough about cause and effect or use the necessary calculations to analyse the problem. If you understand some basic electrical theory and have enough practical experience to recognise common types of fault and damage, most tripping situations yield to a bit of logic.

Maybe I should do a masterclass.

 

[ipf]

Maybe I should do a masterclass.

Maybe give it a mention on BBC Breakfast

 

[Vortigern]

I think @littlespark answered the question. Or at least that's the best stab in the dark so far as there is little to go on. But it sounds no different to turning on the circuits one by one and as stated, you now might know which circuit it is, However that does not identify the precise fault just narrows it down. OP would have to give a more precise description for a more precise answer methinks @nicebutdim, good name by the way.

 

[Vortigern]

Tbh I always get anxious when attending an RCD tripping as it can be such odd things like strapping cables need reversing, or someone just steamed off the wall paper with no evidence of it, and there is water in a socket and other weird events. Real bit of detective work sometimes.

 

[King84]

Thanks everyone for your replies really appreciate it and Here is the video at 5:19 he is talking about this specific test

 

[King84]

post the link on here and it might give people a better idea of what you’re talking about?

 

[King84]

Is no one going to answer the question and explain the unknown method of testing, shown on an unknown video, from an unknown youtuber?

Maybe the OP might provide a link to the video, if they get a chance.

Thanks Sorry about late message and I did provide a link above now

 

[James]

I watched from 5min mark to the end.
didn’t really like the guy and thought he gave very little if any usefull information

fault finding is a mix of knowing common faults that you can check if the symptoms support it and a good understanding of how things work and basic principles.

in my opinion, it is difficult to learn more than the occasional tip that may speed up the process under certain conditions by watching YouTube vids.

 

[Julie.]

I watched from 5min mark to the end.
didn’t really like the guy and thought he gave very little if any usefull information

fault finding is a mix of knowing common faults that you can check if the symptoms support it and a good understanding of how things work and basic principles.

in my opinion, it is difficult to learn more than the occasional tip that may speed up the process under certain conditions by watching YouTube vids.

Agree, I found his "presentation" awful, and struggled to keep watching.

Passing information to his audience is most certainly not his forte!

To the OP - as James stated, although there may be some tips that come out of these videos, there is so much more dross and potentially dangerous practices shown or mentioned in many of these videos. Unfortunately, unless you are already familiar with good practices, you can't tell the good from the bad.

There are some good ones on YouTube, John ward, sparkyninja, David savery electrical - they all give proper information (although their each "unique" styles may or may not suit you, but when learning they are good sources, so do persist with them)

I couldn't really understand what he was saying either, I think it's just disconnecting the rcd neutral and noting the results.

In itself it doesn't tell you anything, if it's a intermittent tripping fault, these are notoriously difficult to find, not one technique will do it as it could be due to....... pretty much anything, and a combination of things as well - linked neutrals (which can be found with testing) only tripping when a large load starts... through to an internal fault in an appliance (which the customer never associates with the tripping, so doesn't even tell you that it was plugged in at the time).

Finding faults is a matter of truly understanding the fundamentals of electrics and how the protection operates, combined with working your way through the issue in a logical process.

 

[Risteard]

He talks about "disconnecting the Rns". This doesn't actually make sense, as Rn is the resistance of a neutral conductor and as such can only be measured and not disconnected. Rn is not a name for a neutral conductor. Sorry to be pedantic but it irritated me.

 

[Lucien Nunes]

I agree, you can't disconnect a measurement. He was trying to be cryptic and avoid saying the word 'neutral', perhaps so that he couldn't be accused of explicitly suggesting a dodgy method. I think he knows his job but what a lot of waffle! I could have said that with 75% less words.

As a few people have stated above, there are multiple techniques needed to cater for all possibilities with faults that cause intermittent or apparently random tripping. What I think is important to recognise is that 'RCD tripping' isn't a kind of fault by itself. The trips are just one symptom that shows up with many unrelated kinds of fault.

The faults most likely to cause intermittent trips can however be narrowed down into some clear categories:

1. Functional / normal leakage
a) No electrical fault but excess aggregate functional leakage for one RCD. E.g. large ring with low load but many appliances / computers etc with RFI filters. Identify by leakage measurements, identifying loads and usage patterns.
b) No fault on tripping circuit, aggregate leakage generally within limits but exaggerated at times, e.g. by voltage transients / spikes caused elsewhere e.g intermittent connection upstream or appliance with functional switching in neutral. Rare, difficult to find, might require logger.

2. Insulation fault
a) Intermittent hard fault from L or N to E, e.g. moving floorboards occasionally pinch cable against pipe. Identify by timing, usage patterns, insulation tests. Can include appliances with timed functions e.g defrost heater in fridge freezer.
b) Marginal continuous insulation fault L to E, e.g. water in external light. Identify by insulation tests, usually easy to find.
c) Hard continuous insulation fault N to E, e.g. neutral pierced by socket fixing screw. Identify by insulation tests. Can be misleading as trips can be triggered by load on other circuits, but faulted circuit will always be on RCD that trips.

3. RCD fault (rare, never seen it myself)
a) Internally faulty RCD. Identify by RCD tests, substitution.
b) RCD being affected by interference e.g. adjacent transmitter. Identify by inspection, testing, substitution, relocation.

4. External influences, e.g. cats, people maliciously interfering with RCD. Identify by psychoanalysis

From the diversity of fault types in that list, I think it's fairly clear that multiple tests and strategies might be needed to pin down the cause of tripping, not just lifting the final circuit neutrals from the bar one by one.

 

[ferg]

Intermittent tripping RCD is one of those really annoying faults that can take 20 minutes or multiple visits.
As others have said there is no magic bullet for finding the issue.
Basic testing and inspection gets most of them. Detective work and luck find the rest.
One thing I have found is that rushing and trying short cuts rarely works for me. Keeping it simple and methodical has served me well.
I recently found an issue that wasn't showing up via testing because it was a dry day. A bit of experience and luck later I found a crappy connection outside under a leaky gutter. On a different day I might have missed it and had to return when the fault showed itself again.