Why is the RCD tripping?

[LastManOnline]

IMO drilling down on each circuit with IR testing is the way forward, and start investigating the the circuits with the lowest IR.

You are assuming that there is "a fault". An accumulation of "intentional earth leakage" is not a fault in the conventional sense. Its what happens when the design of the installation is no longer adequate for the practical needs of the installation. It's a situation that we will encounter progressively more as time goes on due to the inevitable increase of electronics in the home.
Taking a conventional approach to this particular problem is in my view not what's required.

 

[pc1966]

Lets put ourselves in the customers shoes, internment RCD tripping over a very long period of time. We dont know the full story of any intervention over this time.
Changing to RCBO's the expense of this for arguments sake £600 and the fault although narrowed down to hopefully one circuit, BUT it still tripping you are not going to be happy.

If this was a simple case of a reported tripping fault and the first action is to suggest a board change then yes, that is going to be a big disappointment for the customer as it probably won't fix any real fault. They would have every reason not to be happy.

But here they suffer from a total outage on both socket circuits and light circuits 5-10 times a month and this has been happening for over a year with (presumably) several spark's visits not identifying anything as a definite culprit.

In this case suggesting a board change and explaining carefully to the customer that it might be a total cure if the actual problem is accumulated leakage from lots of electronics, but at the very least it will reduce the scope of any outage to just the one circuit, and then help diagnose the source of a genuine intermittent fault by limiting the search to just the wiring and accessories there.

Of course they will hope/expect a total cure, but if not at least they will have far less annoyance than the current situation and can look forward to it being solved completely in the following weeks, not years as gone by so far.

 

[Mikegh]

If you called out to a random installation you'd be taking a few global readings at least before moving onto rcbo board

Larger installations probably need it anyway

Will distribute leakage if its accumulated from appliances and narrow down faults if they occur

Customer is also protected against widespread disruption to supply

 

[7029 dave]

You are assuming that there is "a fault". An accumulation of "intentional earth leakage" is not a fault in the conventional sense. Its what happens when the design of the installation is no longer adequate for the practical needs of the installation. It's a situation that we will encounter progressively more as time goes on due to the inevitable increase of electronics in the home.
Taking a conventional approach to this particular problem is in my view not what's required.

They have low insulation 1.7 megohm on a global reading associated with problems, in my view this needs investigating.

 

[Mikegh]

They have low insulation 1.7 megohm on a global reading associated with problems, in my view this needs investigating.

It's not that low ,It's well above the range of tripping
an rcd

I'm assuming global n-e is a reading taken at the rcd terminals

I'm not clear why there's only n-e or is equipment left connected for the test, first time I heard the term used

 

[pc1966]

They have low insulation 1.7 megohm on a global reading associated with problems, in my view this needs investigating.

It is suspiciously low, but I presume that @HappyHippyDad will be doing per-circuit testing as part of the board change and at that point we will find out if it is 8 circuits in the 13M region, or 7 are > 200M and one is the 1.7M lurking like a leaky toad for investigation.

 

[timhoward]

I do see the logic in the board change with due communication to customer.

It's not that low ,It's well above the range of tripping an rcd

Tangent, but I'm glad you've pointed this out as I've heard more than one person say "I won't bother with IR tests as the RCD would trip if it's a problem!". I think a 0.02Mohm IR results in a current of about 11ma, so even lower IR needed to reach trip current of a 30ma RCD.

 

[pc1966]

Tangent, but I'm glad you've pointed this out as I've heard more than one person say "I won't bother with IR tests as the RCD would trip if it's a problem!".

There are so many reasons that is a stupid attitude!

• L-N insulation faults can start fires, not detected by RCD
• Low IR can point to future problems due to water ingress or degraded cables
• Low-ish IR can reveal 'live' metalwork that is not able to trip an RCD until someone touches it, at which point if the RCD is faulty then someone probably dies.

While the regs have values in the 0.5M to 1M region as a 'pass' that is too low for comfort unless there is a good reason to explain it, for example an old warehouse with dozens of dusty light fittings all adding up to the ~1M result.

Hopefully we will get an update at some point with the results of testing the new board and if that really solved the problem, and if not how it was finally pinned down.

 

[Mikegh]

There are so many reasons that is a stupid attitude!

• L-N insulation faults can start fires, not detected by RCD
• Low IR can point to future problems due to water ingress or degraded cables
• Low-ish IR can reveal 'live' metalwork that is not able to trip an RCD until someone touches it, at which point if the RCD is faulty then someone probably dies.

While the regs have values in the 0.5M to 1M region as a 'pass' that is too low for comfort unless there is a good reason to explain it, for example an old warehouse with dozens of dusty light fittings all adding up to the ~1M result.

Hopefully we will get an update at some point with the results of testing the new board and if that really solved the problem, and if not how it was finally pinned down.

I do believe you have misinterpreted Tim's post

The 1Mohm figure is being talked about in the context of an rcd trip not as a good IR value

 

[timhoward]

I do believe you have misinterpreted Tim's post

The 1Mohm figure is being talked about in the context of an rcd trip not as a good IR value

I think it's ok pal, I know the comments weren't aimed at me!

 

[buzzlightyear]

I think it's ok pal, I know the comments weren't aimed at me!

but the gun is .lol.

 

[Mikegh]

I think it's ok pal, I know the comments weren't aimed at me!

Yes its actually me doing the misinterpreting