RCCD tripping in Domestic TT circuit.

[corvus13]

Sparks and Sparkettes, Last week the 100A 30mA RCCD(Merlin Gerin) tripped for no obvious reason and it reset with no problems. The next evening it tripped again but wouldn't reset. I opened the MCB's feeding the final circuits one at a time until I disconnected the faulty circuit and I could reset the RCCB. Only it woulndn't. All outgoing circuits disconnected and the RCCB would not reset. Clearly a faulty RCCB but a guy at work said that a neutral 'faulting' to earth would stop the RCCB from reseting. As I far as I understand this, even though the neutral(s) are still connected to the common neutral bar, the open MCB stops any volts to cause a differential current in the RCCB. Neutal shorting to earth or not. Am I right or tripe?

As it happened the trip did reset after 20 attempts(mindless desperation) but tripped before I could close a MCB. More mindless desperation and the RCCB eventually reset together with all the MCB's. Another trip after 30mins but solid since then.

So is the RCCD faulty or do I have an earthy neutal despite the MCB's being open?

Also, bearing in mind this is a TT installation, can I replace the 100A RCCB with a 100A trip and used RCBO's on the final circuits? Is this allowed?

Thanks in advance for any help- I'm off into town now to see a Punk tribute band, ACE! Cheers, Tim

 

[clicon357]

Sparks and Sparkettes, Last week the 100A 30mA RCCD(Merlin Gerin) tripped for no obvious reason and it reset with no problems. The next evening it tripped again but wouldn't reset. I opened the MCB's feeding the final circuits one at a time until I disconnected the faulty circuit and I could reset the RCCB. Only it woulndn't. All outgoing circuits disconnected and the RCCB would not reset. Clearly a faulty RCCB but a guy at work said that a neutral 'faulting' to earth would stop the RCCB from reseting. As I far as I understand this, even though the neutral(s) are still connected to the common neutral bar, the open MCB stops any volts to cause a differential current in the RCCB. Neutal shorting to earth or not. Am I right or tripe?

As it happened the trip did reset after 20 attempts(mindless desperation) but tripped before I could close a MCB. More mindless desperation and the RCCB eventually reset together with all the MCB's. Another trip after 30mins but solid since then.

So is the RCCD faulty or do I have an earthy neutal despite the MCB's being open?

Also, bearing in mind this is a TT installation, can I replace the 100A RCCB with a 100A trip and used RCBO's on the final circuits? Is this allowed?

Thanks in advance for any help- I'm off into town now to see a Punk tribute band, ACE! Cheers, Tim

Out of interest is the CU metal clad or insulated?

 

[corvus13]

First off Thanks for all the replies. I've just spent an age typing a responce then I noticed there is a second page.



Clicon357: The RCCB I have is a 0.030A and 100A Merlin Gerin 'Multi 9'. This means, as I understand it, the device will trip on seeing a difference in the Live-Neutral currents of 30mA, and is only designed to carry 100A load current before overheating. Is this right? When I was thinking of replacing this with a trip I meant an overload that would trip at a load of 100A but had no earth leakage trip facility. The CU is metal Clad and the RCCB is double pole.

Topquark-Wirepuller, I can get hold of a 500v Insulation Resistance Tester. As for fractional ohm meters, would have to see what turns up at work. In this situation I would be looking for low(ish) resistance between earth and the neutrals as they return to the common bar in the CU. All switches, MCB's etc off ofcourse. If these circuits were ok then I'm looking at fridges, errr and things plugged in, no electric shower/immersion heater....

MarkieSparkie, I was thinking of the neutral voltage difference to earth on the way to the pub last night but dismissed this. Wrong again.

So to confirm, is it ok or better to replace the 30mA 100A RCCB with:
a 100A Main Switch or
a 100A Overload Trip or
a 100mA S-type RCD rated at 100A- which then feeds the final circuits via 30mA RCBO's?
Sorry if all this is plainly stated but I'm unfamiliar with a lot of these terms. Cheers Tim

 

[malcolmsanford]

First off Thanks for all the replies. I've just spent an age typing a responce then I noticed there is a second page.



Clicon357: The RCCB I have is a 0.030A and 100A Merlin Gerin 'Multi 9'. This means, as I understand it, the device will trip on seeing a difference in the Live-Neutral currents of 30mA, and is only designed to carry 100A load current before overheating. Is this right? When I was thinking of replacing this with a trip I meant an overload that would trip at a load of 100A but had no earth leakage trip facility. The CU is metal Clad and the RCCB is double pole.

Topquark-Wirepuller, I can get hold of a 500v Insulation Resistance Tester. As for fractional ohm meters, would have to see what turns up at work. In this situation I would be looking for low(ish) resistance between earth and the neutrals as they return to the common bar in the CU. All switches, MCB's etc off ofcourse. If these circuits were ok then I'm looking at fridges, errr and things plugged in, no electric shower/immersion heater....

MarkieSparkie, I was thinking of the neutral voltage difference to earth on the way to the pub last night but dismissed this. Wrong again.

So to confirm, is it ok or better to replace the 30mA 100A RCCB with:
a 100A Main Switch or
a 100A Overload Trip or
a 100mA S-type RCD rated at 100A- which then feeds the final circuits via 30mA RCBO's?
Sorry if all this is plainly stated but I'm unfamiliar with a lot of these terms. Cheers Tim

Because your CU is metal clad you will have to protect the tails and have an upfront RCD 100mA S type would be the preferred weapon of choice.

So you will need to fit the 100mA S type RCD in the tails before they enter into that metal clad CU. You can then fit a 100amp double pole main switch inside the CU and then your RCBO's

This will then give compliance to Regulation 531.4.1 for the metal clad CU regulation 531.2.9 for compliance of RCDs in series and 537.1.4 for isolation

 

[corvus13]

Thanks for that but, and I know this sounds like I'm ungreatfull but it's not the answer I was hoping for. TT and the 17th Edition have done for me. Bah! Expect further irritations from me when I get myself together for an adventure into testing earth spikes on TT systems. I'll blast my final circuits this weekend and see what turns up.
By the way, with regards to the feed into the metal clad CU that is not protected by a S-type (only the 100A fuse), is this illegal concidering this installation was done around 20 years ago. Cheers to every one Tim

 

[corvus13]

Right then Lads, to cut a long story short I blasted the Neutrals to the Earth Terminal in the CU @ 500v and got the following results:
Downstairs sockets(ring main) - 2.3MOhms.
The Neutral Bar with all other Neutral connected- 20Mohms.
I then plugged in some appliances(suspect devices) eg an electric radiator, table lamps and a 'Stella' bottle cooler and still got 2.0Megs.
At least if I become plagued by further trips I know where to look but still disapointed by a dicky 20 year old installation. Cheers and Thanks