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With have heard reports of smart meters tripping RCDs, is there any more than anecdotal evidence?
About 20 year sago I upgraded a ring final in a 70s house. I added a 30mA R.C.D. to offer additional protection as there was a toddler about. The R.C.D. tripped off but testing revealed no faults. So I removed all sockets on the circuit and inspected them. Some socket terminal screws were not very tight. I reterminated all cables and retightened the socket screws. The R.C.D. did not trip off after that.
Z.
Around 11 mA background leakage measured on on the meter tails, which is now spread across half a dozen 30 mA RCBOs, so negligible.
The new RCBO for that circuit trips at 27 mA, however I fitted a 300 mA upfront RCD because it’s TT which trips at 210 mA and it has taken that out as well.
So I have ordered a 100 amp 100 mA time delayed RCD which is advertised as a Type A which is something I not seen as yet, up until now I have only ever seen Type AC, if it is what it is said to be I will swap it out for 300 mA to solve the lack of discrimination issue.
I know this is going to turn out to be something really simple, but at half five yesterday evening when I was getting an insulation test result of 1.8 Giga ohms there didn’t seem much point in carrying on stripping the circuit.
The next step will probably be to swap the upfront RCD, test the circuit again and if I get a high insulation value again split the circuit onto two RCBOs to see which half of the circuit trips rather than dismantle the circuit without knowing what I am looking for.
Hardly the most scientific method of testing, but hey ho when needs must.
The meter in the photo is a Megger MIT420/2 and can measure micro Farads, as an installation electrician that is not a feature of the meter I used.
Edit- I have just turned it on and the display is in nano Farads.
I have to own up the meter was brand new on EBay being sold by a firm of motor factors remarkably cheap, I presume they thought they would sell them to mechanics working on electric vehicles and when they did sell they knocked them out on EBay dirt cheap to get rid of them, not being able to resist a bargain I bought one, but still have not worked out what all the features are or used them.
I fitted a time delayed 100mA up front R.C.D. before a new consumer unit which had a TT supply. Each circuit had 30mA R.C.B.Os.
I assured the customer that the system would be reliable as the original 30mA R.C.D. often tripped and plunged them into darkness.
Later I got a call saying that they had lost all power. The 100mA time delayed R.C.D. had tripped off. No R.C.B.Os tripped off.
The installation was converted to a P.M.E. earth terminal system by U.K.P.N. and the 100mA R.C.D. was replaced with a 100 Amp D.P. main switch.
The house was near to the Bacton gas terminals. Was the tripping caused by radio interference?
We may never know.
Z.
well if there is a surge, ever so briefly that SPD will look like a low impedance until the surge has passed- it could, just about, if you had a single wire surge, say an over voltage on L but not N or the other way about create an LE path that would fire the front end RCD but not the RCBOs, but it is a bit of a stretch .
Mike
The Type A 100 A 100 mA S-Type time delayed RCDs are on back order, I just spoke to the wholesaler and hopefully I will have them by the end of the week.
So I ended up fitting a temporary upfront RCD using what was in the back of the van, but the 300 mA doesn’t afford discrimination so is not suitable in the long term. I might swap it for a Type AC 100 A 100 mA S-Type time delayed RCD in the meantime, because there’s no guaranteed delivery date for the Type A.
Unfortunately lack of availability of materials means we cannot actually do the job we want to do at the moment. However I am going to have to another go at clearing faults in the morning.
Fortunately this job is only a couple of streets away from home, if it had been a long way away I wouldn’t have got involved in the first place.
How many surge protected extension leads can you supply from one 30 mA RCD?
The customers have five supplied from one ring circuit and RCD that has been tripping. They have said the RCD still tripped with all of them disconnected.
He customers also think the central heating boiler and controls are causing the RCD tripping, they are on a completely different circuit and 30 mA RCBO that doesn’t trip.
Could a switching spike on the boiler circuit make the socket circuit with all the SPD protected extension leads RCBO trip without tripping the boiler circuit RCBO trip?
From the Eaton website, page 35:
”Recommended connection of installation with RCDs and surge protective devices is depicted on Figure 80. In socket circuits with an RCD with a sensitivity of 30 mA, type G with short-term delay and endurance up to 3 kA must be used.”
Is that referring to a Type G RCD or a Type G SPD, I am assuming it is a RCD but it seems it could be either or both.
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