Circuit energised even after RCD off/MCB off?

[choff]

So, the sparky is coming round today. What testing would you all expect a competent pro to do, to identify/ confirm the absence of a problem - just a V reading with a low impedance meter? Earth loop test? 500V DC insulation resistance across the three wires (testing each pairing?)

 

[securespark]

I really appreciate your response, but how likely would it be that someone has a socket where the earth and are neutral switched ?

No idea, but I have seen it on older installs with no RCD.
With an RCD it should trip as soon as any kind of load was connected.

Guess The Fault Competition

Today I visited a property. The customer was complaining of voltage drop when a hefty appliance was used on the ground floor ring final. He said that fluorescent lights would dim & appliances with motors would slow down. I plugged my trusty Alphatek into the cooker control unit & it...

www.diynot.com

 

[ericmark]

I loved my loop impedance meter, however they are not all the same, with the 13 amp plug leads one meter would measure line - earth for ELI and also line - earth for prospective short circuit current, but the other one switched to line - neutral for PSCC. But one got a feeling for what results to expect, not a case of if not 1.38 Ω or less there must be a problem, but this socket is only 3 meters from that one, why is the result so different.

I well remember testing a board in the C&G 2391 exam, the CU was showing 1.10 Ω and socket less than a foot away 1.20 Ω so I investigated further and found in the cable a 0.1 Ω resistor, clearly a C2, maybe a C1 as if the socket was used that resistor would likely go on fire.

It had been put there not as a fault, but so the board emulated a large premises, however my finding the resistor presented a problem for the lecturer, should he fail those who did not find it? Don't know answer, however my point is when using test equipment day in day out you get to know what to expect, and so readings within spec can still ring alarm bells.

I know a house the size of mine, I can expect to read 0.024 amp leakage total, but with a caravan looking at 0.002 amp, but in both cases the insulation resistance over 1 MΩ.

Get a new instrument and it takes time to work out what one should expect, I have a non contact volt option on new meter, I know from using it that it will not show telephone cables as live, but until used, was not sure if there would be enough of an AC component from the dial tone to show on meter or not. But it shows my laptop as having voltage, and that also has a DC supply. Only by using it does one work out what to expect.

I hope we do get a report on what was found. Faults can go for decades without being found, this house had a borrowed neutral at the hall light switch, could have been like that from when house was built, only found when all RCBO consumer unit fitted. Should be found with an EICR, I would test now, but not sure if it was tested all those years ago when I did my C&G 2391, it was 20 years ago. But I remember trying to find one in a Bank, and in the days before we walked around with clamp on ammeters it was not easy.

 

[ebee]

Reminds me of a test board I made for a friend of mine - Large 8 x 4 ply sheet and mounted three sockets ring fashion and a fourth socket spur fahion, all in plastic boxes and trunking.
So as to emulate a ring final circuit but I had some resistance wire and cut it into calculated lengths to make hidden resistors.
I calculated it to make a ring of length of 80 metres or something realistic anyway.
then you could get the ends and calculate one socket at 1/4 around the ring, one at half way and one at 10% from one end.
The "Spur" was connected via the 1/4 way socket and the resistors emulated a 2m length of 2.5 T & E.
I added six gang switch with a cover to hide switch polarity and to switch in and out various high ohm resistors to emulate faults and natural dampness sort of readings between conductors.
So he could get the "feel" of what to expect for resistance and continuity readings using my test gear (in my presence) and some others he borrowed.
Was a good teaching aid for him.
Unfortunately for him his domestic life shattered unbelievably twice in about 12 months , sadly I don`t think he carried on with Electrics, I had a plan for him to replace me as I retired but I`d still be his mentor for a while and possibly his consultant type on larger jobs and it might have given me the equivalent earnings of a few hours work each week too.
Best laid plans and all of that.

 

[choff]

Sparkie says no faults on the circuit - all clear. Must be an induced (I.e. phantom) voltage.

During my own testing beforehand, I did however find that two of the sockets were full of dead ants, and that two light switches had loose wires...