Fault on domestic home wiring

[Kyleb2210]

110v from switch to switch (see attached picture), tn-cs system with 30mA RCD in Place, trips fine when tested at 100% and 500% customer complained of getting shocked when touching both switches at once but doesn’t trip with this fault, have a few theories, but any suggestions?

 

[KEV 1 N]

Possible poor or no earth at one of those switches, therefore creating a potential difference. Chances are it’ll be the light switch that isn’t earthed properly as there’s more connections throughout the circuit to come loose.

 

[Octopus]

Check the earth continuity from birth switches back to cu

 

[Deleted member 9648]

Did you sort it or leave the customer to fry while you enquired on a forum?

 

[Kyleb2210]

Yeah I told her to ensure her hands were soaking wet before using the switches they’re away on holiday for the week so no panic! Just didn’t have time last night to start fault finding

 

[The Ghost]

IR tests then?

 

[Midwest]

Can I just say you need to attend to the pedicure status of your left hand, its frankly shocking (pardon my pun).

 

[Kyleb2210]

I haven’t had a chance to do any tests yet apart from very quickly testing the rcd, with the customer away im not going asap I’m going to get there this week at some point, what’s concerning me is why the rcd never tripped? As even if there was a loose earth connection, or no earth atall surely the rcd should still of picked up an imbalance between live and neutral and tripped regardless when the customer touched the switches?

 

[Kyleb2210]

Can I just say you need to attend to the pedicure status of your left hand, its frankly shocking (pardon my pun).

Years of abuse sadly it’s beyond repair

 

[Midwest]

I had similar ages ago, customer getting intermittent tingles from metal dimmer switch, no voltage between plate & known earth mind.

I left her to fry, whilst consulting members here (nahh not really, swapped switch to plastic). Went back to investigate with new advice and found there was no continuity between installed switch cpc & earth terminal in CU.

 

[Midwest]

I haven’t had a chance to do any tests yet apart from very quickly testing the rcd, with the customer away im not going asap I’m going to get there this week at some point, what’s concerning me is why the rcd never tripped? As even if there was a loose earth connection, or no earth atall surely the rcd should still of picked up an imbalance between live and neutral and tripped regardless when the customer touched the switches?

Just shows why you shouldn't have an over reliance on RCD's. Guess the flow through her etc to Earth, was enough to give a tingle, insufficient for imbalance. Dunno, forum boffins will say.

 

[Midwest]

Years of abuse sadly it’s beyond repair

Won't ask on a family forum what you've been doing with it.

 

[AJshep]

I'd suspect that the earth connection somewhere is missing (as mentioned probably on the lighting circuit) and you have a low Insulation resistance between L&E. If so, your need to check the whole circuit thoroughly as you have no idea where the fault is. The CPC could be broken to the first light in the circuit and other metal light fittings and accessiores may potentially be live too !
As RCDs only work on earth imbalance maybe the touch current was below 30mA it may have been different if the customer was bare foot on a damp floor either way this is a potential killer.

I' be carryng out continuity and IR tests the breaking down circuits, at a guess you find a snapped CPC and a squashed Live somewhere on one of those two circuits.

 

[Octopus]

I haven’t had a chance to do any tests yet apart from very quickly testing the rcd, with the customer away im not going asap I’m going to get there this week at some point, what’s concerning me is why the rcd never tripped? As even if there was a loose earth connection, or no earth atall surely the rcd should still of picked up an imbalance between live and neutral and tripped regardless when the customer touched the switches?

Maybe time to review how rcd's work ...

 

[shaun1]

Capacitive coupling or inductance between the earth and other cables can be enough to measure 100v and feel a tingle. But if you measured the current discharged it would be tiny. Switch mode PSUs tend to have a bit of earth leakage which will often appear as half mains voltage if they aren't properly earthed.

So first port of call should probably be earth loop impedance test at switch/earth continuity test.