Apologies for digging up a 9 month old thread, but was going to post about a fault-finding job I did today where I can confirm that it is possible to get a shock off the plastic bit of a plastic switch, and this seemed as good a place as any to put it.
Client reported getting a shock off the switch after cleaning it (getting rid of mould nearby), and also that the landing light (LED GLS) was glowing dimly when off (normal brightness when on). House is COLD - really cold, can see your breath cold - elderly resident cannot afford to put the heating on (and no heating in the 3 foot square hallway anyway). Switch is 2G in hall: 2-way for landing, and 1-way for hall lights. No L link wire between hall and landing switches - on the face of it, separate. 2x lighting circuits, neither RCD-protected. Client had turned off both lighting circuits at the DB.
Checked:
- Zs@DB fine (0.20Ω), TN-C-S, incoming polarity good
- Bonding good
- R2 to switch back box/lugs: 0.10Ω (to MET)
- Confirmed polarity on switches
- Confirmed earth continuity to upstairs switch (for and on the landing).
- No cpc at landing light, pendant set, loft boarded above.
- IR (L+N) to E for upstairs and downstairs circuits in parallel 1.06MΩ but a little variable
- IR upstairs N to downstairs N 3.39MΩ
However:
- Continuity upstairs L to downstairs L ~33kΩ
~scratches head~
So upstairs and downstairs lighting circuits are linked "somehow" possibly via a lamp...? Resolve to put both up and down L on one MCB (2 circuits to 1). Having confirmed earthing, polarity, IR, and joined two circuits together (which were "somehow" linked) I restored power to the circuit(s).... and got a shock off the plastic bit of the switch.
- Voltage MET to pattress screws: <10V
- Voltage MET to the plastic bit of the switch: ~ 34V
- landing light glowing dimly
Ah! So downstairs permanent L is tracking across the 2G switch to the upstairs switched L. Gotcha.
Power off, chuck the 2G switch in the bin. New 2G plastic switch...:
- IR upstairs L to downstairs L: now >10MΩ
- Back to 2 separate circuits
- No more tingly tingly, landing light now turns properly off.
So yes, shock off a plastic switch is apparently a thing. Marvellous.