Shock from a light switch, no RCD on lights?

the_amazing_raisin

Hi folks,

Earlier today my wife got a shock from one of the light switches when turning the light off

Luckily she's fine, not more than a sore finger and tingling for a while afterwards

We took the light switch apart and everything seems fairly normal. It's a double switch controlling two sets of lights

The live wires all seems solidly in the terminals

The 4 neutrals were all in one terminal block covered in electrical tape, again they all seemed solid

The 4 earth wires were in the same terminal block (different terminal), again all solid. The earth wires from the metal back box goes to the same terminal block and also seems solid in the terminal

No signs of exposed wiring on the live or neutral wires, or scorching or melting on the switch itself. The switch works fine, so evidence of sticking which would imply a short

There were some exposed bits of the earth wires where the sheathing didn't fully cover it. But no sign of damage to the earth wires

Tbh, we're a bit mystified as to what could have gone wrong

We've wrapped the exposed earth wires in electrical tape just to be sure. Also replaced the tape around the terminal block for ten neutral and earth wires, and put some tape in between the two just to add some separation

Also put some tape over the screws on the switch to give some isolation from anything conductive

Anyone got any ideas? Is it advisable to replace the switch or get an electrician to be on the safe side?

We also noticed there's no RCD on the lighting circuits (except bathroom lights). Is that normal? I thought RCDs were required on all circuits, we just have them on sockets and the appliances?

kirk.

You should replace the switch anyhow , damp is the usual reason for shocks at switches

Make sure the screws / backbox are not live for any reason, use a phase tester if you have to

RCDs on lighting circuits except bathrooms is relatively new

meercat

https://www.boards.ie/discussion/2058288727/shock-from-a-light-switch-no-rcd-on-lights

Is this a metal switch

you may have an induced voltage if the earthing isn’t correctly connected. You could still get a shock off the retention screws. Need to get it checked by a competent electrician. As Kirk has already said,rcd protection on all lighting circuits is a relatively new regulation.

the_amazing_raisin

https://www.boards.ie/discussion/comment/120371018#Comment_120371018

Standard plastic household switch, with a metal back box

I'm guessing the shock must have come through the screws since they're connected to the earth wires

I think you're right, get a sparks out to checo the earthing. Couldn't see anything in the switch that looked like live or neutral could be touching the earth wires, but I guess there could be a fault elsewhere which isn't being earthed properly?

House was built in 2017, so I guess the RCD requirements must be very new

Is it possible to swap out an existing MCB for an RCD? I've seen some slim ones that only take up a single space in the CU, like an MCB

the_amazing_raisin

https://www.boards.ie/discussion/comment/120370961#Comment_120370961

Her hands were dry, but I guess it's possible some water could have gotten into the switch earlier

Might just get the sparks out to be safe and look at replacing the MCBs with RCDs, my main worry is one of the kids getting a zap off the switch

kirk.

Why do you say water is a possibility

It's mostly damp ive seen with plastic switches

Unless it's a shock off a screw- unlikely or a metal switch with earthing issue

the_amazing_raisin

https://www.boards.ie/discussion/comment/120371156#Comment_120371156

Kids tend not to dry their hands properly when coming out of the bathroom, which is right beside the kitchen where the dodgy switch is

kirk.

That's them there off another thread

They're 1P+N rcbos , the neutral isn't switched

They've 2 flyleads, N in and FE( the white leads at the top)

The Continental Op

I've also seen what I call "tracking" on mains light switches. What I believe happens is that once damp gets in you can get an arcing between the live and any earth and from then on a "track" is formed that can conduct electricity on the surface of the plastic. Even if it dries out and is perfectly dry you can still get a shock from the path that has formed.

This is an effect you see far more on higher voltage equipment, car ignition systems can suffer from it and in the old days of points and distributors distributors often suffered from it. However I've seen and felt the effect on a couple of kitchen and bathroom lights as well as plugs and sockets used outside. Everything looks fine but you get a shock from the switch or the plug. If that is the problem normally close examination will show a dark carbonised line of the tracking somewhere on the plastic. Most recently I had this on a plug top that was left plugged in outside in a very damp shed. I couldn't see what was the problem until I opened up the plug top and there was a black line that went all the way around the join between the two halves so no way could you pull the plug out when it was live without getting a shock (and the RCD tripping).

kirk.

https://www.boards.ie/discussion/comment/120371264#Comment_120371264

Got a rattle off a fuseholder at the fuseboards once or twice

Seems to be just gunk on them

Never went near one afterwards without gloves on

Pataman

Is it possible it was a static shock from her earthed through the switch?

2011

https://www.boards.ie/discussion/2058288727/shock-from-a-light-switch-no-rcd-on-lights

A few points:

1) I doubt that your wife got a shock because there was no RCD protection on the circuit. Many of use have received electric shocks from circuits that have RCD protection! She got a shock because she touched something that was at a higher potential than something else that she was in contact with (probably the floor).

2) From what you have said it would seem that you have not verified that the switchbox is earthed. Just because earth cables are connected to it does not mean it is earthed. I would use a wander lead and suitable Ohm meter to measure the resistance between the backbox and the main earth terminal. I suspect that you will find this resistance to be unacceptably high. If the resistance was low this tells its own story i.e. your wife did not get a sock from the screws.

3) Also I would carry out an earth fault loop impedance test at the light switch and ensure that the installation is neutralized.

4) As your wife's hands were dry the most likely reason is that the screws were live. This could be due to a voltage appearing on the earth cable due to an earth fault on a completely different circuit. You could test for this by measuring the voltage between the backbox and a neutral or earth earth point. Do this when all other circuits and appliances are switched on.

the_amazing_raisin

https://www.boards.ie/discussion/comment/120381307#Comment_120381307

It's possible, however she could feel it in her hand an hour later, which seems to indicate she got more than the average static shock

the_amazing_raisin

https://www.boards.ie/discussion/comment/120391610#Comment_120391610

Thanks for that, we've an electrician coming out for some other work so I'll speak to them about performing the checks you mentioned

I agree that there's nothing there to definitely prove the earth wires are connected properly

The switch is working fine for now, we've got the screws covered with electrical tape and we're trying to avoid using those lights just in case

kirk.

It's a stretch to believe the box is live

Assuming the MET isn't live you'd need a couple of issues for the screws to be live and even then you'd have to make contact with them

Never say never though

Antenna

https://www.boards.ie/discussion/comment/120391786#Comment_120391786

That there was still an effect an hour later sounds severe.

Was she earthing herself with the other hand when this happened with the lightswitch ?

In other words the other hand in contact with perhaps a stainless steel sink or metallic (earthed) electrical appliance such as a kettle etc (as you say this switch was in the kitchen).

A mains shock will have a rapid trobbing effect, (the voltage is a sine wave, at 50 cycles a second), whilst a static shock is a sting effect for an instant (rapid discharge)

John.G

Maybe just probing around the switch and screws , even the walls, with a phase tester might tell something.

kirk.

https://www.boards.ie/discussion/comment/120409510#Comment_120409510

Check backbox >> replace switch

Thats a better version of a phase tester below , works with gloves on

https://www.cef.co.uk/catalogue/products/4032841-voltage-tester