<I'm posting this already fixed (as I was writing I realised the problem) but hopefully of some use / interest to others having written it!>
I have known I had some strange things going on with my downstairs lighting circuit for a while now, having touched the switch retaining screws in my lounge and had little shocks... I thought it was just earthing static to start with, but one day I decided to check against my radiator (as an alternative earth) and found that I could measure 60v AC difference between the two supposed earths. I ran this past an electrician at one point and was advised to ignore it because it could be anywhere... It seems to be worse though - our lounge LED lights are now on all the time (dimly)! I retested and we are now up to 72v AC... I could use some advice on where to start with this!
I worry it isn't actually related to the circuit - even when turned off, there is a definite measurable 3.8v AC between the light circuit earth and the radiator earth (which seem to be pretty close to the plugs circuit earth). So I figure the trickle of voltage I can still measure is coming from some other origin, and turning off all the other circuits in turn just gradually reduces the 3.8v AC little by little. So it must be the mains box in some way? I had solar installed 7 years ago, and they had to completely redo the mains box (to make the solar a completely separate box with less sensitive master trip) just last year because it was tripping the whole house. Since they did that, we haven't had the house tripping at all really which is also surprising given these voltage leaks...? We have also had an upstairs shower leaking through the ceiling and down the walls, but I'm doubting that the lighting circuit and some other ?mains circuits are likely to be shorting together anywhere other than the mains box... I am thinking I may be answering my own question, but having just had the solar people completely re-wire the mains box for the second time, I'm still struggling to believe thats definitely the problem either....
Addendum - I figured it out... The lighting circuit earth was not connected at all. The voltage we were detecting was just induced by the current flow in the other lines. Now we just need to find where we can actually connect the earth! Unfortunately it looks like whoever built our house has set up the lighting downstairs as a series of simple spurs and none of it has an earth connection at all. The actual connection in the distribution box is perfect, but where it goes from there is anyone's guess... So we may have to route an earth to the ring (plug) mains from one of the light switches... simply bridging from the light switch screws to an adjacent mains plug screw immediately fixes our always on lights and the voltage issues, and this will save us from some major new distribution box wiring and ceiling removal I think!
Until 1966 there was no requirement for an earth on the lights, and the regulations are not retrospective, so there is nothing forcing people to upgrade.
In 2008 the rules changed for the use of RCD's, until then only required for outside, but in 2008 it was decided having earthed items in the bathroom could introduce danger as well as removing it, so as long as you have 30 mA RCD fitted the requirements for bonding a bathroom were removed.
This is clearly either/or, you can't remove the bonding unless 30 mA RCD fitted.
As EV and Solar panels came out there was also a change, it was found DC can freeze a RCD and stop it working, we have 5 types. Type S was delayed and no longer used. Type AC is for AC only, and should not be used with solar panels or EV charge points. Type A will still work with a 6 mA DC current, and there are 6 mA detection units which can auto disconnect the supply if over 6 mA DC detected. Type F is for high frequency, not sure where required. Type B is able to handle DC.
You can't at the moment buy a single width type B RCBO (that's a MCB and RCD combined) so the use of the 6 mA detection device allowing the use of type A is the most common method. Also a type B RCD will likely not be rated 100 amp, and cost around £250 each, so rather expensive.
Unfortunately there is also a type B MCB, so with a RCBO you can have curve B type AC. I got caught out that way.
The sign for type A [attachment=0]Type A.png[/attachment] type AC only has sine wave, not the line with bumps, and you should also have a warning label [attachment=1]temp-label.jpg[/attachment] if there is no earth on the lights.
You can get plastic switches with little plastic bungs so you can't touch the 3.5 mm screws, there are also plastic screws.
Lack or earths on lights is now causing a problem, it says "A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point." the suspended bit means MR16 lamps if converted from G5.3 to GU10 need an earth, but when 12 volt SELV was used (separated extra low voltage) with G5.3 having an earth would break the rules, so often there is no earth wire. But to use LED 12 volt you need a heavy expensive toroidal transformer, so cheaper to more to low voltage (50 - 1000 volt AC is low voltage).
It seems unlikely a 30 mA RCD will not trip when you measure 70 volt, so seems likely not a 30 mA type A [attachment=0]Type A.png[/attachment] clearly the solar panel installers should know this, but there are some cow boys around.
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