Isolated circuit showing 400V

[endecotp]

I opened up and checked a plug socket and the ground with the line/neutral the volt and cont tester buzzed and showed 400V!

If you plug something (e.g. a lamp) into the socket, and turn it on, while doing that, what happens?

 

[Cakey101]

Can you show a photo of your CU unit breakers and the incoming mains terminal head to determine what type of earthing system you have. (TNS, TNCS, TT)

I will take a photo tomorrow and report back.

Have you any type of Clamp meter to determine if any current / power is being consumed?

No I haven't got one.

If you plug something (e.g. a lamp) into the socket, and turn it on, while doing that, what happens?

Would this blow say a lamp if there was voltage?

Thanks for the responses.

 

[endecotp]

Would this blow say a lamp if there was voltage?

If there really is 400V present, maybe/yes.
But I think more likely it’s some other effect, and that when you plug the lamp in the voltage will disappear.

 

[Cakey101]

Hello,
Strange today. I checked the voltage of a socket and the 400V reading I was getting before was not present today???
I did get some continuity though with N/L. There was some slight lighting of the tester with G and N/L as you can see from the video.
I don't know if it made any difference, but I isolated the boiler switch (as I did last time due to installing a spur from boiler - old immersion heater switch) and doing the same as above there was a buzz with the continuity light.
Plus when I tested the shower switch something strange happened but I only checked when the switch light was in the on position (realised afterwards).
Even though there was no voltage I checked a lamp and nothing.

First here are some images of the CU etc. (images won't embed)
https://www.dropbox.com/s/q315pqqu947b5hw/2021-01-10 10.54.38.jpg?dl=0
https://www.dropbox.com/s/sx5ckmxeyu95tfl/2021-01-10 10.55.12.jpg?dl=0
https://www.dropbox.com/s/qk1bbm61exr0r9g/2021-01-10 10.55.29.jpg?dl=0
https://www.dropbox.com/s/ll5tl11xi4fd6qo/2021-01-10 10.55.43.jpg?dl=0
https://www.dropbox.com/s/s25zvq3r6m6ahx2/2021-01-10 10.58.25.jpg?dl=0

https://www.dropbox.com/s/b1ezo71qsmnqkcm/2021-01-10 10.59.40.jpg?dl=0

Here are the vids:
CU was isolated along with all MCBs and RCBs
1. socket with boiler switch on
https://www.dropbox.com/s/4acmj8jy1swpxrq/IMG_2962.MOV?dl=0

2. socket with boiler switch off
https://www.dropbox.com/s/8jyng7quulzzuqz/IMG_2971.MOV?dl=0

3. Shower switch boiler switch on
https://www.dropbox.com/s/rxdukuej2zehy4s/IMG_2967.MOV?dl=0

4. Shower switch boiler switch off
https://www.dropbox.com/s/pd3dqxk8kqscch3/IMG_2975.MOV?dl=0

For 3 and 4 why is there that light and buzz?
And for the rest what is happening?
Many thanks.

 

[JohnD]

you can insert pictures into your post using "copy and paste"

 

[333rocky333]

If you actually had 400v present there then you would likely have it throughout the house and you would be witnessing more serious issues, if you really want to do electrical work, my advise is invest in a tester like the Fluke T1000 that you set to the relevant test you are actually doing and also has a digital read out.
I work with people that have them automatic type with leds and often see them lighting up unneccessary, I think the things are tricked into trying to do a continuity test, showing misleading indication, you are likely getting some continuity, both by other things plugged into the circuit or by the Neon indicater on the switch, due to the resistance of them, the tester will not give a positive continuity indication, like you get when you touch the probes together.
Do you have any resisters knocking about, put your meter across them and you will likely see the same as what your seeing.

 

[Cakey101]

Thanks for the response.
I ended up buying the tester I had after watching some YouTube videos from respected electricians like John Ward and one or two others.
I won't be buying the T1000 for one off electrical work though.
I have a resistor somewhere and will try with the meter.
I assume I should bring an electrician in to test the circuits. If fine, I can proceed with the work.