Isolated circuit showing 400V

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Cakey101

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Hello,
I am a DIYer and in the process of fitting a spur from a socket (and from the ring). Using a voltage and continuity tester I turned off all the MCBs and RCBs plus the main switch in the Consumer Unit.
I opened up and checked a plug socket and the ground with the line/neutral the volt and cont tester buzzed and showed 400V! I also checked the shower on/off switch which was the same - 400V.
They day before I did convert an old immersion switch into a plug socket. It was linked to the boiler and I had to isolate the boiler after there was continuity with the N/L.
Any ideas what happened here? I also tested with the boiler switched on and isolated, with all the CU off and it was the same. The boiler circuit did not show the 400V.
Cheers.
 
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What tester specifically are you using?

What setting is it set to?

Photos would be helpful here.

400V in a domestic property would be very unusual, and if this is actually the case then urgent action would be required.
 
Not conversant with that tester, but some show all the lights when doing a continuity test, the same actual lamps that would indicate a higher voltage like 400volt when doing a voltage check.
The Auto/Test button may do similar.
Touch the probes together and do a continuity test and you should see them light up.
 
Last edited:
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The continuity test - the light indicating continuity turns on and the buzzer sounds.
The auto test button the light goes right up to 690 V.
Cheers.
 
What does it do if you just touch the two probes together and do the test?
 
Touching the two probes together alone - creates a beep/buzzer plus light to indicate continuity.
 
Oh, I did that before. The same thing happens as I explained above.
 
I have a similar Steinel and find it very useful.

But it can't show accurate voltages. I suppose it has zener diodes.

It's possible electronic equipment on the circuit could have odd effects.

Buy yourself a multimeter.

In my house, the precise voltage is usually about 244.
 
But why am I getting any voltage reading with an isolated CU and when not isolated shows 230V?
 
Do you live in a Semi detached House/Bungalow? I've known the odd circuit to be fed accidentally from a Next door neighbour's supply who could be on a different phase!
 
chivers67 said:
Do you live in a Semi detached House/Bungalow? I've known the odd circuit to be fed accidentally from a Next door neighbour's supply who could be on a different phase!
Click to expand...
It's like a modern terrace.
 
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)
 
Cakey101 said:
But why am I getting any voltage reading with an isolated CU and when not isolated shows 230V?
Click to expand...
Well quite simply you shouldn't! You need to make sure there's absolutely no voltage/current leaving your DB. Have you any type of Clamp meter to determine if any current / power is being consumed? This is a strange one.
 
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