Why is a cable live when the CB is tripped?

Al Brum · Feb 24, 2020

Hi,
Forgive me if it's a dumb question, I'm a qualified aircraft electrician but not trained in domestic lighting and want to be sure this is ok.

I am replacing a light fitting on the top floor of a town house (12 years old). I have tripped the two CBs at the fuse box marked downstairs light and upstairs lights (there are no other marked lighting CBs). Luckily I decided to check that all was safe with a meter because the red cable is still live.

As I type the washing machine is running so I haven't tried tripping the main fuse to see if that renders it safe but I assume it would but is the situation normal? Is it even legal?

Andy78 · Feb 24, 2020

The light could be supplied from another circuit or the reading you are getting may not be reliable. what sort of meter are you using and between which terminals ? What are the readings ?

Strima · Feb 24, 2020

As above, what are you testing for voltage with?

Al Brum · Feb 24, 2020

Andy78 said:
The light could be supplied from another circuit or the reading you are getting may not be reliable. what sort of meter are you using and between which terminals ? What are the readings ?

Ha Ha, I'm a twit! Thanks to your questions I put aside the single pole tester and went and got my multimeter, the voltage is only 2.1 v AC measured live to earth and live to neutral. I double checked the other tester and realised I was using it incorrectly bu using both probes - it only gives a straight yes/no without enough detail in terms of voltage.
Thankyou for taking the time to read and answer my question, it's much appreciated.