Hi guys. Last year l changed a light fitting for a friend. I isolated the circuit l was working on, which was the first floor lighting circuit, served by a MCB 6A Type B, leaving the ground floor lighting circuit on, which is a separate circuit also MCB 6A Type B.

Both of these circuits are protected by a 30mA RCD.

I noticed that whilst l was changing the fitting, the RCD kept tripping, whenever l touched certain conductors (l can't remember which, as it was last year), even though the circuit was isolated.

I presented this information to my tutor, who told me this wasn't possible if the circuit was isolated.

My question to all sparky's is: Could this have resulted because of a 'borrowed' neutral? I have read about them on HSE Website and would like to know if this is a possiblity with an explanation, if anyone is able. Thanks...  

Quote:


He is correct but the circuit you were working on wasn't isolated as you had only switched off the MCB.

For a circuit to be isolated both live and neutral need to be disconnected.

Thanks for the assistance everyone. Very much appreciated and l dare say that ill be back with another question quite soon...