Question: I have a 30 mA sensitivity differential switch which cuts each time I lift the power switch even if the circuit breakers for the sockets and the lighting are off (even if all the circuit breakers on the panel are off).

I know that the differential switch cuts off if there is a current leak, but all the circuit breakers which supply the sub-circuits of the house are cut previously, I have searched a lot to solve this problem but the differential switch remains tripped, I replaced the differential switch but the problem is still happening.

Any idea why this problem still happening?

[![enter image description here](https://i.stack.imgur.com/d5LwZ.jpg)](https://i.stack.imgur.com/d5LwZ.jpg)

Answer: 
As usual, DrSparks beat me to it :)

But yeah, what's going on is the differential device (RCD or GFCI as we call it) is monitoring the current on both hot and neutral, and comparing them. They should be equal. If they're not equal, current is going somewhere it should not.

Your circuit breakers are single-pole. They switch hot, but they do not switch neutral. See the flaw in your testing? You are disconnecting the hot wires, but not the neutral wires. They are still in-circuit.

So what is going on?

First, we can cross off (eliminate) current going from protected hot to anywhere, since all the breakers are off. That leaves current going from protected neutral to anywhere else.

We would guess the current is moving to earth - but it could as easily be to any unprotectetd wiring, another apartment's load, or commons space loads.

#### Possibility 1: Poached neutral. A hot *not fed from this panel* is using your neutral.

Electrical codes requires every neutral be partner to a hot wire\*, and only serve loads served by that hot wire. RCD/GFCI keeps you honest. But before those, people were sloppy, and would attach any load to the most convenient neutral. (bad for other reasons). You find out about this when you try to add GFCI/RCD protection: the device trips instantly, and you're forced into a "bug hunt".

*However, in your case, all your circuit breakers are off, so this would have to be a circuit not served from this panel. Are you in a building with other panels or services?*

#### Possibility 2: Leakage from your neutral to earth

I say that because your diagram shows a [TT type](https://en.wikipedia.org/wiki/Earthing_system#TT_network) earthing arrangement. With TT, you have a local earthing rod attached to your earth wiring... but *you do NOT bond it in your service panel to utility's neutral*. You are placing blind faith in the energy supplier to have the neutral bonded to earth before you receive it.

As such, there will inevitably be a (small) voltage difference between the power company's neutral and your locally derived earth. That difference means that neutral-ground leakage will result in current flow, which will trip the RCD.
If you have a neutral ground fault somewhere, having the sub CBs off will not prevent the RCCB from tripping. You probably have a neutral ground fault somewhere.