Fuses blow when I put phase and ground wires in contact even when light switch is turned off

[daz01FR]

This is the specific answer to the original question. It suggests that your MCB is single-pole (some European installations use SPSN or DP MCBs) and only disconnects the line. When the short occurs, there is a path through any other loads for a small current driven by a small difference in voltage between neutral and earth, tripping the RCD. That voltage is too low to be detected with the handheld tester.

What was confusing was your comment that 'fuses blow when...' Normally we wouldn't use that description for an RCD trip because the MCB is equivalent to a fuse, not the RCD, and any short that trips an MCB tends to create a bang!

Sorry for the confusion.
Does the RCD trip because it detects a slight current going to the ground? because it says 63 Amps on it.

 

[Lucien Nunes]

RCDs used in the UK for additional protection trip at a level between 0.015 and 0.03A of current imbalance. Yours may be different according to the purpose for which it has been installed, although the trip current will be clearly marked on it as IΔn (I-Delta-n, the differential current). The 63A refers to the maximum load it is rated to handle and has no relationship with the tripping sensitivity

 

[daz01FR]

There's no 'culprit', the behaviour is quite normal. It might be the power factor correction capacitor in it that is providing the path from switched line to neutral.

The only thing wrong in the present equation is using that nasty pen thingy to prove dead.

If a capacitor discharges through me when i change a bulb in the bathroom I assume it could be dangerous. Is this normal? Because I really always just turn the switch off before replacing a bulb. Have I been playing with my life all that time? It says 63 Amps on the RCD.

 

[Lucien Nunes]

Capacitors in light fittings store very little energy and are normally designed self-discharge within seconds, even if they happen to be charged at the moment you open the switch. There might not even be one, especially if it is a small light. I was merely giving an example of a possible path for the trip current based on the little information I had about your bathroom!

 

[daz01FR]

RCDs used in the UK for additional protection trip at a level between 0.015 and 0.03A of current imbalance. Yours may be different according to the purpose for which it has been installed, although the trip current will be clearly marked on it as IΔn (I-Delta-n, the differential current). The 63A refers to the maximum load it is rated to handle and has no relationship with the tripping sensitivity

Okay I see it also says 30 mA in smaller type. I get that there's no danger then. I'm going to test with my tongue.
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Thank you all for the helpful replies. I guess I was just scared for nothing.

 

[Strima]

I'm going to test with my tongue.

I hope this is a joke.

 

[telectrix]

I hope this is a joke.

course it is. he meant a wet finger.

 

[Strima]

course it is. he meant a wet finger.

That's OK then.

 

[daz01FR]

I hope this is a joke.

It was, don't worry.

 

[Strima]

It was, don't worry.

Had to ask, someone out there would try it.