Why does my RCD switches trip when a light bulb goes out?

my bad but: i have a several double pole mcbs in a box in my garage does that mean that theyre real rare and i may get lots of money on ebay?
do they onlyprotect the house wiring? just curious as my outside shed/garage is protected by a mcb which in turn in backed up by a rcd?
im guessing that as the installation is quite old that it is an early 16th edition board? and only has the 1 rcd? depending on what type of earthing arrangement you have this rcd may possibly back up the full installation.
i dunno maybe i should go back to making pizzas?

british jobs for british workers
March 2010

There are two types of circuit breaker - actually there's more than two types but no matter.

An RCD usually controls all the power and lighting circuits. It measures the current difference between Live & Neutral and if it exceeds 30mA (usually 30mA) it will trip - the assumption being that the "missing" current may be passing through a person - a safety device to prevent electrocution. RCD stands for residual current device and RCDs have two poles - Live & Neutral.

An MCB or miniture circuit breaker has just one pole and limits the current through a particular circuit - downstairs lights or upstairs power etc. Too much current on the circuit and the breaker will trip. They protect the house wiring and prevent wires overheating and catching fire and the house burning down.

When a fillament lamp fails the broken pieces of the fillament sometimes fall across the metal supports of the fillament and cause a brief overcurrent - this causes the MCB to trip.

In my house candle shaped bulbs are the worse culprits for tripping breakers - then regular bulbs that point upwards.

It is not unusual for an MCB to trip when a lamp fails but it is relatively rare for and RCD to trip for a blown bulb.

Peccavi
March 2010