Post
by ericmark »
Wed Jul 28, 2010 3:24 pm
An RCD detects imbalance. A fuse or overload detects too much current. The devices can be combined and a RCBO has three separate devices.
1) Detects imbalance line to neutral
2) Detects the thermal effect of an overload and will trip before the cables can heat up.
3) Detects short circuit using a magnetic device and the letter in front of the amps says how much current will trip it. For example a B16 MCB will trip at 5 times 16A with magnet trip so will trip at 80A within 0.1 of a second.
There is also a forth as some RCD's will fail to work with imbalance if the volts drop so the active type of RCD will also trip due to volt drop i.e. fail safe.
A RCD plug or socket is normally active type but the one in a consumer unit will normally be passive type. There are also specials that auto reset or give warning that they are reaching the limit at which they trip.
All these devices have a special arrangement inside to reduce arcing to minimum and the only noise is likely to be one click as they fail.
Some trips when the trip only move operating leaver half way so show tripped not turned off. And with some they must be turned off before you can turn them on.
However a buzzing noise would make one expect arcing and likely a lose wire or similar. This should be investigated as lose wires can cause heat and need correcting. And of course a lose wire may touch the wrong thing as it is a turn off all power first before looking job.
As to rcd blow like a fuse 30mamp? No but of course they can become faulty.
However in the UK we use ring mains and one lose wire is unlikely to cause a power failure but can cause overloading so I would want to see proper tests completed to ensure it's not only lose wire.
Main worry must be fire. And it does require knowledge and test equipment to inspect and test so not really a DIY job.
