Another common issue with electrical systems is the fact that the additional protective devices (RCCB's, RCD's, RCBO's) are not tested properly. I'll briefly describe what they do, why they are so vital in the progress they bring to safety in electrical systems and then show how to test yours in your property (if the techno waffle isn't for you then feel free to skip to this part as from your point of view this is the most important and could be vital to your safety). It is something that is simple to test and doing so regularly will help they stay in better condition so they activate when you need them the most.
What are they?
As defined in BS7671 18th edition :
Residual current device (RCD). Mechanical switching device designed to make, carry and break currents under normal service conditions and to cause the opening of the contacts when the residual current attains a given value under specified conditions.
NOTE 1: A residual current device can be a combination of various separate elements designed to detect and evaluate the residual current and to make and break current.
NOTE 2: RCD includes devices such as RCCB, RCBO, CBR and MRCD.
NOTE 3: MRCD is a modular residual current device.
Residual current operated circuit-breaker with integral overcurrent protection (RCBO). A residual current operated switching device designed to perform the functions of protection against overload and/or short-circuit.
Residual current operated circuit-breaker without integral overcurrent protection (RCCB). A residual current operated switching device not designed to perform the functions of protection against overload and/or short-circuit
Each device gives additional protection under fault conditions to help a circuit disconnect from the supply. They are (in my personal opinion) potential life savers, while the old fuse wires and MCB would disconnect ("trip") due to a short causing an over current these will pick up an imbalance between the live and neutral conductors when an earth leakage is detected.
What do they do?
This is an image of their inner workings, taken from BS7671 on site guide:
In usual conditions the current flowing through live and neutral (L/N) will be almost perfectly balanced and this will have no affect on the Thyroid (the central ring all the conductors are looped around) and no current will flow through the Thyroid. When there is a fault (due to circuit design) a current will also flow to earth through the circuit protective conductors (Earth/E). As an example 10 Amps flowing on Live, 10 Amps flowing on Neutral in usual conditions, if a fault occurs then (for instance) 2 Amps will flow to earth so there will be 12 Amps now flowing "into the circuit" through the 10 Amps L and 2 Amps E but only 10 Amps returning through N (just to keep things simple). This will create a current in the Thyroid and cause it to trip within 300ms for additional protection.
Usual circuit breakers would not have detected this fault and can continue for some time. I have been to call outs where they said they ocasionally get a loud bang in the wall then the sockets go off but they've just got used to it, testing proved there was a short on live-earth which had just been getting worse over time.
Sorry for the waffle but its hard to describe some things in brief terms. Now for the important bit from you.
How to test your RCD/RCBO/RCCB
Because there are mechanical parts in your devices, over time they will seize and may not operate when you need them to. They are ordinarily located inside your consumer unit but some are fitted after the board in order to save costs on a board swap (prolonging the inevitable in my opinion, but that is just my opinion).
Here is a couple images, first is a RCCB and second is an RCBO (I've not got an image of an RCD to hand but I'll update when i do, it looks pretty similar to an RCCB though)
As a word of warning the next bit will disconnect your circuits that it is protection so its advised to turn off any expensive equiptment and unplug. I've performed many of these and haven't had an issue yet but thats not to say you wont. Also it is best practice to turn off MCB's (they look similar to the second pic without a yellow test button) individually before pressing the test button, by pressing the switches to the off (down) position.
Both the devices have a yellow button (some are different colours eg black but it will do the same), this is for manual testing, it is safe to be pressed and it should trip down the switch. The switch can then be reset, reset your MCB's and your good to go for another 6 months. If, when you press the test button, it either doesn't trip the switch (first try operating the switch manually a couple of times then retrying the test button) or it does trip but wont reset, then it would be time to call someone in to get it checked out properly.
Another point to note would be some RCD's dont full go down when they trip (had a few call outs off this one) so it would be worth pulling the switch down and then return up to the on position. The last and most frequent board I had this issue with is pictured below.
