What to do if you have an electrical power failure
Electricity is off
Some or all of the electrical circuits in the house have stopped working.
Sockets or lights have stopped working.
If all of your power is off check neighbours and/or street lights. If these are off then there has been a supply failure, in which case patience is a virtue!
If not access the fuse box or consumer unit and read on.
What to look for
In many house-fault situations one or more RCDs will be fitted and one has tripped. If you have a modern consumer unit it will have one or two RCDs, that's the switches with an adjoining yellow test button - sometimes the buttons are a different colour. MCBs replace old style fuses so there is one for each circuit. Hopefully your board will be marked up to tell you what each circuit is. Don't worry if this is not the case.
In all cases up is on and down is off.
The red switch is the main on/off switch - this should be up. It can't 'trip' itself, it can only be turned on or off manually.
Identify if one of the RCDs or MCBs has tripped i.e. is down. The chances are an RCD has tripped.
Firstly turn off (down) all the associated MCBs. Now reset it by pushing it up. In some cases you have to push down first and then up.
If the RCD resets then push up the associated MCBs one by one.
If everything is working then the chances are you just have a blown light bulb. Check all bulbs and replace as necessary. If you were trying to use an appliance when the power tripped then there's a good possibility that the appliance is the cause of the problem. Unplug it and put it to one side. If it's a toaster or kettle the bin is probably the next stop for it. If it's a washing machine, dryer or dish washer then check the appliances service guide in the instruction book or book a repair.
If the RCD won't reset then there is probably a fault on the circuit. Most faults are caused by appliances or circuits that supply something wet or that can get wet e.g. outside lights, garden circuits or central heating. Unplug (not just switch off) everything you can by pulling out plugs and in the case of items such as central heating turning off the isolating switch, typically a switch with a built in fuse. If the RCD will now reset plug items back in one by until it trips again - now you will know where the fault is. If you can't reset an RCD with all the MCBs off (down) and all appliances unplugged then it's time to get help.
If an MCB only has tripped then there is a fault on that circuit. Identify what the circuit is. If it feeds power sockets then unplug all appliances before resetting the MCB. Then plug them back in one by one until it trips again. Then you will know where the problem is. If the MCB feeds lights then turn them all off before resetting and try them one by one. The chances are a bulb has blown.
There are a few variations on the above theme. Some older and overhead supply installations will have a form of incoming RCD, sometimes in a separate unit. Some installations will have an integrated RCD and MCB for several circuits. The same principles apply in these cases.
Finally please remember not to touch anything that could be live. If something smells or looks burnt then do not use it. Don't take anything apart unless you are qualified to do so. If you think something is dangerous turn it off or turn off all power. Be safe!