Your fuse/mains board Explained

The diagram refers to the model of mains board which we usually fit, although it can also apply to other models. All circuit descriptions are examples and you may not have as many or may even have more circuits in your mains board than pictured. Please note for clarity the diagram only shows the part of the split load mains board with the trips inside, not the whole unit. Open the cream or clear flap in the lower two thirds of the unit to reveal these trips.

All information contained within this page is for guidance only, Allsuns Electrical Limited can not accept responsibility for misuse or misunderstanding of this information. If you feel you need further advice please do not attempt anything and contact us on 01283 732323 / 01332 605560 / 07798 575722 or email

The main switch marked "M" is always turned on unless maintenance is being carried out and total isolation (switching off) of the board is required. When the main switch "M" is turned to the off position all circuits within the mains board will be isolated (switched off). If one of the MCBs marked "B or D" trips try and reset it by pushing the switch up, if it trips again check that everything is unplugged from the circuit that the trip controls and then try again, if it still trips or it is not a socket circuit and is something else I.e. Shower seek a qualified electricians advice. It is quite normal for a light bulb blowing to cause the trip to activate, if this occurs simply reset the trip and find then replace the blown light bulb.

If the RCD marked "A" is turned off this will isolate (turn off) the circuits from the RCD "A" onwards marked by the red arrow up to the next RCD in the board marked C, these circuits are normally socket and lighting circuits.

If the RCD marked "C " is turned off this will isolate (turn off) the circuits from the RCD "C" onwards marked by the yellow arrow, these circuits are normally socket and lighting circuits.

If one of the RCDs (marked A or C) in the board trips it may indicate a fault either with an appliance or with the wiring, first try resetting the tripped RCD, if it trips again within a short period or immediately then there is possibly a fault, the next way to identify the possible fault is to switch off all of the MCBs after the RCD that has tripped, for the RCD A this is the MCBs marked with the red arrow, for the RCD C this is the MCBs marked with a yellow arrow. Try to reset the RCD again, if it continues to trip then seek a qualified electricians advice, if it remains on then switch on each MCB one by one, when the RCD trips take a note of what MCB caused it to trip again, if it is a socket circuit unplug all of your appliances and try the same procedure again, if the RCD resets with no appliances plugged in and all of the MCBs on, go round plugging in appliances until the RCD trips, the appliance which caused the RCD to trip is to be considered as faulty and should be discarded. If the RCD continues to trip with nothing plugged in to the sockets or the circuit causing it to trip is not marked up as being a socket circuit you should consult a qualified electrician to rectify the fault.

The RCD "A or C" should be tested at regular 3 month intervals by pressing the small button marked "T" or "Test", the unit should trip when this button is pressed, if the unit does not trip please seek a qualified electricians advice. If the unit trips when the button is pressed just reset it by pressing the switch upwards.

If you require assistance at any time please do not hesitate to call us on 01283 732323, 01332 605560 or 07798 575722 for 24hr call out assistance, or visit our website at