There is no such thing as an electrical fire extinguisher, because electricity is not a fuel. What is burning is plastic, insulation or something nearby, and the electricity is the ignition source and the hazard to the person holding the extinguisher. The question is therefore which agents have been tested as safe to use near live equipment.
Isolate first if you safely can
Switching off or unplugging removes the shock hazard and often removes the source of heat, which can be the whole answer for a small appliance fire. If isolation is safe and quick, do it before reaching for anything. If it means crossing the fire, or if the switchgear itself is involved, leave it, get out and let the fire service deal with it.
Carbon dioxide is the usual choice
Carbon dioxide leaves no residue, will not conduct back to the user in the way a water jet can, and does not destroy the equipment it is used on. That is why it is the standard extinguisher beside distribution boards, server racks and laboratory equipment. It is not rated class A, so a carbon dioxide extinguisher alone is not adequate provision for a room that also contains paper and furniture.
Dielectrically tested water and foam fire extinguishers
Some water and foam extinguishers are tested against a standard dielectric test and carry a statement on the label about use near live electrical equipment, usually with a minimum distance. That makes them a practical single extinguisher in an office where the realistic fire is a bin or a laptop. Where the label says nothing about it, treat the extinguisher as unsuitable near live equipment.
Dry powder outdoors and in vehicles
ABC powder is electrically safe and is the normal provision for vehicles, forecourts and external plant where residue and visibility matter less. Inside an occupied building it is discouraged for the same reasons as always: a discharge blinds the room, irritates the airway and leaves a corrosive residue that will finish off any electronics the fire did not.
What type of fire extinguisher is used for electrical equipment
Carbon dioxide is the standard answer, and the reason is what it leaves behind, which is nothing: no residue on the equipment, no conductive path, no cooling of a live conductor. Dry powder also works on live equipment and is kept for outdoor and vehicle risks because indoors it destroys visibility and everything it lands on. Water and foam are not suitable as a general rule, with one important exception: certain water mist and foam extinguishers are dielectrically tested and labelled as safe near live equipment up to a stated voltage at a stated distance, and those labels mean what they say. What matters more than the agent is the sequence: isolate the supply if it is safe to do so, because an electrical fire with the power still on is a fire that keeps being re ignited, and once the power is off the fire is whatever is actually burning, usually plastics and cable, which is a class A fire for a water or foam unit.
Questions people ask about fire extinguishers for electrical fires
What extinguisher would you use on an electrical fire?
Carbon dioxide is the usual answer. Some water and foam extinguishers are dielectrically tested and say so on the label. Powder is electrically safe but discouraged indoors.
Is there an electrical fire class?
No. The UK classes run A, B, C, D and F with no class E, because electricity is an ignition source rather than a fuel. Extinguishers are instead tested for safe use near live equipment.
Should I switch the power off first?
Yes, if it is safe and quick and does not mean crossing the fire. Isolation removes the shock hazard and frequently removes the heat source as well.
What type of fire extinguisher is used for electrical fires?
Carbon dioxide, in almost every case, because it leaves no residue on the equipment and does not conduct back up the jet. Dielectrically tested water and foam units exist and are marked with the test voltage and a minimum distance. The first move is still to isolate the supply where that can be done safely, because once the power is off the fire is whatever the equipment is made of rather than an electrical fire.
Is an electrical extinguisher a type of its own?
No, and that is the useful thing to know. There is no electrical class and therefore no extinguisher made only for electricity: what the label tells you is whether the unit has been tested as safe to use near live equipment and at what voltage and distance. Carbon dioxide is the usual answer, dielectrically tested water and foam units carry the test on the label, and once the supply is off the fire is whatever the equipment is made of.