The invention provides an external switch, an electric energy meter and a modular metering box. The external switch, the electric energy meter and the modular metering box are formed by clamping a plurality of module units with the same shape, wherein one module unit is an electric operating mechanism and is arranged at the end part, the remaining module units in which phase poles are arranged insequence and close to the electric operating mechanism, each module unit is square, and a boss is arranged on one side surface, that is to say, one side surface of the module unit is formed by a platform and the boss. The advantages are that the external switch, the electric energy meter and the modular metering box are more beautiful in appearance, greatly reduce the volume and save the space; and the problem that household appliances of users are burnt out due to unbalanced three-phase voltage caused by the fact that the contact resistance of a N pole is increased due to abnormal disconnection of the N pole of a traditional neutral phase or the poor contact although the N pole of the traditional neutral phase is abnormally disconnected is avoided.