A system for calculating an electric quantity relative to an electrical installation comprising a primary electrical conductor (34, 36, 38, 39) and several secondary electrical conductors (42A, 44A, 46A, 48A,..., 42N, 44N, 46N, 48N) electrically connected to the primary electrical conductor (34, 36, 38, 39), the calculating system comprising: - a first module including a wireless transmitter, - a plurality of second modules (62A, 62B, 62C), each including a wireless transceiver (86A, 86B, 86C) and a current sensor (83A, 83B, 83C) capable of measuring the intensity of a current circulating in at least a corresponding conductor from among the primary and secondary electrical conductors, the first module including transmission means (70, 72, 74) for transmitting a first time synchronization message to each second module (62A, 62B, 62C), each second module (62A, 62B, 62C) being capable of measuring at least one intensity value using its current sensor upon reception of the first message and including first means (84A, 86A, 88A; 84B, 86B, 88B; 84C, 86C, 88C) for receiving the first message and second means (84A, 88A; 84B, 88B; 84C, 88C) for transmitting a second message (M2A, M2B, M2C), containing said at least one intensity value (IA1, IA2, IA3; IB1, IB2, IB3; IC1, IC2, IC3) measured by the corresponding current sensor (83A, 83B, 83C) upon reception of the first message, to a third module, the intensity values (IA1, IA2, IA3; IB1, IB2, IB3; IC1, IC2, IC3) being measured quasi-simultaneously by the various current sensors (83A, 83B, 83C), that is to say with a synchronization margin of error smaller than 10 μs, and the calculating system comprising the third module, and the third module includes a wireless receiver, second means (102, 104) for receiving second messages (M2A, M2B, M2C), the third module further comprising a calculating unit for calculating the electric quantity from intensity values (IA1, IA2, IA3, IB1, IB2, IB3, IC1, IC2, IC3) measured quasi-simultaneously and received via said second messages (M2A, M2B, M2C), characterized in that each second module (62A, 62B, 62C) is capable of transmitting the second message (M2A, M2B, M2C) corresponding to a predetermined transmission order to the third module, according to an order number attributed to each second module (62A, 62B, 62C), each second module (62A, 62B, 62C) receiving, during an initializing step, a third message specific to each second module (62A, 62B, 62C) and comprising the order number. - a first module including a wireless transmitter, - a plurality of second modules (62A, 62B, 62C), each including a wireless transceiver (86A, 86B, 86C) and a current sensor (83A, 83B, 83C) capable of measuring the intensity of a current circulating in at least a corresponding conductor from among the primary and secondary electrical conductors, the first module including transmission means (70, 72, 74) for transmitting a first time synchronization message to each second module (62A, 62B, 62C), each second module (62A, 62B, 62C) being capable of measuring at least one intensity value using its current sensor upon reception of the first message and including first means (84A, 86A, 88A; 84B, 86B, 88B; 84C, 86C, 88C) for receiving the first message and second means (84A, 88A; 84B, 88B; 84C, 88C) for transmitting a second message (M2A, M2B, M2C), containing said at least one intensity value (IA1, IA2, IA3; IB1, IB2, IB3; IC1, IC2, IC3) measured by the corresponding current sensor (83A, 83B, 83C) upon reception of the first message, to a third module, the intensity values (IA1, IA2, IA3; IB1, IB2, IB3; IC1, IC2, IC3) being measured quasi-simultaneously by the various current sensors (83A, 83B, 83C), that is to say with a synchronization margin of error smaller than 10 μs, and the calculating system comprising the third module, and the third module includes a wireless receiver, second means (102, 104) for receiving second messages (M2A, M2B, M2C), the third module further comprising a calculating unit for calculating the electric quantity from intensity values (IA1, IA2, IA3, IB1, IB2, IB3, IC1, IC2, IC3) measured quasi-simultaneously and received via said second messages (M2A, M2B, M2C), characterized in that each second module (62A, 62B, 62C) is capable of transmitting the second message (M2A, M2B, M2C) corresponding to a predetermined transmission order to the third module, according to an order number attributed to each second module (62A, 62B, 62C), each second module (62A, 62B, 62C) receiving, during an initializing step, a third message specific to each second module (62A, 62B, 62C) and comprising the order number.