The current consumed by the electric device depends on its power and also on power supply tension. The minimum section of the wires used for giving on loading of supply voltage is defined by consumed current.
Instruction
1. Transfer basic data to the units of measure used in the SI system: tension - in volts, power - in watts. If eats direct current loading, just divide power into tension, and you learn the current consumed by it expressed in amperes.
2. Alternating voltage has two values: acting and amplitude. On power supplies the first of them is usually specified. Communication between these values depends on a form of tension and on quantity of phases. If tension sinusoidal, and network single-phase, increase the operating value by a square root from two, and you receive amplitude. To the contrary, having divided amplitude value into the same size, you receive operating. Consider that power is defined by the operating values of tension and current. If it is required to learn amplitude value of the last, the way in the beginning stated above acting, and then increase it by a square root from two. Count the current on which the bringing wires and safety locks have to be calculated also proceeding from the operating value of this size.
3. The loadings intended for food from three-phase network project so that the currents consumed by them on all three phases were relatives. The small difference of currents in phase wires caused, in particular, by existence not only power chains, but also control circuits can usually be neglected. When calculating the current consumed by three-phase loading you divide power into tension operating between any two phase wires, but not between any of them and a zero wire. To receive the first of this tension, increase the second by a square root from three. Divide total current of all three phases into three, and you learn current in each of phase wires.
4. Besides active loadings, there are reactive - inductive and capacitive. Besides power consumption, they are characterized by one more parameter - power factor. Usually it is specified on the case of the device. To learn reactive power, increase active by this coefficient. Then, having divided active power into tension, calculate an active component of current, and having divided reactive power into the same tension - a reactive component of current. Having put both components together, consider result when choosing current of operation of the safety lock and also section of the bringing wires.