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Combination 230V and 400V circuits

Q. What happens when we have a three phase consumer main and a single phase final sub circuit?

A. When there are a combination of voltages for voltage drop calculation, the calculated voltage drop must be a of one designated voltage.

e.g. consumer mains are 400V and final sub circuit is 230V, we must calculate the consumer mains voltage drop in 230V in order to obtain the total voltage drop.



The consumer mains for the example 2 were 16mm V90 building wires installed in a conduit. The length is 18 meters and the maximum demand for the house is 48 amps. This time we will make the mains 400V.

Vd = 18 x 48 x 2.55 / 1000 = 2.2V (@ 400V)

Vd = 18 x 48 x (2.55 x 1.155) / 1000 = 2.5V (@ 230V)

Two calculations are required to obtain the single and three phase voltage drop values. By calculating both the 230V and 400V voltage drop figures, it will make your final sub circuits and consumer mains easier to add together. Once you have the final sub circuit voltage drop value, it can be added to the relevant value from the consumer mains.

230V final sub-circuit has a voltage drop of 8.5V. Calculate the total voltage drop 2.5V + 8.5V = 11V.

400V final sub-circuit has a voltage drop of 6.8V. Calculate the total voltage drop 2.2V + 6.8V = 9V.



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