A four-wires cable runs into an apartment building to supply it with three-phase 380/220V alternating current. Each apartment is connected to one phase, different apartments are connected to different phases with interleaving so that phases are hopefully loaded equally.
Now it turns out that voltage between phase 1 and the neutral is something like 215 volts and the voltage between the other two phases and the neutral is about 203 volts each.
One of the tenants is connected to a phase which is 203 volts relative to the neutral and has problems with appliances malfunctioning because of undervoltage. He calls a serviceman and the serviceman claims the substation transformer feeds such voltages and the only thing he can do is to disconnect the tenant from his phase and connect him to the phase with 215 volts.
What causes such unequal voltages? Is it unequal load on different phases or anything else? Also has the serviceman done the right thing or did he just put extra load on the higher voltage phase and induce risk of distribution failure?