One thing I don't understand is it's said that places with lots of electronic SMPSUs like data centres and that type of thing can have higher currents in the neutral than the phases how is this possible? I can't really understand it hope someone can explain it
only a problem in systms with more than one phase.
in a 3 phase system with 3 similar resistive loads (orr indutive or capacitive, so long as the current waveforms are sinewaves), the 3 currents in the neutral sum more or less to zero.
But if we have anything with a bridge rectifier feeding a capacitor or a battery, the current waveform is far from sinusoidal, but takes the form of no current at all while the mains is lower than that voltage on the capacitor, perhaps until 3/4 of the way up to peak, then a large current for the top bit of the waveform, while the wave is forward biassing the diodes, and then falling back to no current at all once the voltage of the incoming wave is less than the DC again.
3 such waveforms of short duration pulses offset by 1/3 of a cycle do not even overlap in time, let alone cancel, so when each live carries 2 pulses per cycle period, and the neutrral carries 6. = 3 times as much heat.
In reality it is rarely quite as bad as this, as some efforts are made to make the current waveform a bit more sinusoidal ('power factor correction' is not always just about phase shifts, it can be about stretching out short pulses as well)
only a problem in systms with more than one phase.
in a 3 phase system with 3 similar resistive loads (orr indutive or capacitive, so long as the current waveforms are sinewaves), the 3 currents in the neutral sum more or less to zero.
But if we have anything with a bridge rectifier feeding a capacitor or a battery, the current waveform is far from sinusoidal, but takes the form of no current at all while the mains is lower than that voltage on the capacitor, perhaps until 3/4 of the way up to peak, then a large current for the top bit of the waveform, while the wave is forward biassing the diodes, and then falling back to no current at all once the voltage of the incoming wave is less than the DC again.
3 such waveforms of short duration pulses offset by 1/3 of a cycle do not even overlap in time, let alone cancel, so when each live carries 2 pulses per cycle period, and the neutrral carries 6. = 3 times as much heat.
In reality it is rarely quite as bad as this, as some efforts are made to make the current waveform a bit more sinusoidal ('power factor correction' is not always just about phase shifts, it can be about stretching out short pulses as well)
