Discuss 3 X single phase showers in the UK Electrical Forum area at ElectriciansForums.net
Crikey, it's a long time since I saw so much gibberish condensed into one thread. Reminds me of a nursery rhyme;
Up and down the single phase
In and out of the neutral
That's the way the current goes
Pop! goes the cable.
The neutral current will never exceed the highest line current provided the loads have either unity power factor (as in this case, with resistive heating in the showers), or a non-unity power factor caused by phase displacement only, similar on all phases. In practice, with a mixed load it is very unlikely that the neutral current will ever reach the circuit rated current.
The neutral current can easily exceed the actual line current with phase-angle controlled loads such as dimmed tungsten lighting. The waveform distortion introduces a third-harmonic component which adds in the neutral rather than cancelling. Also any assymmetry, such as half-wave rectification, can produce additive harmonics. If the harmonic distortion is severe, and can take place when the line currents are at maximum, then the neutral conductor may need to be larger than the lines.
So in reality the current in the neutral will be no more than 1.7 x each individual load.
Sorry mine on the Stun settingPhasor diagram anyone.
Knew there was a reason you are in the history books!A shower passes a current of Iphase.
There are 3 phase currents I1, I2 and I3
Taking I1 as reference at 0deg, the I2 is =120 phase angle and I3 is 240deg (or -120deg)
Assume two showers on using I2 and I3, then In is I2 + I3 =
Iphase(cos120 +jsin120) + Iphase (cos-120 +jsin-120) =
Iphase (-0.5 + j0.58) + Iphase(-0.5 -j0.58)=
Ip (-0.5 + j0.58 -0.5 -j0.58) = -Iphase = -7000/240.
If you now add in a switched on I1 fed shower In = I1 + I2 + I3 =
Iphase-Iphase = 0
So, one shower magnitude of In = 7000/240A
Two showers magnitude of In = 7000/240A (but in anti-phase to the current the third off shower would pass).
Three showers In = 0A
Thus In is 7000/240 A for one or two showers or 0A fro three showers.
No need for N csa to be larger than line csa.
Reply to 3 X single phase showers in the UK Electrical Forum area at ElectriciansForums.net
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