3 X single phase showers

[David Rann]

Haha i like it. So it okay to do or not

 

[Deleted member 26818]

If, you’ve stopped posting for a bit, I’ll try to explain.
25mm2 is over sized for 100A to allow for imbalances.
The outgoing circuits from the 3 phase board may all be single phase, 3phase or a mixture of both.
The conductors for each outgoing circuit should be sized appropriately.
When the neutral current from phase L1 gets back to the board, it can now use the L2 neutral conductor to flow to the L2 phase, and the neutral current from the L2 phase can use the L3 neutral conductor to flow to the L3 phase, etc.

So once the neutral currents get back to a single point, they can then start to balance themselves out.

In the OP’s situation, there is a very good chance that the 3 showers will not be used at the same time.
However there is a chance that 2 will be used at the same time.
If only 1 or 2 are used, the neutral currents will not be able to balance out.
If all 3 are used at the same time, they will balance out.
As such you need to size the neutral conductor to handle up to 2 lots of current.

 

[David Rann]

Thanks spindon. So if you have two showers then you got 64amp flowing down the neutral but if you put the third on then it cancels it out?

 

[Deleted member 26818]

Thanks spindon. So if you have two showers then you got 64amp flowing down the neutral but if you put the third on then it cancels it out?

Yes.

 

[David Rann]

Okay thanks so the cable needs to be able to handle 64 amp then.

 

[Deleted member 26818]

Okay thanks so the cable needs to be able to handle 64 amp then.

Hence why I suggested 16mm2.

 

[David Rann]

Got ya. Why wouldn't just two phases cancel each other out a bit?

 

[Risteard]

Got ya. Why wouldn't just two phases cancel each other out a bit?

They will. You will draw less than 32A but still nowhere near 0A.

 

[David Rann]

Okay two conflicting views here.....one says you double it to 64amp and one says it brings it doen

 

[Wilko]

Picking up the big hint from @westward10 - I had a go at a phasor diagram. If phase 1 shower is on, I get 30A (say) on the distribution circuit N. If phase 1,2 and 3 showers are all on then I get 0A on N, as they all cancel out. No big surprise as it's a balanced 3 phase load at that point. So what about when 2 showers are on? Hint - I was wrong before in #14 - it's my brain that's been flogged .