Thinking in traffic

[Dylboy]

Hello

So was sitting in traffic as one does in laodshedding and had a thought...

The neutral conductor shall at least be the same CSA as the phase conductor.

Now the above is great for single phase but then with 3 phase we now have 3 current carrying conductors.

So let's say all wired in 16mm cable the phases and Neutral. On a 60Amp triple pole CB.

But if each phase had to pull 50Amps that neutral won't be able to carry 150Amps !

So is this just due to domestic homes and diversity being used or am I missing something ?

I get it there where 3 single phase machine always running at 50Amps then the Neutral is sized accordingly i.e for 150Amps (well more but for sake of conversation and maths let's stick with easy numbers)



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[GCE]

If each phase drew 50 amps it would be balanced and the neutral would not carry any current , in the perfect world without losses, harmonics etc .

We work on a star point config , so a vector system - if phases are imbalanced then the neutral will carry the difference to earth

[Dylboy]

Yes sorry I meant that it's not a 3 phase load, rather 3 seperate single phase loads.

So red phase does geyser
Yellow does oven
Blue does microwave

Above is just examples as they don't pull 50A but it's just some theory im working with.

I guess if you say a 3 phase supply but the

Red cottage A.
yellow cottage B.
Blue cottage C.

Then if they all use the ovens and kettle at the same time that Neutral would have to carry all that but it's normally always sizes same as the phase

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[GCE]

Yes sorry I meant that it's not a 3 phase load, rather 3 seperate single phase loads.

So red phase does geyser
Yellow does oven
Blue does microwave

Above is just examples as they don't pull 50A but it's just some theory im working with.

I guess if you say a 3 phase supply but the

Red cottage A.
yellow cottage B.
Blue cottage C.

Then if they all use the ovens and kettle at the same time that Neutral would have to carry all that but it's normally always sizes same as the phase

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Same story - There is still a point were all 3 come together

[Dylboy]

Ahhh interesting... What about the time it takes for the Neautral to take to earth would it not carry more current than the cable ?


I rememeber something I think from Kirchof about a node having no voltage or amps, can't remember but that may then be why there is no excess current in the Neautral or all the phases because they come to a node...

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[Dylboy]

Thinking now they also 120degrees out so the Neautral will carry let's say the Red phase first then Yellow then the Blue, so it does not actually add up on the Neautral.



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