On 27/08/2020 20:54, Scott wrote:
On Thu, 27 Aug 2020 20:25:37 +0100, Harry Bloomfield, Esq.
wrote:

Scott brought next idea :
A wholly ignorant question but how does the neutral work? Is it
another earth or is it returned to the substation?

The neutral will be at or around the earth potential, maybe 20v
maximum.

It is there to balance up the differences in the loading of individual
phases. One way to look at it, is a street of houses, where each house
is sequentially on phases 1,2,3 then 1,2,3 and so on all along the
street. Adjacent houses will be across three different phases and if
reasonably balanced loading between the three, there will be little
actual current flowing in the neutral.

Sometimes the sequence can be 1,1, 2,2, 3,3, 1,1 and so on. I share the
same phase with the other half my semi.

Suppliers like a nicely balanced load across the three phases, because
it is more efficient.

Between phases the voltage is 415, between any phase and earth/neutral
it is 240v.

Current will flow from say house 21 on phase 1, to 23 on phase 2, then
to 25 on phase 3 rinse and repeat at 50 hertz, but the neutral acts as
the return linking the three houses. That assumes all three houses are
each consuming the same current. If not, then the neutral has to carry
the return current to a more distant house, to balance itself against.

If you compare the three phases to a three cylinder engine, they are
out of phase with each other by 120 degrees - one phase will be
sucking, one blowing and the last one doing neither.

That over simplifies it, it might seem complex, but the basic idea is
simple once you grasp it.

Thanks. I saw a video that related the phases to a magnet and a
clockface: https://youtu.be/iMn7dq7B1oo

Does this mean the neutral within the flat may not be zero volts?


Neutral will be close to earth potential (it is joined to it
*somewhere*), but may not be exactly. In any given property its carrying
the same load as the live so since it does not have zero resistance it
will have some voltage drop on it. So at point of use it may be rise a
bit away from true earth. (and the live will fall a bit toward it)

PME (TN-C-S) supplies will suffer less from this since the neutral is
separated from the earth at the property, and there are multiple
connections to earth along the way.

(its the main reason that neutral is considered to be a live wire)


--
Cheers,

John.

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