Neutral

Hi Danny,

I assume you are referring to a "floating" neutral.

If that is the case have a look at some of these.

Regards - KJK

Hi Danny,

You are 100% right - in South Africa there seems to be a lot of confusion regarding the cause and effects of a floating neutral.

As you are aware, in SA our supply line voltage is phase to phase 400v and phase to neutral 230v (may vary slightly from area to area). The supply comes from the secondary of the stepdown transformer where the output is connected in Star where the Star point becomes the Neutral and this is earthed at this point.

Now in order to explain the phenomenon of a 'floating neutral' we should look at a building which is supplied by from a three phase + neutral + earth supply connection - everything would operate correctly if the neutral remained connected.

Should the neutral be disconnected (in SA usually stolen) the building wiring system would now be effectively connected in Star (all the neutral wires from the various 3 phase circuits taken to a common neutral bar). So long as the three phases are balanced (equally loaded) the neutral would be stable but as soon as an unbalanced load is connected the unbalance affects the voltage at the Star point (the neutral bar) and this is your 'floating neutral' which would continually vary according to the unbalance across the three phases.

The practical effect of this is that instead of the phase to neutral voltage being 230vac you are likely to measure between 280 & 320vac which is why so much damage is done to appliances etc. connected to a system where the neutral has been disconnected.

In other countries where I have worked a Protective Multiple Earthing (PME) system is used where the neutral line is earthed at multiple points e.g. at every distribution board and this helps to overcome this problem.

In SA the cable theft problem (in a lot of cases just the neutral & earth wires) has become a major problem not only because of the loss of cable but also the resultant damage to the end user's appliances.

Hope this helps you!

Regards, Keith