Low Voltage System

Sometimes four is just not enough?

I've worked on 4 wire distribution systems, 5 wire system is interesting learning.

Earthing conductors aren't often used on overhead lines. The risk to persons as a result of a tree branch fracturing it and a fault occurring downstream of it are too substantial to contemplate.

The best opportunity to observe overhead earthing conductors, and hence 5-wire systems, are on long-distance medium- and high-voltage distribution networks. Low-voltage to domestic premises run overhead will usually go for TT, which doesn't involve running the earth conductor in the trees; the Earth itself is the earth conductor.

However, in distribution systems, there isn't much call for the neutral conductor, so in the 3n+1 wires seen, the odd conductor is simply a protective earth conductor. 3n+2 is a rare spot - take the I-Spy book!

http://www.eetimes.com/design/power-management-design/4011518/Neutral-Wire-Facts-and-Mythology

The fifth conductor (if you refere to the low side thin one) is used for street lighting and is live only at night. S.M.

I should have remembered that. The street I lived on had them, but that's going back in to the mist of time.

It is called TN-S system and the 5th wire is the Protective Earth conductor.