I remember borrowing 2 radios a Murphy B41 and B40 these were ex marine sets which improved my listening experience no end. However I soon found out that both radios chassis were live to earth i don't know by how much i didn't have an AC voltmeter at that time. I do know that there were no incorrectly wired plugs or sockets i checked carefully also the first time i got a shock the sets were in a temporary location not in there final place in my shack. The estate were i lived then had OH 5 wire distribution all round fed from ground mounted TXs interestingly I found out later that someone who lived the other end of the same estate had a similar problem getting shocks from taps and metal kitchen sink units they were fed from a different TX although I think the neutral on the pole was continuous all the way round what in your opinion mite of been going on? The radios had transformer PSUs so were supposedly isolated internally from the mains
5 wires on poles is TN-S. I expect that the Earth was broken somewhere and had moved from real Earth a significant amount. I had a B40 once and its chassis was certainly isolated from the mains, although it is possible there were RF decoupling capacitors on the mains supply. Even so there should not have been a significant potential on the case if you had an Earth to go with the Aerial connection.
I had an RF earth to help improve reception and keep the noise down a bit although there's not much you can do with most of it as its airborne. The way I found out about the live chassis was when I first got the receivers I set one of them up in my outhouse connected a length of wire to the aerial input just to try the radio out whilst I was doing it my bare ankle touched a gas pipe and you guessed it I got a big shock talk about finding out the hard way
5 wires on on poles may not indicate TN-S. It could be three phase and neutral, with an extra switched live for street lighting. This switched live carries a relatively small current and is often smaller than the other 4 wires.
Overhead supplies are seldom TN-S. TT or TNC-S are much more common.
I agree with Broadgage. Traditionally, DNOs did public lighting. We use a 5-wire overhead system, where the top conductor is the “switch wire” for the public lighting. It is a smaller conductor than the remaining four, as it doesn’t need the same current carrying capacity. A lot of our underground network is 5-core too, although it is more usually referred to as 4.5 core, as the switch wire has a smaller cross sectional area.
I seem to remember that the 5th wire was thiner looking than the other 4 originally the estate was lit by having a rather puny single bulb in a fancy fitting every few poles but they all got scrapped and replaced with modern concrete columns which had much better brighter lights on icant be sure what type of lights they were all I remember is they were bright white. Getting back to earthing when allthe houses on the estate were rewired about 1980 ish the main earth was to the cold water pipe then a few years later the whole area was PMEd
Your right B40 and B41 Rx.s were Admiralty receivers used in the 1950/60s on ships and shore based installations. The chassis should have been earthed even with the double wound transformer for the valve heaters and HT supply. Your shock would have been as David says probably due to earth leakage no do doubt not an issue when bolted to the hull of a ship.
