A visit from the electricity company.

Yesterday, I was out walking when I got a call from a network manager for the electricity distribution company.  I had been expecting to hear from him about land access permissions for maintenance.  Of course, I was at the furthest point from the car when he called, so I had to run 3 kilometres to make it on time back home!

The land access took very little time to sort out, so I ventured to ask the manager about PME mains supplies and RF earth.  So far as I knew, I have complied with the regulations by installing 10 square millimetre conductor from each station RF earth (I have two), back to the distribution panel ('consumer unit') next to the incoming supply.  But I noticed the earth cable from the panel to the incoming (sealed) mains fuse was only 6 sq. mm, which is apparently not something to worry about, because it was there before the current regulations came into being, and so cannot be made retrospectively applicable, plus the likelihood of a fault is not very high.

Now, I've seen a lot of operators who are completely lost as to why they are providing earth for their stations (most, wrongly, think it is something to do with electrical safety), and very many variations on how they do it.  It has even led to a highly embarrassing and quite dangerous situation about a year ago, when the RSGB published an article that did not take PME supplies into account, and did not tell people to check or how to provide the correct earthing system if they had such a supply.  I did advise RadCom about this error, which they accepted, but I never did see a correction published, although they did ask me and others if we would be willing to write such a correction (I am not qualified, so of course, declined!)

The 'virtual' earth in a PME system.  The earth in the house is actually connected to the incoming neutral.

In brief, PME is a rather peculiar system where the neutral line provides the conductor for the earth.  In other words, any accidental break to earth sends the current down the neutral line, to which an earth connection is made every few poles along the line.  There is therefore no separate earth line, except a 'virtually' separate earth line in the property itself.

The problem with PME and RF earths is that, unless you connect each copper rod or tube that provides the RF earth point back to the distribution panel, a neutral break somewhere along the transmission line will see the circuit trying to complete by going down the alternative earth the operator has (for the electrons), usefully provided.  This could see several properties' worth of current trying to do the same thing.

In summary, if this were to happen, your radio equipment may well catch fire and quite easily spread, burning your house down.  Worse, a proper fire investigation would almost certainly identify your now blackened RF earth as the cause, and your insurance may not pay out, because you didn't conform to the regulations.  In the UK, all work to mains supply is now meant to be done by certified electrical installers, so DIY changes that used to be (and still are) common, are always, technically, a breach of the regulations.

Anyway, I was able to confirm that I had done everything correctly, but that there was some uncertainty as to the type of mains supply.  The manager was very helpful and well-informed, so he has offered to come in his spare time to check the supply type in some days, and have more discussions about the network.  I'm only too happy to learn more about these things, and I think the manager is too, because he had not really come across such a situation very often before.

Unfortunately, for legal liability reasons, the manager doesn't give talks on electrical safety, nor does he write articles of the kind that would properly correct the RSGB's efforts, which is a real pity.