Tuesday, 12 October 2021

FVM versus the residual current device.

Sorry I have been absent for a while. This has been due to work pressures and a bit of a medical issue which hopefully should be resolved soon.

I have been having a problem keeping my mains electricity on. The mains distribution board was receiving me infinity dB over S9.

When I started using my Tajfun 70cm amplifier I started to have issues with RF tripping protective circuits in various mains circuits. This was not such a big issue, but it really became crucial when it was our own trip that was going. 200W of RF would trip our main residual current device - RCD (also called a ground fault interrupter in foreign parts). This caused me to limit power to 100W on 70cms and think a bit more about it.

I have looked a various websites and I found almost no references to amateurs tripping mains electricity protection circuits. There were a couple of references in the US going back ten years or more, but they affected only one make of device, not a 240V one of course, and not 70cms, so they did not seem relevant.

A few tests proved pretty conclusive. 200W would cause it to trip if beaming that way, and it was instantaneous. If I let the first few moments of transmission pass at low power and then increase the power back to 200W it did not trip. This suggests that there is a spike from the radio (an IC7100) which is momentarily over driving the linear. But, whatever, the RF was clearly tripping the device. Erm, in my view anyway.

I asked a few people who know about mains electricity and they doubted that RF could do such a thing. Nevertheless, I reckoned it was the RF. I just parked the problem as there was plenty going on, and 95W on 70cms seems to be doing all right for me if I stay off moon bounce. The problem is compounded as the beam heading where the moon generally rises passes the point where the RF cuts the mains power. So no EME at high power, with the Tajfun sidelined and my old 95W Microset back in use.

An added point was that as the FVM house is divided into two mains circuits each with its own independent RCD, and only one half was tripping off. As luck would have it, the half which does cut off is not the half powering the shack, so I motor on without being aware that Mrs FVM's machinery (dunno what, I guess sewing machines and irons, plus the TV), has got cut off. This seemed to cause some strife, but I cannot understand why. The radios kept working, so everything seemed pretty well OK to me.

Proteus residual current device at GM4FVM (on the right, others are circuit over current trips)

All went well in the sense that I was ignoring the problem (because people who knew about these things told me I was imagining it), until I renewed my correspondence with Scottish Gas. I might explain that I stopped being a Scottish Gas customer years ago when I transferred my contract to another, cheaper, provider. Generally I was not greatly impressed by their service then. About a decade later I changed my provider again to one called "Robin Hood Energy" hoping that Robin Hood was no longer the ruthless bandit he used to be. Sadly, after three weeks, Robin Hood Energy ceased to be, causing all manner of headaches for the taxpayers of Nottingham City Council, who owned the operation.

This was before the current disaster whereby the UK government has set a maximum price for energy supplied to the public which is lower than the suppliers can buy it for, which not surprisingly is driving many suppliers out of business. Back when Robin Hood went belly-up there was some semblance of order in the market and my account was transferred to another supplier - guess who - Scottish Gas - on existing terms. I got some slight compensation that I still got the same price terms from them as I had been on at Robin Hood, which was a lot cheaper than I could have got from Scottish Gas 3 weeks earlier. So I have two years to enjoy that.

In due course British Gas informed me that my mechanical meter was outdated, liable to be unreliable, and I must change to a new mechanical meter. At the same time Scottish Gas tried to persuade me to change to a "smart meter". This is not a mistake by me, they call themselves British Gas when giving bad news (pay your bill, change your meter) but Scottish Gas when they are giving good news (have a free smart meter, isn't life good?). They are, of course, effectively the same organisation as they are both owned by Centrica. Anyway they said that I need to change it, though it does not seem so long since it was last changed. A smart meter will send readings wirelessly to the supplier meaning I would not need to take manual readings (if it worked ...)

Mechanical meter at GM4FVM, which seemed to be fine to me.

Faced with changing the meter anyway, I opted for a smart meter after news in the RSGB magazine that there was little risk of it causing RFI to my radios. A pleasant chap from Scottish Gas arrived, fitted the new "smart meter" and it promptly tripped the RCD. Many tests, same result. It was clear to me that the RF was to blame, as it had been before. After discussing the possibility of re-fitting the mechanical meter we compromised by his agreeing to temporarily isolate the RF side of the smart meter and promising to return.

Scottish Gas smart meter at GM4FVM, meter on the bottom, "Communications Hub" RF unit on top.

I spoke on the phone to a "bigger man" at Scottish Gas who ran through what he thought might be happening. He still thought that some small earth leakage must be happening which was rendering the RCD liable to trip. As the smart meter is up stream of the RCD it seemed to me to be unlikely that it was earth current which causing the tripping. After all, the smart meter is not in the circuits protected by the RCD (and neither are my radios).

Anyway, I contacted an electrician with a view to having the RCD replaced. He asked for a photo of the RCD and promised to replace it the following week. I never heard from him again.

In order to find a trustworthy electrician I used the tradesman's network instead. I asked a house painter in the village to recommend an electrician. This worked brilliantly. The guy he suggested turned out to be knowledgeable and very willing to change the RCD if I wanted to. However he suggested that I go instead for equipping each circuit in the bank with its own combined current trip and RCD. He would then isolate the old RCD. This seemed like a perfect solution to me because if there is some small earth leakage then I can narrow it down to one circuit and maybe not knock off the TV, which seems to matter more than anything else for some reason. He arrived within days and did the work neatly and cleanly.

New arrangement, separate earth protection on each circuit, main breaker now isolated.

You can see from the photo that the RF Communications Hub unit on the smart meter, the thing that makes it "smart", is right below the distribution board. The inverse square law means it was getting lots of RF from the wireless unit right below. It seems certain to me that it was RF from that unit which was affecting the RCD because now that the RCD is isolated the tripping has stopped. My RF has no effect on the new arrangement at all.

In due course, Scottish Gas returned to turn on the radio or "wireless" side of the smart meter which should have started sending readings to the Scottish Gas system to update my account.

I might add that since the system has been fully activated in smart mode it has has not worked at all. My Scottish Gas (a.k.a. British Gas) account is showing zero readings, so nothing is reaching them. I have activated their app which is designed to work with the smart meter and it shows no readings either. What point a smart meter is which does not relay any information I cannot say.

It cost me £250 to upgrade the distribution board ("fuse board") for half my mains system to allow for a smart meter which doesn't work. On the other hand it is not RF sensitive. Next task no doubt is to replace the other half for another £250, though it has been no trouble --- yet.

My Granny always told me to avoid people who change their name depending on what suits them. I thought she meant rogues, vagabonds, or the Duke of Rothesay. I now know it applies to British Gas and Scottish Gas too.






  1. Interesting post Jim, since installations vary from country to country. We can have a max of 4 current trip devices after one RCD. But normally in modern installations all circuits are equipped with a own RCD. Unfortunately once and a while the shack's circuitbreaker trips here after I switch on my 50A Astron, although I got a current limiter built in. Not shure what the cause is. By the way, I see in the UK they use a lot of that grey cable for house wiring, I saw that in Ireland as well. In the Netherlands it is common to use separate wires in tubes. The idea is that it is easier to refit the wires in case of malfunction. By the way, I learned for electrician but never actually worked much in that field. However, of course, I do all house wiring myself. Never heard about RF(I) does trip the RCD though. 73, Bas

  2. This seems to be a common problem with smart meters, a relatives doesn’t communicate with the energy company at all therefore I have resisted the temptation to get them installed.

    How do you find the tajfun? Is it reliable?

  3. Once again I am struggling to get Blogger to accept my comments. 3rd time lucky maybe ...
    1) Bas. Yes here and in Ireland we often use "Twin and Earth". It is clipped to wooden structures and walls and you cannot pull it through like you can with wires in conduit tubes. We do have conduit tubes, but mostly in garages and factories to protect the T&E from damage.
    2) Gavin. I bought the Tajfun when I was having trouble with the Gemini. It is a great linear. Works on either 2m or 70cms but you need a bandpass filter for 2m. 500W peak, 300W data, smaller, quieter, and lighter than the Gemini. But I have hardly used it. I do not think they make to 2m/70cms one now, but they make more powerful ones for 2m, 4m and 6m, which were more expensive and I do not need that type of power anyway.

  4. Just a further note, Arqiva, who run the long distance network fed by the communications hubs on the meters, have a large site on the headland south of me, with the towers clearly within sight. My spectrum analyser can receive them easily, though which sites they use for this purpose is not known to me. Other properties in the street are getting communications, so it is surprising (to me anyway) that I am not.
    I suspect that the problem lies somewhere other than the communications with Arqiva. My gas meter is not communicating with the electricity meter either, a distance of just over 4 metres. So is the communications hub working properly and was the RF interference a sign of that?
    Will I ever know?
    Jim GM4FVM