My consumer unit keeps tripping, is this connected to the smart meter?

There is evidence that the response to polling the meter for data - as happens twice each night, once for readings and once for usage data - can cause an RCD to trip, for example: https://www.electriciansforums.net/threads/rcd-tripping-straight-after-smart-meter-install.200818/post-1783565 

The two remedies I’ve seen involve (a) replacing the breaker that trips with a new, higher-spec one, and (b) moving the meter further away from the CU. A third which I’ve not seen tested but may be worth investigating: replacing a plastic CU enclosure with a metal one. If the CU is old and perhaps not up-to-code any more, this might be a longer-term solution. Sadly, it’s not a cheap option.
 

Thank you for your suggestions.

I will discuss them with the electrician tomorrow, hopefully he will find a solution. I will post result.

Thank you

​@Firedog At first I was going to dismiss your suggestion of the meter polling but as a radio engineer it does have some merit and we are staring at the bottom of the barrel and possibly the electrician too. ​@Jan71 has already said the RCD has been replaced so it's unlikely to be fault.

Puts on radio engineer hat

There may be some kind of resonant circuit going on here (feasible but I'm thinking unlikely) where the proximity of the meter to the wire run to that RCD and the exact length of that wire is the factor. How do we fix that? Reroute that wire away from the meter if it passes close to it?

Ok.

1) Have the electrician check the insulation on that ring final circuit

2) If ok, check to see if the cable from that RCD passes close to the meter. If so reroute it even if on a temporary basis

3) As a test, add a choke on the cable associated with the RCD. You make one of these by taking some small guage, insulated solid core wire (one of the wires in a twin and earth for example) and wind about 10 turns around the cable and make a connection between the two ends. Insulate the whole thing. It needs to be close to the RCD. If that fixes it then it is the transmitter in the smart meter causing it. The electrician will have to find another solution. The choke is only proving a point. I doubt if it can remain there.

To be honest I've never heard of this happening before but radio is a strange beast and it can do weird things given enough power.

Peter

Thanks for your insight, ​@Peter E . 

It was my understanding that an RCD works by detecting any tiny bit of EMF radiation emitted from a nearby coil through which current only passes if there is an imbalance. If it’s designed to detect tiny bits of radiation, then is it impossible to imagine that a sudden transmission burst from a smart meter’s comms hub could generate enough to trigger the RCD? How else would you explain tripping that stops when the RCD is replaced by one with a higher spec?

Yes. RCDs work by looking for the difference in currents between the live and the neutral at 50Hz. What a sufficiently high level of RF could do is spoof / replicate the level of imbalance such that it trips. Normally, the level of RF is low enough not to cause a problem but if you have a resonant length of wire passing near to the smart meter communications hub then it could cause an issue but I've never heard of it before in this context but I have seen it elsewhere and had to fix the issue.

Interesting conversation.

Would I be right in thinking that the length of the wire is significant to the resonance, ie. simply replacing it with a shorter or longer wire would change the resonance and thus cure the issue?
Or would it take more than?

Spot on. The resonant length is dependent on the frequency. At 300MHz the wavelength is one metre. The resonant length is a quarter wavelength or an odd multiple thereof. We call these resonant lengths aerials because that is exactly what they are. So you can see that even short lengths of wire have the capacity to couple efficiently into the smart meter transmitter aerial.

It's further complicated if you have a 3G signal system because the mobile phone basestation will ask the smart meter to shout louder (transmit at a higher power level) if the signal it is receiving is low because it's buried inside a house. I think radio systems in the north have a fixed power.

Hi All,

Just to let you know the electrician came and moved the sockets to the other side of the board,  so nothing on the rcd side now.

The RCD has tripped again at 03.50, so am I right to think it is the smart meter transmitting.  I have a plastic CU so thinking it will need to be changed for a metal one.

A question that may help get to the bottom of this:

How do you know that it tripped at 03.50?
Presumably you were in bed asleep, so what is telling you it tripped at that particular time?

PS. If there is nothing on that RCD now then does it matter for the moment whether it trips out? You could just leave it off.

Hi ​@Jan71 thanks for continuing with the feedback. That is really useful.The metal enclosure should help and it's a good move anyway. I hope it fixes the issue.

Does the cable for the RCD that trips pass near to the smart meter? If it does then would there be a possibilty of rerouting the cable as a lower cost alternative?

Peter

 Thank you, Peter, and apologies to you, Jan, for going off at a technical tangent, but this is such a strange phenomenon that I think it deserves technical discussion involving people who know what they’re talking about (which rules me out!). My reading is getting me more and more confused, but this graphic helped:
  

Since most households now use many of the devices that call for a type A at least (e.g. LED lighting, variable-speed-drive washing machines), Could this influence Peter’s response at all? (I was happy to see when I checked that my breakers are all Type A RCBOs). I still wonder, though, whether the type of RCD or of the CU enclosure could in any way explain this unexpected tripping apparently in response to a burst of EMF radiation in the middle of the night. Someone must have done the tests - OVO’s own meter scientists, DCC and the CH manufacturers EDMI, WNC and Toshiba. 

There are certainly additional influences with installed equipment on RCD/RCBO devices - hence the array of options when fitting. DC (or DC behaviour) can affect triggers but the fundamental question here is .. what happens in the near vicinity at, or around, 3:50am?

Depending on the surroundings, external influences might be a cause .. if you remember, I quoted some device tripping on a large building site, caused by 2 way radios used during construction.

I wonder if the data from the meter usage gives any clues about on-site activity at that time  

Hi,

For the previous 2 nights I have been awake at 3am and stayed awake, so I know the time it tripped.

I have decided to go with a new CU as I think it's good to upgrade after 26 years.

The cable doesn't run past the meter.

I am not even sure the metal CU will fix the problem.

It will be fitted next week, so I will let you all know either way.

Thank you all for your advice.

​@Jan71 you are so good at feeding back and ticking off the questions I wish there was some kind of leader table / reward for having spent the time to do that.  So many times we get ghosted when trying to narrow the options that you just get left hanging wondering if you even got close to solving the issue.

If the plastic CU has been there that long then a metal one would be a timely replacement. If it went away then it would be support for the RF idea but still not definitive. The cable not running past the meter is a blow but I'm not completely sure it's RF triggered anyway.

Regarding the diferent types of RCD I would be trying all of them to see if any of them worked there and if they did what was special about that particular type.

As for testing RCDs against RF fields, well, you could spend a lifetime exploring combinations of different parameters: Near field / E coupling / M coupling, Far field EM coupling, direct coupling, cable coupling, frequency, power, continuous and pulse are just for starters. RCDs are generally immune to RF fields they are likely to encounter it's just that they may have a particular sensitivity based on their particular manufacturer but it seems to be so rare as to be not worth the effort. In this case given the frequency band in use (GSM or radio) the RCD is actually in a Near Field situation (within a small fraction of a wavelength) and the effects fall off as the cube of the distance not the square as for Far Field EM coupling. Most devices are tested in a Far Field environment.

Peter

Thank you Peter for your reply.

The new CU is the only option at the moment as the electrician cannot find the cause of the tripping.

There is nothing on the rcd section now, so cannot understand what would cause it to trip in the early hours?

If this doesn't fix it, at a loss what else to try.

I will keep you posted.

To be honest this is not a common problem so it wouldn't have been on OVO's list of suggestions to change to a metal CU case anyway. It was a bit of a head scratcher for us on the forum as well but because of your excellent and detailed feedback it seems likely there was an interaction between the meter and the RCD after all.

Peter

Just to add some confirmation about the interaction, at least between RCBOs and smart meters, I successfully got Scottish Power to pay for an electrician to replace an RCBO after I proved that their smart meter, installed only a couple of inches away from my CU had caused tripping.  The RCBO tripped twice a day like clockwork from the day the meter was installed.  An aluminium foil shield loosely placed around the meter stopped it doing so.  The problem was solved by replacing the RCBO, which unlike all the others in the CU had a neutral tail.  When replaced with one with no tail everything was perfect.  I think all the power utilities should be aware of this problem.  I’m an engineer not an electrician so if any terminology is wrong forgive me, but I thought it worth sharing!

That is the best conclusion possible. Your electrical installation should be well-protected for years to come, and the tripping problem has gone away. Thanks so much for sharing the outcome with us.

I’d just say that sadly this isn’t incontrovertible proof that it was the CU enclosure at fault. However, if that’s all that was changed (i.e. all the innards of the CU are still the same), it’s pretty compelling.

I should probably add that the neutral tail, of course, might not have been the critical issue; the point is that the RCBO was the only one immediately affected in the CU.  Changing it to match the other 5 unaffected ones cured the problem.  The CU is plastic as a matter of interest. 

Incidentally, another power utility had previously said they could not install a Smart Meter for me within my enclosure because it had to be a minimum 200mm from the CU.  Scottish Power’s installers thought different.