Electrical report shows no final ring continuity...

[nigelord]

Just had an electrical report for my house revealing a fairly lengthy list of minor problems - most of which I can deal with myself. However, rather more worryingly, it seems there's a problem with two of the ring main circuits which are described as: "No final continuity on sockets tested on circuit. Possible spurs on spurs".
The sparks said the 32A rating of the RCDs on these circuits suggested they were originally ring mains (rather than radial circuits), but that continuity had somehow been lost. He also said he couldn't simply treat them as radials (and lower the RCD rating) as there might be unconnected cables buried somewhere in a wall or under the floor.
I have to say, this sounded very unlikely, but I wasn't in a position to argue. And I'm now faced with the problem of what to do about it. Having just finished decorating all the rooms affected and laid new laminate floors - I'm ill-inclined to start pulling everything apart, but I'm really not sure how to deal with this. Any help would be gratefully received...

 

[Taylortwocities]

This will need to be investigated and resolved. You have circuits that can be overloaded. Overloaded cables get hot and this can be the cause of house fires.

As you say, it sounds like additions/changes to the original wiring has meant that the integrity of the final circuits has been compromised.
What has caused this can only be determined by detailed investigation. Depending on the nature of the problem, this could be resolved by creating two separate final circuits with 20amp MCBs (note, MCBs not RCDs!). Investigation is needed to make sure that the circuit can be split in this way, but note that would limit the maximum current of the circuit to 20 rather than 32amps - would that be enough for your loads?

This is not something that could be discovered on an Internet forum! You need to engage an experienced, competent electrician to spend time (and it will take time) to make a detailed survey of the circuit(s) and to detail a plan to resolve. Would this cause disruption to the decoration, possibly. It depends on the solution he/she comes up with.

The person who prepared the report would appear to be a possible candidate for the work?

 

[oldbutnotdead]

Hmmm. Did you do the floors yourself or did someone else do them? And, perchance, did you or they put some screws or nails in wobbly floorboards before putting the new flooring down? Or spike a load of 4mm ply or similar down before laying the laminate? Or use overlong nails on those nasty skirting board trims? Just a thought......

Yes you have to find out what is going on- first job is to map the wiring to the sockets. If you have a multimeter and a spare day and some familiarity with electricity you can do this yourself but it is going to be very tedious and involve a bit of working inside the consumer unit- if you're not comfortable with doing that then get a professional in.

 

[stem]

a problem with two of the ring main circuits

To lose continuity on one ring as a result of damage or fault happens from time to time, but to have the same thing happen on two circuits in the same property sounds to me like deliberate action by someone. In any event, as already said investigation will be required, but out of curiosity, what prompted you to have the report made?

 

[Taylortwocities]

Hmmm. Did you do the floors yourself or did someone else do them? And, perchance, did you or they put some screws or nails in wobbly floorboards before putting the new flooring down? Or spike a load of 4mm ply or similar down before laying the laminate? Or use overlong nails on those nasty skirting board trims? Just a thought......

But the survey showed no ring final continuity.
Nails and fixings would produce an insulation resistance fault, or (just maybe) a single broken conductor. I am assuming, from the above, that there is no continuity on any of the conductors, and not just one.

 

[oldbutnotdead]

But the survey showed no ring final continuity.
Nails and fixings would produce an insulation resistance fault, or (just maybe) a single broken conductor. I am assuming, from the above, that there is no continuity on any of the conductors, and not just one.

Ahh yes, fair point Batman. V unlikely a nail would separate all 3 conductors, a circular saw would but that's a whole other scale of woe. Map the circuits, see what's what from there.

 

[ericmark]

I found no continuity on a ring and on further inspection I found it was a 4 mm² radial which had been extended clearly the person extending thought it was a ring and used 2.5 mm² cable. It simply was never a ring. Also found where house had 20A radials but person replacing the consumer unit had fitted 32A MCB's. So you have a problem working out if MCB is wrong size or ring is broken. An electrician should have a loop impedance tester, using that and recording the line - neutral loop impedance one can quite easy work out which is the last socket, I know I had a lead made up so it was simply a plug in to each socket and note reading. Once you know which is last socket or pair of sockets if broken ring it is quick and easy to remove that socket to test it. Also in the consumer unit having two wires into the MCB will show likely a ring. So for an electrician with his tools it is an easy job to identify last socket of a radial which one would hope has one cable only. With spurs from a radial it gets harder as you can have many ends. But without the loop impedance tester or special low ohm meter the job is far harder. So as stated by others best option is to get an electrician to do it for you, and the test gear required is so expensive.

 

[nigelord]

Thanks for these replies... and just to answer a few of the points raised. No, I definitely haven't been careless with my nailing (can't remember the last time I actually used nails inside the house!) - or screws or anything else. And, as has been pointed out, this couldn't cause the loss of continuity anyway. And sorry for the RCD/MCD slip-up - I really should stop putting pen to paper at 2am! My reason for getting the test done was the usual demand by my insurance company for an up-to-date report.
Checking for two wires into the MCB looks like my first job - once I've established whether they actually were rings, I can go from there. I too was very puzzled by the same fault occurring twice, but put this down to the house being changed and extended several times over the years, rather than anything deliberate.
As I said, my main concern is to avoid major disruption to the rooms in question - if at all possible. Having lived in the house for many years and used several high-current appliances (such as fan heaters) there's never been a time when the MCBs have tripped. Given that they are 32amp rated (for rings), isn't that significant in terms of potential circuit overloads?

 

[JohnW2]

As has been said, there clearly is a need to have the circuits fully investigated, followed by appropriate remedial action, depending upon what is found. However, am I the only one who does not really understand exactly what is meant by:

... a problem with two of the ring main circuits which are described as: "No final continuity on sockets tested on circuit. Possible spurs on spurs".

??

Kind Regards, John

 

[oldbutnotdead]

I'm assuming that the guy doing the testing on the rings hasn't removed any faceplates for the continuity tests. I don't know how spurs on spurs would fail with no continuity if the main ring was intact. It would be useful to know whether the test failed on checking end to end of the 'ring' from the CU or on the crossover tests (I'm looking at installation testing here rather than periodic testing)

And for the OP, your whatever circuits (ring finals or radials) may very well have performed faultlessly over the years with a fair load on them but the 32A MCB is not protecting the cable properly if the ring final isn't wired correctly as a ring. Usual deal- damage takes more than one thing to go wrong. In your installation one thing has already gone wrong (the rings that appear not to be rings)- if you load the circuit to 30 amps say then the single piece of 2.5mm will get very very warm before the MCB gets anywhere near overload current.

You've got to map the circuits and determine what is connected to what. Mapping is a lot easier with the professional tools but can be done with a standard cheapie multimeter, a long test lead, a screwdriver and the power off. You're not looking for variations of 0.5 ohm, you are looking for circuit or no circuit.

And now you are aware of this problem you absolutely have to address it- maybe not today but certainly this month. Until you've mapped the circuits there is no way to determine how much (if any) disruption is necessary. You may find that the circuit is indeed a pair of radials that have been bodged onto 1 breaker, or a radial with a spur connected at the CU or many other scenarios that won't require floorboard lifting.

 

[ban-all-sheds]

Strange to decorate and lay laminate flooring before sorting out the electrics....

 

[JohnW2]

Strange to decorate and lay laminate flooring before sorting out the electrics....

Yes, that would be strange - but you seem to be 'assuming the worst' again. My reading of the situation (which, of course, may be wrong) is that the OP had no reason to think that the electrics needed "sorting out" at the time the decoration and flooring was done - the request for an 'up-to-date electrical report' from his insurers probably having come after those works had been undertaken.

The OP will be able to clarify.

Kind Regards, John

 

[Taylortwocities]

@nigelord
Just a thought. You have two ring final circuits that do not have continuity, is that correct?

I want you to try something. Plug a light, or something into one of the sockets on one of those circuits. Turn off the MCB for that circuit.
Does the light go off or does it stay on?
If the light stays on, leave the MCB off and see if the light goes off if you switch off teh second MCB.

What I am thinking about (and I have seen this a few times) is where an electrician has mixed up the ends of two rings and has put one leg on one MCB and the other leg on a second MCB.

Depending on how the electrician tested continuity, he may have assumed not continuity rather than investigating if the other leg of the ring is somewhere else on the board. To be fair, his job was to test and report, and not to fix anything.

Give it a try and let me know what you find….

 

[EFLImpudence]

Wouldn't there BE continuity at the sockets when/if that is done?

 

[JohnW2]

Just a thought. You have two ring final circuits that do not have continuity, is that correct?

As I wrote, I for one am not totally sure whether that is correct or not. It all depends upon what you can make of

"No final continuity on sockets tested on circuit. Possible spurs on spurs".

As you say, if it simply means that there was no end-to-end continuity seen for either of the circuits at the CU, then that could well be due to the two rings being incorrectly connected at the CU (one leg of each 'swapped') - but where would "spurs on spurs" come into that?

Kind Regards, John