My first EICR and I'm confused! I'm industrial this is domestic

[Inteificio]

Hi,

I'm an industrial spark and taking my 2391 next week (wish me luck, I need it).

I decided to get a bit of practice and started an inspection on my own house.

I got as far as, b32 socket (ring?!) breaker looks slightly browned, better check it.

3 cables in the breaker two identical and one that appears to be a spur to an adjacent socket.

Q1) Let's start with the adjacent socket as that one should be easy:

It's a double socket.

There is no way a load can be put on that will stress the 2.5mm without blowing the bs1361s...however, the 2.5 is undersized to the b32.

clearly dodgy, but just curious how some experienced guys would treat this.


Q2) Ok now for the confusing bit.

The 'ring' is only a ring on the N. Live and E are open.
All sockets pass inspection (well small arcing on one N, which is fixed)
IR passes (on this circuit).

The board is split RCD so a borrowed N would take out the RCD.

All sockets have an in/out feed apart from one.

r1/r2 unsurprisingly no reading.

r1/rn would have been a bit more interesting, but haven't done yet.


Does anyone have any advice, this seems a strange one?

Thanks

 

[Julie.]

The spur wouldn’t overload because as a double socket, the most that can be plugged in is 2 x 13A… 2.5 cable can take 26A, (although the double socket itself might struggle!)
If a dead short, then the 32 breaker would trip.

Looking for the fault could be the case of taking off every socket and testing every cable between. There may be hidden joints you yourself are unaware of, even if it is your own house.

And… unfortunate positioning of dodgy advert on previous message……

View attachment 93674

Wtf...

Great advert yet again

 

[pc1966]

If you see an open RFC conductor then you know there is a fault. Unless you know exactly what it is you have to assume the worst and that potentially the ring's cable could be overloaded (if open at one end so really a 2.5mm radial on 32A MCB) and/or there is a loose terminal at one or more location (back of socket, junction box) that could result in arcing/overheating. So in this case it is C2 as not the extreme danger that exposed live parts or reversed polarity causes, but it is far worse than C3 "improvement recommended".

That is not unique to the RFC, the same risk applies to a radial. But with a radial an open on a live conductor results in one or more socket not working at all, so it is more likely to be fixed. On open CPC on a radial of course is likely to be missed outside of testing, where as the RFC ought to have some redundancy in providing a path for fault currents to hopefully clear safely.

The issue of a spur on the RFC is more complicated, as 2 * 13A could just overload 2.5mm though it is unlikely to do so in practice and the test current for a double socket is 20A which is usually OK for 2.5mm and in most cases a more realistic maximum.

As said above, test the RFC systematically by some means such as linking L/E at one end of the ring at the CU and checking socket by socket for L-E continuity/resistance until you see a fault (open or suspiciously high R), then remove that socket and see what you find. If good, go back check the last good one as it might be open on the cable going 'out' in the direction of test.

Of course, in most houses you will have no idea of just how the ring was routed, so it is a bit of a guess, but you can generally get some sense after a couple of sockets in order are found and from the general practically of how it could be done.

 

[Inteificio]

Well I've had a good root around.

The zs/rn readings are so low that they are useless for analysis.

Excluding the spur at the board the circuit is:

Downstairs 2 ring sockets on leg 1.
Upstairs 2 ring sockets and a spur on leg 1.
Upstairs 1 ring and 1 spur on leg 2.

Cpc and live split at same point.

I can't get any further without ripping up carpets and floor boards!

Is it safe enough to just swap to a b20 and sign it off as a split ring?

Or should I fit a new fangled arc detection doohikey (yeah I know nothing about them)?

Or do I have to start pulling floor boards as the risk is too high?

Industrial is so much easier, no nice carpets to worry about =)

Thanks

 

[nicebutdim]

Complile the report and pass remedial work on to another spark

 

[brianmoooore]

Have you removed the sockets either side of the fault? Chances are that it's wires pulled out of one of those sockets. Far more common than an actual cable fault.
Even if it were a cable fault, and you decide to split the circuit into two radials, you would still have to disconnect the faulty leg completely at the two sockets at either end.

 

[Inteificio]

All the sockets are fine.
When separating the legs I've identified which sockets are on which side.

Fortunately as only one ring socket is on one leg I'm pretty certain the fault lies between that socket and another. Finding the 'another' will be a faf.

My next step is to remove all the ring socket covers and separate the cables. A bit of long leading the N will help find the dodgy leg.

I can then remove that one cable from each end leaving (hopefully) two spurs.

What a faf.

I hope the actual exam isn't this bad or I'm going to run out of time massively!

 

[brianmoooore]

If the fault is near to one end of the RFC, you are going to end up with a spur that loops back on itself, so are going to end up with a spur that uses much more cable than one that was designed as a spur from the start.
You will need to check that loop impedance and voltage drop are all acceptable, and access the likely maximum load of the circuit, to ensure it doesn't exceed the rating of the smaller MCB.

 

[UNG]

All the sockets are fine.
When separating the legs I've identified which sockets are on which side.

Fortunately as only one ring socket is on one leg I'm pretty certain the fault lies between that socket and another. Finding the 'another' will be a faf.

My next step is to remove all the ring socket covers and separate the cables. A bit of long leading the N will help find the dodgy leg.

I can then remove that one cable from each end leaving (hopefully) two spurs.

What a faf.

I hope the actual exam isn't this bad or I'm going to run out of time massively!

Rather confused by the fact that you have identified what sockets are on each side of the fault but then you say you haven't and that finding the other socket on the ring will be a faf

I would suggest buying a cheap continuity tester https://cpc.farnell.com/tenma/ten01049/continuity-tester/dp/IN05723 rather than spending a lot of time removing all the sockets

With the continuity tester you can work along one leg of the ring quite quickly and identify where the break is and then do the same on the other leg which should bring you to a point where you can then diagnose the cause of the fault and repair the ring

 

[pc1966]

The zs/rn readings are so low that they are useless for analysis.

What are you using to measure things?

Generally speaking Zs measurements are not that precise, not when you get down to under an ohm and more so if "no trip" due to RCD action so testing at very small L-E currents, so you are unlikely to get far finding a RFC break on that alone.

However, DC low ohm measurements using a typical MFT or similar usually are good enough but you have to allow for dirty switch contacts and socket pins so sometimes you have to insert/remove the test plug adaptor (or lead) a couple of times and operated the switch a could of times to get a low stable reading.

Even then you are likely to only reliably see differences in cable distance of several meters as, for example 2.5m T&E has R1+R2 of about 0.02 ohm/meter and (I guess) most low ohm meters likely to be at hand resolve around 0.01 ohm.

 

[pc1966]

I would suggest buying a cheap continuity tester https://cpc.farnell.com/tenma/ten01049/continuity-tester/dp/IN05723 rather than spending a lot of time removing all the sockets

I don't think that is CAT rated, so I would rather not use it on anything that might be live!

Maybe a cheap voltage tester that has a continuity buzzer?

 

[UNG]

I don't think that is CAT rated, so I would rather not use it on anything that might be live!

Maybe a cheap voltage tester that has a continuity buzzer?

So is he is going to disconnect all the sockets while they are live, I think that would be a no

Given the OP is an industrial electrician I would like to think he would be able to use a simple continuity tester to locate a simple ring circuit fault

 

[Inteificio]

I'm using a Megger mft1721.
I've also got my fancy multimeter for precise testing.

You're right, the Zs is useless for this, I'll do a dc test as that may have more accuracy. Good tip, thanks.

What I'm hoping is that the failure is directly between two ring sockets. All I need to do is identify the cable between and disconnect it at both ends.
If that is the case then I know which socket is on one side. I don't know where the next one in the supposed ring is (there are 3 probables).
Unfortunately I don't know where the spurs cut in, which adds a wild card.



Hopefully the accuracy of the r1rn dc test will give clues.

As for splitting the ring, my whole house was using 14A in total. This circuit is just skirting board sockets. Unless I suddenly start loving electric room heaters the load will be limited.

Now the question is do I fit the b16 from my spares, or go buy a b20


P.s. That's a good tip about turning the sockets off before splitting them too. I wish I'd known that last night as the burns on my hands are really smarting this morning

 

[UNG]

I'm using a Megger mft1721.
I've also got my fancy multimeter for precise testing.

You're right, the Zs is useless for this, I'll do a dc test as that may have more accuracy. Good tip, thanks.

What I'm hoping is that the failure is directly between two ring sockets. All I need to do is identify the cable between and disconnect it at both ends.
If that is the case then I know which socket is on one side. I don't know where the next one in the supposed ring is (there are 3 probables).
Unfortunately I don't know where the spurs cut in, which adds a wild card.



Hopefully the accuracy of the r1rn dc test will give clues.

As for splitting the ring, my whole house was using 14A in total. This circuit is just skirting board sockets. Unless I suddenly start loving electric room heaters the load will be limited.

Now the question is do I fit the b16 from my spares, or go buy a b20


P.s. That's a good tip about turning the sockets off before splitting them too. I wish I'd known that last night as the burns on my hands are really smarting this morning

While splitting the ring is an easy fix and while it is very rare that a cable is at fault I think actually locating / repairing the fault would be more beneficial from a learning point of view for you

 

[pc1966]

So is he is going to disconnect all the sockets while they are live, I think that would be a no

Given the OP is an industrial electrician I would like to think he would be able to use a simple continuity tester to locate a simple ring circuit fault

Here, no it should be fine to use that kit.

It is more of a general dislike on my behalf of having test equipment that is not mains-fault rated in use where mains is about. Sooner or later we all make a mistake and probe the wrong circuit (or discover they are mislabelled somewhere) that is live, and then having something that does not explode on you is nice.

 

[Inteificio]

Here, no it should be fine to use that kit.

It is more of a general dislike on my behalf of having test equipment that is not mains-fault rated in use where mains is about. Sooner or later we all make a mistake and probe the wrong circuit (or discover they are mislabelled somewhere) that is live, and then having something that does not explode on you is nice.

I think we all knew what you meant.

Exploding kit aka audiovisual alert.