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

 

[westward10]

The fact you have open end to ends on the lines and cpcs is an issue which would attract in most people's eyes a Code 2. The fact you have continuity across the neutral conductors suggests it was a ring final circuit.

 

[Julie.]

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

Why is it dodgy to not have overload protection on a cable (spur) which cannot be overloaded?

433.3.1 would clearly be applicable

If you have a break in the rfc then it would automatically require a C2.

It needs fixing, either split into two at the break in which case both would need 20A mcb, or fix the fault.

 

[Julie.]

The fact you have open end to ends on the lines and cpcs is an issue which would attract in most people's eyes a Code 2. The fact you have continuity across the neutral conductors suggests it was a ring final circuit.

I think it's the line which is the ring, both n & CPC are broken.

 

[Julie.]

To the op, have you looked at gn3 - do you have a copy? You need to be familiar with this (and the regs) before you consider periodic inspections.

This explains how to test rfcs

 

[westward10]

I think it's the line which is the ring, both n & CPC are broken.

He says Live and E are broken?

 

[Julie.]

He says Live and E are broken?

Sorry, yes he does, but I got confused by him thinking that the n was made via borrowed neutral, albeit discounted.

 

[Inteificio]

wow, thanks for the fast responses!

I've been doing my best to memorise GN3.

It's doing the ring tests that I've come across the faults.

Why is it dodgy to not have overload protection on a cable (spur) which cannot be overloaded?

433.3.1 would clearly be applicable

If you have a break in the rfc then it would automatically require a C2.

It needs fixing, either split into two at the break in which case both would need 20A mcb, or fix the fault.

That's why I'm asking, I'm checking what the skilled inspectors think.

If there was a short on the back of that socket the cable would potentially (not done the calc) overheat before the b32 trips. So there is a small chance of an unprotected fault.

433.3.1 nails it, thanks.

The fact you have open end to ends on the lines and cpcs is an issue which would attract in most people's eyes a Code 2. The fact you have continuity across the neutral conductors suggests it was a ring final circuit.

I would have thought C1, can you explain why C2?

My thinking is that the circuit can overheat in non-fault conditions hence C1. Functionally I've got a 2.5mm spur that can happily maintain 32A without a trip.


So the simple solution is a break in the L/E, it just seems such an unlikely fault to me. Is there anything else that I could be overlooking, or is it time to start ripping up floorboards before my house burns down?

Downstairs
spur
Zs - 0.25 - Zn - 0.19

Near socket
Zs - 0.54 - Zn - 0.31

Far socket
Zs - 0.58 - Zn - 0.35

Upstairs
Landing
Zs - 0.38 - Zn - 0.26

Vlad's bedroom - Spur
Zs - 0.43 - Zn - 0.31

Mordecai's bedroom
near 0.46 - 0.3
far 0.39 - 0.26

My room
0.33 0.29

I'll check for patterns shortly, but pizza has arrived.

Thanks for the help, understanding how other people tackle problems is good training.

 

[westward10]

We cannot assume the breaks have occurred in the same place but you will have to carry out contuity tests. Have you tried an insulation resistance test across the open ends to see if there is a tenuous connection.

 

[Inteificio]

We cannot assume the breaks have occurred in the same place but you will have to carry out contuity tests. Have you tried an insulation resistance test across the open ends to see if there is a tenuous connection.

I have not, good idea, thanks

 

[Julie.]

wow, thanks for the fast responses!

I've been doing my best to memorise GN3.

It's doing the ring tests that I've come across the faults.


That's why I'm asking, I'm checking what the skilled inspectors think.

If there was a short on the back of that socket the cable would potentially (not done the calc) overheat before the b32 trips. So there is a small chance of an unprotected fault.

433.3.1 nails it, thanks.

I would have thought C1, can you explain why C2?

My thinking is that the circuit can overheat in non-fault conditions hence C1. Functionally I've got a 2.5mm spur that can happily maintain 32A without a trip.


So the simple solution is a break in the L/E, it just seems such an unlikely fault to me. Is there anything else that I could be overlooking, or is it time to start ripping up floorboards before my house burns down?

Downstairs
spur
Zs - 0.25 - Zn - 0.19

Near socket
Zs - 0.54 - Zn - 0.31

Far socket
Zs - 0.58 - Zn - 0.35

Upstairs
Landing
Zs - 0.38 - Zn - 0.26

Vlad's bedroom - Spur
Zs - 0.43 - Zn - 0.31

Mordecai's bedroom
near 0.46 - 0.3
far 0.39 - 0.26

My room
0.33 0.29

I'll check for patterns shortly, but pizza has arrived.

Thanks for the help, understanding how other people tackle problems is good training.

If there is a short then it would be a fault, normally this is assumed to be zero resistance and therefore your Zs check would show it would disconnect within .4s - if it is a high resistance arc, then yes it could pass just enough not to trip due to fault, but more than the cable rating (remembering the arc itself is more of a likely fire issue than being able to overheat the cable over several hours).

Why C1 - C1 means it is an immediate danger (for example live contacts exposed)
Why C2 - C2 means that there is a danger if something else occurs to cause the danger.

In this case it doesn't present an immediate danger, there has to be a previous problem (overload etc).

As to where is the fault, you can usually narrow it down without ripping up too much, split the rfc at the cu, short one end l-n then go round the sockets looking for l-n continuity (just use the standard plug from the mft - no need to remove sockets), then repeat for the other end, this generally narrows it down to between two sockets (then it's a bad connection in either socket, or the cable between).

Then repeat for the cpc

There is no guarantee that you have just the one point of fail - you may find a couple of breaks in the same conductor and/or different points of break between conductors.

 

[Inteificio]

If there is a short then it would be a fault, normally this is assumed to be zero resistance and therefore your Zs check would show it would disconnect within .4s - if it is a high resistance arc, then yes it could pass just enough not to trip due to fault, but more than the cable rating (remembering the arc itself is more of a likely fire issue than being able to overheat the cable over several hours).

Why C1 - C1 means it is an immediate danger (for example live contacts exposed)
Why C2 - C2 means that there is a danger if something else occurs to cause the danger.

In this case it doesn't present an immediate danger, there has to be a previous problem (overload etc).

As to where is the fault, you can usually narrow it down without ripping up too much, split the rfc at the cu, short one end l-n then go round the sockets looking for l-n continuity (just use the standard plug from the mft - no need to remove sockets), then repeat for the other end, this generally narrows it down to between two sockets (then it's a bad connection in either socket, or the cable between).

Then repeat for the cpc

There is no guarantee that you have just the one point of fail - you may find a couple of breaks in the same conductor and/or different points of break between conductors.

Good to know, thanks.

 

[Inteificio]

urgh, just thought about this more.

OK I now get why it's not a C1 for the reason I gave (someone would need to plug something in to make it overload).

However, you mentioned arcing and fire...

Is that not an immediate problem?

Or is the arcing a cause that could create a future problem (fire) which is why C2?

 

[Julie.]

urgh, just thought about this more.

OK I now get why it's not a C1 for the reason I gave (someone would need to plug something in to make it overload).

However, you mentioned arcing and fire...

Is that not an immediate problem?

Or is the arcing a cause that could create a future problem (fire) which is why C2?

You mentioned a short at the back of a socket, how could you get that unless it was either a full short , or an arc causing just the correct amount of current?

This fault could occur anywhere.

The likelihood of an arc occurring with just the right amount of current to not cause a fault protective device to trip, but cause a fire is the same irrespective of what you have found to date.

If there is a reason to believe a fault such as this would occur then yes that particular issue may draw a code.

 

[littlespark]

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……

 

[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.