Confused about a fault with downstairs lighting, any ideas?

[jonnyb]

Hi chaps I have a query and wouldn't mind any suggestions. I've been preparing a consumer unit swap, ran the usual tests and no major worries except a low insulation resistance test on a ring. Going to swap the board tomorrow morning. Customer asked me to swap some lighting switches whilst I was there prepping today. Pulled the fuse for the downstairs lighting and this reversed the polarity on the ring sockets. Double checked and happened every time I pulled the fuse. Will investigate further in the morning but has anyone ever had this happen?

 

[Midwest]

Ehhh? I'd be sorting that before doing anything with a new CU.

 

[jonnyb]

Yeah I'm going to, just never had this particular fault before and wondered if anyone else had. As it is, I suspect I'm going to be doing a lot of fault finding tomorrow before the board is in!

 

[Midwest]

I would start at the beginning with the RFC, testing wise and locating the reason for the low IR, what values did you get?

 

[jonnyb]

Looking at my notes the ring has a L/N issue, I've written that it has various results below 2Mohms ( it seemed to vary a bit but was always too low) I was going to double check all the neons etc and retest in the morning. There is a definite issue there but I don't know how the polarity on the sockets can swap because a fuse is pulled on a separate circuit. I'm sure I'll find out but it's annoying. So long as imI not missing anything blindingly obvious.

 

[Pete999]

Looking at my notes the ring has a L/N issue, I've written that it has various results below 2Mohms ( it seemed to vary a bit but was always too low) I was going to double check all the neons etc and retest in the morning. There is a definite issue there but I don't know how the polarity on the sockets can swap because a fuse is pulled on a separate circuit. I'm sure I'll find out but it's annoying. So long as imI not missing anything blindingly obvious.

 

[buzzlightyear]

what voltage did you do for RFC, IR test ?

 

[Octopus]

Looking at my notes the ring has a L/N issue, I've written that it has various results below 2Mohms ( it seemed to vary a bit but was always too low) I was going to double check all the neons etc and retest in the morning. There is a definite issue there but I don't know how the polarity on the sockets can swap because a fuse is pulled on a separate circuit. I'm sure I'll find out but it's annoying. So long as imI not missing anything blindingly obvious.

What are you using to confirm polarity swap ?

 

[jonnyb]

Sorry pete999, I wasn't very clear that I was still on about the ir test, the end to ends were fine, I had to do it early on as a radial was in with the ring and I needed to know which was which. Didn't do the figure 8 yet though as I knew I'd be retesting it. The reason I knew the polarity changed was because the telephone had been plugged back in and it made a whiney beep. Quickly used a socket tester then unscrewed and used my volt tester. Will look more in depth in the morning.

 

[buzzlightyear]

Sorry pete999, I wasn't very clear that I was still on about the ir test, the end to ends were fine, I had to do it early on as a radial was in with the ring and I needed to know which was which. Didn't do the figure 8 yet though as I knew I'd be retesting it. The reason I knew the polarity changed was because the telephone had been plugged back in and it made a whiney beep. Quickly used a socket tester then unscrewed and used my volt tester

what the f88k ,now I am confused .

 

[jonnyb]

Initially did a l/n to e at 250 full board ir test in the vain usual hope everything would be good, then had to separate as I didn't get what I wanted haha. Tested the ring at 250 then 500, I always do it like that.

 

[westward10]

If the ring final and lighting circuit are electrically separate with no interconnection to me, this is not possible. Removing the lighting fuse should not affect the ring final.

 

[telectrix]

Sorry pete999, I wasn't very clear that I was still on about the ir test, the end to ends were fine, I had to do it early on as a radial was in with the ring and I needed to know which was which. Didn't do the figure 8 yet though as I knew I'd be retesting it. The reason I knew the polarity changed was because the telephone had been plugged back in and it made a whiney beep. Quickly used a socket tester then unscrewed and used my volt tester. Will look more in depth in the morning.

a whiney beep on a phone is not a recognised test or a clue for fault finding. start with the basics, continuity.IR. polarity. as taught.

 

[westward10]

Is polarity correct at the board.

 

[Deleted member 9648]

I'd be getting in an exorcist.

 

[jonnyb]

Yeah polarity at the board is fine, I quickly checked it again after the sockets went cuckoo. I'm going to just continue with testing in the am and see.

 

[jonnyb]

..

 

[jonnyb]

The phone actually stated on the screen that power was lost so i quickly chucked a socket tester in and then the confusion began. Fuse in - normal, fuse out same thing. Just wondered if anyone else has had it happen, before the testing gods give me a beat down!

 

[ChipFanDave]

If the ring final and lighting circuit are electrically separate with no interconnection to me, this is not possible. Removing the lighting fuse should not affect the ring final.

If only the "fuse was pulled" then they are not electrically separated as the neutrals will still be linked at the C.U. providing the opportunity for the circuits to become connected in series this would tie in with the poor IR. Most likely to be an earth fault on the RFC or even some equipment with high earth leakage.

 

[westward10]

There is definitely no interconnection between the two circuits.

 

[MDJ]

Hi chaps I have a query and wouldn't mind any suggestions. I've been preparing a consumer unit swap, ran the usual tests and no major worries except a low insulation resistance test on a ring. Going to swap the board tomorrow morning. Customer asked me to swap some lighting switches whilst I was there prepping today. Pulled the fuse for the downstairs lighting and this reversed the polarity on the ring sockets. Double checked and happened every time I pulled the fuse. Will investigate further in the morning but has anyone ever had this happen?

Sounds strange, could be two faults, a short between L and N on the ring but not enough to blow the fuse, a nail clipping the cable behind sheathing possibly, and maybe a neutral connected between both circuits, make sure you let us know the outcome, this is a strange one, I have seen some faults over the years but this--well lol

 

[westward10]

Are you sure the phone socket is not actually on the lighting circuit.

 

[Pete999]

a whiney beep on a phone is not a recognised test or a clue for fault finding. start with the basics, continuity.IR. polarity. as taught.

My phone. Whines, but only when her indoors is using it, and my polarity is OK

 

[Pete999]

Sorry pete999, I wasn't very clear that I was still on about the ir test, the end to ends were fine, I had to do it early on as a radial was in with the ring and I needed to know which was which. Didn't do the figure 8 yet though as I knew I'd be retesting it. The reason I knew the polarity changed was because the telephone had been plugged back in and it made a whiney beep. Quickly used a socket tester then unscrewed and used my volt tester. Will look more in depth in the morning.

What type of volt tester do you have?

 

[ChipFanDave]

There is definitely no interconnection between the two circuits.

Is this a question or a statement ? If the socket is live/reverse polarity then it is still connected to the CU, if the lighting circuit only has it's fuse pulled then this also is still connected to the CU. So it looks like they are connected.

 

[jonnyb]

Cheers for the replies chaps, I've had a drink and a think. Will see what's what.

 

[Dave OCD]

I'm just wondering if this could be something to do with a 'borrowed neutral' from the RFC connected to a light, can't really get my head round it though.

 

[Midwest]

All appliances should be disconnected. Chuck the phone and ignore its chaffinch chirpings.

 

[Pete999]

I'm just wondering if this could be something to do with a 'borrowed neutral' from the RFC connected to a light, can't really get my head round it though.

I think the problem may lay with th OP's testing methods, hope he gets it sorted

 

[Lucien Nunes]

From a common-sense perspective, even if the two circuits are interconnected, the polarity of the ring cannot reverse. That would involve the circuit line being disconnected from the supply line and connected to the neutral instead, while the neutral is diconnected from the supply neutral and connected to the line. Four separate changes cannot follow from pulling one fuse. So whatever method has been used to discover this so-called reversal is flawed and giving a false impression. The reality will be simpler.

 

[Octopus]

I'm just wondering if this could be something to do with a 'borrowed neutral' from the RFC connected to a light, can't really get my head round it though.

Like this one of mine ?

L-E 199v, N-E 199v ............... real readings - https://www.electriciansforums.co.uk/threads/l-e-199v-n-e-199v-real-readings.168792/

 

[Pete999]

Post 24 question, "what type tester are you using" to prove polarity?

 

[alasdairp]

My best guess: Telephone skt fed by lighting circuit L but has N borrowed from RFC. Removing lighting cct fuse would mean that if any incandescant bulbs were 'on' they would provide a low resistance path to the lighting circuit N. So, as there is a L-N problem on the RFC - that may produce just enough (reverse) voltage for the very low power requirement telphone to try to power-up via the N connection. This would not show up as a reverse-phase skt using a proper cct tester. The OP has not answered what meters (etc) he is using. The installation needs a full EICR, methinks. Something is very wrong.

 

[markythesparky]

What type of earthing system is it?