Confused about a fault with downstairs lighting, any ideas?

[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?