Odd lighting singles...

[AAAMUSEMENTS]

My sister's old BS3036 CU has now gone and the new dual RCD is installed.

All of the 1mm and 1.5mm previously went into one 6amp fuse. There are from memory 6 t&e and one pair of single + earth. Bearing in mind this is an average, 2 bedroom ex council place it seemed excessive to have so many, but as the installation has evidently been bodged and badly added to/removed from over the years it's no great surprise.

First off I connected up the singles, to see what part of the house they supplied - as I knew that there were singles in the loft supplying the upstairs lighting.

The kitchen and living room lights worked, but nothing upstairs - BUT the landing (two way) compact flu bulb was flashing slightly, as if it was trying to start but didn't have enough power.

As I was running out of time and light, I randomly connected all of the rest of the lighting over the two sides of the CU. This resulted in both RCDs tripping when the hall or landing lights were switched on.

As time and light had now run out, I connected all of the lighting onto two 6amp MCBs on one side of the CU. All was fine and all lighting worked.

I am thinking that this has got to be a shared neutral on the two way hall and landing, but I am having difficulty getting my head around it because of the surfeit of lighting cables...

what's the best way of systematically testing what goes where and does what?

 

[ProDave]

Continuity test between all the different neutrals arriving at the CU.

Once you find which one(s) are connected together, you either need to put those on the same side of the CU, or work out where the borrowed neutral is and rewire that bit.

 

[AAAMUSEMENTS]

Thanks... any idea on the oddly flashing light though?

Could this be related to the probable neutral issue?

 

[aptsys]

Continuity test between all the different neutrals arriving at the CU.Once you find which one(s) are connected together, you either need to put those on the same side of the CU, or work out where the borrowed neutral is and rewire that bit.

That's not how you test for a borrowed neutral. The neutrals aren't joined together, so you won't get continuity between any of the neutrals.

 

[ProDave]

That's not how you test for a borrowed neutral. The neutrals aren't joined together, so you won't get continuity between any of the neutrals.

You will if all the lights are turned on. That's how I test it, you will read the impedance of the light bulbs not a dead short. If there was no borrowed neutral, then even with the lights all turned on, there would be no reading between any of the neutrals.

If you have a better method, I'm keen to learn it.

 

[ianmacd]

That's not how you test for a borrowed neutral. The neutrals aren't joined together, so you won't get continuity between any of the neutrals.

I think you mean are unlikely to be joined together.

Wander lead is probably the easiest way. Short each L&N pair in turn and see what fittings/accessories have continuity to the join in the CU on either L or N but not the other.

 

[M107]

When looking for the infernal borrowed neutral in the domestic enviroment you'll normally find it in the 2 way lighting for the landing/hall.

I always take a look in the loft & fitting of the landing light first on the older installations, more often than not you'll find the line is from downstairs lighting circuit (usualy a jb under landing floor used as the old octopus system) & when you look in the loft you'll find a T/E running from upstairs circuit to landing light with only one conductor in use & connected to the neutral.

 

[AAAMUSEMENTS]

When looking for the infernal borrowed neutral in the domestic enviroment you'll normally find it in the 2 way lighting for the landing/hall.I always take a look in the loft & fitting of the landing light first on the older installations, more often than not you'll find the line is from downstairs lighting circuit (usualy a jb under landing floor used as the old octopus system) & when you look in the loft you'll find a T/E running from upstairs circuit to landing light with only one conductor in use & connected to the neutral.

I did wonder why there was an old octopus under the stairs!

ROTFWL

Seriously though it's really a confusing one, there are two lots of T&E that wander off somewhere under the stairs, I felt sure that the upstairs would be the singles too but the singles do the downstairs... apart from the oddly flashing landing light that is!

:_|

 

[Apache]

apart from the oddly flashing landing light that is! :_|

loose connection?

Why not just leave all the lighting on the one breaker?

Say owner wouldn't pay for you to find borrowed neutral. Was like that before?

 

[AAAMUSEMENTS]

loose connection?Why not just leave all the lighting on the one breaker?

Say owner wouldn't pay for you to find borrowed neutral. Was like that before?

Tempting, but as my sister lives there I would like it to be right! Plus I will undoubtedly have to work on it again in future...

 

[Apache]

Tempting, but as my sister lives there I would like it to be right! Plus I will undoubtedly have to work on it again in future...

As you like. I have never lived in a house with more than 1 lighting circuit. When it's dark there's usually something like the TV on that will let you see enough to reset the trip.

 

[AAAMUSEMENTS]

As you like. I have never lived in a house with more than 1 lighting circuit. When it's dark there's usually something like the TV on that will let you see enough to reset the trip.

Well, I do have to say that I am glad I did not take your advice this time!

After some testing I established that the singles were supplying the downstairs lights, and sharing a neutral with the upstairs lighting that was on one of the other 1.5 radials. So both upstairs and downstairs have had to go on one side of the board for the time bring.

Another two 1.5 radials traced to the light in the the understairs cupboard where the cu is, this cupboard must have been carved out of a small pantry and the back hall, hence the back hall is on ANOTHER 1.5 radial (these two lights are all of a meter apart and on separate radials! :innocent ).

Another 1.5 radial traced to a double socket in the living room... the other two remaining 1.5 radials were untraceable. I suspected that one may have fed an obsolete extractor upstairs in the bathroom.

As I didn't have a 10 amp breaker I left the 1.5 supplied double socket disconnected, as well as the two untraceable radials. I thought, "Oh well, we will find out if they are important when something stops working"!

Big mistake... after my sister returns form her weekend away she phones on Monday to tell me that her freezer is rapidly defrosting. X(

The two sockets that I didn't check right behind the freezer, which is stacked on top of the fridge and is, unsurprisingly, really difficult to move, are fed from one of the two unidentified 1.5 radials. :_|

Went out and got a 10amp breaker and put both of the 1.5 supplied double sockets into it. This should comply with the regs I hope?

?:|

Certainly a damn sight better than it was... these two double sockets were either fed from the single 6 amp rewireable, along with all the rest of the lights, OR from the rewireable 32 amp ring circuit - but through 1.5mm T&E!

bad day explode

So anyway getting somewhere now... just need to sort out the borrowed neutral... or should I just leave them on one side of the split as they are, and put the cupboard and the hall light on separate sides of the split so that whichever side goes there will be a light near to the CU?

 

[ProDave]

So anyway getting somewhere now... just need to sort out the borrowed neutral... or should I just leave them on one side of the split as they are, and put the cupboard and the hall light on separate sides of the split so that whichever side goes there will be a light near to the CU?

Your easiest option is of course put the two independent light circuits on the other RCD until or unless you can sort out the borrowed neutral.

That's naughty wiring sockets in 1.5 You have done the best you can, unless of course you can rewire the sockets. Of course it's often handy to have the fridge/freezer on a separate circuit, so I would put that on the other RCD to most of the other sockets in the house.

It reminds me of when I was doing some minor modifications and encountered a whole socket ring circuit wired in 1.5 3 core & earth, using red for live, blue for neutral and yellow for earth, with the cpc core unused. The best I could do with that one was fit a 16A MCB for that circuit.

 

[AAAMUSEMENTS]

Your easiest option is of course put the two independent light circuits on the other RCD until or unless you can sort out the borrowed neutral.That's naughty wiring sockets in 1.5 You have done the best you can, unless of course you can rewire the sockets. Of course it's often handy to have the fridge/freezer on a separate circuit, so I would put that on the other RCD to most of the other sockets in the house.

Pretty much my thoughts, so thank you for the confirmation that I am working along the right lines.

I may rewire the two sockets in the future, but as the wiring is in good condition and is now on the correct maximum rating I think I will leave it for the time bring, unless the fridge/freezer turn out to be prone to nuisance tripping due to the lower than normal rating of course...

I feel that I have already spent enough of my life on this job, which started out as a simple request to enable connection of a shower, and has damn near turned into a complete rewire....

:|

 

[ProDave]

I feel that I have already spent enough of my life on this job, which started out as a simple request to enable connection of a shower, and has damn near turned into a complete rewire.... :|

You get jobs like that. I was called once to "move a couple of sockets" in preparation for an extension being built. That job DID end up as a complete rewire.