Easy Solution to Borrowed Neutral?

[Piratepete]

Hi Guys
Semi detached with 16th Ed box. Upstairs and downstairs lights on seperate ccts and mcbs

Just extended the downstairs lighting cct into a conservatory and fitted an RCBO after checking (not very well, it seems) whether the landing light was on a borrowed neutral. All tested Ok. All lights worked.

A couple of days later, customer rings to say that RCBO sometimes trips when the landing light is switched on. Seems landing light is a 7 watt CFL which equates to about 30mA.

When I explained the problem and the mess I was going to make either to feed an upstairs live to the downstairs switch or a downstairs neutral to the pendant, he thought a bit and says 'no problem - I'll fit a 3watt LED bulb and it'll never trip - go away!' So I do making a mental note to check landing light ccts more thoroughly.

Couldn't think of a suitable reply! Can you?

Pete

 

[Richard3009]

Neutral to pendant airing cupboard is always a good route

 

[Hawkmoon]

Why did you miss it when testing? What tests did you carry out?

 

[davesparks]

Out of interest, why did the conservatory lights need RCD protection?

 

[NDG Elecs]

I always say it is good that the rcbo/rcd is tripping because it shows it is working correctly.......safety device....safety device!!! Luckily I deal with a lot of bungalows and flats without shared/borrowed/nicked N's..

 

[Octopus]

Fitting a lower wattage bulb is a "fudge" not a proper fix.

 

[GLENNSPARK]

have you actually PROVED that theres a shared neutral in there?

 

[Richard3009]

Prove the ciruits are either separate or not, drop the neutrals from the bar and IR between the neutrals from each circuit and then the lives, you are checking to make sure you have two independent circuits. It is usually the live that is linked at one of the landing switches giving an inbalance.

 

[Badged01]

Fitting a lower wattage bulb is a "fudge" not a proper fix.

But what a novel "fudge"! Not saying its right but what smart thinking by the householder

 

[plugsandsparks]

Not really a solution as RCD will be sat under threshold, needs to be around 3mA max. When he fits the LED be interesting what happens when he first turns it on. Cct needs to be moved onto same RCD otherwise its simply wrong.

 

[davesparks]

Cct needs to be moved onto same RCD otherwise its simply wrong.

No! The interconnection needs to be found and fixed, the dangers associated with a borrowed neutral will still be present even if the two circuits are on the same RCD.

 

[plugsandsparks]

No! The interconnection needs to be found and fixed, the dangers associated with a borrowed neutral will still be present even if the two circuits are on the same RCD.

yep same mcb is how it shoud be left is what I meant

 

[Hawkmoon]

No! The interconnection needs to be found and fixed, the dangers associated with a borrowed neutral will still be present even if the two circuits are on the same RCD.

Agreed, although not so much of an issue if on same rcbo as in this case - though not ideal (landing not separate/No. of lights on one circ etc)

The main danger with borrowed neutrals if left (as I see it) is when some unsuspecting sparky carefully isolates upstairs circ (locks off etc) then proceeds to change fittings in the bedrooms or bathroom - then someone (the customer on the way up to offer him tea) switches the landing light on....result - he gets fried!!

If you're gonna leave it you should at least label it on CU.

 

[Badged01]

Millions if not trillions of "17 edn" boards (and 16th) out there with exactly that --- both on the same MCB! Clearly whoever was changing them at the time hadn't done proper checks or wasnt too concerned about no seperation of circuits. Although as one learned 'electrician' once told me, "they've got sockets and standard lamps" .....

 

[Badged01]

Edited: OK, so I exagerated with the numbers ......