Easy Solution to Borrowed Neutral?

[davesparks]

The only test you need to do is to find out if you have two completely separate circuits IR test between the neutrals from each circuit then the lives, all done at the CU dont forget to take the neutrals off the bar
(Nudge)

You've made the same mistake I did earlier, testing neutral to neutral won't identify a borrowed neutral.
Testing live of 1 cct to neutral of another with loads connected is the only way. A borrowed neutral is where a live is connected to 1 cct but the neutral of another cct is used.

The classic example is the upstairs/downstairs 2 way. A 2 gang sw at the bottom of the stairs has a T+E from the hallway light connected as live and sw live, this live is used to feed the 2 way to upstairs.
A twin is run from this switch to the upstairs switch and forms the strappers.
A sheathed single is run from the upstairs switch to the upstairs light.
The upstairs light gets its neutral from the upstairs feed, often another sheathed single.

End result is a live from one circuit and a neutral form another.

 

[Richard3009]

Ohhhh yes when they use the singles method fair point

 

[Hawkmoon]

In my neck of the woods (Portsmouth) this must have been the 'install method of choice' back in the 60s/70s - bottom switch fed, strappers only between switches, neutral from upstairs.

If you work in an area where this is common you are less likely to be caught out/confused by it - like everything in this game, the more experience you have in a particular area, the more 'competent' you are in it.

 

[dazza1981]

In my neck of the woods (Portsmouth) this must have been the 'install method of choice' back in the 60s/70s - bottom switch fed, strappers only between switches, neutral from upstairs.

If you work in an area where this is common you are less likely to be caught out/confused by it - like everything in this game, the more experience you have in a particular area, the more 'competent' you are in it.

I personally have not come across this yet hawkmoon and must admit it has taken a few reads to get my head round it.... but i feel armed with a bit of knowledge to tackle it if and when i do come across a borrowed neutral..... cheers buddy

 

[davesparks]

Ohhhh yes when they use the singles method fair point

By any method a borrowed neutral won't show up by testing between neutrals of different circuits.
A borrowed neutral is where a load is connected between a live of one circuit and a neutral of another, not an interconnection between two circuit neutrals.

 

[7029 dave]

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

This was a very common practice, 2way lighting, no 3core bridge the live on downstairs lighting circuit (com), twin to upstairs (strappers) s/l for landing light. (com)