Still unsure about testing for borrowed neutrals.

[baldsparkies]

@baldsparkies. The situation is dangerous when say you change an upstairs light for the customer in the bedroom for example. You turn off the upstairs MCB and then test for voltage. As youd expect thered be no voltage and you then begin to carry out the work. Once you have disconnected the core and seperated them, someone accidently turns on the 2 way switch for the landing light. One of the neutrals in your separated cables is now live and ready for you to touch =) that is why it is dangerous.
Live supply is linked from downstairs light and then travels to upstairs light, obviously if the switch is in the on position this will send a live supply through the lamp, down the neutral which you may have disconnected making it live.

I completely agree with you. The situation you describe is far from ideal.
The real answer, if your customer won't agree to re wiring the lighting circuit is to put both circuits with the shared nuetrals into one mcb.
That way it would be a departure from the regs at code 4 rather than a borrowed neutral situ code 2.
I can't remember the last time a borrowed neutral ambushed me. Or even what profanities I used to make others aware of my lack of approval.
As a competant person, you should never assume, cus it makes an --- out of U and ME.
With domestic installs its easy to cover yourself ie check in advance identify and isolate as neccassary.
The borrowed nuetrals are out there right or wrong, sparky beware. If not you will learn, the hard way. Not a good answer I admit, but its a real world answer as many on the forum will confirm.
Oh yes it was an emergency lighting circuit in an office block, back in the 80s I believe. Thats the last one that got me.
Anyways, with all these people raving about rcd's you will only get a tingle if that. (Im such a bad lad, what a wind up merchant)
One other point, Non competant persons should not be touching the installation.
You are the sparky working on the lighting circuits, you are the sparky disconnecting the nuetrals, and to be fair you are the sparky who created the situation. It was safe before you started tampering, sorry but true.

 

[oldtimer]

In 36 years in Scotland I have never come across a shared neutral or have I lived a sheltered life ?

 

[baldsparkies]

In 36 years in Scotland I have never come across a shared neutral or have I lived a sheltered life ?

Hate to say it Old timer, but maybe Scottish sparkies are better than us English boys. Either that, or your a lucky old bu##er.
Listen to me mate, talk about pot calling the kettle black

 

[SW1970]

I completely agree with you. The situation you describe is far from ideal.
The real answer, if your customer won't agree to re wiring the lighting circuit is to put both circuits with the shared nuetrals into one mcb.
That way it would be a departure from the regs at code 4 rather than a borrowed neutral situ code 2.
I can't remember the last time a borrowed neutral ambushed me. Or even what profanities I used to make others aware of my lack of approval.
As a competant person, you should never assume, cus it makes an --- out of U and ME.
With domestic installs its easy to cover yourself ie check in advance identify and isolate as neccassary.
The borrowed nuetrals are out there right or wrong, sparky beware. If not you will learn, the hard way. Not a good answer I admit, but its a real world answer as many on the forum will confirm.
Oh yes it was an emergency lighting circuit in an office block, back in the 80s I believe. Thats the last one that got me.
Anyways, with all these people raving about rcd's you will only get a tingle if that. (Im such a bad lad, what a wind up merchant)
One other point, Non competant persons should not be touching the installation.
You are the sparky working on the lighting circuits, you are the sparky disconnecting the nuetrals, and to be fair you are the sparky who created the situation. It was safe before you started tampering, sorry but true.

But this should only be done if both circuits were originally on MCBs of the same rating. E.g. if an upstairs lighting circuit (6A) has borrowed a neutral from a downstairs ring (32A), then it is not advisable to put both circuits on the same MCB (presumably 32A) because there is not enough overcurrent protection for the upstairs lighting circuit (most likely installed in 1mm2 or 1.5mm2 T&E). A design exercise should be carried out before this is done and if it's not pretty some additional wiring is the best way. However, for the benefit of this scenario, would anyone consider putting an appropriately rated FCU in line adjacent to the CU for the lighting circuit therefore allowing both circuits to go on the higher rated MCB?

 

[the pict]

Interesting topic this any one got drawn examples of a "borrowed N " as I to can get a mental fog over this at times
Pict

 

[alex trician]

With the Mains off. Regarding the insulation test. Test between the 2 neutral bars. If all clear no problem. If you are getting a reading then proceed to seperate the neutrals from neutral bar 1 and test from neutral bar 2 until you can identify the circuit neutral that is the problem. If all clear then replace all neutrals from neutral bar 1 and test from neutral bar 1 to the individual neutrals on bar 2.

For individual circuits being up graded to individual RCD when testing the circuit be sure to link the strappers on the 2 way so you are getting all conductors tested.

 

[i=p/u]

its simple a switched live comming from lighting circuit and neutral and earth going off on differnt lighting ciruit or even a socket outlet circuit. heres my two pence. never touch the shinny copper and touch the neutral to earth and it should trip. correct me anyone

 

[growler]

can someone give me an example of where u would get a borrowed neutral on a landing night. cheers.

 

[Guest111]

on a lighting circuit downstairs your landing light is normally a 2 gang switch with the hall light on one and the landing on the other,you have a live and switchwire from the downstairs light and a 3 core for the 2 way to landing ok,now if you take a link from the live off hall light at switch to link with 3 core you then have your live for landing light.however when you get to the top you have no neutral for light and at one time it was common to pull the neutral from nearest upstairs light usually the bathroom.

 

[telectrix]

i prefere to call it a borrowed live. it happens when the landing light has it's N from upstairs lighting circuit ( as you would expect ) but the L is fed into the 2 way switching from the downstairs circuit, usually from the hall switch when the hall/landing switches are a 2 gang. it was done to get out of running a 3 core between switches.

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fast fingers phil. how's the GSD btw?

 

[Guest111]

i prefere to call it a borrowed live. it happens when the landing light has it's N from upstairs lighting circuit ( as you would expect ) but the L is fed into the 2 way switching from the downstairs circuit, usually from the hall switch when the hall/landing switches are a 2 gang. it was done to get out of running a 3 core between switches.

- Updated - - -

fast fingers phil. how's the GSD btw?

Doing ok Tel,only thing is she has took to frightening people with her bark,the other day a bloke walked past car and she didn,t bother,next one was on edge of pavement she barked and he jumped and fell off the kerb.I swear to god that dog was laughing all the way home lol.- -

 

[telectrix]

she's starting to feel secure then, protecting her ( and your ) territory. all the best to her from our 2lb. attack chihuahua ( see avatar)

 

[Top Cat]

i prefere to call it a borrowed live. it happens when the landing light has it's N from upstairs lighting circuit ( as you would expect ) but the L is fed into the 2 way switching from the downstairs circuit, usually from the hall switch when the hall/landing switches are a 2 gang. it was done to get out of running a 3 core between switches.

- - - Updated - - -

fast fingers phil. how's the GSD btw?

Well Tel that's the first time i have ever heard it called a borrowed live (and you are probably correct) only you could buck the system! Good for you!

 

[telectrix]

well, my logic is that the landing light is upstairs, gets it's neutral from upstairs but the live ( or line if you're under 21 ) from the downstairs. so it's got it's own neutral and has pinched the L from downstairs. Q.E.D.

 

[oldtimer]

Remember when doing a CU change you may not catch or find it until you energise the circuits and the RCD trips as I said earlier it is not that common up here in fact I was asked by a mate who was running a small business he is 63 and he could not figure it out so he gave me a call I turned up and clocked it sraight away . That was the first time he had seen this hence his confusion