borrowed neutral
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It's as the name suggests a neutral path borrowed from a different circuit on the CU.
Classic example is 2 way lighting on stairs - only a live run from downstairs the neutral taken from upstairs lights.
Bad because when you isolate lighting circuit (for example) juice may be there from another circuit
AFAIK
Classic example is 2 way lighting on stairs - only a live run from downstairs the neutral taken from upstairs lights.
Bad because when you isolate lighting circuit (for example) juice may be there from another circuit
AFAIK
A borrowed neutral is when a neutral from one circuit is used in another circuit. This is best explained by an example that you will find in many homes.
The most likely instance where you will find a borrowed neutral is the hall/landing light circuit with a two way switch which enables you to switch on the light from the bottom or top of the staircase.
Domestic lighting is usually split into an upstairs and downstairs circuit each with it's own breaker being a fuse or MCB. Now when the house was rewired back in the 80's a not very scrupulous electrician (but following what was very common bad practice) decided he could save himself a bit of time and cable when wiring the landing light. He used the live wire from the downstairs light circuit to provide the supply to the downstairs light switch, which was wired in with the upstairs light switch in two way configuration. So the live supply to the landing light upstairs was from the downstairs light circuit.
But, he also needed a neutral supply to the upstairs landing light and what could be more easy than running a neutral to this light from the upstairs light circuit. He thinks this is no problem because all neutrals are connected together back at the fuse board anyway. Electrically the circuit will work.
Now, assume you have this arrangement and you decide to fit a new light fitting in the bedroom and pull the fuse on the upstairs lighting circuit (or switch off the MCB). You carry out a voltage test on the ceiling light that you are about to disconnect and happy that the circuit is dead you continue to disconnect the wires from the ceiling rose. Whilst wiring up your new light somebody in the house comes up the stairs and turns the staircase light on.
The reason, because of the borrowed neutral. When the landing light which was on the downstairs circuit is switched on and you were working on the upstairs, this current flowed through the light bulb and into the upstairs neutral circuit. Whilst the neutrals on your upstairs fitting were connected together they were at neutral potential. When you took the neutrals out of the terminal block the one that went back to the landing light became live because it was connected through the light bulb to live supply. When you touched it the current that would have flowed through the neutral circuit back to the main neutral at the fuse board is now trying to flow through you to ground.
Electricians have been killed as a result of borrowed neutrals so be advised, the best solution is to switch off at the main switch.
The most likely instance where you will find a borrowed neutral is the hall/landing light circuit with a two way switch which enables you to switch on the light from the bottom or top of the staircase.
Domestic lighting is usually split into an upstairs and downstairs circuit each with it's own breaker being a fuse or MCB. Now when the house was rewired back in the 80's a not very scrupulous electrician (but following what was very common bad practice) decided he could save himself a bit of time and cable when wiring the landing light. He used the live wire from the downstairs light circuit to provide the supply to the downstairs light switch, which was wired in with the upstairs light switch in two way configuration. So the live supply to the landing light upstairs was from the downstairs light circuit.
But, he also needed a neutral supply to the upstairs landing light and what could be more easy than running a neutral to this light from the upstairs light circuit. He thinks this is no problem because all neutrals are connected together back at the fuse board anyway. Electrically the circuit will work.
Now, assume you have this arrangement and you decide to fit a new light fitting in the bedroom and pull the fuse on the upstairs lighting circuit (or switch off the MCB). You carry out a voltage test on the ceiling light that you are about to disconnect and happy that the circuit is dead you continue to disconnect the wires from the ceiling rose. Whilst wiring up your new light somebody in the house comes up the stairs and turns the staircase light on.
The reason, because of the borrowed neutral. When the landing light which was on the downstairs circuit is switched on and you were working on the upstairs, this current flowed through the light bulb and into the upstairs neutral circuit. Whilst the neutrals on your upstairs fitting were connected together they were at neutral potential. When you took the neutrals out of the terminal block the one that went back to the landing light became live because it was connected through the light bulb to live supply. When you touched it the current that would have flowed through the neutral circuit back to the main neutral at the fuse board is now trying to flow through you to ground.
Electricians have been killed as a result of borrowed neutrals so be advised, the best solution is to switch off at the main switch.
Nicky Tesla
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Its when somebody takes your roll of blue singles or blue meter tail
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:^O :^O:^O:^O:^O
do you want that roll of 1.5mm blue single back yet nicky?????
only borrowed it to prop the door open!!
It's not really borrowed though] 
, as they had no intention of giving it back
, as they had no intention of giving it back
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A more accurate term is probably..
shared or combined neutral..
Two (or more circuits) having the neutral joined together BEFORE they reach the fuse box.
as said by others.. most common upstairs & downstairs lights
other culprits include..
a downstairs light joined to a neutral on the upstairs socket circuit!!
coming across this alot when upgrading CUs in council propperties.rcbo's sense the inbalance and trip so rather than the hassle of rewiring the upstair lights neural back to the board the circuits are double up! not good practice but solves the problem
Borrowed neutrals are to be found mostly on house rewires and are as described above.
I think that years back sparks didn't do any re-plastering,mini-trunking didn't exist so if you could only get a pair of strappers up the oval conduit to the landing switch and a single to the loft , borrowing the neutral became a norm. I think it stopped by the time the 15th edition came in.
As posted above , can cause havoc when upgrading a CU.
Deke
I think that years back sparks didn't do any re-plastering,mini-trunking didn't exist so if you could only get a pair of strappers up the oval conduit to the landing switch and a single to the loft , borrowing the neutral became a norm. I think it stopped by the time the 15th edition came in.
As posted above , can cause havoc when upgrading a CU.
Deke
Has anybody seen my neutral. I only left it over there in the corner for a few minutes and its gone :OX( ; \
I have also seen problems when the 2, 2 way switches have been wrongly interconnected on a stairs and hall. It only shows up if the switches are in a particular position.
oh was that yours s&s i saw it there in the corner and didnt realise anyone owned it, unfortunetly ive used it now though, but ill order a replacement and get it sent to you!! :^O :^O
