Borrowed neutral - again!

[KeenPensioner]

As I've said before, I'm not a qualified electrician but have worked as a mate a few times. I'm retired now and as a hobby I study all things electrical (domestic). I know this has been asked before on this forum but as an amateur I still can't understand how the wiring for "borrowed neutrals" was actually carried out in the "old days". The way I understand it - upstairs circuit and downstairs circuit are separate (in singles?). The customer now wants a "landing light" that is 2-way switched. The feed for the new light is taken from downstairs (say) and the neutral from upstairs. My basic question is - if they were taking a new feed to the light (or switch) from the downstairs circuit, why didn't they take a neutral at the same time? I've read many articles and watched many videos (John Ward and others) but still don't get it. What I really would appreciate is a wiring diagram.
John Ward's videos -

View: https://www.youtube.com/watch?v=IBcw2JJsELs

View: https://www.youtube.com/watch?v=7C7Tkge5gvQ

 

[Wilko]

Hi - I’ve never built one (honest Gov, it wasn’t me ...) but I thought the problem comes about because the 2 lights are physically far apart and the linking cables only contained L (?). So the temptation was to use the nearest available N which might then be from 2 different circuits.

 

[EricMark]

The problem is the line not neutral, the name is confusing, it's call borrowed neutral, but is borrowed.

So years ago electricians would put two switches together and take one line feed for both switches, and in the main this was OK, however when we started using down lighters we regularly found five amp was not enough, and although regulations allow up to 16 amp for lighting, the ceiling roses are typically rated 5 or 6 amp, so if there were any ceiling roses they could not use over a 6 amp supply, also the tungsten bulb should have a built in fuse, so if when the filament ruptures there is ionisation, the fuse will rupture so only that bulb fails, but many imports don't have this fuse in the bulb, so when the bulb blows, the high current has been know to melt the solder on the bulb contacts and weld the bulb into the holder, so it makes sense to limit the lighting supply to 6 amp.

So to draw more than 6 amp the supplies were split, some times it was split to start with, but often this split was done latter, when split the electrician should clearly check that there is no borrowing of a line which will technically result in borrowed neutral, however pre use of RCD protection everything would still work, so often missed.

As to what to do when found, returning to a single MCB for all lights is the easy way, your not making any worse, you just returning it to how it should be, however putting the two MCB's on the same RCD may work, but is clearly wrong, and once you realise there is a borrowed neutral to put both MCB's on one RCD leaves no excuse, if an accident then the person doing it could be excused, no body is perfect, but doing it when you know there is a borrowed neutral is criminal.

What we now consider is should a power circuit trip, we don't want this to affect lights, so it is considered safer to have two RCD's split so the sockets in a room should they trip the RCD will not take out lights in that room.

However clearly a main fuse will take out both, as will a power cut, so really down to a risk assessment, some houses do have stair wells in centre of house with very little light from outside, my old house had windows above the internal doors to light landing, which really was not good enough, I fitted an emergency light, this house there is a window at top of stairs, however I have a rechargeable light plugged in which will auto light with a power cut.

This house sockets split front to back, lights split up and down, so only way with two RCD's is all lights on one RCD and all sockets on other RCD, this means loose one socket due to RCD trip and you loose all, so the all RCBO consumer unit (CU) is clearly the way to go. Which is easy enough as TN supply.

MK do a kinetic switch, that is the easy way around the two way switch problem, but the standard wiring for two way switching the line is taken to second switch, you can see from diagram earths missing for clarity and loops around the cables you need three wires between the two switches but one of the three is permanent line. So this was "borrowed" from another switch, so twin and earth could be used between the two switches. It is a bad idea anyway as it can cause mains hum on some equipment if you send a line in one direction only.

The two way switch shown between them has 4 options with a truth table, two are off so not interested in them, of the other two if different lines are used, from different RCD's one will trip RCD the other will not, so it is easy not to realise there is a problem.

In my own house at front door a block of 4 switches, upstairs landing lights, hall lights, and two sets of outside lights, and an error had been made, wrong line selected, both lines were in the switch, just some one selected wrong one.

If you think of it as borrowed line instead of borrowed neutral does it make more sense? Remember both Line and Neutral are considered Live, I try to remember to call it Phase or Line, but some times I forget.
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Does this help, the right hand light line feeds the switch second from left which will work the left hand light, it will work, but the line can feed between the two lamps with both left hand switches down, and with just second from left down light is powered from right hand fuse instead of left hand fuse. As can be seen it is line that is borrowed, but it is called borrowed neutral.
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Just watched John Ward no wonder you can't work it out, he shows line to com, but that is not the way most of us wire it, we connect all terminals to the like terminal in other switch, so L2 to L2 and L1 to L1 and com to com. The com only connects switch to switch, so if L1 is line in than L2 is line out to light.

 

[Pete999]

Best way overcome this common problem is run a 3 core and earth between the 2 way downstairs and the 2 way on the landing, take L and SL from the landing light to the upstairs 2 way switch

 

[EricMark]

Best way overcome this common problem is run a 3 core and earth between the 2 way downstairs and the 2 way on the landing, take L and SL from the landing light to the upstairs 2 way switch

For DIY may be, however it would in most houses cause a lot of disruption rarely can one get three and earth to replace twin and earth without needing to re plaster.

The MK Echo switch is very expensive, however compared with re plastering I think a better option. There are cheaper wireless this switch needs batteries but a lot cheaper, I don't think I would be able to justify the cost of re plastering when one can use wireless.

 

[KeenPensioner]

The problem is the line not neutral, the name is confusing, it's call borrowed neutral, but is borrowed.

So years ago electricians would put two switches together and take one line feed for both switches, and in the main this was OK, however when we started using down lighters we regularly found five amp was not enough, and although regulations allow up to 16 amp for lighting, the ceiling roses are typically rated 5 or 6 amp, so if there were any ceiling roses they could not use over a 6 amp supply, also the tungsten bulb should have a built in fuse, so if when the filament ruptures there is ionisation, the fuse will rupture so only that bulb fails, but many imports don't have this fuse in the bulb, so when the bulb blows, the high current has been know to melt the solder on the bulb contacts and weld the bulb into the holder, so it makes sense to limit the lighting supply to 6 amp.

So to draw more than 6 amp the supplies were split, some times it was split to start with, but often this split was done latter, when split the electrician should clearly check that there is no borrowing of a line which will technically result in borrowed neutral, however pre use of RCD protection everything would still work, so often missed.

As to what to do when found, returning to a single MCB for all lights is the easy way, your not making any worse, you just returning it to how it should be, however putting the two MCB's on the same RCD may work, but is clearly wrong, and once you realise there is a borrowed neutral to put both MCB's on one RCD leaves no excuse, if an accident then the person doing it could be excused, no body is perfect, but doing it when you know there is a borrowed neutral is criminal.

What we now consider is should a power circuit trip, we don't want this to affect lights, so it is considered safer to have two RCD's split so the sockets in a room should they trip the RCD will not take out lights in that room.

However clearly a main fuse will take out both, as will a power cut, so really down to a risk assessment, some houses do have stair wells in centre of house with very little light from outside, my old house had windows above the internal doors to light landing, which really was not good enough, I fitted an emergency light, this house there is a window at top of stairs, however I have a rechargeable light plugged in which will auto light with a power cut.

This house sockets split front to back, lights split up and down, so only way with two RCD's is all lights on one RCD and all sockets on other RCD, this means loose one socket due to RCD trip and you loose all, so the all RCBO consumer unit (CU) is clearly the way to go. Which is easy enough as TN supply.

MK do a kinetic switch, that is the easy way around the two way switch problem, but the standard wiring for two way switching the line is taken to second switch, View attachment 55400you can see from diagram earths missing for clarity and loops around the cables you need three wires between the two switches but one of the three is permanent line. So this was "borrowed" from another switch, so twin and earth could be used between the two switches. It is a bad idea anyway as it can cause mains hum on some equipment if you send a line in one direction only.

The two way switch shown between them has 4 options with a truth table, two are off so not interested in them, of the other two if different lines are used, from different RCD's one will trip RCD the other will not, so it is easy not to realise there is a problem.

In my own house at front door a block of 4 switches, upstairs landing lights, hall lights, and two sets of outside lights, and an error had been made, wrong line selected, both lines were in the switch, just some one selected wrong one.

If you think of it as borrowed line instead of borrowed neutral does it make more sense? Remember both Line and Neutral are considered Live, I try to remember to call it Phase or Line, but some times I forget.
[automerge]1579612586[/automerge]
View attachment 55401Does this help, the right hand light line feeds the switch second from left which will work the left hand light, it will work, but the line can feed between the two lamps with both left hand switches down, and with just second from left down light is powered from right hand fuse instead of left hand fuse. As can be seen it is line that is borrowed, but it is called borrowed neutral.

The problem is the line not neutral, the name is confusing, it's call borrowed neutral, but is borrowed.

So years ago electricians would put two switches together and take one line feed for both switches, and in the main this was OK, however when we started using down lighters we regularly found five amp was not enough, and although regulations allow up to 16 amp for lighting, the ceiling roses are typically rated 5 or 6 amp, so if there were any ceiling roses they could not use over a 6 amp supply, also the tungsten bulb should have a built in fuse, so if when the filament ruptures there is ionisation, the fuse will rupture so only that bulb fails, but many imports don't have this fuse in the bulb, so when the bulb blows, the high current has been know to melt the solder on the bulb contacts and weld the bulb into the holder, so it makes sense to limit the lighting supply to 6 amp.

So to draw more than 6 amp the supplies were split, some times it was split to start with, but often this split was done latter, when split the electrician should clearly check that there is no borrowing of a line which will technically result in borrowed neutral, however pre use of RCD protection everything would still work, so often missed.

As to what to do when found, returning to a single MCB for all lights is the easy way, your not making any worse, you just returning it to how it should be, however putting the two MCB's on the same RCD may work, but is clearly wrong, and once you realise there is a borrowed neutral to put both MCB's on one RCD leaves no excuse, if an accident then the person doing it could be excused, no body is perfect, but doing it when you know there is a borrowed neutral is criminal.

What we now consider is should a power circuit trip, we don't want this to affect lights, so it is considered safer to have two RCD's split so the sockets in a room should they trip the RCD will not take out lights in that room.

However clearly a main fuse will take out both, as will a power cut, so really down to a risk assessment, some houses do have stair wells in centre of house with very little light from outside, my old house had windows above the internal doors to light landing, which really was not good enough, I fitted an emergency light, this house there is a window at top of stairs, however I have a rechargeable light plugged in which will auto light with a power cut.

This house sockets split front to back, lights split up and down, so only way with two RCD's is all lights on one RCD and all sockets on other RCD, this means loose one socket due to RCD trip and you loose all, so the all RCBO consumer unit (CU) is clearly the way to go. Which is easy enough as TN supply.

MK do a kinetic switch, that is the easy way around the two way switch problem, but the standard wiring for two way switching the line is taken to second switch, View attachment 55400you can see from diagram earths missing for clarity and loops around the cables you need three wires between the two switches but one of the three is permanent line. So this was "borrowed" from another switch, so twin and earth could be used between the two switches. It is a bad idea anyway as it can cause mains hum on some equipment if you send a line in one direction only.

The two way switch shown between them has 4 options with a truth table, two are off so not interested in them, of the other two if different lines are used, from different RCD's one will trip RCD the other will not, so it is easy not to realise there is a problem.

In my own house at front door a block of 4 switches, upstairs landing lights, hall lights, and two sets of outside lights, and an error had been made, wrong line selected, both lines were in the switch, just some one selected wrong one.

If you think of it as borrowed line instead of borrowed neutral does it make more sense? Remember both Line and Neutral are considered Live, I try to remember to call it Phase or Line, but some times I forget.
[automerge]1579612586[/automerge]
View attachment 55401Does this help, the right hand light line feeds the switch second from left which will work the left hand light, it will work, but the line can feed between the two lamps with both left hand switches down, and with just second from left down light is powered from right hand fuse instead of left hand fuse. As can be seen it is line that is borrowed, but it is called borrowed neutral.
[automerge]1579613469[/automerge]
Just watched John Ward no wonder you can't work it out, he shows line to com, but that is not the way most of us wire it, we connect all terminals to the like terminal in other switch, so L2 to L2 and L1 to L1 and com to com. The com only connects switch to switch, so if L1 is line in than L2 is line out to light.

Thank you very much for your prompt and comprehensive reply. Your diagram explains the 2-way switching well and I can see that under certain configuration of switches this can introduce a potential hazard when working on these lights (as John Ward explains). I'm probably over thinking this because I understand 2-way switching with 3-core between switches. I'm trying to imagine the electrician (in the old days) running cables to the new fitting. In his videos John Ward says that a feed would be taken from downstairs circuit to the new light (on the landing) and a neutral from a different circuit. If the electricain has to get a live cable from downstairs circuit to the fitting why couldn't he just run a neutral at the same time - again in the old days?

 

[Pete999]

For DIY may be, however it would in most houses cause a lot of disruption rarely can one get three and earth to replace twin and earth without needing to re plaster.

The MK Echo switch is very expensive, however compared with re plastering I think a better option. There are cheaper wireless this switch needs batteries but a lot cheaper, I don't think I would be able to justify the cost of re plastering when one can use wireless.

I meant from the word go Eric

 

[EricMark]

I meant from the word go Eric

Clearly we should have always used three core and earth, however I have seen many where the twin and earth was used, and to be fair the originally had all lights from one fuse, so it complied, it was only latter when supply to upper and lower floors was split, was there a breach of regulations.

Today the modern master and slave set up used with electronic switches would likely cause EMC problems if twin and earth was used, also a problem if the cables go through any ferrous hole, even if supplied from same fuse.

 

[Lucien Nunes]

If the electrician has to get a live cable from downstairs circuit to the fitting why couldn't he just run a neutral at the same time

Clearly we should have always used three core and earth

This is the crux of it: Economy. The 'downstairs line / upstairs neutral' configuration allowed the installer to run just a twin + earth strapper cable between the switches instead of 3C+E, thereby avoiding having to stock 3C+E or make two runs of T+E.

With 3C+E, any of the normal 2-way configurations is possible without any borrowing. For 'conventional' 2-way one permutation is to carry L1, L2 and PL through the strapper cable to the downstairs switch. But by picking up the PL from the other gang of the 2g, only L1 and L2 need to be run.

 

[davesparks]

I'm probably over thinking this because I understand 2-way switching with 3-core between switches. I'm trying to imagine the electrician (in the old days) running cables to the new fitting. In his videos John Ward says that a feed would be taken from downstairs circuit to the new light (on the landing) and a neutral from a different circuit. If the electricain has to get a live cable from downstairs circuit to the fitting why couldn't he just run a neutral at the same time - again in the old days?

Three core and earth was far less commonly available, it existed but was less common, and only needing a few metres for each house most people didn't bother buying it.

The downstairs live was not extended up to the upstairs light fitting.
The downstairs switch would be a 2 gang switch, a twin and earth would go to this switch from the downstairs light carrying live and switched live. The live is used to feed both switches.
A twin and earth was taken from this switch to the upstairs switch carrying the two strappers (L1 and L2 of the 2 way switch)
A single red (or twin with the black cut off) was taken from the upstairs switch to the light at the top of the stairs.
The upstairs light gets its neutral from the upstairs circuit.

 

[KeenPensioner]

This is the crux of it: Economy. The 'downstairs line / upstairs neutral' configuration allowed the installer to run just a twin + earth strapper cable between the switches instead of 3C+E, thereby avoiding having to stock 3C+E or make two runs of T+E.

With 3C+E, any of the normal 2-way configurations is possible without any borrowing. For 'conventional' 2-way one permutation is to carry L1, L2 and PL through the strapper cable to the downstairs switch. But by picking up the PL from the other gang of the 2g, only L1 and L2 need to be run.

Thanks for the reply. All this time it was simply to avoid carrying a stock of 3 core. I have been trying to figure this out for ages. I can't believe it was that simple!!
Thanks to everyone who helped me on this.
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Thanks to everyone who helped me on this. All this time it was simply to avoid carrying (or not having) a stock of 3 core. I have been trying to figure this out for ages. I can't believe it was that simple!!

 

[captaincaveman]

Bit late reading this thread lol. But it just occured to me to use a kinetic switch to overcome this problem. I've found a good reliable one for £30 (a lot cheaper than a couple of years ago) which I've used in garden lighting a couple of times. I think I'll give it a go with a replacement ccu job I'm doing. That way I can still have the split lighting still and at not much extra cost

 

[EricMark]

The problem has now become worse, with the use of Smart relays, and having the switches switch extra low voltage.

I have found with my own house an intermittent fault with the light switches, the lamp is not easy to access, needs an access platform, so when the light switch failed, I did not jump in to fix it, next day was working again.

However since we rarely use the switches, it does not really matter, we have got use to saying hey google turn on or turn off, or use the phone.