Borrowed neutrals?

[Taffyo]

Hi all, can anyone tell me if I have a borrowed neutral and explain the concequences of this.
I have a 3 gang two way switch dowstairs for the dining room (2 way switching), light at the bottom of the stairs (downstairs circuit, 1 way switching) and light at the top of the stairs ( upstairs circuit, 2 way switching) so the 3 core + E comes from the 1 gang 2 way switch on the upstairs light circuit to the 3 gang downstairs. Is this OK.

Taff

 

[Spark123]

As you have a 3c+e from the upstairs light switch to the downstairs light switch then the probability of you having a borrowed neutral is very low.
There should be no electrical connections between the switch to the upstairs light switch and the other two.
The consequence of borrowed neutrals is when someone is working on the upstairs circuit, they may recieve a shock caused by the downstairs circuit feeding into it, you will also have loads from two circuit protective devices using the same neutral return which could (albeit very unlikely given nature of the loads) cause an overload, but like I said yours doesn't sound like yours is.

 

[davelx]

Hi all, can anyone tell me if I have a borrowed neutral and explain the concequences of this.
I have a 3 gang two way switch dowstairs for the dining room (2 way switching), light at the bottom of the stairs (downstairs circuit, 1 way switching) and light at the top of the stairs ( upstairs circuit, 2 way switching) so the 3 core + E comes from the 1 gang 2 way switch on the upstairs light circuit to the 3 gang downstairs. Is this OK.

Taff

Taffyo, please confirm that you have two separate lighting circuits, one up and one down, protected by separate MCBs.

I ask because many older houses (mine included) only have a single lighting circuit, so although the neutral may not be running in the same cable as the live/switched live, it's not actually borrowed (unless someone re-wires without realising and splits up and down onto separate MCBs)

 

[Taffyo]

Yes I have two 6amp MCB's 1 up and 1 down and as far as I know this 3core + E is the only cable that up and down have in common and it definaltey comes from the up switch into the down switch.

Taff

 

[ban-all-sheds]

As spark123 said, the type of 2-way strapping you have doesn't lead to borrowed neutrals.

If you look at the details in the For Reference topic & the Wiki on how 2-way switching works you'll see why.

You'll also find a superb diagram showing why borrowed neutrals are a Bad Thing™....

 

[Stoday]

As spark123 said, the type of 2-way strapping you have doesn't lead to borrowed neutrals.

That is plain wrong.

The type of 2-way strapping has nothing to do with the neutrals and a borrowed neutral is just as likely with either method.

Yes, look at the wiki and you'll see for yourself.

Hey BAS don't feel too bad; we all make mistakes from time to time...

 

[davelx]

As spark123 said, the type of 2-way strapping you have doesn't lead to borrowed neutrals.

That is plain wrong.

The type of 2-way strapping has nothing to do with the neutrals and a borrowed neutral is just as likely with either method.

Yes, look at the wiki and you'll see for yourself.

Hey BAS don't feel too bad; we all make mistakes from time to time...

No, it's correct - you said it yourself:

"The type of 2-way strapping has nothing to do with the neutrals and a borrowed neutral is just as likely with either method."

Therefore BAS's statement is true - that method of strapping does not LEAD to borrowed neutrals.

 

[ban-all-sheds]

It's the top one:

which leads to it when the two switches are on different floors and then someone splits the lighting circuit into one per floor.

With the bottom one this doesn't happen....

 

[davelx]

The bottom one certainly makes it very unlikely. But given what I've found in the lighting wiring in my house, I wouldn't rule anything out without checking.

 

[RF Lighting]

Well yes, don't take anything for granted. We all know that assumption is the mother of all f-ups.

But the point being made is that, generally if there is a 3 core and earth linking the switches there should not be a borrowed neutral, and if there is a twin and earth, then there may well be (but not always)