Cu change

[philbas]

Take it easy. I think prodaves input to this forum is great and everyones taking digs. we all get things wrong from time to time. Give him a break. Thought I'd logged onto the darkside for a minute there. Cheers

I have to agree, prodave has made some very good posts, but in this case it;s just wrong.

 

[Lurch]

Wow, just wow. I can accept the odd mistake or misguided practice but to actually try and pass dangerous scenarios off as good advice is just wrong and dangerous and displays a complete lack of understanding of the basics and some serious holes in the basic fundamentals of being an electrician.

 

[Lurch]

No it doesn't. The LIVE for a particular light fitting only ever comes from one circuit, and nobody has ever got a shock from the borrowed neutral.The other "danger" with lighting circuits is often the downstairs hall / landing light switch will have two live feeds, one from each circuit, so both need to be isolated before changing the switch. But again, that is not a borrowed neutral problem, though perhaps a better argument why the lighting circuits should be fed from one MCB.

I'd look up borrowed neutrals as I don;t think you actually understand what one is, and therefore have no idea how to avoid them.

If borrowed neutrals were fine and dandy then by your reckoning the only way to safely isolate any point of any installation would be to isolate the whole supply entirely, i.e. turn off the main switch.

 

[Andy™]

I'd look up borrowed neutrals as I don;t think you actually understand what one is, and therefore have no idea how to avoid them. If borrowed neutrals were fine and dandy then by your reckoning the only way to safely isolate any point of any installation would be to isolate the whole supply entirely, i.e. turn off the main switch.

and next door too, just incase.

 

[ProDave]

here's a diagram. if anyone is unable to work out how you can get a shock from the neutral' date=' i suggest you go try it in your own house. just make sure you call an ambulance first.

[img']http://i22.photobucket.com/albums/b314/andrew2022/borrowedneutral-1.jpg

Oh dear, my comments seem to have upset some.

so let me explain my thought process and understanding of why I gave the advice I did.

The circuit you have shown there is a loop through circuit. Any such loop through circuit that is likely to be of an age to be a candidate for a borrowed neutral would be loop through in the light fitting (loop through at the switch is mostly a more recent configuration)

Now, I FULLY ACCEPT that in the case of a loop through circuit with a borrowed neutral, then unlooping the neutral in the process of changing a light fitting could lead to you receiving a shock.

BUT, and here's the but, the whole point of a loop through circuit is you have a live and it CORRESPONDING neutral at EVERY light fitting. So you would have to be working really really hard and make some really stupid and deliberate mistake to ever manage to get a borrowed neutral on a loop through circuit.

Consequently, I have NEVER encountered a loop through circuit with a borrowed neutral so never ever gave a thought to the fact that it could happen and could be dangerous.

The ONLY time I have encountered a borrowed neutral is with the old "all back to one junction box" circuit (usually one junction box per floor). Borrowed neutral is common with those to save on the number of cores going from upstairs to downstairs.

So here is the next BUT. With the "all to one junction box" circuit, there is only ONE live and only ONE neutral to each light fitting. So even with a borrowed neutral, and two supplies, changing a light fitting is not dangerous as you will never be splitting the neutral when you remove the fitting. The usual rules apply, the only way you will get a shock is by not isolating the supply to that light fitting and not testing for dead.

The ONLY time you would split the neutral and hence risk a shock with an "all to one junction box" circuit is if you were doing some major work in the big lighting junction box. That I assume is beyond the realms of a DIY light fitting change and would only be done by an electrician who knows what he is doing.

So I still stand by the fact I would be happy personally that two supplies to a borrowed neutral lighting circuit of the "all to one junction box" type does not pose a significant danger, and operationally is preferable.

I fully accept a borrowed neutral in a loop through circuit DOES poses a significant danger, but re iterate I have never encountered that, and can't imagine how it could occur.

This discussion is about a CU change. The main criteria of a CU change is to ensure the installation is "no less safe" than before. As such we are not required to bring everything up to current standards. We have to make a judgement that the work we do improves safety. Taking all the above into consideration, I still contest that having a borrowed neutral lighting circuit on two MCB's, sharing the same RCD is still a lot safer than it was before. After all that borrowed neutral circuit has been there for probably 30 years or more posing the same risk.

I take my job seriously and always try to do a safe, well thought out job. I have thought out the consequences and possibilities of a borrowed neutral lighting circuit, but came to a different conclusion to others. I don't think that makes me reckless or a bad electrician.

I try to consider each job individually, and like I have already said, if ever I do encounter a loop through lighting circuit with borrowed neutrals that really could pose a real danger I would not put them on separate MCB's. But better still, if it was a loop through, it should be simple to find and correct the borrowed neutral in the first place.

I think what this highlights is that I try to analyse the circuit and make an informed judgement on each individual case as to what is safe and what is not safe. Some prefer to read a regulation and apply a blanket ruling, without actually considering if there is any real danger or not in a particular situation. That does not make one person right and the other wrong, it just highlights a different approach (I come from an industrial background so am perhaps a little more used to "problem solving" than some might be)

The important thing is we are discussing possible scenarios and it may highlight dangers some had not anticipated, or may show that some perceived dangers are not real. But if it gets us all thinking and analysing what we are doing, then that has to be for the better.

 

[Andy™]

I fully accept a borrowed neutral in a loop through circuit DOES poses a significant danger, but re iterate I have never encountered that, and can't imagine how it could occur.

you really do have no idea.

its very common.

i.e you have 1 circuit for up and one for down.

landing light gets its live from downstairs switch, to upstairs switch, to light, and neutral back to upstairs lighting.

unfortunatly, its very common

and then there is the borrowed neutral on lighting - ring.

live from light switch to wall lights, neutral straight down to sockets.

doesnt take much imagination to think of many other ways of this

you will also find that very few houses are still wired in all from one. most are radials all the way to last light. loop normally at the light, sometimes at the switch

and locating borrowed neutral may be easy in some situations, but the repair rarely is, without installing new cables to relevant circuit

 

[Lurch]

Nope, still not got it.

I can;t quite follow what you're trying to say above, but I think what you're saying is borrowed neutrals are an unlikely occurence, and if people take care when altering existing installations then there shouldn;t really be any.

Borrowed neutrals are rarely caused by design, in so much as they aren;t wired like that from day 1. Usually they are caused by someone doing some works on the installation and introducing 2 sources into a circuit where before there was only 1. The most usual place for this to occur is on the lighting circuits, more specifically the landing light. The loop in at the light, loop in at the switch and junction box methods have nothing to do with it.

Like I said, I don;t think you fully grasp what a borrowed neutral is and the scenarios in which they occur, and why.

 

[Hawk81]

Oh dear, my comments seem to have upset some.Because you have handed out dangerous advice then tried to defend it

so let me explain my thought process and understanding of why I gave the advice I did.

The circuit you have shown there is a loop through circuit. Any such loop through circuit that is likely to be of an age to be a candidate for a borrowed neutral would be loop through in the light fitting (loop through at the switch is mostly a more recent configuration)

Now, I FULLY ACCEPT that in the case of a loop through circuit with a borrowed neutral, then unlooping the neutral in the process of changing a light fitting could lead to you receiving a shock.

BUT, and here's the but, the whole point of a loop through circuit is you have a live and it CORRESPONDING neutral at EVERY light fitting. So you would have to be working really really hard and make some really stupid and deliberate mistake to ever manage to get a borrowed neutral on a loop through circuit.

Consequently, I have NEVER encountered a loop through circuit with a borrowed neutral so never ever gave a thought to the fact that it could happen and could be dangerous.

The ONLY time I have encountered a borrowed neutral is with the old "all back to one junction box" circuit (usually one junction box per floor). Borrowed neutral is common with those to save on the number of cores going from upstairs to downstairs.

So here is the next BUT. With the "all to one junction box" circuit, there is only ONE live and only ONE neutral to each light fitting. So even with a borrowed neutral, and two supplies, changing a light fitting is not dangerous as you will never be splitting the neutral when you remove the fitting. The usual rules apply, the only way you will get a shock is by not isolating the supply to that light fitting and not testing for dead.

The ONLY time you would split the neutral and hence risk a shock with an "all to one junction box" circuit is if you were doing some major work in the big lighting junction box. That I assume is beyond the realms of a DIY light fitting change and would only be done by an electrician who knows what he is doing.

So I still stand by the fact I would be happy personally that two supplies to a borrowed neutral lighting circuit of the "all to one junction box" type does not pose a significant danger, and operationally is preferable.

I fully accept a borrowed neutral in a loop through circuit DOES poses a significant danger, but re iterate I have never encountered that, and can't imagine how it could occur.

This discussion is about a CU change. The main criteria of a CU change is to ensure the installation is "no less safe" than before. As such we are not required to bring everything up to current standards. We have to make a judgement that the work we do improves safety. Taking all the above into consideration, I still contest that having a borrowed neutral lighting circuit on two MCB's, sharing the same RCD is still a lot safer than it was before. After all that borrowed neutral circuit has been there for probably 30 years or more posing the same risk.

I take my job seriously and always try to do a safe, well thought out job. I have thought out the consequences and possibilities of a borrowed neutral lighting circuit, but came to a different conclusion to others. I don't think that makes me reckless or a bad electrician.

I try to consider each job individually, and like I have already said, if ever I do encounter a loop through lighting circuit with borrowed neutrals that really could pose a real danger I would not put them on separate MCB's. But better still, if it was a loop through, it should be simple to find and correct the borrowed neutral in the first place.

I think what this highlights is that I try to analyse the circuit and make an informed judgement on each individual case as to what is safe and what is not safe. Some prefer to read a regulation and apply a blanket ruling, without actually considering if there is any real danger or not in a particular situation. That does not make one person right and the other wrong, it just highlights a different approach (I come from an industrial background so am perhaps a little more used to "problem solving" than some might be)

The important thing is we are discussing possible scenarios and it may highlight dangers some had not anticipated, or may show that some perceived dangers are not real. But if it gets us all thinking and analysing what we are doing, then that has to be for the better.

So what you are saying is that because someone borrowed a neutral 30 years ago you are happy to leave it even tho its not safe?? That is not a viable reason. Would you leave tails that were too small because someone else did 30 years ago? In the case that started this whole debate the lights were all on the one fuse therefore the borrowed neutral would not come into play. BUT you advised to split the lights onto two separate mcbs therefore you are making the installation less safe. It was the fact you gave out bad advice and then kept trying to defend it that bothered me

 

[steptoe]

Nope, still not got it.I can;t quite follow what you're trying to say above, but I think what you're saying is borrowed neutrals are an unlikely occurence, and if people take care when altering existing installations then there shouldn;t really be any.

Borrowed neutrals are rarely caused by design, in so much as they aren;t wired like that from day 1. Usually they are caused by someone doing some works on the installation and introducing 2 sources into a circuit where before there was only 1. The most usual place for this to occur is on the lighting circuits, more specifically the landing light. The loop in at the light, loop in at the switch and junction box methods have nothing to do with it.

Like I said, I don;t think you fully grasp what a borrowed neutral is and the scenarios in which they occur, and why.

I would debate that to a degree, although perhaps not intentionally by design , but whilst I was serving my time(15th) and 2way lighting was usually via singles to each fitting and T&E strappers it was common practice to have the landing sw live from the downstairs switch(2gang hall & landing,and therefore DS circuit) and simply pick up a N from the US circuit..

thus when you disconnect a neutral from a current carrying capacity you are in similar realms to losing a neutral from a TNCS earthing system, except the earthing is unaffected, simply that now the N is looking for a path back to star point for its current, which will usually be via YOU.

advocating the use of 2 MCBs for a circuit with shared neutrals is akin to saying it is OK to have a ring final on 2 separate 16A MCBs.

 

[Lurch]

I would debate that to a degree, although perhaps not intentionally by design , but whilst I was serving my time(15th) and 2way lighting was usually via singles to each fitting and T&E strappers it was common practice to have the landing sw live from the downstairs switch(2gang hall & landing,and therefore DS circuit) and simply pick up a N from the US circuit..

Well, I have no experience in installing in the olden days so I'll just have to agree! Most of the time, IME, they are originally derived from one fuseway.

 

[steptoe]

Well, I have no experience in installing in the olden days so I'll just have to agree! Most of the time, IME, they are originally derived from one fuseway.

OLD OLD OLD

you calling me old now.!!!!!?????

still, nothing that cant be solved by using one MCB,

not ideal, I think we will all agree on, but sometimes a new cable isnt an option(for various reasons).

 

[PC Electrics]

Oh dear, my comments seem to have upset some.so let me explain my thought process and understanding of why I gave the advice I did.

The circuit you have shown there is a loop through circuit. Any such loop through circuit that is likely to be of an age to be a candidate for a borrowed neutral would be loop through in the light fitting (loop through at the switch is mostly a more recent configuration)

Now, I FULLY ACCEPT that in the case of a loop through circuit with a borrowed neutral, then unlooping the neutral in the process of changing a light fitting could lead to you receiving a shock.

BUT, and here's the but, the whole point of a loop through circuit is you have a live and it CORRESPONDING neutral at EVERY light fitting. So you would have to be working really really hard and make some really stupid and deliberate mistake to ever manage to get a borrowed neutral on a loop through circuit.

Consequently, I have NEVER encountered a loop through circuit with a borrowed neutral so never ever gave a thought to the fact that it could happen and could be dangerous.

The ONLY time I have encountered a borrowed neutral is with the old "all back to one junction box" circuit (usually one junction box per floor). Borrowed neutral is common with those to save on the number of cores going from upstairs to downstairs.

So here is the next BUT. With the "all to one junction box" circuit, there is only ONE live and only ONE neutral to each light fitting. So even with a borrowed neutral, and two supplies, changing a light fitting is not dangerous as you will never be splitting the neutral when you remove the fitting. The usual rules apply, the only way you will get a shock is by not isolating the supply to that light fitting and not testing for dead.

The ONLY time you would split the neutral and hence risk a shock with an "all to one junction box" circuit is if you were doing some major work in the big lighting junction box. That I assume is beyond the realms of a DIY light fitting change and would only be done by an electrician who knows what he is doing.

So I still stand by the fact I would be happy personally that two supplies to a borrowed neutral lighting circuit of the "all to one junction box" type does not pose a significant danger, and operationally is preferable.

I fully accept a borrowed neutral in a loop through circuit DOES poses a significant danger, but re iterate I have never encountered that, and can't imagine how it could occur.

This discussion is about a CU change. The main criteria of a CU change is to ensure the installation is "no less safe" than before. As such we are not required to bring everything up to current standards. We have to make a judgement that the work we do improves safety. Taking all the above into consideration, I still contest that having a borrowed neutral lighting circuit on two MCB's, sharing the same RCD is still a lot safer than it was before. After all that borrowed neutral circuit has been there for probably 30 years or more posing the same risk.

I take my job seriously and always try to do a safe, well thought out job. I have thought out the consequences and possibilities of a borrowed neutral lighting circuit, but came to a different conclusion to others. I don't think that makes me reckless or a bad electrician.

I try to consider each job individually, and like I have already said, if ever I do encounter a loop through lighting circuit with borrowed neutrals that really could pose a real danger I would not put them on separate MCB's. But better still, if it was a loop through, it should be simple to find and correct the borrowed neutral in the first place.

I think what this highlights is that I try to analyse the circuit and make an informed judgement on each individual case as to what is safe and what is not safe. Some prefer to read a regulation and apply a blanket ruling, without actually considering if there is any real danger or not in a particular situation. That does not make one person right and the other wrong, it just highlights a different approach (I come from an industrial background so am perhaps a little more used to "problem solving" than some might be)

The important thing is we are discussing possible scenarios and it may highlight dangers some had not anticipated, or may show that some perceived dangers are not real. But if it gets us all thinking and analysing what we are doing, then that has to be for the better.

Dave, why do you suppose the ESC BPG for PIRs gives borrowed neutral a code 2?

You have astounded me tonight.

 

[superspark]

that poor chap on post one only wanted some advice on what requirments are needed for his friends house that he is planning to rent!!!!!!!

 

[PC Electrics]

god i hate y plan wiring

Well in that case send your central heating work my way. If I do say so myself, I'm good at CH wiring.

 

[batty]

So if you put all the lighting on one circuit it could be argued you have left the property in more dangerous condition than before you started the work. Little old lady falls down the stairs due to circuit breaker going when bulb blows.

 

[Hawk81]

So if you put all the lighting on one circuit it could be argued you have left the property in more dangerous condition than before you started the work. Little old lady falls down the stairs due to circuit breaker going when bulb blows.

Are you being serious??? I really hope not. Look at it this way, if the lighting circuits are split over 2 mcbs but both on the same rcd due to the borrowed neutral and the rcd trips for some reason then the "little old lady" still has no lights. So does that mean by upgrading her cu and adding rcd we have made the job less safe? I dont think so!!! Spltting the lighting circuits onto 2 mcbs and not fixing the borrowed neutral is a far bigger danger to leave behind. I really hope that noone has done this and left borrowed neutrals behind. I am in disbelief at some of the replies trying to condone this dangerous act.headbangheadbang Also i have seen fuses blow when a bulb has blown, all the lights were on 1 fuse before so by putting them on 1 mcb is actually leaving it the same not more dangerous.

 

[kme]

Also i have seen fuses blow when a bulb has blown, all the lights were on 1 fuse before so by putting them on 1 mcb is actually leaving it the same not more dangerous.

I think we have all seen this; however, if installing a new CU, and the Zs is acceptable; using a C6 can avoid the issue. I think most of us do this now......

 

[Hawk81]

I think we have all seen this; however, if installing a new CU, and the Zs is acceptable; using a C6 can avoid the issue. I think most of us do this now......

I agree that is what I was saying

 

[kme]

Thought it may be; but it is at a tangent to the O/P, and ensuing discussion, mate......

 

[Foxmeister]

For renting purposes, im sure the building regs state that the dwelling now must have mains powered smoke alarms in all properties!