Borrowed neutral discovered when changing CU and discussion on DIY CU change

[kingeri]

Re: Borrowed Neutral discovered after changing CU

Why do electricians even bother existing any more?

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Why do electricians even bother existing any more?

I'm very glad they do, really do hope I've not implied otherwise.

I'm one of these people who likes a challenge. Main reason I did my own rewire ? I know the installation inside out, I designed it the way I wanted - which is a bit unconventional in places (I built a bespoke architectural lighting control system, Lutron is more than a little pricey but I like the functionality it offers) but above all because I wanted to...

 

[D Skelton]

Re: Borrowed Neutral discovered after changing CU

Did you ascertain whether supplementary bonding was needed or could be omitted?

Yes

How did you do this?

Were you able to differenciate between exposed and extranious conductive parts?

Yes

Please explain the difference

Did you carry out the correct calculations to ascertain the current carrying capacity of each cable taking account of grouping, ambient temperature and thermal insulation?

Yes, most are clipped direct, a few are within plasterboard walls, none are within or under any insulation, again this was all considered before deciding what cables to use.

Grouping and ambient temperature?

How did you ensure that your voltage drop on each circuit was lower than the maximum allowed for the type of circuit?

Again, this was worked out at the time. Exactly how isn't fresh in my mind, but it was something that was considered

Sorry buddy, I don't believe it, most average domestic sparks wouldn't even do this regardless of whether or not they knew how. A competent person would know both how to work out voltage drop and the minimum allowed on a circuit without having to carry out research. You should know this.

When performing your dead, then live tests, did you carry them out in the order specified in BS 7671?

Yes

What is the order then

How did you confirm continuity of main and supplementary bonding conductors, visually or by measurement?

The resistance was measured

What would have been the highest acceptable resistance reading for these?

Again, this was something that was researched (and would be again if I was repeating it) but is not fresh in my mind as I don't do this every day.

Again, a competent person would know off by heart the maximum ohmic value for a length of main bonding. I'd also expect a competent domestic spark to know off by heart the maximum length of 10mm main bonding conductor allowable for the resistance to fall within this value.

How were test results recorded, were they recorded on an electrical installation certificate as required by BS 7671?

Well that depends what you mean by 'certificate' - they take the same format, but I expect it would not be considered a valid certificate as it wasn't completed by an electrician.

Forgetting any other reasons but because of this alone, you're working outside the regs. Should any electrical work you carry out ever go wrong and cause harm to anyone, the courts would throw the book at you!

Nope I just endanger us, no kids. I do have a partner, and she understands it about as well as me (maybe not much by your estimation) but we are both quite happy with the results.

Until your house goes up in smoke and your wife with it!

Personally, no, but some people will - and some will do it safely.

If they're gas engineers yes, if not, I pitty the neighbours of the muppets who mess around with gas when their entire block goes boom! And I also pitty the kids that could potentially be killed by carbon monoxide poisoning as a result of an installation carried out by someone who 'read a book once on boilers'.


You also haven't replied to the following questions:

What system were you on and what would have been the highest Ze reading acceptable for that type of supply?
Which protective measure did you utilise?
What were the reference methods used with regards to how the cables were mounted?
How did you ensure that the selection and erection or wiring and accessories minimized the spread of fire throughout the installation?
Where exactly in the installation were you required to determine the prospective fault current under both short circuit and earth fault conditions?

Edit: You also mention Lutron. I'm guessing you utilised one or more of the GRAFIK Eye units yes? If so, what type of cable did you utilise to connect to the wall units and how did you maintain segregation between the band I and band II cables inside the GRAFIK Eye enclosure?

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

Will address other points when using something more than a phone to read your reply. Multiple quotes are tricky using the mobile ui.

Sorry that I don't remember all the allowed / typical resistances and what cable should be used for what / relevant information for calculating current carrying capability etc. I need to look it up, that doesn't make it any more dangerous - just slower.

As far as Lutron - I didn't use it due to the expense and I don't like proprietary systems.

Whilst I'm sure it will open a whole new can of worms I built my own. The central control unit outputs DMX. The dimmers are off the shelf dimmer racks as used in theatres ( which I'm familiar with ) and the cables to the "light switches" are SELV and RS485 serial data over cat 5. There is no mains voltage at the switch so separation is not an issue.

Each light fitting and 5A outlet is wired individually back to the dimmers.

The kitchen and bathroom lighting are low voltage with their own DMX drivers - an advantage of using DMX over Lutron is it can control rgb and variable ct fixtures

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

I'm beginning to think I should have started a thread for my house ;-)

I'd post it in show us your installs except I'm sure the ensuing 50+ post thread about not doing your own wiring wouldn't go down well there

It is relatively neat though - not on par with some of the expert jobs though but a good first effort imho

 

[D Skelton]

Re: Borrowed Neutral discovered after changing CU

Will address other points when using something more than a phone to read your reply. Multiple quotes are tricky using the mobile ui.

I'm looking forward to your response.

Sorry that I don't remember all the allowed / typical resistances and what cable should be used for what / relevant information for calculating current carrying capability etc. I need to look it up, that doesn't make it any more dangerous - just slower.

In my opinion, your lack of knowledge demontrates that you are not a competent person, therefore making you dangerous as an electrical installer and potentially making your work dangerous.

As far as Lutron - I didn't use it due to the expense and I don't like proprietary systems.

I thought you said you did use it?
"I built a bespoke architectural lighting control system, Lutron is more than a little pricey but I like the functionality it offers"

Whilst I'm sure it will open a whole new can of worms I built my own.

Well to be honest, without seeing it I couldn't possibly decide whether it is fit for purpose or not, you're in the theater industry so you will know far more about the system you created than me.

an advantage of using DMX over Lutron is it can control rgb and variable ct fixtures

You can use DMX control interfaces with GRAFIK Eye QS?

 

[rsmck]

Sorry for ambiguity. I meant I like the functionality of systems like Lutron et al - so implemented similar myself.

Cost saving ( whole system was less than a 6 ch Lutron system ) and lets me program it in my own way / control remotely etc.

 

[D Skelton]

Oh I see, yes, if you were using homeworks you'd be paying out a fair whack.

Anyway, goodnight, and I eagerly await your response to my previous questions.

 

[whitestu]

From my experience I'd bet many people working full time as electricians wouldn't be able to answer the questions being asked of the OP of the top of their heads. God knows the lot who did the wiring on my last house building project wouldn't have a clue! However they were legally able to notify and issue an EIC.

 

[plugsandsparks]

I suspect you were not expecting this type of backlash at the moment, but the industry is a bit sensitive around Part P, and the general dumbing down of the industry plus the internet allows two way transmission of opinions and ideas much faster than the old days.
The real issue really is competence which is a function of knowledge and experience.
Bascially you have banged in a CU change, its about the lowest of the low for getting any type of empathy from a spark.
Doing a Cu change is alot about the tester. Tester gets hammered before you even remove the old one, gets hammered again when you have all the cables poking up at you and lastly hammered again when its all back together.
You have missed a massive opportunity to confirm the installation is safe in absolute terms. Saying its better than when you started wont cut it as you may well have put faults on that were not there before. Without testing how would you know for sure.
I confess to have forgotten to tighten up an earth screw before but guess what it showed up immediately when i did a Zs

 

[rsmck]

Re: Borrowed Neutral discovered after changing CU

I'm assuming these questions pertain more to the rewire rather than the swap of consumer unit which I've already admitted the testing for was inadequate or at the very least, substandard.

What system were you on and what would have been the highest Ze reading acceptable for that type of supply?

One I know from memory (perhaps only because I did look it up before the aformentioned CU change, so more recently than my rewire) TN-S and the maximum Ze would be 0.8 I believe?

Which protective measure did you utilise?

Automatic disconnection of supply - any exposed live conductor is insulated or fully enclosed, protective earthing is used, and automatic disconnection is provided by RCD (and MCB) in the event of a fault condition.

The RCD disconnection time was within the required limits (don't ask me to remember exactly what - but the limit is somewhere around 400ms and the actual tests were much, much lower than that)

What were the reference methods used with regards to how the cables were mounted?

Again, the exact code escapes me, but this was checked and it is 'clipped direct' or 'enclosed in wall' where appropriate

How did you ensure that the selection and erection or wiring and accessories minimized the spread of fire throughout the installation?

I'm not sure what sort of answer you're looking for here. Obviously as with making any hole in a wall consideration is given to the increased risk of fire spreading however most outlets are in existing positions so the biggest concern is probably the addition of some downlighting which changes the fire resistance of the plasterboard. All of this is LED and relatively low temperature, there is also no insulation between joists so the risk of fire caused by these accessories is minimal compared to traditional halogen downlights. All terminations are fully enclosed (and are mainly WAGO, none of these 'choc blocs covered in electrical tape' so commonly favored by the DIYer)

Where wiring passes through the floors of the building it uses an existing route, so the rewire dd not adversely affect (nor improve) this. There are no 'back to back' outlets or accessories within the same cavity of any stud partition wall.

Where exactly in the installation were you required to determine the prospective fault current under both short circuit and earth fault conditions?

Where as in at what stage ? Pretty early on - before deciding on protection devices as otherwise it'd be possible to select ones that were inadequate.

 

[rsmck]

I suspect you were not expecting this type of backlash at the moment, but the industry is a bit sensitive around Part P, and the general dumbing down of the industry plus the internet allows two way transmission of opinions and ideas much faster than the old days.
The real issue really is competence which is a function of knowledge and experience.
Bascially you have banged in a CU change, its about the lowest of the low for getting any type of empathy from a spark.

Yep, because I was asked to ... in hindsight testing the installation as if it was new (and as I did with my own) would have made a lot of sense... but again, when asked to do a favour a short notice I did what was asked. A professional electrician would quite possibly have refused to do a CU change without undertaking such testing but - that said - I've seen it done (by so-called professionals)

I say 'so-called' because it has become apparent that most of the electricians on here do jobs properly and actually take care over them. However, I have met those that do not. A friend had a 1930s house rewired some time ago by an electrician which was 'recommended' to them, they advertise as an electrician locally and yet when I added a socket for them (simple spur next to an existing socket on a ring) last year it was clear the installation had not been done to the standard you would expect of others - notably the conductors were weakened (apparantly when the insulation was stripped they thought it appropriate to notch about 1/4 out of the copper core too) and the connections so overtightened that when I removed the socket from the wall the cable simply snapped off)

Whilst I'm not out to deride any genuine professional electrician what I will say that there's potentially a lot of people who arguably are no better (and possibly considerably more haphazard) than I was in my own installation, which worryingly advertise themselves as electricians.

I asked this friend if they had a certificate for their (paid for) rewire - none was issued, and they didn't know they were supposed to get one.

Doing a Cu change is alot about the tester. Tester gets hammered before you even remove the old one, gets hammered again when you have all the cables poking up at you and lastly hammered again when its all back together.
You have missed a massive opportunity to confirm the installation is safe in absolute terms. Saying its better than when you started wont cut it as you may well have put faults on that were not there before. Without testing how would you know for sure.

Fair point - and one that will be taken on board should I ever do it again - although I'm unlikely to do so for a very long time (unless I buy another old property I guess, but by then chances are someone else will have gotten to it first)

I confess to have forgotten to tighten up an earth screw before but guess what it showed up immediately when i did a Zs

Too true - likewise in the theatre, we've all made up cables etc and forgotten to tighten something properly once or twice, or not noticed some damage in the cable (they are often reused, chopped, ends changed to suit requirements of a show) - always shows up if the cable's tested but as an industry it's one that has a bad habit of plugging in a cable first, if it doesn't work, find another cable... probably best theatre techs don't do the actual installations

 

[rsmck]

Oh I see, yes, if you were using homeworks you'd be paying out a fair whack.

Sorry for the off-topic off-topic reply (this thread has snowballed somewhat) but yes, homeworks would have been somewhat cost prohibitive but I'm a lighting person and I like my creative lighting (see https://pbs.twimg.com/media/A3EwGldCMAAoNoq.jpg for an example - dining room - uses 4 dimmer circuits)

The eventual costs of my own solution are still not 100% certain (the company that was making my faceplates is no more, so I only have two working switchplates, we use the remote most of the time) but I picked up used installation dimmers for about £100 each, annoyingly these have 10A per channel breakers which really should be replaced with 6A, a bit of a non-issue at the moment as the actual supply to each rack is through a 6A MCB, and I'm unlikely to need 10A per channel at home

The controller itself is a raspberry pi now, £40 or so, and an Ethernet to DMX interface. Each faceplate was about £35. The whole system works every bit as well as the commercially available alternatives.

There is also some redundant T&E in the walls to each switch position, if we were to move out of the house and the new owners didn't want some bodged bespoke lighting control system we could easily put a domestic dimmer switch at each position and replace the dimmer rack with an enclosure with DIN rails mimicking the role of traditional ceiling roses and providing a switched live from each of these switches to the lights I guess, but where would the fun in that be

 

[D Skelton]

I'm assuming these questions pertain more to the rewire rather than the swap of consumer unit which I've already admitted the testing for was inadequate or at the very least, substandard.



One I know from memory (perhaps only because I did look it up before the aformentioned CU change, so more recently than my rewire) TN-S and the maximum Ze would be 0.8 I believe?



Automatic disconnection of supply - any exposed live conductor is insulated or fully enclosed, protective earthing is used, and automatic disconnection is provided by RCD (and MCB) in the event of a fault condition.

The RCD disconnection time was within the required limits (don't ask me to remember exactly what - but the limit is somewhere around 400ms and the actual tests were much, much lower than that)



Again, the exact code escapes me, but this was checked and it is 'clipped direct' or 'enclosed in wall' where appropriate



I'm not sure what sort of answer you're looking for here. Obviously as with making any hole in a wall consideration is given to the increased risk of fire spreading however most outlets are in existing positions so the biggest concern is probably the addition of some downlighting which changes the fire resistance of the plasterboard. All of this is LED and relatively low temperature, there is also no insulation between joists so the risk of fire caused by these accessories is minimal compared to traditional halogen downlights. All terminations are fully enclosed (and are mainly WAGO, none of these 'choc blocs covered in electrical tape' so commonly favored by the DIYer)

Where wiring passes through the floors of the building it uses an existing route, so the rewire dd not adversely affect (nor improve) this. There are no 'back to back' outlets or accessories within the same cavity of any stud partition wall.

I see you did your research before answering these questions Well at least you're making an effort to redeem youself, it still doesn't cut it in my opinion. I'm pretty sure without your extensive research over the last few hours you would have struggled to answer these questions.

Where as in at what stage ? Pretty early on - before deciding on protection devices as otherwise it'd be possible to select ones that were inadequate.

It was a straight forward question and your answer again demonstrates your lack of knowledge. 'Where' means at which points or at what places are you required to measure the prospective fault current.

 

[rsmck]

It was a straight forward question and your answer again demonstrates your lack of knowledge. 'Where' means at which points or at what places are you required to measure the prospective fault current.

Or simply a misinterpretation - consumer unit and furthest point of the circuit (for short circuit current) ? , again, I'll freely admit I am a little rusty - it was sometime ago I did this..