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

[rsmck]

I'm pretty sure without your extensive research over the last few hours you would have struggled to answer these questions.

Well the Ze I knew from memory, as with the RCD disconnection times (as these matter in my other work too, although the permitted values are considerably different for circuits over 32A, and are tested reasonably regularly to ensure they are working correctly)

The prevention of spread of fire is pretty much common sense - it applies to making holes in walls in general, not just electrical work, and being regularly working in buildings where we have small doors in walls to pass cables through from stage to front of house which are then stuffed with 'fire bags' after it's a concept I'm familiar with.

However - you make a good point without research you're right I probably wouldn't be be able to answer them, and they're not fresh in my mind - but the point being I *did* undertake pretty extensive research and referred to the regs and the OSG as I went along at the time.

 

[D Skelton]

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..

Not quite

 

[D Skelton]

Anyway, I'm done, the point has been made by myself and others. You are not competent enough to carry out rewires and consumer unit changes. You may disagree but the fact remains the same.

I'm sure you are an intellegent guy, you must be to be able to work in the field you do, however my advice would be to stick to what you are competent at.

Best regards.

 

[rsmck]

Anyway, I'm done, the point has been made by myself and others. You are not competent enough to carry out rewires and consumer unit changes. You may disagree but the fact remains the same.

By that standard I'd expect there's a number of trading electricians that fall short of your definition of competence too.

If I was going to rewire something right now, I wouldn't, I freely admit I don't remember everything I need to know, and I'm not inclined to go through the same process and studying of things I did before rewiring my home just to answer questions intended to test my competence.

I guess it's up to how you define competence - can someone be competent at the time, but no longer competent ? Is a demonstrable lack of competence (in anyone, not just this) *now* proof that they were not once competent or, in this case, that the installation was not done competently at the time ?

At the risk of reviving a very old thread I might remember to update this when the place is fully and professionally rewired - will let you know if the CU specified and installed by me is left in place or not, and what observations are made by the electricians who do rewire it.

 

[rsmck]

Thanks also to those who advised, and gave good reason, for putting both lighting circuits on the same MCB even though this is obviously still less than ideal - it will be changed this evening.

Out of interest - if you (any electrician) are hired to carry out a CU change and the testing before the change shows faults (e.g. take a broken ring final circuit as a likely example) would you still carry out the CU change and note the fault exists? Would you be inclined to split the ring into two radials (obviously this would involve finding where the break is if it was only in one conductor) ? Would you insist on fully rewiring this circuit?

Taking the same case - What if the customer, who at the end of the day is the one paying for the work to be carried out, and is the one that has to suffer disruption through rewiring if required, still asked you to replace a CU despite knowledge of faults - would you ?

 

[MDJ]

Re: Borrowed Neutral discovered after changing CU

TN-S

(need to add more text as the forum won't let me post a 4 character reply)

TNS? with a 0.4 reading, a good solid connection then?

 

[SJD]

Out of interest - if you (any electrician) are hired to carry out a CU change and the testing before the change shows faults (e.g. take a broken ring final circuit as a likely example) would you still carry out the CU change and note the fault exists? Would you be inclined to split the ring into two radials (obviously this would involve finding where the break is if it was only in one conductor) ? Would you insist on fully rewiring this circuit?

Typically the break is only in one conductor, and if in a cable (rather than an accessory) I'd prefer to locate it and either repair the cable or replace the damaged section.

Had one some weeks back, turned out the cable had been punctured by a screw right through the earth of T&E, but also nicking the live insulation and it had flashed over (could see the marks inside the cable) - seems whoever did it removed the screw, replaced the fuse, and didn't worry about testing - probably been like that for 20 years when the house was extended. In this case, I replaced one section of damaged cable as the damaged section was difficult to access, luckily the new cable pulled through using the old cable.

Actually I replaced the CU first, then went back the next day to fix the broken ring.

 

[plugsandsparks]

Broken rings are common, tracing the break actually gets me excited as i like a challenge to break the tedium of endless ccts within spec however once found, it then depends what entails to make the installation safe. I have split the ring and created two radials because i could not get at the cable to replace it, the loads looked good for a 20A radial and there was spare ways in the CU. I have also replaced a damaged cable (like when the kitchen fitter caught the cable with his hacksaw) - plaster was already hacked off and i needed a ring or that kitchen.
So it depends, the end game though is to leave it safe even if that means downgrading the cct and getting the odd overload trip, the client is made aware of the limitations and cost / disruption involved in making the ring whole again.

-

 

[SparkyJoe]

Image removed

 

[whitestu]

Very PC!

 

[ackbarthestar]

Re: Borrowed Neutral discovered after changing CU

Call me silly, but how could a screw head be live and not blow a fuse?? Surely you had earths at the fcu's??

Ok, if I must

I looked at a job a couple of weeks ago where someone in the household was receiving shocks from a screwhead on an unearthed lighting circuit.

The previous occupant considered himself an expert in the domestic electrics field and I was called in to rectify another problem where one of the lights kept blowing the fuse when I was told about this.

Checked it out and sure enough the 3-ganged switch place was installed just above a cooker so it was evident that making fortuitous contact with the screwheads each time the stair lights were turn on would happen.

I did tell the chap that at some point soon the house would need a rewire, but he assured me it had been ok for the last 21 years.....