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Electrician advised against just updating the fuse box
- Thread starter JP_
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They are both reasonable. It will easily take that length of time (plus more to write up the Report).
How can you condemn something which has not failed anything?
Can you?
Probably not, given the lack of knowledge your posts here betoken.
May you? Yes, you may if you can do it safely, and then we are back to square one.
- For a circuit to supply a given load, how would you go about deciding what cable and protective device to use? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
- Do you know which circuits can be ring finals and which cannot, and what the advantages and disadvantages of each are? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
- How do you calculate maximum demand and how can diversity be used?
- Can you correctly identify all components and connections of a circuit by method of testing or otherwise? In doing so can you identify or recognise anything wrong or dangerous with the circuit? You cannot assume that what's currently installed is OK, and you need to check it before starting work.
- Do you understand how the way in which cables are installed affects how much current they can carry? (No, you can't just copy what's there because it's going to become your responsibility and what's there might be wrong.)
- Where cables need to be joined, how should this be done / not be done and in what circumstances are different methods acceptable?
- Can you identify extraneous conductive parts, and do you know the requirements for main and supplementary bonding of them?
- Which circuits should be RCD protected?
- What about the testing that you should do on your existing installation before you change the CU, if you want to be sure of avoiding grief from new RCDs tripping?
- And what about the tests you should carry out after the installation? What sequence will you do them in and at what point will you energise the installation, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?
- How do you propose to isolate the supply so that you can install the CU?
- Do you believe you are qualified to issue an Electrical Installation Certificate for the replacement?
- Are you aware that you'll need to apply for Building Regulations approval in advance, and as part of that you'll have to say how you'll ensure that your work complies with P1?
I'm not saying this to make you feel small - nobody in the world knows everything about everything, and it's been several hundred years since anybody could conceivably have known everything there was to know.
The thing is rewiring a house, installing a new CUs etc is not a trivial job, and I can assure you that it involves knowing far more than you think it does.
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thanks for the long reply, it really is appreciated! But that was the Royal "I"! What I should have asked is, given that I have this strange (maybe only to me!) TT type of electric, can the house still be rewired, or would I need something altered in the incoming power before that can be done. I was never suggesting that I'd rewire it - I find the whole electric thing pretty scary to be honest. Light bulbs I can do, and at a push, changing light switches and ceiling lights. But beyond that, I don't touch it!
I did wonder if that might be the case - but, as you have seen, there are some people who always 'see/assume the worst' in everything they hear or read!
There's nothing 'strange' about TT (I have it, for a start!). Even though it is gradually becoming less common, the is still an awful lot of it about.
You could have your CU changed for a modern one, or your whole house rewired, whilst still keeping it as TT. In fact, it's not a foregone conclusion that your DNO would be able/willing to provide an earth (so that you did not have to stay with your TT rod) even if they were asked.
Kind Regards, John
Where the supply is overhead the DNO may refuse to offer an "earth" and will insist that the install is TT.
If the supply is two separate wires ( and not a single cable with both Live and Neutral in a single outer sheath ) then TT is the only safe option. The risk in a two wire drop of the Neutral wire snapping while the Live remain intact is too high to be acceptable. In PME systems the Neutral supply wire also provides the "Earth" for the installation, if it breaks with the Live still intact then the "Earth" in the house becomes Live.
One might have thought so, and it might be true of literally overhead (i.e. 'suspended') sinces, but it's certainly not true as a generalisation for 'outdoor supply singles' with my DNO.
For a start, my supply comes 'overhead' from the pole to the wall of my neighbour's house in a 3P+N 'ABC cable' - which, although called 'a cable', is essentially three twisted singles .....
From there the supply travels about 25m to my house as 4 singles 'clipped' (sometimes more like 'draped!') to the neighbour's wall.....
Although it is not all that difficult to envisage situations in which just the neutral could be broken (as can be seen, it's well within 'snipping range' of someone pruning the neighbour's bay tree, and the vermin are not beyond walking along the ABC cable and having a nibble!), I have been offered (but have declined) PME.
All true, but particularly in the case of a break in a CNE conductor supplying a single property, what you describe would presumably not in itself be directly hazardous if all the necessary main bonding was in place (i.e. if the interior of the property were an equipotential zone).
Kind Regards, John
External water tap would need to have a one metre long non-conductive section in the pipe supplying it otherwise the tap would be 230 volts above ground potential. Similar concerns for gas pipes in the outdoor meter box.
is considered "safe" from incidemt that would result in one conductor snapping.
The adjacent retail unit has two separate conductors running along the wall. It was previously overhead with the open 2 wire span attached to the next building and feeding three buildings ( two retail and one residential ). It was TT at that time and there was no offer to provide PME when the span was replaced by UG to the next building. The UG cable was simple run up the wall to the point where the span had been attached.
We know that (particularly given the number of times it has been mentioned here!!), but that risk is no different with a lost overhead 'single' CNE than it would be with an underground one within a multi-core cable (and, as we know, once in a blue moon the latter do develop CNE-only faults) - so that point is irrelevant to this discussion.
Presumably it is, but I would not have thought that the same would be true of the lengthy and iffy run of ordinary singles along my neighbour's wall, would you?
Kind Regards, John
Far less likely to snap due to being stretched tightly as an overhead between two anchoring points.
Yes, I'm not disagreeing with that, but the consequences of it breaking (e.g. in relation to the infamous 'outside tap'), if it does, would be exactly the same as if it were an underground cable. Since you raised the 'outside tap' (or 'gas meter box') issue, I thought you were implying that it was in some way specific to overhead cables.
Kind Regards, John
The risk of a lost Neutral and hence "Earths" of a PME rising to 230 volts above ground is far greater in an open wire overhead supply than is is in any other distribution system.
Hence the consequential hazards are more likely to be present with an open wire overhead supply to a PME install. So avoid that risk by not supplying PME "Earth" in that situation
Hence the consequential hazards are more likely to be present with an open wire overhead supply to a PME install. So avoid that risk by not supplying PME "Earth" in that situation
As I said, I'm not disagreeing with that.
However, from what I understand of your many past writings on the subject, this is a matter of concern for you even when the supply in not overhead.
Kind Regards, John
Yes, deriving an "Earth" from a Neutral does concern me. Reason for that is experience of Neutral bounces and high currents flowing to the ground rod from the PME "earth".
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