Help! What are the black wires for?

[Kris]

I have a bit of an issue with my electrics.

The issue is that the consumer unit / main feed looks like spaghetti junction, I have no clue to how the thing is earthed, and I have what looks like redundant wires running all over the place.

Description of CU.

The main feed is from an underground circuit to a fused unit (the suppliers box) the live and neutral run from this to a large circuit breaker type box with a test switch. This circuit breaker then runs into a black consumer unit that is hanging off the wall. The consumer unit itself has ceramic fuses with fuse wire. 3 circuits run of the unit; lights, ring main and shower. I have traced these around the flat. Also there was an alarm wired into the lights along with a doorbell (these have now been removed). I have also noticed that 2 black cables run up into the loft but seem to be wired to the earth and not the live (maybe the nuetral) they look like a steel type cable not copper. I cannot see any other connections to the earth (except the lights, shower and ring main). also the black cable go into a roof void where I cannot access (above the kitchen), so i do not know where they go.

Phew!!

My questions are this.

what are the black cables likley to be?

is my system earthed / how can I tell if its earthed?

I have a new consumer unit that I would like to fit would it be best to install an earth rod and run the cable thru the loft to the consumer (over the entire loft space 25m) and them rejoin the circuits? and if so what cable should I use?

I would also like to learn more about the electrics area could anyone recomend a good book, website or course.

Thanks

K.J

[usenet]

In a flat you probably have a TN-C-S system (depends how old it is), in this case the 'earth' will be the incoming supply neutral, you should be able to find how this is connected to the earth block in the CU.

Presumably a whole system RCD or similar, could just be a switch. It's useful anyway as it enables you to isolate the CU making it easy to replace.

These *could* be earth bonding connections to pipework etc., they should be copper though, why do you think they're steel? If it's just because they have 'silver' coloured conductors it may just be that they are made of tinned copper wire.

From what you say (and especially as you say 'maybe the neutral') it does sound like you have a TN-C-S (or PME) system where the supply neutral provides your earth connection. If you can confirm that the incoming neutral wire is also connected to the earthing block then that is what you have. No other earth connection should be present.

Bonding wires as I suggested above, though they should really be green/yellow nowadays.

As I said check for a connection between the incoming neutral and your flat's earth wiring.

It's *very* unlikely that you'd need an earth rod in a flat, if you did then other wiring changes would also probably be required. However it's worth investigating the "large circuit breaker type box", does this have any notes on it or indication as to what it is? I suppose it's *possible* that you have a TT system and this is the RCD (or even ELCB if it's old) required to protect the whole system. Then maybe the black wires are your earth connections.

[stefek.zaba]

This would be a good idea, Kris. The electrical section of the Collins and Which d-i-y bumper volumes are a good place to start, as is the Which? Book of Wiring and Lighting; and from your description of your current electrics I'd suggest limiting yourself to the jobs they describe in there for now. (Even that may be less than safe: from the state your place sounds it's in I'd want to do a pretty comprehensive rewire: and that's not really a great candidate for "first electrical d-i-y job".)

Beyond the d-i-y general tomes, there are a couple of classic books which practising electricians train with alongside the CityAndGuilds course. Of these, a particularly good single-volume work is "Modern Wiring Practice" by Steward & Stubbs, now in its mumblyeth edition. If you properly assimilate what that tome contains, you can do good, sensible, regs-compliant wiring with an understanding of the engineering principles; it's a better desert-island volume than the IEE On-Site Guide (which is the second "proper" tome you should get).

But in the nicest way possible, let me encourage you to either get a full rewire done for you, or at least for you to put in a couple of up-to-standard power and lighting circuits with final testing and installation of the new CU done by a Real electrician. In your next house you'll know enough to do a full rewire, safely; but perhaps you don't yet...

HTH, Stefek

[Kris]

It does not look like copper more like a galvanized metal

It does not look like the neutral wire is connected to the earth block (I suspect i will see when the CU is removed).

I completely stripped the kitchen to the brickwork and installed new walls and floor. there it no connections to the pipework in the kitchen or bathroon (yet). if the black cables are earths they do not seem to be connected. I planned to do this after the new CU was installed. Does it matter where you earth the pipes E.g should I earth the pipework in the kitchen away from the CU or near hall near the CU? and as the pipes are connected do I need to earth each only once?

I will check this tonight

I will examine the CU and try to trace the black wires. if they are earths i will pull them out an replace them with yellow and green and connect them to the various items that need earthed.

Thanks for your help

K.J

[BillR]

[SNIP}

DANGER, WILL ROBINSON! A good example why the new restrictions on who can fiddle with electrics are coming in ...

I hope he doesn't live near me!

[Kris]

I have not fiddled with the electrics yet! someone else has before I moved in the only reason for posting was to find out if my system was safe for my family.

I will not be fitting the CU myself but getting an electrician to do so, I will be running the earth cable myself in the loft to points in the house.

Also any wires I have removed where connected to nothing (alarm and doorbell)

As I do not have a great deal of knowledge in this area and I will be relying on a "tradesman" to do the work, I did not want to have him/her turning up at the door and state that the whole system needs re-wiring (unless it does). This was another reason for the post.

I suppose you where born with your all-encompassing knowledge and therefore never had to ask questions!!!!!!!!!!!!!!

Thanks anyway

K.J

[Kris]

Thanks to the helpful comments on this group I have now worked out how my system is wired.

There is a ELCB connected to the meter, the elcb then goes to a old CU made from wood. The earth block on the CU is connected to the gas meter that is 1.5 meters from the CU. The other cables for the ring main lights and shower are all earthed to this block.

The two black wires that ran thru the loft and where stuck in the wall between the kitchen and the lounge. Thanks to my hammer and a few holes in the plasterboard I now know they are old cables connected to nothing but were plastered in. These cables have now been removed from the earth block. I have some nice pictures of the entire setup that i will post. Also the ELCB test button does not work.

I plan to do / have the following done and suggestions / improvements

I plan to add an earth rod in the front garden and run this into the system thru the floorboards approx 8m.

Fit a new CU

Connect the pipes bathroom to the earth on a new CU

also as the ELCB does not work can anyone recommend what to install in its place

thanks

K.J

[BillR]

No, I went to college and eventually got a degree in electrical engineering :-)

One thing thats occurred to me is that could the thick black wires have been going to overhead fed supply at some point? Why they would be connected to earth now though is strange..

[stefek.zaba]

THe "right 80% of the time pure guess" answer is "a 100mA time delayed RCCB reated at 80A or preferably 100A". The *right* answer is "ask your sparks": as the Right answer depends on how your supply is earthed, why the older-style ELCB was fitted in the first place, etc. etc. etc., to a degree which a dialogue over Usenet really isn't adequte to solve; nor will you be getting advice from anyone with an appropriate financial and company-continuity interest in giving you the Right answer ;-)

Putting in your own earth rod, as you mention earlier in your posting, is very unlikely to be positively unsafe, but is far from necessarily going to make things better, BTW.

HTH, Stefek