Old Electrical Wiring

[jonesy]

Am I not correct in thinking that modern installations have a distributed earth and the bonding to the plumbing is more a case of making the plumbing safe rather than providing an earth. I believe it's a nono to install a radio earth. It's possible with some systems to have a considerable potential between protective earth and an external ground rod.

Yes. The idea is that any metalwork that could become in contact with live wiring if there is a fault is bonded to earth. This means the current has a direct path back to the supply, and should safely trip the RCD, instead of taking a route via someone touching the metal and the ground. So trying to use the pipework to provide the earth connection is dangerous- e.g if you were to connect the earth terminal in your sockets to the pipes, then a faulty appliance could make them live, the opposite of what you want.

 

[jonesy]

If you are miles from a substation, ground rods can be considerably better.

In a modern system the connection between earth and neutral is made at the main board isn't it?

 

[slowmotion]

In a modern system the connection between earth and neutral is made at the main board isn't it?

I think the general principle is that you really don't want the neutral conductor to be floating at a voltage potential far above true Earth. If the distance between your house and the substation is considerable, and if the current that the cable carries is large, there is a voltage difference between the earthed neutral cable at the substation and the earth point in your house because the neutral supply conductor has a finite resistance......hence it's a good idea to provide a better, local earth point at your property.

V= I*R

or something

 

[midlife]

If you trace the wiring back is there some sort of old bike battery ?

Shaun

 

[raleighnut]

In a modern system the connection between earth and neutral is made at the main board isn't it?

If you touch neutral to earth an RCD will trip, conversely if you were to hold live in one hand and neutral in the other an RCD will not trip it'll just treat you as a lightbulb.

 

[Mr Celine]

The wiring in the OP sounds more like an industrial installation.

As for the earthing arrangement it'll be one of these in this wikipedia page.

 

[ClichéGuevara]

I modernised a house in phases, changing the old lead water main quite early on, mainly because I 'found' a great big length of plastic pipe.

One of the next jobs involved moving the washing machine. It was as I uncoupled a union on a copper pipe, I found out the lead water main had been acting as the household earth, with the internal pipes being cross bonded.

I needed the washing machine quite quickly after the belt I got.

 

[jonesy]

If you touch neutral to earth an RCD will trip, conversely if you were to hold live in one hand and neutral in the other an RCD will not trip it'll just treat you as a lightbulb.

I think what i had in mind is 'TNCS', described in this useful summary of different types of earthing: http://wiki.diyfaq.org.uk/index.php?title=Earthing_Types

 

[Levo-Lon]

My house used to be earth rod type..
i got it checked by NG and they altered my feed so its now earthed via the supply.
we have a post to house supply ,not the newer prefered under ground type.
as said all pipework is now earthed to that,Not the earth rod which was interupted as i found and only parts of my house actually earthed ..

 

[Mr Celine]

..... if you were to hold live in one hand and neutral in the other an RCD will not trip it'll just treat you as a lightbulb.

Only if you are insulated from earth.

 

[jonesy]

[QUOTE 4167592, member: 9609"]So is the best way to test for a good earth, to check the resistance between the neutral and earth at the plug? I'm going down to dodgyville tomorrow.

I have just done this test at home (modern wiring) and I am getting about 0.5 ohms. I did the test with the electric switched off as I was told you could get ghost readings if it is on ?[/QUOTE]
Surely it is easier to get the £8 plug in socket tester I mentioned earlier? That way you can quickly check every socket in the house, for several possible faults at the same time.

 

[jonesy]

[QUOTE 4168025, member: 9609"]spending £8 is never easier. Presumably all the plug in tester does in respect of earth is to check for resistance, so a plug wired up to a choc block and multi meter should do the same job.

seriously though I will get one of these plug in devices, presumably they will also show things with the live neutral swapped (of course my multimetered plug will also do the same) and I have found one case of a live neutral swap, what I don't qute understand why things were working in it, (charges etc)[/QUOTE]
I was thinking of time saving, and not having to turn the power off, or worry about faults to earth or stray currents, so safer.

A long time ago I saw a simpler home-made version in an electronics magazine. Basically it consisted of 3 neon lights connecting the three pins: L to N, N to E, L to E. They were fitted into a plug that had three holes drilled in it for the neon lights.
If all is well, then when plugged in lights LN and LE should light up, but not NE, as N and E should be at the same potential.
If E is open circuit then lights LE and NE are effectively in series between L and N, so will either both come on dimly, or not at all, depending on the lights used.
If L and N are reversed, then LN and NE will light, but not LE. Various other combinations show other faults.

 

[sidevalve]

Don't wast your time - if the building is inspected/surveyed the electrical system will be condemned. Just get it rewired, the red black wiring alone is a no no now. Don't worry about the TNC or TNCS systems or resistance to earth just get it done. If you want to hurt your brain get hold of a copy of the IEE wiring regs 17th edition and study that but TBH it's easier and safer if electric isn't your thing just to get it done.

 

[jonesy]

Don't wast your time - if the building is inspected/surveyed the electrical system will be condemned. Just get it rewired, the red black wiring alone is a no no now. Don't worry about the TNC or TNCS systems or resistance to earth just get it done. If you want to hurt your brain get hold of a copy of the IEE wiring regs 17th edition and study that but TBH it's easier and safer if electric isn't your thing just to get it done.

Fair point! That's what has to be budgeted for.

 

[subaqua]

The electrician will throw up his hands in horror and tell you it needs rewiring and it does need rewiring, for sure, because mixing modern alterations with old wiring won't work. Look on it as an opportunity to get the house sorted and wired to a modern standard; you can get the electrician to make provision for all those modern conveniences like bathroom extractors, heated towel rail, underfloor heating in the utility or downstairs loo, heated mirrors, garden power socket and lights, 5 amp sockets in the lounge for table lamps that are controlled by one switch and so on.

what utter tosh. simple 2 colours exist in this installation label as prescribed in section 514 of BS7671 wiring regs

lets get things some things straight, and this is based on not seeing the installation.

1) the conduit is the CPC* but all mounting boxes will need to have at least one fixed lug or a fly lead will be required to the earth terminal at the socket.it is still anacceptable method but all joints need to be properly made- on an old house they probably were, youngsters today rely far too much on the separate CPC
2) the conduit will be connected back to the earth and the OP has proved this by using a test meter. when the sparks comes he will use a meter to correct spec giving at least 200mA , but really should use a high current low impedance meter.
3) generally the incoming earth is from the sheath of the cable and goes to a terminal somewhere close to the meter.
4) rewireable fuses ( semi enclosed to BS3036 to give proper name ) are not "illegal" as long as the Earth Fault loop Impedance does not exceed the maximumvalue stated in BS7671
5) if the cables are PVC they will be fine as they have not been lifed yet.
6) putting an earth rod in and testing to that only tests the earth rod resistance and will give you a higher resistance than there actually is.


get a sparks registered with ELECSA or NICEIC to do a " Electrical installation condition report " which will be an inspection ( inspection can tell you far more about the installation than just a test) and proper test.


it is likely there will be a lot of Code 2 ( potentially dangerous) and Code 3 ( Improvement recommended) items http://www.electricalsafetyfirst.org.uk/mediafile/100404922/Best-Practice-Guide-4-Issue-4.pdf is a good reference point if the sparks tries and pulls the wool.

*CPC - circuit protective conductor - Earth