Absent Earth Cables to Consumer Unit in 1956 House


Postby Tomgo » Sun Mar 04, 2018 1:28 pm

In a 1950's house I have 2 core cables running back to the consumer unit ( L & N) no earth. On checking the 3 pin sockets they all have an earth connected. I have a good reading for earth presence at the consumer unit! All I can presume is that the contractor back in the 50's decided to save money and wire the house with 3 core to the 3 pin outlets and connect 2 core via a connection block or similar back to the consumer unit and connect all the earths to a mains water pipe, but I cannot find anything! I have lifted floorboards to no avail. Have any of you guys any ideas please? Any help will be most appreciated.
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Postby Mr White » Sun Mar 04, 2018 8:36 pm

Could you be more specific to your question, as I for one do not understand what it is you are asking.

A few pictures would also be helpful.

I do get the impression you do not understand how things were done then.
Lighting for example had no earth.
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Postby Tomgo » Mon Mar 05, 2018 11:20 am

Thank you for responding Mr White and, yes it certainly could be clearer. Here is my problem. We are in the process of replacing the consumer unit in a 1950’s house.
1. On inspecting the wiring connected to the old fused consumer unit we find that all the cabling at the consumer unit is 2 core ( L & N) NO EARTH feeding 1 ring and 2 radial circuits. The latter being lights.
2. On inspecting the power outlets on the ring, every 3 pin power outlet has L, N and Earth cabling.
3. On testing the power outlets with an outlet tester they all pass the test for ‘wired correctly’ including the earth.
4. The TNS is excellent.
5. This baffles me as I cannot find any other earth connection on water pipes, earth rod or any other ground media where the earth cabling from the power outlets are earthed.
I would be most grateful if anyone could help this oldish learner!
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Postby Tomgo » Tue Mar 06, 2018 7:45 am

This is a re- post as my previous explanation of this issue was rubbish!
We are in the process of replacing the consumer unit in a 1950’s house.
1. On inspecting the wiring connected to the old fused consumer unit we find that all the cabling at the consumer unit is 2 core ( L & N) NO EARTH feeding 1 ring and 2 radial circuits. The latter being lights.
2. On inspecting the power outlets on the ring, every 3 pin power outlet has L, N and Earth cabling.
3. On testing the power outlets with an outlet tester they all pass the test for ‘wired correctly’ including the earth.
4. The TNS is excellent.
5. This baffles me as I cannot find any other earth connection on water pipes, earth rod or any other ground media where the earth cabling from the power outlets could be earthed.
I would be most grateful if anyone could help this oldish learner!
Many thanks.
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Postby ericmark » Thu Mar 08, 2018 10:42 am

If I talk about my late mothers house then likely your house is similar, built 1954, originally no gas this was added latter so in street it is plastic, water was earthed however in the old pantry so near impossible to see where the earth was, the only earth rod was fitted by the GPO to work the party line telephone.

As a lad I made some errors, so know line to earth fault would blow a fuse, so although not measured clearly a good earth loop impedance as it would rupture a fuse with a loud bang.

Over the years the water main was changed to plastic, came to fit new consumer unit 2004 had offer from electrician fitting under floor heating in wet room £100 extra and would fit whole new consumer unit rather than a sub consumer unit for wet room.

Him and builder ran off, leaving us to complete the work. So step one is meters out and measure. We found once the earth link removed for testing, i.e. water pipes, and gas pipes plus all circuits disconnected, there was no earth, careful inspection of DNO head showed never has an earth connected, the electrician had tried to use the GPO earth rod, but this only had bare 2.5 mm cable to it.

So DNO was got onto the telephone and they were asked "What type of earth is provided at this property?" They could not tell me, and it is up to the DNO to tell you, not up to you to tell DNO what you think you have.

This is because TN-C-S and TN-S can look the same at the head, you as the user have no idea if in the street the same conductor is used for earth and neutral or not, and properties like Petrol stations are banned from using TN-C-S also adjoining properties should have same earthing arrangements, so it has to be up to the DNO to say what it is. However if TT you need to sink the rod.

When they arrived I lied, I said next door was TN-C-S however I really did not have a clue what next door had, so they measured and connected in earth to incoming cable and gave me a TN-C-S supply without any charge.

I would guess the house never had an earth connected, it used water pipes and other metalwork to get an earth, which is likely the reason the waste pipe has corrosion on the base.

I am sure if we had tried to measure the ELI before the electrician started it would have been around the 5 ohm mark with all earth bonding connected, it may have even been as low at 0.35 ohm with is considered max for TN-C-S or 0.8 considered max for TN-S but this would have been through all the bits and pieces earthed through the house, not an official earth which one knows will not be removed.

Pre 1966 many houses had no earth to lights, so built 1954 this house did need at least the lights re-wiring, and additions through the years were not to regulations, dad told me he was proud of his new house, he had 5 sockets, my grand fathers house only had 2, but by time I moved back in there were sockets every where some in imperial cable and some metric, the imperial was slightly thicker so spur off spur with imperial not so bad, but metric cable you could see where it had been over heated at some time, so it really did need a rewire.

When the electrician had tried to fit a RCD it was tripping again and again, never found the fault, in 2004 did not need RCD protection so sockets ended up without it until full rewire in 2016.

The DNO can charge if you ask for TN-C-S instead of TT, but if it should be TN-C-S then they have to maintain it or convert every house in the street because of danger with different systems being too close the 15 meters fire gap for caravans is considered enough to have main building on caravan site TN-C-S and all caravan plots TT, so if more than 15 meters between houses then they can fit different systems, but to get TN-C-S free of charge needs careful wording of the request, you ask them what it is, not other way around.

You say earth is OK? How have you measured it? There are two basic ways to measure an earth, one involves test spikes and a very special meter in the main not used on existing houses as you need to put in prods at 15 and 30 meters from house, which would likely mean your in some one else's garden. The other is with an earth loop impedance meter, as a quick test yes simply plug in and press the button, but to do it proper you have to switch everything off and test just the incoming earth with nothing connected to it, with TN you get a direct reading, however with TT the reading is both the resistance to your earth rod, and the connection to the DNO earth rod, so pass is normally between 16 and 200 ohms, over 200 it is considered unreliable. With an earth rod you must have some sort of RCD, it could be the old ELCB-v now withdrawn. The old ELCB-v can give you poor readings typically 500 ohms the resistance of the coil in the unit.

I have never found a RCD tester that can test the old ELCB-v and pre-2008 the standard size of RCD was 100 mA for a TT supply, dropping to 30 mA required today is a problem for many old houses. You can't stop them tripping until complete re-wire is done.

So before changing a consumer unit testing is required to see what the insulation resistance is, or a clamp-on ammeter to measure the leakage, too late once fitted, today you will end up with circuits not connected as they will cause the RCD to trip, bit of a problem if that is the ring final.

Although 5 Mohm is not the pass figure, I would say any circuit under 5 Mohm and your looking at problems, do test first.
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Postby Tomgo » Fri Mar 09, 2018 5:38 pm

ericmark, Thank you for the script in reply to my problem. It was excellent. I have only just read it and I need to digest the info and will reply to you more fully when I have got my head aroung the problem and the appropriate elements of your reply. Many thanks again.
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