What earthing system is this ?

Discussion in 'Electrics UK' started by caffreys, 20 Feb 2021.

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  1. caffreys

    caffreys

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    Just curious , it's a 1930s house - the main cable is inside steel conduit and the earth comes out of the conduit along with the main cable - the steel conduit then has a bonding strap attached to it.
    Main fuse is 63amp

    earth.jpg earth.jpg
     
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  3. sparkwright

    sparkwright

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    Can send a picture with the cut-out, meter, consumer unit in it as well please?

    Also, have you seen any earth looking things outside? If so, send a pic.
     
  4. flameport

    flameport

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    It probably was TN-S, looped from next door.
     
  5. ericmark

    ericmark

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    I think back to some of the systems I have seen, which includes a suspended floor in Liverpool with TT system and the earth rods were under the floor, there were plans for an assess hatch, but not a clue if ever built.

    But it seems in order to ensure you don't have a TT and a TN in two next door premises so you can have a voltage difference between the two, the DNO has to say what the earthing system at the head will be, OK I do know of some exceptions where the owner was a radio ham and the whole house was TT but all neighbours were TN-C-S but this was an odd one out, so all it should take is a phone call the the DNO and they should tell you.

    Yes it does go wrong, my son rewired a house in Queensferry North Wales, and he phoned the DNO to find earth type, which he was told would be TN-C-S so he left the tails for a TN-C-S but he was in middle of a divorce, and moved out of his house and went to live in a narrow boat, so of no fixed abode, the result was he was never told when the DNO connected, and out of interest some months latter visited to see how it went, only to find no earth had ever been connected, the DNO had changed their mind and given a TT supply. Earth rod was then fitted.

    My parents were the same, I know there was an earth, as when a kid I had caused a short to earth and blown the fuse, but some 40 years latter no sign an earth had ever been connected. Only earth was for the old party line phones fitted by GPO. A phone call and DNO did FOC fit an earth making it a TN-C-S supply.

    But what this all means is you can't guess, in the main below 0.35Ω it is TN-C-S, below 0.8Ω it is TN-S and above 0.8Ω it is TT with domestic premises, but it does not always follow, and on commercial premises it can be much lower, if anywhere on the supply transformer to house earth and neutral are combined it is TN-C-S it does not need to be combined at the head, so you may see it is TN-C-S but you can never be sure it is TN-S unless the DNO tells you. So there is really no option you have to phone DNO.
     
  6. caffreys

    caffreys

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    Cheers, I'm just curious as I may be looking at getting an Electric Vehicle and they need good earths apparently. From what I know the houses in the street are connected serial and this one looks like the end property - There has been no history of issues

    Here's a pic of the setup , there is no earth arrangements outside - I'm wondering if that steel conduit was an early earth rod? Maybe the conduit goes back to the source - if so It's probably rotted out by now as it's probably 50+ years old.

    Purple stuff is network and that's a UPS at the bottom feeding a cab

    PXL_20210220_131850595.jpg
     
  7. Taylortwocities

    Taylortwocities

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    You may want to ask the DNO to upgrade the supply. 63A plus EV charging doesn’t give you much headroom.
     
  8. ericmark

    ericmark

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    There are a number of ways to ensure electric vehicle charging is safe, back years ago boats, caravans, and other mobile units that needed power would need a TN-S or TT supply, in the main it was TT, and because of fire regulations the mobile unit would be at least 2.6 meters from any building, so having a motor caravan supplied with a TT supply and main building with TN supply was not a problem.

    However with the electric car they are often parked a lot closer to the building, I know there are regulations stopping a vehicle from being parked in front of windows, I have seen where garages have been converted to a room the drive has to be altered so vehicle has a set distance from window, but it is still a lot closer to what fire regulations allowed for caravans etc.

    So a whole new system has been designed, so you can safely have a charging pod close to the home. But it is not just one system, there are a few different ways to make it safe. So you have DC detection so a type A RCD can be used, and current transformers to ensure the charging pod does not draw over the available supply, and it seems each firm is trying to say their system is the best because it has some patented device fitted.

    And the installers have to go on courses, and be registered to be able to claim grants etc. So it has become rather specialist. And it seems each time some one says you can't do that, it seems there is some firm with a patented unit that is approved to do it. Everything is turned on its head, we always said you can't switch an earth, but it seems with electric car charging they do.

    So you select your installer and leave it to him.
     
  9. Harry Bloomfield

    Harry Bloomfield

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    My guess is that the actual earth is the one exiting out from the open end of that conduit and the conduit is simply being bonded by that earth strap. That 10mm then passes up behind the cut-out and on towards where ever your consumer unit is located.
     
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  11. caffreys

    caffreys

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    63 Amp should be okay as it'll be charged using the 3 pin granny charger on a 2.5mm radial with one socket and a 20amp rcbo (It's the single external socket on the property)
    Also charging will be done when there's almost zero load

    Might contact the DNO to see if I can get a 80 amp upgrade

    I'm not planning on a EV socket installation, I believe a lot of those need an earth rod?

    Things are changing all the time see BS7671 amendment 1
     
  12. RF Lighting

    RF Lighting

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    Looks like TN-S to me. As with any supply, the only way to tell if it’s actually any good it to perform an earth fault loop impedence test on it.
     
  13. JohnW2

    JohnW2

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    I'm rather confused by that photo. Whilst what is above the clamp is clearly steel conduit, although it may be an optical illusion, what one sees below the clamp looks (to me) more like cable, of smaller diameter than the conduit. Particularly if the latter (and, I suppose, even if it isn't), it begs the question as to where the G/Y disappearing into the conduit goes.
    The problem in this case would seem to be in knowing 'what to test'. As you recently pointed out, one does not want to be mislead by testing an earth in the presence of a bonded extraneous-c-p (which one can't rely on always being there).

    I suppose one could disconnect the G/Y which disappears into the conduit from the clamp, and then test both that conductor and the clamp - but I think that there are certain combinations of 'pairs of answers' which could still leave one wondering about what the impedance of 'the actual earth' was!

    Kind Regards, John
     
  14. caffreys

    caffreys

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    The 10mm G/Y is just connected to the clamp - it doesn't enter the conduit and goes to the CU, the old green earth (6mm?) comes from the conduit and is connected to the clamp
     
  15. Harry Bloomfield

    Harry Bloomfield

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    I wonder if that one disappearing down the conduit, might go down and out to an earth rod?
     
  16. chivers67

    chivers67

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    I'm was a bit confused by this photo initially as I couldn't see how the DB was connected.
     
  17. caffreys

    caffreys

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    I've never found an earth rod, I'm wondering if it's connected to next door somehow via the conduit as the power is in series.
     
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