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Earth or no earth


paul b b

Question

Hello chaps!

There has been, in recent days a spate of questions on TT systems (is TT the new black?)

so my question is....

if, say you go to a house, and are not sure if it is earthed, what is the best test to comfirm, as the 6mm or 10mm cable could be bondings.

many thanks, as ever

paul

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12 answers to this question

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There is only one way to cofirm any earth in any house and that is to perform a Ze test.

This is a test between phase, neutral and any physical earthing point, provided by the supplier.

The Ze test is external to the installation.

Zs is the internal loop test taken at the extremes of any circuit.

For TNCS earthing the maximum reading is 0.35

For TNS earthing the maximum reading is O.8

For TT earthing the maximum reading is ambiguous (andy just for you) lol

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if you did the ze and it was a bonding not to a spike is it not possable that you may get a reading through the mains water?

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Ze is performed with ALL bonding disconnected.

Ian.

sorry shoul have explaned better, if you disconnectd the bonding and performed a ZE is it not possable to still get a reading?

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this is, of cause, if you cannot find the end of the bonding cable.

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I'm not sure what you are asking now. The test should be performed from the MET with only the distributor supplied earth (if any) connected.

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I understand that ian, but if you are not sure if the house has an earth rod, is there a test to proove that? I.E testing from the met to the pipes etc?

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Just had a thought, would a Zs on a cooker circuit for example show it up? as the reading would be very high.

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If you have TN you should see the earth at service head. if you have TT, then there may or may not be a rod. a count of earths leaving board should tell you if there is a rod or not, along with checking connection on gas/water (to make sure its not one cable to rod, one to gas/water looped).

if you cant find a rod, you could test earth loop to unknown cables, and remove earth connection from gas/water. then it should give no reading on those, and if your left with a earth rod type reading, there is probably a rod somewhere

with TT and bonding in place, it can be almost impossible to tell if there is a rod or not by an earth loop at socket etc (obviously if you get a reading of 1500, there is a problem somewhere)

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I disconnect the Main Earth to do a Ze test. If the house is occupied, Naturally the occupants have to be informed. Even though the Main Switch is off.

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You need to seek permission before removing power. You don't need to tell them again you are doing a Ze test if the power is already off.

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Paul, in a domestic installation of TNS or TNCS you should be able to verify the means of earthing by inspection at the service head { and then measure it}........In a TT system you will have to verify this by physically locating the Rod....If any doubts exist as to the integrity of this conductor along its route then Disconnection of the Main Earth conductor is then usually carried out at the C.U. and a resistance measurement undertaken with a wander lead from this end of the conductor to the rod end ....Earth Rod Connections are required to be readily accessible for inspection, therefore if you cant locate it then you cannot verify its existance ,therefore you cannot state the installation is effectively "Earthed" ,even if your subsequent Ze measurement at the C.U give acceptable readings......it a nutshell ! youve got to be able to see the rod ...!

a1 spark

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