Earth Rod Question

[Lee8210]

The house I have moved into has got a CU under the stairs with no earth at all.I have put a earth rod in the floor below the CU and run 10mm earth to CU earth for now, is the earth rod meant to be outside the house or is it ok where it is?
I am thinking of getting a PME soon so if it needs to be outside would it be ok left where it is untill the PME is done?

Thanks.

 

[Spark123]

An earth electrode needs to be tested with an earth fault loop impedance tester to ensure it is in good contact with mother earth, it is impossible to say if it is OK where it is however it is the norm to have them outside and even better if you can get them down to the water table.
In anycase I urge you to have an electrician come and inspect and test the electrode and also ensure your installation is correct as a TT system requires all circuits to be RCD protected.

 

[JohnD]

getting PME would have been a lot less trouble, and might even have worked out cheaper.

It is also very reliable.

 

[ericmark]

The supplier is suppose to supply all properties from same transformer with same system. So it is not up to you as supply types. However there are some items for which it is not permitted to supply as PME so there are cases of a mixture for example petrol stations, boats and caravan are not allowed to have PME supply.

The earth rod may be inside the property and since you must ensure no one can contact the earth very close to the rod as under fault conditions there can be a high voltage gradient there are some advantages in having it inside.

However as already said it is not just a case of banging in a rod. There are two main methods of testing. The first uses a special meter with at least 3 leads often 4 which are very long and are placed on the earth and at 15 meters away and 30 meters away approx and is only method when there is no supply.

However also the rod can be roughly tested using the supply. I say roughly as one does not know the impedance of the supply but it is likely within an ohm of correct figure. However there are dangers in testing this way and during the test lethal voltages can be imposed on earthed items so not really a DIY job. But the meters for second method are more freely available and are called earth loop impedance meters.

Having said that if I didn't have the meter I would do as you have done and just banged in a rod it has to be better than nothing. however it is highly unlikely that the reading will be less than 1 ohms so to work the supply will also need to be protected with a RCD which detects imbalance in the supply and removes it should it reach a preset level.

For many years we used 100ma RCD's on TT (earth rod) systems but new rules have resulted in multi 30ma RCD's now being the norm.

 

[RF Lighting]

The supplier is suppose to supply all properties from same transformer with same system.

My DNO are not bothered.

I've even seen TN-S and TN-C-S supplied to the same building

 

[ericmark]

The supplier is suppose to supply all properties from same transformer with same system.

My DNO are not bothered.

I've even seen TN-S and TN-C-S supplied to the same building

I would agree that some DNO do not seem to follow the rules which in some cases would be impossible where for example a petrol station has same supply transformer as houses.

However it is impossible to have a TN-S and TN-C-S from same transformer. If the neutral and earth use the same conductor (I don't mean bonded together at transformer) then it is classed as TN-C-S.

This I have raised a few times as although you may think your supply is TN-S it may be TN-C-S and as you know supplies to caravans and boats for example are not allowed from a TN-C-S system but are allowed from a TN-S system.

Only if supplied from different transformers can you get TN-S and TN-C-S in same building which when some building cover vast areas could happen but not likely in a house.

Thoughts are if two houses where supplied one with TN-C-S and other with TT and they are close there could be a different voltage between the two earth systems so touching extraneous-conductive-parts from both building could produce a shock.

 

[ColJack]

do us some photo's so we can see what you've got..

 

[RF Lighting]

Me or the op?

 

[securespark]

getting PME would have been a lot less trouble, and might even have worked out cheaper.

It is also very reliable.

John, matey, you must be ill: hope you get well soon.

[You've not mentioned RCBO's]