Impedance value

[allsorts]

I am having to put an earth rod into the ground to supply the individual earthing for the garage supply, however the ground is pretty much chalk based below the first 12"-18", any suggestions on improving the earth impedence value, as it is oviously not going to be that good.

 

[securespark]

Why use rod?

What is wrong with cpc (earth) in supply cable?

 

[allsorts]

I was under the impression that the garage would be deemed to be a remote building as it is not attached to the home and therefore requires a seperate earthing arrangement, particularly as it is protected by its own RCD, I stand to be corrected

 

[toasty]

Steady if you are using more than one earthing system.

RCD's can act strangely if you have multiple earthing paths.

I'd need to know more about your setup before I commented further, but having two earth rods (for example) is usually always a bad idea, unless you know what you are doing

 

[ban-all-sheds]

How far from the house is the garage, and what type of supply do you have? Is the house TT as well?

 

[allsorts]

The home is not a TT system, and the garage is no more than 1500mm from the home. I was under the impression that the supply from the home to garage was not to have the earth connected at the home CU, but is to be connected to the garage CU to provide protection for the supply cable, then the garage was to be independantly earthed. Would this also stand to be correct if I wanted to supply power to my shed which is 12m from the home??

 

[Lectrician]

It is recomended on PME earthing systems to use a seperate earthing arrangement in the out building, as this doesnt normaly form part of the equipotential zone of the house.

However, this is a recomendation from the REC, and is not a regulation from the IEE.

If you were to apply this rule in general, all outside lights, sockets etc would need rodding down.

You should also be aware that any rod installed SHOULD be tested to ensure the impedance is of an acceptable value, a job to be done by a spark, as he will have the correct test kit.

It is possible to carry the equipotential zone of the house to the garage, and this must be done in any case (and the same earthing system used from house to garage) if there is any common metalwork such as water, gas or central heating pipework.

If you do use a seperate earthing arrangement, you must ensure that the cable from the house, if armoured, has the armour earthed from the HOUSE side, and this must be fully insulated from the garage side.

 

[plugwash]

You should also be aware that any rod installed SHOULD be tested to ensure the impedance is of an acceptable value, a job to be done by a spark, as he will have the correct test kit.

i would call that a must
the problem with rods is that its so easy to end up getting an inadequate conenction even though you've folowed all the normal procedures so they really do need proper testing

It is possible to carry the equipotential zone of the house to the garage, and this must be done in any case (and the same earthing system used from house to garage) if there is any common metalwork such as water, gas or central heating pipework. You must also ensure that the cable from the house, if armoured, has the armour earth from the HOUSE side, and fully insulated from the garage side.

if isolating yes if using a common earth then you would gnerally connect the armour to earth at both ends (you may even be using it to carry earth though i advise against this for diyers)

 

[Lectrician]

Hey plug....aint seen you at novaserve for a while, yea I know my spelling is 'A' touch 'O'ff perfect - LOL

 

[Damocles]

lec,....What is the difference connecting the earth inside the armoured cable and the earth formed by the armouring?

 

[Lectrician]

The armour need earthing - a must. This must be from the house side, as this is where the protection for that cable is.

If you are not taking an earth to the garage, there is no need for a third core, so it will be un terminated each end, non existant, or earthed at the house end, and isolated at the garage end.

 

[Damocles]

You said:

It is possible to carry the equipotential zone of the house to the garage, and this must be done in any case (and the same earthing system used from house to garage) if there is any common metalwork such as water, gas or central heating pipework. You must also ensure that the cable from the house, if armoured, has the armour earthed from the HOUSE side, and this must be fully insulated from the garage side

What is the point of insulating the armour if you are connecting the core earth? Or how else are you going to carry the equipotential zone into garage?

 

[ban-all-sheds]

The armour need earthing - a must. This must be from the house side, as this is where the protection for that cable is.

Yes it must be connected at the house, but no reason, surely, for it not to be connected at the garage as well?

If you are not taking an earth to the garage, there is no need for a third core, so it will be un terminated each end, non existant, or earthed at the house end, and isolated at the garage end.

I don't think that not taking an earth to the garage is a Good Idea.

 

[plugwash]

i can see the pros and cons to making the garage a seperate TT

if the house is a TT it is a good idea to seperate because diring a fault the ground potential on a TT will rise significantly (until the rcd kicks in) so there is no point carrying this to the garage unessacetally

if the house is a TN-S then its probabblly a bad idea to seperate TN-S is probablly the safest system overall having a pretty low earth loop impedence and not suffering from the risks of PME

TN-C-S is less clear cut on the one hand having the low earth loop impedence in the shed is a good thing on the other hand it has its own problems which may be more significant outside the equipotential zone

 

[Lectrician]

Post gone way weirdly wrong.