Taking cables from a house to a garage

[bluetof]

it depends on what type of earthing system you have,if you have TN-S then it is fine to take an earth from the MET,

if you have TT then you don't usually take the earth out, you provide another spike for the garage outside

if its TNC-S you don't take it outside (never, in normal circumstances), you need to make your garage into a TT system and provide a separate spike for it on its own earthing system.

Hi Steptoe

Where did you get this info - particularly on the TNC-S. i.e not taking the earth outside ? Guinness

 

[Andy™]

tncs can be dangerous if used outside the equipotential (or in in!) zone, which includes exporting. same reason its banned from supplying caravans etc

 

[steptoe]

Hi SteptoeWhere did you get this info - particularly on the TNC-S. i.e not taking the earth outside ? Guinness

I really hope you are not seriously expecting a reply to this.

 

[bluetof]

I really hope you are not seriously expecting a reply to this.

What page ?

 

[ianmacd]

What page ?

Do a search on here for exporting earths and TNCS. Also ask your DNO what they think of exporting their TNCS supplied Earth.

 

[ADS]

Do a search on here for exporting earths and TNCS. Also ask your DNO what they think of exporting their TNCS supplied Earth.

Funny you should mention that coz I rang Scottish Power and asked them what to do if I wanted to run power to my shed ... they said run it from the main earthing terminal (tn-c-s supply) - they actually told me they'd prefer the equipotential zone extending than any other method.

I think the only time it becomes a problem is with metal framed out-buildings etc connected to your bonding.

There seems to be a lot of myth about all this but no regs.

I'm starting to think that when they say you can't export PME they are actually talking about the PEN conductor itself and that you are not allowed to extend it to other buildings etc - coz obviously you can't have TN-C in this country.

I really don't think they mean you can't run a CPC or Bonding out to your garage

As for the loss of supply neutral - If that happens your in the poo poo anyway with tn-c-s .... whether you've got a garage or not

 

[spinlondon]

You wouldn't be in poo poo if there was a rod, or some other path for the neutral current to return.

It is only really a problem if you become that path.

 

[PBC_1966]

Except that according to some people putting an extra earth electrode on the installation will make the universe implode...... Or something like that!

 

[ADS]

You wouldn't be in poo poo if there was a rod, or some other path for the neutral current to return.It is only really a problem if you become that path.

In a normal situation (eg my house) there won't be a rod, so it's down the good old extraneous conductive parts it goes.

But like I said, it wouldn't matter if I had a garage/shed or not, the same thing would just be happening in there

 

[steptoe]

one more time folks,

if you export the earth from a TNCS you may be introducing a false potential to your out building.

you have taken a false earth to that building.

ie, the earth on your electrical cable may not be at the same potential as the general mass of earth,

therefore a potential can occur between cpc and true EARTH.

 

[ADS]

one more time folks,if you export the earth from a TNCS you may be introducing a false potential to your out building.

you have taken a false earth to that building.

ie, the earth on your electrical cable may not be at the same potential as the general mass of earth,

therefore a potential can occur between cpc and true EARTH.

I understand (and agree with) what you are saying - but by the same theory, the taps in my kitchen are likely to be at a different potential to the true earth by my back door - what's the difference. (I could reach the taps from outside, by the way;\)

 

[PBC_1966]

the earth on your electrical cable may not be at the same potential as the general mass of earth, therefore a potential can occur between cpc and true EARTH.

Exactly the same situation could occur within the house itself though, with a difference in potential between the earthing system of the installation and true earth.

That's why in other parts of the world an earth electrode is required at the service entrance to the house, and at each outbuilding.

 

[ianmacd]

Yes but the one at the cutout needs to be on the PEN and the cable to the other one needs to support the PFC of the installation (probably 16mm).

 

[ianmacd]

In a normal situation (eg my house) there won't be a rod, so it's down the good old extraneous conductive parts it goes. But like I said, it wouldn't matter if I had a garage/shed or not, the same thing would just be happening in there

Plastic incoming pipes for services? Only way then it will got to earth is, again though someone.

 

[ADS]

Plastic incoming pipes for services? Only way then it will got to earth is, again though someone.

Same answer again, then - it wouldn't really matter if that happened in the house or in the garage.

 

[ianmacd]

Same answer again, then - it wouldn't really matter if that happened in the house or in the garage.

If course it would as in a house everything should be at the same potential (bonded) no to current will flow unless you have concrete floors with no floor covering. Step outside and you could be standing on the concrete floor of a garage and touch a class I accessory and ADS won't kick in soon enough to save you .

 

[steptoe]

I understand (and agree with) what you are saying - but by the same theory, the taps in my kitchen are likely to be at a different potential to the true earth by my back door - what's the difference. (I could reach the taps from outside, by the way;\)

but that is why you have bonding in your house, to ensure the protective device cuts out fast enough,

if your taps go "live" then you should have enough leakage to earth for the PD to operate before you touch them.

Exactly the same situation could occur within the house itself though, with a difference in potential between the earthing system of the installation and true earth. That's why in other parts of the world an earth electrode is required at the service entrance to the house, and at each outbuilding.

and why I keep saying that TNCS in this country is DANGEROUS, because IMO it is not implemented properly.

If course it would as in a house everything should be at the same potential (bonded) no to current will flow unless you have concrete floors with no floor covering. Step outside and you could be standing on the concrete floor of a garage and touch a class I accessory and ADS won't kick in soon enough to save you .

wish I could put it this simply, Im not good with big words. Blushing

 

[ADS]

........ and ADS won't kick in soon enough to save you .

I'm not saving anyone bad day explode

 

[ADS]

but that is why you have bonding in your house, to ensure the protective device cuts out fast enough,if your taps go "live" then you should have enough leakage to earth for the PD to operate before you touch them.

We weren't talking about them going "live" - you were saying about

introducing a potential to the garage/shed through the CPC -

I replied that the same potential could be introduced to my taps (via

bonding) , and that I can reach them whilst standing on 'true earth' outside -

so what's the difference?

 

[ianmacd]

We weren't talking about them going "live" - you were saying about introducing a potential to the garage/shed through the CPC -

I replied that the same potential could be introduced to my taps (via

bonding) , and that I can reach them whilst standing on 'true earth' outside -

so what's the difference?

I would suspect that your ability to touch your taps when outside is quite unique and maybe you should invest in a rubber mat for outside.