TT system cable size

[paul35]

Hi all. Can anyone tell what size the earth cable should be from CCU to the earth rod. To clarify I am installing an TT system in a two bed regular house.

 

[Octopus]

What do you think it should be?

 

[shocking_eg]

Ffs ! :#

 

[paul35]

Would 10mm sq. be enough. Thanks

 

[shocking_eg]

what size is the usual main earth conductor ????

and the one stated in the OSG ?

 

[Octopus]

what size is the usual main earth conductor ????

and the one stated in the OSG ?

the OSG size shown for TT is not correct.

 

[shocking_eg]

the OSG size shown for TT is not correct.

LOL i know.

and they expect us to follow these books and they cant even get it right !! FFs

 

[paul35]

OSG states it should be 25mm sq. if unprotected. Not sure what they mean though, would that mean clipped direct. 16mm sq. if protected against corrosion. But it says you can get away with 2.5mm sq. if protected agains corrosion and mechanical damage. Why is there such huge difference. Can the 2.5 carry the fault current anyway

 

[ARK]

thats what they say, but if you read it it looks like 25 mm, unless its it coduit i suppose

 

[Richard Burns]

OSG states it should be 25mm sq. if unprotected. Not sure what they mean though, would that mean clipped direct. 16mm sq. if protected against corrosion. But it says you can get away with 2.5mm sq. if protected agains corrosion and mechanical damage. Why is there such huge difference. Can the 2.5 carry the fault current anyway

Unprotected means without a sheath.
Mechanically protected means with a protective cover enclosing it, such as conduit.

Those csas are for where the conductor is buried.
Once it is mechanically and corrosion protected then it can revert to above ground levels of csa.

Calculate what the earth fault current would be with a standard TT system and you will see why 2.5mm may be acceptable if it is suitably protected.

 

[D Skelton]

Blatant wind up! I had a good chuckle thanks paul35

 

[Knobhead]

You're getting cynical, must be an age thing.

 

[D Skelton]

Haha, I'm really not that old! It's gotta be a wind up though

 

[Knobhead]

Can't wind me up now, my springs broken!

 

[Engineer54]

As the earth rod (electrode) is going to be in place a long time, probably for a good 30 years or so, it makes sense to use 10mm cable, rather than anything thinner if it doesn't have a decent means of mechanical protection.