earthing for tt system

[gazspark]

can anybody help me, a mate of mine has a tt system at home and asked me to test his house as he wants to rent the property. i would just like to no what size earth should it be for a tt system, at the moment its 6mm and without diging me books out am not sure if it requires upgrading and knew you lads would no, thanks

 

[Deleted member 26818]

Minimum size is 2.5mm² if mechanically protected, 4mm² if not mechanically protected.
Weirdly the minimum size bonding conductors is 6mm².

 

[gazspark]

that is weird for the bonding, so 6mm is fine. thanx for that

 

[leeweimaraner]

i would upgrade his bonding 16mm to the main earth rod then 10mm to your gas and water or oil

 

[Engineer54]

Do some earth fault calculations on the TTsystem earthing cable, ... and the bonding cables for TT system and you'll understand why!!

The standard cable size for bonding cables on TN-S systems was for many many years 6mm, and if you care to do some more calculations, you could well find, that they would also comply today too...

 

[IQ Electrical]

i would upgrade his bonding 16mm to the main earth rod then 10mm to your gas and water or oil

Why would you run a 16mm to a TT earth electrode?

 

[telectrix]

was just wondering that. given the Ze attainable on a TT, 6mm should be adequate . i would be more concerned as to wheter RCD protection was fitted

 

[tony mc]

I bet the adiabatic equation comes up with a really low csa when you do your calcs!

 

[IQ Electrical]

I bet the adiabatic equation comes up with a really low csa when you do your calcs!

And there's the problem Tony, how many actually know how to use the adiabatic or actually understand the 'mechanics' of a TT system?

 

[Engineer54]

Alas, ....Not many i fear!!

 

[Deleted member 26818]

Just been involved in a discussion about the adiabatic equation on another forum.
Apparently it is a dodgy calculation, based on inaccurate measurements of Ze and PFC.
As such we should now use Table 54.7 when sizing earth conductors.

 

[Engineer54]

Really, ....that's a new one on me. So, the adiabatic equation formula's that have been the backbone of many crucial electrical design calculations are now deemed dodgy!!! Hmmmmm, i think maybe more a case of those that don't understand, ....or don't want to understand them!! lol!!!

 

[IQ Electrical]

Stay on this forum, the adiabatic works here!

 

[Engineer54]

Works everywhere else too!!....lol!!!

 

[tony mc]

I was expecting it on the 2391 but it never came up but IMO if your doing a PIR and state the earth is not big enough you need to evidence it on the report ,well thats my way of thinking.