ZS on a TT system

[VoltzElectrical]

What do we do about testing for ZS on a TT system? sorry, but never covered this in college. I know Ze should be below 200 ohms, and that the max Ze can be 1667 to give disconnection time when covered by 30mA RCD. But I've never given thought to actually testing and certifying a TT installation. What do you put on the form? Do you even test Zs at live points?

Sorry if this seems a bit basic, but college only covers TN system testing and I don't really deal with much TT.

 

[telectrix]

test the same as for a TN system. the Zs readings will generally be a lot lower than expected, due to the gas and water bonding providing parallel paths and reducing the Ze.

 

[VoltzElectrical]

cheers tel. there's no tables to compare to so you just enter your values i suppose?

 

[telectrix]

yeah, say you get a Ze of 90 ohms, you may get a Zs of 3 ohms ( or anything, really ). you enter the value as measured, but for the max. allowed, it's 1667, as you mentioned.

 

[VoltzElectrical]

ah, of course, the 1667 is the max value. Thanks again, and sorry for you having to explain the bleedin' obvious. I've been p to my eyes fault finding today and my head is fried!