TT Max zs

[Frosty69]

Hi People,

Just had a friend call me asking what the max zs is for a 3 phase, c type, 60898, 40A when its on a TT supply. The supply to the board is from an rcd 300ma, he says the niceic front page in installation book says 0.46 ohms but he's getting results of 4.03 ohms. I told him as its a 300ma then the result can be up to 167ohms? I will have a proper look later in the bgb but I just wanted peace of mind whilst I'm out.

Thanks

 

[telectrix]

you are correct.

 

[Farmelectrics]

4.03 is not a bad reading for a tt system your a loud up to 220ohms

 

[Farmelectrics]

and higher if backed up by rcd

 

[Frosty69]

Thanks guys the circuit is only 10 metres but I will let him know i was right and invoice him! ha ha

 

[IQ Electrical]

4.03 is not a bad reading for a tt system your a loud up to 220ohms

Don't forget that the Zs measured will include parallel paths through protective bonding-the Ra value could be 1000 Ohms for all we know.
Where do you get the 220 Ohm max from?