TT Zs

smartspark · Apr 12, 2011

Where are the max Zs for TT circuits to be found in the regs, I have 32.9 ohms at the stake, which is great, the readings for Zs on the circuits are between 18.81 and 19.69 ohms, does this look correct, dont do much TT work so excuse me for being green

RWJ · Apr 12, 2011

There's no max Zs listed for a TT. It's recommended you get it below 200ohms although and RCD a still operate above this up to 1666ohms.

If you've 32.9 ohms at stake you haven't done bad.

smartspark · Apr 12, 2011

I did find table 41.5 in the red bible, wasn't sure. It does state 1667ohms but only up to 32A, Ive installed a 45A for the range cooker newly installed, guess that must be OK at those results, awesomely quick reply, thanks.

telectrix · Apr 12, 2011

asa long as all circuits are RCD protected. no problem.

smartspark · Apr 12, 2011

yep new C/U.

telectrix · Apr 12, 2011

it's because , due to the high Ze, you can't achieve disconnection times with the overcurrent device, and so you rely on the RCD for fault protection.