What we offered here...
Earth fault loop impedance reading on TT System in domestic premises
...still stands, Chris. The Regs aint changed in 4 days!
Is there a specific question you don`t feel has been answered satisfactorily?
Re: the Q`s in this post; as already stated you`ll need 30mA RCD`s for any bathroom/shower room circuits + socket outlets + for ccts with cables installed in walls at less than 50mm. As that`s likely gonna include your lighting circuits (& you`ll need 2 or more) you`ll require 2 or more RCD devices (could alternatively be RCCB or RCB0) so as to provide discrimination between devices.
Basically, nowadays TT`s are much the same as TN`s in requirements for CU`s
The 100mA is required only for ccts not requiring the `Additional Protection` of 30mA RCDs, would have to be of the `S` type (delayed) for discrimination of devices, & may be done away with entirely if you can meet the applicable criteria listed at table 41.1 of the Regs. (then you adopt TN values)
Seriously mate, you`ll have to read up on the Regs to get thru your assessment, so have a peak now
On the Ze front, while the official figure is min 200ohms, i`m pretty sure the NIC require 100 (which i`d always look to get even tho` i aint with them) so if it`s an NICe assessment you`ll need <100ohms
Hope that clarifies it further for you