maximum Zs

[havoone]

for a TT system in domestic house with 0.2 disconnection time, with either mcbs or fuses. do i use the max Zs values in Tables 41.2- 41.4 which have 0.4 and 5 s disconnection times ? obviously depending on type of circuit.

 

[topquark]

My reading would be 411.5.4 rule should be applied (Zs x Ia <= U0). But also refer to 411.5.2 which says to prefer RCDs for protection. Maybe someone with more experience of TT systems can clarify.

 

[Des 56]

In a TT, earth fault protection is mostly by way of an Rcd
You will be very unlikely to have a low enough Zs for those tables to apply
Rcds are the prefered option

Table 41.5 refers to Rcd rating and max Zs for TT
These are the values

 

[havoone]

ahh so when filling in a cert for a TT system the max ZS value to be entered is taken from table 41.5 . so for domestic most likely 1667 ohms. another question then. if im filling a cert for a Tns system say with 32A breaker and Rcd protection, which Table should i refer too. thank you

 

[JUD]

ahh so when filling in a cert for a TT system the max ZS value to be entered is taken from table 41.5 . so for domestic most likely 1667 ohms. another question then. if im filling a cert for a Tns system say with 32A breaker and Rcd protection, which Table should i refer too. thank you

Table 41.3