Disconnection times and Zs values

Table 41.1 requires disconnection time of a 120v Uo 230v TNS supply as

• 0.4

• 0.07

• 0.2

• 0.1

The disconnection time seconds for a 230-400v circuit DC TT system

• 0.8

• 1

• 0.4

• 0.2

The symbol Zs is

• The insulation resistance total value

• The resistance of the line conductor only

• The impedance in ohms of the fault loop

• The Zoo Society

To achieve the maximum disconnection time of 0.4 secs

The maximum Zs value of a 25A BS88-2 fuse system E & G

• 2.43

• 1.68

• 1.29

• 0.99

To achieve the maximum disconnection time of 0.4 secs

The maximum Zs value of a 45A BS 3036 fuse

• 1.68

• 0.40

• 1.04

• 0.56

To achieve the maximum disconnection time of 0.4 secs

The maximum Zs value of a Type D 60898 Circuit breaker rated at 100A

• 0.11

• 0.14

• 0.17

• 0.27

To achieve the maximum disconnection time of 5 secs

The maximum Zs value of a 80A BS88-3 fuse system C

• 0.29

• 0.68

• 0.51

• 0.38

What is the maximum ZS value when a non delayed RCD to BS EN 61008-1

if the RCD is rated at 30mA

• 100

• 167

• 500

• 1667

What is the maximum ZS value when a non delayed RCD to BS EN 61008-1

if the RCD is rated at 300mA

• 0.3

• 167

• 1667

• 100

Discrimination with regards protective devices means upstream devices are rated..

• lower than downstream devices

• The same as down stream devices

• Higher than down stream devices

• nicely