Earth Fault Loop Impedance...

[davesparks]

Aware of this, however the original ACTI9 RCBOs wouldn't operate without a decent reference to earth through the functional fly lead. Meaning in poor TT conditions, they may never operate.

I wonder how may other RCBO's which have the earth reference connection have the same limitation?

 

[Wilko]

Not for a TN system under the 18th edition

Hi - just my read of it, but I had interpreted Reg 411.4.204 from the TN section to indicate we should use Table 41.5 from the TT section, giving 1667 Ohms again for 30mA. (?)

 

[Ian1981]

Hi - just my read of it, but I had interpreted Reg 411.4.204 from the TN section to indicate we should use Table 41.5 from the TT section, giving 1667 Ohms again for 30mA. (?)

Agreed I’ve done the same

 

[Strima]

Why?
You don’t need DP rcbo’s on a TT
A DP main switch or 4 pole will give you your isolation

If you read their instructions they state that their single pole RCBOs are not suitable for TT systems.

 

[Ian1981]

If you read their instructions they state that their single pole RCBOs are not suitable for TT systems.

Wonder why that is ?.
There is no requirement to switch/disconnect the neutral during over current conditions for a TT or TN arrangement except for certain requirements in part 7

 

[Taggle]

I think their preparing the ground for combined AFDDs and RCBOs where there is a need to switch off the neutral, also 536.3.1 mentions RCDs needing to be switched for all live conductors.

 

[Strima]

Wonder why that is ?.
There is no requirement to switch/disconnect the neutral during over current conditions for a TT or TN arrangement except for certain requirements in part 7

I know, maybe you should ask Schneider.

 

[Ian1981]

I think their preparing the ground for combined AFDDs and RCBOs where there is a need to switch off the neutral, also 536.3.1 mentions RCDs needing to be switched for all live conductors.

No such regulation exists in bs7671 536.3.1 I mean

 

[Taggle]

No such regulation exists in bs7671

I miss typed it should be 531.3.1got over excited being on the forum!

 

[Ian1981]

I miss typed it should be 531.3.1got over excited being on the forum!

That’s for IT earthing arrangements.

Except where 531.3.1.201 applies.
531.3.1.201
For protection against electric shock there is no requirement to disconnect/switch the neutral in TT or TN systems
It would mean that all single pole rcbos are non compliant even on TN arrangements.

Also 531.2.2.201