Earth Fault Loop Impedance...

[davesparks]

Been a while since I last used a Schneider RCBO but they also stated that they couldn't be used on TT installations.

I think with the new generation this caveat has been removed.

I think it's still the same, ive just fitted a board with the new plug in neutral type, I'll see if any of the instructions are still hanging around tomorrow.

 

[Strima]

Been a while since I last used a Schneider RCBO but they also stated that they couldn't be used on TT installations.

I think with the new generation this caveat has been removed.

Schneider make both single and double pole RCBOs so you need to be careful which ones you order.

 

[Ian1981]

Not for a TN system under the 18th edition

Haven’t seen this change I’ll have to have a look

 

[Ian1981]

Schneider make both single and double pole RCBOs so you need to be careful which ones you order.

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

 

[Bobster]

Schneider make both single and double pole RCBOs so you need to be careful which ones you order.

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.

 

[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