Zs measurements in the Cert column

[cliffed]

Still having a discussion @ work about this…TNCS system DB/CU is a split 30ma RCD configuration,5/5
MCB’S are 60898 what Max Zs would you put in the column for Max measurement for the MCB

 

[buzzlightyear]

what Max Zs would you put in the column for Max measurement for the MCB

What would you put.and see if can get correct.

 

[cliffed]

I would put 1666 for the Rcd measurement & the normal Zs measurements for the MCB’s

 

[buzzlightyear]

I would put 1666 for the Rcd measurement & the normal Zs measurements for the MCB’s

Are you testing TT or PME.
in your tick box for Max measurement tested.

 

[cliffed]

Are you testing TT or PME.
in your tick box for Max measurement tested.

PME Cheers

 

[cliffed]

It’s actually in the column Max permitted Zs for installed device ie: MCB 60898

 

[buzzlightyear]

It’s actually in the column Max permitted Zs for installed device ie: MCB 60898
What the regs say what mcb you have installed.

 

[Pretty Mouth]

1667 ohms for any circuit protected by a 30mA RCD

 

[pc1966]

On a TN system I would normally base it on the MCB Zs value.

Yes, you can disconnect according to regs on 1667 ohms with 30mA RCD, but on TN-C-S it ought to be pretty low and unless it is an unusual situation, anything above the usual OSG sort of tabulated values suggests a fault in the circuit implementation which needs fixing, not a planned use of the RCD.

High current sub-main, or TT earthing, are a very different kettle of fish.

 

[cliffed]

1667 ohms for any circuit protected by a 30mA RCD

Well that’s the dilemma & some disagreement here… To be fair I’ve seen both measurements recorded on Certs… personally I prefer the Zs for the MCB, with the 1666 only for the MCB