Is my Zs too high?

[metro.solar]

Hi There,

I have installed a 16A radial circuit into mycustomers loft via a new DB. The current system is a TT system with the Main Bonding Conductor being a 6.0mm. We have noted this to be an issue. However, on testing, the electrode resistance came out as 9.96ohms, and then a Zs on our circuit, being only a couple of meters away, at 9.97ohms.

This is all fed from a new 2 way DB, with a 61008 RCD main switch rated at 63A 30mA trip. The protective device for the circuit is a 60898 Type B 16A. Therefore, with the Zs being at 9.97ohms, does the presence of the RCD main switch rectify this?


Any help would be much appreciated.

 

[malcolmsanford]

yes..............................with RCD protection your Zs will be 1667 ohm. What is your R1 + R2 for this radial??

Why is the 6mm main bonding conductor an issue on a TT system. what size is the main earthing conductor?

Your Ra for that electrode is 9.96 ohms? Very good.

 

[metro.solar]

The R1+R2 was 0.20ohms.

Sorry, i ment the main earthing conductor not bonding conductor. Appologies

Thanks

 

[telectrix]

as malcolm says, 6mm main earthing conductor should be adequate. your R1+R2 suggests that your new radial is approx. 10m.

 

[Superspark23]

It is fine. The circuit will disconnect within 0.4 secounds due to the 30ma rcd. And your protected against overloads by the mcb. So nothing to worry about.