Poor Ze

[yellowvanman]

Did an EICR on a small office unit. TT system, and Ze of stake was >800 ohms.

Zs of DB was just 8 ohms, which I suspect is due to the structural steelwork.

If I did this installation I would have used the steelwork as the 'stake', in which case I'm inclined to forgo the bad Ze of the stake and say the Ze of the steelwork is enough!

Any comments?

 

[Deleted member 9648]

Structural steel has to be embedded in the foundations to be used as an electrode.....might be difficult to ensure it meets the requirements if it's existing and not inspected while being built. Might also be difficult on an existing system to verify an Ra reading off steel is genuine and not affected by parallel paths. Unless there was an initial verification cert available I would not rely on steel as an electrode on an existing install.

 

[Guitarist]

Did an EICR on a small office unit. TT system, and Ze of stake was >800 ohms.

Zs of DB was just 8 ohms, which I suspect is due to the structural steelwork.

If I did this installation I would have used the steelwork as the 'stake', in which case I'm inclined to forgo the bad Ze of the stake and say the Ze of the steelwork is enough!

Any comments?

8 ohms!!! Get that down below 1, or Eng will have your guts for garters!!!

 

[Marvo]

Yeah, Eng isn't gonna like that Ra reading

I agree the problem with the 8ohm steelwork reading is you don't know how much contribution parallel paths are making therefore you don't know what you'll be left with if the plumber/gasman etc replaces his copper main with plastic.

You could try extending the existing rod with another 2.3m rod on top of it, if the existing rod is one of those 1 meter specials that seem quite popular then the Ra should drop dramatically for relatively little work and cost.