earthing

[dave-gardiner]

i have a agricultral site that has a 3 phase feed into a boiler house but if this feed fails there is a changeover switch that puts a different feed from another site.
firstly is this allowed?
secondly what sort of earthing arrangement should there be, as potentially a different earth from 2 different sites.

 

[johnboy6083]

If you have two different feeds from different sites/potentials, then I feel that you will need to tie the earthing system to earth, with earth electrodes. As for regs, I can't comment because I don't know!!

 

[malcolmsanford]

and make sure it is well labelled

 

[johnboy6083]

I also feel that the earthing conductors from each site will have to be sized to take the largest fault current from the sites. If there is a Potential difference, current will flow.
Common practice in my experience is to install earth bars with disconnect links, so that the earthing conductors from each installation can be isolated when required.