TT or PME

[seajayess]

Hi I am currently rewiring a premises that has a Hydro Generator as well as a DNO supply , it is connected to the DNO service so when it generates more electricity than is being used it supplies the grid. My question is at the moment the system is TT, do to the fact I have installed SWA cables to different areas, I would like to PME the system so I do not have to RCD the whole installation, does anybody know if I can do this, I have installed back up generators before and know these have to have a seperate Earthing system TT and a change over isolator, but have never done one that is connected to the DNO, as I don't want to request it if this is not possible thanks CJS

 

[green-hornet]

Under normal circumstances the answer is a definate no, you must never change any earthing arrangements from one type to another.

You would have to go through a long process where an engineer does an on-site visit and determines if the earthing would be changed if it is possible, which I would doubt.

You would not require a 30mA RCD so you would have no problem with discrimination and if the installation is a TT then it should already be RCD protected.

 

[seajayess]

The system is already protected by a 100ma RCD, and I know that an engineer would have to come to see if it is possible, the premises has had a major restructure and we have installed one three phase board rather than the 3 boards it had, and would have been nice not have had to protect the whole installation with an RCD, if we have to leave it on TT may be an idea to fit time delayed at supply, but I was just wondering if it is possible to do, CJS

 

[Apache]

Wait until Steps hears about this!

 

[Andy™]

TT.