generator regs

[tomasi]

We have a switch cubicle which is being taken out and
replaced with a new one as part of extensive building
works.
The exist cubicle at the moment only supplies another
large building with a 240mm 4 core swa and a supply
to construction site cabins and a local tpn board.
A company is coming in to disconnect the public supply
to the existing cubicle so it can be taken out,whilst
the new cubicle is being fitted the supplies that were
being used are to be temp fed from a 150kva 400v generator
situated out doors.
As a matter of interest what would be the supply type ,can it be tns or tt and how do you earth it with regard to
the already fixed installations it will supply and
do you need rcd protection where there was none before
when connected to the public supply and what is max ze
or earth electrode resistance.
sorry to be so long winded but would like to no as a matter
of interest.

 

[Spudnik]

Please dont post duplicate threads in different forums. Thanks.

 

[Guest123]

Hi there.

There is no problem with using the TN-S supplied from the generator to supply the existing installation during switchover.

As always the gen frame should be rodded to earth, and as a matter of precaution I always install a rod at the distribution board you are supplying as a just incase.

You just need to make sure that the earth is "floating" inside the geney as if it is strapped to neutral (larger geneys usually are) this would give you a TN-C-S supply and obviously different rules apply with regard to earthing and bonding and the use orf RCD's, best to leave as TN-S.

Obviously the geney will have an RCD upfront, usually along the lines of 100mA (sometimes adjustable) this would then protect all of the existing installation.

Ze/Zs will be the same for a mains powered installation as you still need to be able to achieve the same disconnection times i.e 100mA RCD on TT = 500ohms. As it will be a TN-S though you should be looking at max Ze of 0.80ohms.

Hope this helps.