ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Generators

Hello fellow sparks.. long time no type..

work has gone crazy and i cant keep up..
i have a small problem if any one can help..

A small factory is installing a generator to supply there 3 phase machinery as the supply company want millions to put in 3 phase..when the genny is running it will power the lights and sockets as well via a change over switch,, my problem is the earthing,, i would myself stake the genny and bond to the earth of the building, your thoughts please.

Paul

PS .. anyone know the calculation to convert Kva to Amps

[This message has been edited by PaulCornwall (edited 05-12-2004).]

Three phase system
kVA/volts/1.73=amps

Thanks for that Ron,,, would i be right in saying that a 140kva genny would be 100 amps.. {per phase of course}

140kVa / 415V / 1.73 = 195 amps.

The genset certainly needs its frame bonding to the building's earthing system. You also need to make sure that the genny's neutral is earthed, but in such a way as not to create parallel neutral paths via the earthing system.

I have installed many Gen sets over the years, and they should all be bonded to the Building Earth, however it is also a good idea to stake them as well.

I agree with Paul, you need to ensure that the Neutral is not parallel grounded or there could be serious consequences.

If they are going to run their 3 phase kit from a Gen set, would it not be a wise idea to run the entire installation from it..then use the single phase mains as an emergency backup for essential services in the event of Gen set failure?

Paul,
Genny earth reference electrode is not an option, it is a must! Regulations require it to be independent of po-co supply earth, just in case that earth is lost.

Thanks for your replies..
i have been on holiday..

Thanks Paul for the calculation advise..forgot to call 140kva ..140,000..that would give me approx 65 amps per phase??

In reply to all your replies.. the building has a mains single phase supply, i will be installing a 3 phase dis board,, fed off this via a change over switch will be the buildings existing single phase supply, so when the genny is running it will have to power everything, machines and building,, when the genny is stopped he can then put the lights and power back on to the mains,, he would not obviously be able to have both on at the same time..

With regard to the neutral, i would assume a 4 core cable (3 phase and neutral) would run to the genny where the neutral would be bonded to to the gennys earth..
i cant see that any parrallel paths would be created if it was connected in this way..

i said i have just come back from my hols in Portugal.. if any one is interested the colours in domestic houses are black,,phase.. blue neutral.. ??? will they be changing too??

many thanks guys..

Welcome back to Blighty! Looks like you brought some summer back with you.....

Nope. 140kVa / 415V / 1.73 = 195A per phase, assuming an evenly balanced load.


What is the earthing system on the existing single-phase supply? TT? TN-C-S?

Hello Paul

Ok i am havin a blonde day here, got it now.. yes i am a spark

I will have to presume the earth is a TT,, it is very rural.. if you want i can check it out later in the week..

[This message has been edited by pauluk (edited 05-25-2004).]

look i cant even get the smilies to work.................... :rolleye