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Posted By: PaulCornwall Generators - 05/12/04 06:55 PM
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).]
Posted By: Ron Re: Generators - 05/12/04 08:00 PM
Three phase system
kVA/volts/1.73=amps
Posted By: PaulCornwall Re: Generators - 05/12/04 09:50 PM
Thanks for that Ron,,, would i be right in saying that a 140kva genny would be 100 amps.. {per phase of course}
Posted By: pauluk Re: Generators - 05/13/04 11:33 PM
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.
Posted By: FWL_Engineer Re: Generators - 05/16/04 01:14 PM
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?
Posted By: lyledunn Re: Generators - 05/18/04 10:39 PM
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.
Posted By: PaulCornwall Re: Generators - 05/23/04 06:35 AM
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..
Posted By: pauluk Re: Generators - 05/23/04 07:16 PM
Welcome back to Blighty! Looks like you brought some summer back with you..... [Linked Image]

Quote
forgot to call 140kva ..140,000..that would give me approx 65 amps per phase??
Nope. 140kVa / 415V / 1.73 = 195A per phase, assuming an evenly balanced load.

Quote
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..

What is the earthing system on the existing single-phase supply? TT? TN-C-S?
Posted By: PaulCornwall Re: Generators - 05/23/04 09:25 PM
Hello Paul

Ok i am havin a blonde day here, got it now.. yes i am a spark [Linked Image]

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).]
Posted By: PaulCornwall Re: Generators - 05/23/04 09:34 PM
look i cant even get the smilies to work.................... :rolleye
Posted By: pauluk Re: Generators - 05/25/04 10:27 AM
You need to use rolleyes with a colon both sides. I've edited your first post for you.....

Guide to Smilies

Reason I asked whether TT or TN-C-S is that the bonding issue will be affected by that. You need to make sure that (a) everything that should be earthed is earthed, whether on mains or genny, and (b) that you don't get parallel neutral paths via earthing conductors. These arrangements need careful planning.
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