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Posted By: Alan Belson 3 phase- neutral needed on alternator? - 04/11/05 10:22 PM
I've built a 415v 6kva 3-phase alternator set, powered by two 3hp, in-tandem single ph. 240v motors, to run some renovated antique woodworking machines (only one at a time). It all works fine. The alternator is wired Y (Star) and the machine motors are wired Delta. Do you guys think I should fit a neutral at centre Y at the alternator? and should I ground (earth) it? My neighbour, a dour ex-pat Scot, keeps tut-tutting about it and he's driving me nuts! I cannot see the point-I've got 3 linked breakers on the 3 ph, breakers on both single ph motors, residual current trip (30ma RCD), NVR , the shop has its own copper ground (earth) rod buried 4 ft in wet clay near my well, and I only run the 2 machines on the generator.
Posted By: e57 Re: 3 phase- neutral needed on alternator? - 04/11/05 11:23 PM
Of course, ground it! The machines are in your shop, it should be grounded to its system............
Posted By: mxslick Re: 3 phase- neutral needed on alternator? - 04/12/05 12:54 AM
Would this set-up qualify as a separately derived system? If so, Art. 250-30 would apply.

I see Art. 250-20(b) may also apply.

250-21(2) may permit this setup to remain ungrounded if the machines are controlled with electronic inverter drives...

An ingenious solution Mr. Belson! Thumbs up!
Bonsoir Alan:

i dont know if you did connected the machine on wye side but only catch it got my attetion is you should bring out netural for your electric motor[s] and make sure you earth it well also

Merci , Marc
Gentlemen, thanks for the input.
Connected the neutral to ground this morning, as advised, all works ok. Popped round to the dour Scot, John. Told him about ECN. Did a hint of a smile flicker for a fraction of a second on that impassive face?
"Aye.", he ventured after a long pause, then poured two small glasses of his best malt. (I usually get the cheap crap). We finished our dram in silence and went to look at his vegetable garden.

J'ai mis le neutre au terre ce matin, comme vous avez dit, et tous marche bien. J'ai visite l'ecossais grave, mon copain John aujourd'hui, et j'ai explique l'ECN. Est-ce-que il y a une hombre d'un sourire qui tremblota, pour un quart d'un seconde, sur son visage compose?
"Ouaay", il dit eventuallement, puis il versa deux petit verres du malt-whisky, le mieux. Ordinairement, c'est de la camelote.
Nous avons fini le grog en silence, et allons regarder ses legumes au jardin.


l'ahh qui bon et moi suis heureux il wonderfull de travail ce qui nous pouvons vous aider avec cette installation avec la machine vous ont là

Merci , Marc

[english verison]
ahh that good and i am glad it work wonderfull what we can help you with this set up with the machine you have there.
Another question on the alternator. Yesterday I bought 2 new 18A NVR motor starters, one for each single-phase motor, to have a better set-up. (Currently I was starting with a mish-mash of ancient contactors and relays.) Each new NVR has the usual start/stop buttons and an integral adjustable overload switch. Question? -is it OK to have 2 such devices in parallel, because each motor has its own overload too. I can't bypass the new NVR overloads, because each Stop button operates by a lever to the overload module itself.
I intend to start the motors in sequence to reduce Amps.
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