V-O-V Generator - doing my head in!

[Andrew_van_Zyl]

After brushing up on my 10142 the other day I came across a MacAfric Diesel genset that befuddles the mind - N-E 154V (Yes..read that again!) and L-E 66V. WTF!!

Client has this connected to his DB.

I didn't fully understand VOV until today - what is the solution? (Apart from dumping the very expensive diesel gen?)

[Dylboy]

There are a couple of threads on this, hit the search and they should pop up.

Some options are to disconnect the output earth of the genny and then bridge the the Neautral and the Earth going to the DB. How ever it has to be before the changeover as you can not have the permanent bridge there. Don't just bridge the Neautral and earth of the genny output as the earth is a centre tap. It you do. Ridge the centre tap you may damage the genny and basically short out half the coil.

Some are to disconnect the earth centre tap in the genny itself too.

But search the forum and a bunch should pop of for reading and I may have missed some stuff.. been a long day of beer...

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[Dylboy]

Thinking again... Use a contactor rather to make that N E bridge... Doing a perm one even at the change over at the input of the genny would still not have it disconnect when in change over so if the grid as issues it may be the N and E point for the street...

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[Derlyn]

Regarding the diesel genset, find the live and neutral wires coming from the stator, disconnect them and megger each one down to earth. If open circuit then there is not an internal connection from the main stator to earth. Ie no centre tap earth connection.

If that is the case, one can quite safely bridge the neutral to earth on the genset. We do that regularly on genny installations.

It is very important to first ensure that there is no centre tap earth connection before bridging anything otherwise you will be shorting out half the stator and the genny wont survive for any length of time after that.

[Dave A]

Thinking again... Use a contactor rather to make that N E bridge... Doing a perm one even at the change over at the input of the genny would still not have it disconnect when in change over so if the grid as issues it may be the N and E point for the street...

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When on mains supply, the neutral from the generator must be disconnected from the installation as well as the live. Therefore the N to E bridge on the generator doesn't become the N to E bridge point "for the street". The generator neutral will remain connected to earth only.

[Dylboy]

When on mains supply, the neutral from the generator must be disconnected from the installation as well as the live. Therefore the N to E bridge on the generator doesn't become the N to E bridge point "for the street". The generator neutral will remain connected to earth only.

Yes ya, will draw it out but surely the change over would break that Line and Neautral if genny when on Grid thus breaking the N and E of the street ?

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[Isetech]

Yes ya, will draw it out but surely the change over would break that Line and Neautral if genny when on Grid thus breaking the N and E of the street ?

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If you wire it correctly. the neutral earth bond should be done in the changeover DB before the generator input at the changeover switch.

Just be careful with inverters, its not the same.

[Dylboy]

If you wire it correctly. the neutral earth bond should be done in the changeover DB before the generator input at the changeover switch.

Just be careful with inverters, its not the same.

Yes that's where I have it in my mind to do it there

Ya inverters are different but that is where i use contactors for that.

I mean you can buy a N E bridge box from Segen but using a contactor is the same.

But appreciate all the input as always guys. Learning stuff everyday with this forum

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