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manta avatar image
manta asked

120v/240v generator and victron with isolation transformer and neutral to ground

On a older boat we are currently refitting we have a generator with the following connections as shown in the manual (Kohler 7CCo) : schermafbeelding-2023-05-13-190934.png

Also we have a Multiplus II 24/3000 and a isolation transformer the transformer has neutral to ground on the secondary side. We have a 240v net one-phase to ground. After the multiplus there are 5 16a breakers.

There is a switch to switch from shore to generator (not wired yet) i would like to feed the generator 240v line voltage to the multiplus. (Should have bought quattro) Is this the right way, because the neutral to ground is 120v as described in the diagram. Currently i am not feeling confident to connect something because i am afraid i will put a voltage on the ships hull.

How can i wire this?


Generator
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5 Answers
svabundance avatar image
svabundance answered ·

Here is a proper wiring diagram for your configuration for shore power, isolation transformer and generator, operating at both 240v and 120v. This diagram is from a boat electrical system standards book.

screen-shot-2023-07-24-at-10538-pm.png


screen-shot-2023-07-24-at-10538-pm.png (748.3 KiB)
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manta avatar image manta commented ·

Thanks this is just perfect!

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Mike Dorsett avatar image
Mike Dorsett answered ·

Are all your loads 240v?

Ideally, the isolation transformer needs to be used for SHORE power only.

The transfer switch should be wired between the secondary of the transformer and the input to the multi. The generator earth is then DISCONNECTED from L0, and connected to L1 instead. While the earth connection is removed, check the isolation from L1 to ground using a 500V ground leakage tester. (A normal ohm meter won't do the job as it only tests at low voltage.) If the secondary of the isolation transformer has a centre tap, this should not be grounded.

If you have 120V loads, this then becomes a lot more complicated - and the easiest and safest solution would be to use an autotransformer on the output side of the multi.

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manta avatar image manta commented ·

Thanks Mike for your imput. greatly appreciated. Let me explain my intentions. I am using EU grid, since i am in the Netherlands, my isolation transformer has L1 and N. N is connected to ground, as needed for GFCI protection. Primary is shore input. The isolation transformer is directly connected to the Multiplus. I would like to disconect the secondairy and run the genset L1 to L2 directly on the multi. But how about the neutral since the wire is connected to the generator frame by default. and L1 - L0 will give 120v. is this safe or can i disconnect neutral and isolate the wire from the genset since i don't need 120v. Is it safe to use 2 hotlines what will happen if accidentially one touches the steel hull. Will my breaker react?

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manta avatar image
manta answered ·

Pleas don,t judge me on my MS Paint skills, but this is the situation :naamloos.jpg

To be clear the users are conencted trough GFCI breakers (16A). If i touch live or neutral (both are live when on genset) will the GFCI activate, since i think on most GFCI neutral is not switched.


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manta avatar image
manta answered ·

Tryed, this weekend, everything seems to work, but is it safe I don't know yet.

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manta avatar image
manta answered ·

Using, (just 240v) loads, everything works fine, i used a GFCI tester in the socket, and on generator and shore power it works as it should. (manual)Transfer switch is on secondary side of the isolation transformer. Dynamic load balancing works like a charm, keeps my small 7-8 Kva generator running when the multi connects to generator and transfers the load. Tried with a total load of 6 kw (Induction cooker & 70A battery charging) I realy love this setup! Normally the generator would drop significantly with a sudden load more than 4-4.5 kw. Now it only drops 2 hz and AVR and governor pick it back up to 50Hz. Only the genset runs little hot, but thats something else, nominal load would be around 4kw.

Thanks for support & opinions.

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