How to ground an isolation transformer?

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christern asked Feb 22, '22

How to ground an isolation transformer?

First post.

I have some difficulties understanding the installation manual of my 3600 VA isolation transformer I recently bought.

A quote from the manual:

“Figure 5: Output neutral grounding

A Residual Current Device (RCD) or Ground Fault Circuit Interrupter (GFCI) must be installed in the output cable of the isolation transformer. For this RCD to operate correctly, the output neutral must be connected to ground (= all the metal parts in the boat). This is achieved by placing a jumper on male push- on connectors J21, J33 (see fig 5), and by grounding the enclosure of the isolation transformer.”

The last sentence, does that mean I should add a separate grounding cable from the green/yellow grounding cable connected to the enclosure to my ground plate - or - is the grounding made by connecting the J21 and J33 connections?

I’m sorry if this question has been asked before. Grateful for help.

Grounding Isolation Tranformer

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kevgermany answered · Feb 22, 2022 at 06:52 PM

I read it that you need to add the cable from case to earth as well as the jumper. Does the transformer have a terminal for this?

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christern commented · Feb 22, 2022 at 09:06 PM

There is a green/yellow cable provided that could be used to connect to the ground plate using the screw in the casing.

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kevgermany ♦♦ christern commented · Feb 28, 2022 at 02:45 AM

That's what it's for.

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Answer 1 · 2022-02-22T20:10:20Z

wkirby answered · Feb 22, 2022 at 08:10 PM

J21-J33 forms the Neutral - Earth bond. This is the only place where this should be done. This is the link that defines the neutral wire and inherently makes the other one line.
Then you'll have three positions at the output terminal block. A connection from PE connects to the grounding plate and then connections from PE neutral and line go to the distribution board.
Your electrician would know what to do here according to your local wiring regulations.
Any current more than the RCD rating passing from line back to the transformer via PE will cause an RCD to trip.

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christern commented · Feb 22, 2022 at 09:09 PM

Thanks! I still think the manual is a bit unclear on this but trust your explanation.

(All electricians that I have talked to have no clue on these thing as it is on a boat. So I don’t have much confidence in their advices around this.)

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christern commented · Feb 27, 2022 at 09:37 PM

@WKirby

Continue reading the manual once more (sure it’s the 20th time) and read:

2.1.4. Connect the enclosure to ground (= all the metal parts in the boat).

This is achieved by establishing a ground connection to the M4 stud on the bottom of the enclosure.

Isn’t this the way I have done by connecting a cable between the M4 bolt (stud) on the bottom of the enclosure and my ground plate which has all metal parts in the boat connected???

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Answer 2 · 2022-04-08T11:06:13Z

christern answered · Apr 08, 2022 at 11:06 AM

I believe the solution is as @kevgermany stated above and this is supported by this image I found on Victron examples where I interpret it as the grounding (of the case) is to be made to "Central boat ground" . https://www.victronenergy.se/upload/documents/4-PHOENIX-CHARGER-AND-INVERTER.pdf

Anyone disagreeing on this?

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