Isolation transformer earth connection

DIY
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This has been discussed in the past, here https://community.victronenergy.com/questions/27100/isolation-transformer-earth-connection.html

If I’m reading this correctly, this is only useful for metal hull vessels. If so, why on earth (pardon the pun) doesn’t the manual say that? There is no benefit I know if to connecting shore and boat ground while ashore for FRP vessels, and doing so is an invitation for forgetting to remove the jumper when relaunching.

Perhaps more importantly, even a metal hull, or metal underwater fittings, have no reference to the primary/input power, so even if the hull or a metal fitting became energized with secondary/output power, someone standing on the ground could not be shocked by it, for the same reason a bird can stand on a wire carrying thousands of volts and not be shocked. The secondary of a transformer behaves like a power source, all faults return to the source, with no reference to the “dirt” under the vessel. So, I remain confused by this ‘shore’ grounding guidance.

A few other questions/comments on this transformer…https://www.victronenergy.com/upload/documents/Isolation_Transformer_3600W_Auto/108939-Isolation_transformers-pdf-en.pdf

  1. It has a fixed 1:1.05 boost, so if used with 240 VAC, it boosts to 252, which is higher than normal. It seems this transformer is really designed for use with 230 VAC, which it boosts to 242?
  2. It can accept 120 or 240 primary, and passes that voltage through, with the aforementioned boost, but it cannot provide split phase aboard, so for 60 Hz/N. Am use, it’s essentially limited to 120 primary and secondary, 30 amps, unless you use an auto transformer after the secondary?
  3. The installation manual shows a shield. As far as I know, no toroidal transformers have shields, but this one does? It also shows the shield grounded on the vessel and chassis grounded to shore, the inverse of the ABYC E-11 standard.
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@Dieselista Hello yes, it would be unusual to provide an isolation transformer and then defeat the purpose of the isolation by joining the grounds. I guess we have to consider that these devices are shipped to all corners of the globe and perhaps that is the reason for this rather strange inclusion. Let’s imagine a scenario where the following occurs.

  1. The transformer is shipped to a location that does not mandate the use of RCDs on mains circuits.
  2. The vessel is on the hard.
  3. A worker is using a power tool plugged into marina power, not boat power.
  4. The power tool has a fault, the earth is open circuit and the tool is live.
  5. The tool is touching the metal hull or for a fibreglass hull a thru hull fitting which is bonded internally.
  6. Another worker is working on the boat in bare feet and holding the hull or thru hull fitting and standing on the ground.
  7. The worker suffers an electric shock.

If the isolation transformer has the ground to ground link, when the faulty power tool livens up the hull or bonding, the fuse will blow. in Australia, that would simply trip the RCD but in some jurisdictions, an RCD is not provided.

I think Victron have provided a way forward so that in any jurisdiction, even those without mandatory RCD protection, the scenario above will not cause injury.

I cannot think of any scenario that would require it to be linked if the supply is protected by an RCD.

It is an interesting subject and I guess the problem is it has a high likelihood of bypassing the very isolation the transformer provides if mistakenly linked.