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Old 11-28-2015, 07:34 AM   #1
City: Webster, Ny
Country: USA
Vessel Name: The Edge
Vessel Model: Mainship 400
Join Date: Sep 2014
Posts: 3
Isolation Transformer on Mainship 400T

I have a 2005 MS 400T with an isolation transformer. I just read on the Mainship Yahoo group forum that the isolation transformer was installed to send a current when first connected to shore power to test for a ground fault. The problem is that this test current is enough to trip the newer GFCI outlets. Does anyone know the solution to this problem?

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Old 11-28-2015, 08:45 AM   #2
caltexflanc's Avatar
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 3,436
Then it is not an isolation transformer. It is some sort of galvanic isolator. Two different things. There is a long recent discussion on this at the Trawlers and Trawlering list, entitled "GFCI shore power vs inverter" which gets around to the subject of galvanic isolators.


"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
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Old 11-28-2015, 09:48 AM   #3
djmarchand's Avatar
City: Essex, Ct
Country: USA
Vessel Name: Bella
Vessel Model: Mainship Pilot 34
Join Date: Aug 2012
Posts: 1,999
On my 2006 Mainship 34T, the isolation transformer was installed improperly. The ground on the secondary (the one that serves the house loads) was not connected to the case of the transformer and resulted in an open ground when you plugged in a three prong tester to an outlet.

You may have a similar problem that is causing the ground fault trip on the primary.

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isolation mainshp gfci

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