Isolation transform = no grounded plugs?

[q240z]

Hi guys. Merry Christmas!

My AC units were delivered recently, and that's got me thinking about electrical things. I've got an isolation transformer that's wired for 240 --> 240, so only the two hots and ground come aboard. The ground goes to the transformer case. Two hots and a neutral come out of the transformer to the distribution panel...no ground. All of the OE wiring uses two prong outlets; no grounds.

Do those of you with transformers have grounded plugs on your boat? If so, where is 'earth' for your floating electrical system?

One reason I ask is because every generator I've owned has 3-prong plugs. And that got me thinking that even on power systems not connected to the grid, there must be an 'earth' somewhere.

Thx
Q

 

[SKYCHENEY]

I may be wrong and I can't be sure without pulling out my schematics but I believe the neutral and ground are tied together in the panel. The case on the transformer is also tied to ground and the ground in the panel is tied to the bonding system. If you want, I could look it up next time I'm at the boat.

 

[q240z]

Hmmmm. Interesting. Let's see how others chime in.

 

[Boatsb]

Being a metal boat novice I'm not sure how things are supposed to be on it but on the hatts there is no earth ground when running. Shore power brings an earth ground to the isolation transformers and connects it to the earth but the boats systems have neutral and ground connected.

 

[Pascal]

Ground and neutral should only be tied at the source, i think it s an ABYC standard. That would be thru shorepower, at the generator or at the inverter. This is why marine inverters have circuitry to tie G and N when in inverter mode and relase it in charging or pass thru mode.

 

[krush]

This article will help....I think the ABYC has updated slightly since he wrote it (see GFP comment below). It also references the ABYC. Notice there is a difference between Isolation and Polarization wiring. http://qualitymarineservices.net/Tr... vs. Isolation, Exchange Article, 10-2006.pdf

Charles has the ABYC diagrams too: http://www.charlesindustries.com/marine_manual/38kvaISO.pdf
Please note on page 6 there is a typo in the message. Method 1 and 2 are different than 3 and 4 (latter use Ground Fault Protetction)

 

[tonytrakovich]

Great article

 

[davidwigler]

Great article

Yes. So how I’d Hatteras wire them?

 

[tonytrakovich]

Mine was a 1989 65MY. Here is the transformer wiring diagram. I would be surprised if yours wasn’t the same. By the way this is the diagram to flip the transformers to allow for voltage boost.

 

[q240z]

Thx krush. Great article.