isolating circuits for inverter installation

rmeador · #1 07-19-2011

I'm finally getting around to hooking up the inverter half of the inverter/charger I installed in my boat 9 months ago. According to the instructions, I'm supposed to isolate the ground and neutral of the inverter-powered circuits from the general ground and neutral of the shore power connection, presumably for safety reasons. Easy enough. Or so I thought. I've been taking the ground wires off one by one and then going around the boat with an outlet tester until I find the outlet that no longer has a ground, then if it's one I want on the inverter, moving it to the inverter ground block. One of my outlets seems to always be grounded, even though I've disconnected every ground wire. I can't figure out how that is possible. Any ideas on how I can identify where it is getting its ground from? Any thoughts on a more efficient procedure to do the neutrals, since I'm getting darn tired of turn off the power, climb into lazarette, remove wire, climb out, turn on power, test all outlets, repeat.

Thanks!

BTW, I've been away from the forums for a couple months... I went on vacation, then I got a new job (which, gasp, actually requires me to work!). I've got a huge backlog of posts to read

Hopefully I'll be more active henceforth. I've been doing a ton of sailing, though!

mitiempo · #2 07-19-2011

Which inverter/charger do you have?

mitiempo · #3 07-19-2011

Grounds are common and do not require isolation. Doing what you are trying to will leave you without the benefit of the shoreside ground if there is a fault in the inverter's output.

The hot and neutral powering the inverter. either from the main breaker, or from a breaker on the main panel, has to be kept separate from the hot and neutral output of the inverter, which is best wired to a sub-panel for inverter loads.

The section below is from the manual of the Xantrex 1800HF.

rmeador · #4 07-19-2011

Hmm... I have a Xantrex Freedom HF1800. It would seem I misread the manual. I guess I just need to isolate the neutrals. Well, that was 2 days of work down the drain... thanks for setting me straight.

mitiempo · #5 07-20-2011

Are you going to a sub-panel exclusively for inverter loads?

rmeador · #6 07-20-2011

It's effectively a sub-panel. The electrical panel in the boat is a custom design built as original equipment by Gulfstar. The AC breakers (hot wire) are divided into two sections, and it's just a matter of removing a jumper wire between them to create a "sub panel" within the main panel. It just so happens that the wall outlets are all on the same half of the AC panel, so I can very conveniently inverterize just those (and not the water heater or battery charger). I was trying to replicate this hot wire setup with the ground and neutral wires by rerouting the ones from the outlets to separate ground and neutral busses. Why do you ask?

mitiempo · #7 07-20-2011

Just curious. A sub-panel arrangement is the best solution as there is less chance of trying to run a high load like a water heater with the inverter.

Make sure you keep the neutral in to the inverter separate from the neutrals out, a separate bus is best. I recently replaced a Freedom inverter that failed after not doing this and removed another for the same reason after a small fire - not sure if this caused it but it didn't help. Only the ground is common.