I have a 1000 watt Xantrex inverter that I would like to use as a backup to
my 3000 watt Vector. The Vector works fine in my house with standard wiring
which includes a grounded neutral. The Xantrex on the other hand says the
neutral cannot be grounded. I let the smoke out of a smaller inverter when I
plugged it into the house wiring with a grounded neutral.
My question is:
Is it safe to disconnect the neutral from ground?
Q
Are you talking about the wiring in your house? (I assume so, since no
inverter has an internal connection between AC output and ground.)
Are you entirely off the grid?
If so, you could disconnect neutral from ground at the AC distribution
panel in a pinch, hopefully temporarily. After all, being connected to
ground at the panel is what makes it "neutral" in the first place, and
much of the safety strategy is built around the assumption that this
connection exists. It is not a recipe for instant death or anything
(if it was, all those little car inverters would be slaughtering
people regularly) but I wouldn't leave things that way.
Using your Xantrex (or any non-isolated inverter) with the neutral to
ground connection broken and the DC negative input grounded, the
(former) hot and neutral AC terminals will both be at 60VAC with
respect to ground. So, e.g., the threaded connection of a lamp socket,
which should normally be at ground potential, would have 60VAC on it.
Equipment and circuits that are supposed to be turned off (switches or
panel breakers thrown) would still have 60VAC on their neutral
terminals. Like I said, not exactly instant death scenarios, but
certainly a lot less safe than normal.
FYI the real problem with non-isolated inverters isn't anything to do
with ground per se, the problem is connecting one of the AC output
terminals to one of the DC terminals by any means. It happens when you
ground both DC negative and AC "neutral" as in your house, but even if
you had a battery and your Xantrex inverter sitting apart from the
rest of the world on a rubber mat, and you connected "neutral" to DC
negative (or positive for that matter) with a wire, it would still let
the smoke out. Without isolation (transformer) between input and
output, any connection between the two is a no-no.
So back to the house - another option is to leave the neutral grounded
and lift the DC negative-to-ground connection instead. Then you have a
new twist - AC voltage with respect to ground on the DC terminals, but
hey, only when the inverter is actually running. The DC loads
shouldn't notice. I don't think.
Either solution is suboptimal IMHO, but in a pinch they will work. For
a temporary fix, I'd choose the former, i.e. leave the batts grounded
and lift the neutral.
Last thought - you could buy a honking isolation transformer that will
take the full output of the Xantrex (and then some - it will probably
get a little warm with all those unexpected harmonics) so you can
ground both ends of the inverter/transformer combination properly.
Then you've built yourself a fake Trace DR, with no charger.
Electrically it makes sense, economically it may not. Unless you get a
damn good deal on the iso-trans (not impossible at surplus, ham swap
meets etc.) that solution would be pretty silly compared to just
getting a better inverter with isolation built in.
-=s
