Lots of offshore machines USA here use seperate ground and common wires.
You see green ground and green with a stripe common . One is ground
the other is common


"Peter T. Keillor III" wrote in message
...
On Sun, 14 Nov 2004 16:23:25 GMT, "Karl Townsend"
wrote:



I designed a rig with a Sola 24 VDC power supply which is powered by 3
phase 460 VAC, no neutral. The 0 VDC(-) side is isolated, and is not
tied to the frame. The old e.e. I had check my design said that was
the correct way to set it up.

If it were me, I'd stick with the way the equipment was originally set
up.

Pete Keillor


I see a couple votes for "do it like it was", and one vote for tie DC
common
to frame. The wiring on the Camsoftcontrol retrofit was a total
abortion.
Never seen such a mess in my life. The pile of wire looked like a big bowl
of spaghetti. I got this fine lathe for just over scrap price because it
would not run reliably for the business that owned it. One of the
problems
is way too many wires on one terminal on the terminal strips, plus no
connector ends. The various commons had six or more wires twisted and
stuck
under one screw with some wires pulled out. I've found the common wire
stuck under a screw on the machine frame in various spots - I know that's
wrong.

So far, I've installed a terminal strip just for all the common wires and
brought them to one terminal strip just for this purpose. Eliminated a lot
of the mess this way. I put the power supplies for the DC near this
strip.
I'll take the suggestion and put blue tape on all the DC commons so I have
white wire with blue ID.

Now, do I tie all these DC commons to anything other than the - terminal
on
the supply? One concern I have is "what if 110 VAC accidentally connects
to
a DC wire somewhere?" In this case you need a good path to neutral/ground
so a fuse blows.

Karl

In my case, the DC commons (terminated on DIN rail connections)
connect only to the - terminal of the supply, and are not connected to
ground. I was advised that at least with this power supply, it would
not function if I tied it to ground.

I distribute the + side through DIN rail mounted individual fuse
holders with appropriate fuses. These have led's to show blown fuses.
These are mainly powering 4-20 mA process instruments through
Brad-Harrison Nano-Change connectors. Since this is a research rig,
we can change the configuration and instrumentation by just plugging
stuff in.

In my case, the 120 VAC on the rig is provided by an on-board
transformer, also powered by 460. I feed most of the 120V stuff
(heaters, mostly) through an equipment protection GFI circuit breaker
(trips at 20 mA, IIRC) safety relays (tripped by overtemp logic or
selector switch) and individually controlled SSR's for temp control.
The GFI protected 120V commons come back to a bus that's grounded
through the GFI breaker. The other 120 V commons connect to a
grounded neutral bus.

If you sort all the wiring, shouldn't you be able to assure yourself
you don't have errant 120V connections? In my case, any heater
failures will go to ground, which is tied to the structure ground, and
will trip the breaker.

Good luck with it.

Pete Keillor