Transfer switch

Does the transfer switch isolate the Neutral, as well? Should it? I've got
3 phase 220V, L1 L2 L3 neutral. The neutral is a huge earth grid
underground, and I was wondering if I should use this when running off the
gennie. (That is, tie the neutral of the gennie to the utility neutral)

The main power feed goes to a warehouse, and then to 2 separate, smaller
buildings. (Office and sleeping area, each about 100M away)) The office is
fed with a seven-core cable, but I'm only using 2 wires at the moment.
(office load is 5 CF's and a computer) The sleeping area fed with heavy 4
core. (some lights, fridge, TV)

The feed to the office is basically a long extension cord from the
warehouse. When there is a power failure, I start the gennie in the
warehouse (3.3KW), unplug the office feed and plug it into the gennie. Then
I run ANOTHER extension cord from the office up to the living area for some
lights/TV etc. This is a bit of a hassle.

What I'm really grappling with is how to improve this! Ideally, what I'd
LIKE to do is use 1 phase for 'gennie power'; where I leave the other phases
on, and only use a transfer switch on, say L1. Is there a safe, practical
way of doing this? Can I do this?

William.

 

I prefer all phases and neutrals to switch. There are some "soild neutural"
switches out there. I have better preformance and less call backs when I
used a "switched neutral"transfer switch.

I believe your incorrect. Your neutral is a grounded conductor. Connected to
your electrical service grounding conductor.

How is the genny grounded? If it is attached to the electrical service
ground then yes. If not then there could be issues.

Using only one phase depends a lot on the wiring of the genny. The US
military has gensets that can be switched from 3 phase to single phase. Some
will even put out a huge amount of amps at 120v. The gensets are built for
that.
Best check with your manufacture to be sure about only using one phase.

The extension cord concept might be a hassle but is a good method to keep
everything separated so your not making a mistake.

 

Our transfer switch switches the neutral. We switch between the
battery/inverter, and the generator. We treat the battery/inverter as
grid power. When we start the gen, it disconnects the inverter, and lets
gen power through to the house ac panel.

http://www.green-trust.org/wiki/index.php?title=Automatic_Transfer_Switch

 

Considering you seem to be in South Africa, I can't speak to your electrical
codes. But I'll put my 230/400V hat on and try to shed light.

Neutral: You must only have ONE ground-to-neutral bond in your facility.
Unless you feed the outbuildings with higher voltage and step it down with
its own transformer (separately derived ground). I didn't get the
impression this was the case. You will be fine with a solid neutral, but
your generator must then have ISOLATED GROUND-NEUTRAL connection. I prefer
this type of installation where we can preserve the single bond at the
electrical mains. You can still ground the EQUIPMENT FRAME of your
generator to rods or another earth system at the gennie (which itself is
bonded back to your mains ground), but don't make the bond to neutral at the
gennie.

You can go switched neutral too (this requires an extra pole on the transfer
switch), and you must then BOND GROUND-NEUTRAL at your genny. Underground,
the electrical mains ground rods should be bonded to your generator ground
system. Notice that either way you choose, you must have neutral bonded to
ground in one location ONLY. You can't share neutral current with the
ground wire.

Should you go single or three phase? In North America, single phase often
still means 120/240V. There are two legs 180 degrees apart. Three phase
isn't available everywhere. In your case, (if I understand this correctly)
you don't have that option. Your appliances are either 230V or 400V 3
phase. As is typical in Europe (SA?), since most homes receive 3 phase,
many motor loads are 3 phase too. The availability of 3 phase is taken for
granted. If this isn't an issue, then go ahead and go single phase. Make
sure there are not other 3 phase loads that will malfunction or provide
feed-thru power to the other 2 phases. Check with your local codes.

RF Dude