I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

KD wrote:
I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

Ask your electrical supply store for a "manual double throw three phase
transfer switch" with sufficient ampacity for the heavier of the two
loads. Wire it in where you can easily reach it to throw the handle.

Lots of companies make them.

If cost is a factor and you've got a well stocked electrical junk pile,
but no transfer switches in it...... You could use a couple of three
phase disconnect switches (fused or unfused) and rig some kind of a
mechanical interlock between them so that they won't both be "on" at the
same time. It shouldn't take much more than appropriate mounting
locations and some sort of center pivoted lever to accomplish that. (No
warranty from me on an electrical or insurance inspector "buying" it
though. G)

Good Luck,

Jeff

--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"My luck is so bad that if I bought a cemetery, people would stop dying."

On Tue, 22 Jun 2004 12:35:19 -0400, the renowned Jeff Wisnia
wrote:

KD wrote:
I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

Ask your electrical supply store for a "manual double throw three phase
transfer switch" with sufficient ampacity for the heavier of the two
loads. Wire it in where you can easily reach it to throw the handle.

Lots of companies make them.

If cost is a factor and you've got a well stocked electrical junk pile,
but no transfer switches in it...... You could use a couple of three
phase disconnect switches (fused or unfused) and rig some kind of a
mechanical interlock between them so that they won't both be "on" at the
same time. It shouldn't take much more than appropriate mounting
locations and some sort of center pivoted lever to accomplish that. (No
warranty from me on an electrical or insurance inspector "buying" it
though. G)

Good Luck,

Jeff

I'd probably wire the two up and just remember not to switch both on
at once... but that would be wrong.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Why not just use a 3 phase power plug for the switching?
Either that or a large switch will do.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works every time it is tried!

Do you mean a static phase converter, a rotary phase converter or a VFD?

If you don't have a VFD and your machines have their own power switches, you
can keep both machines hooked up to the converter, you don't need a switch.
If you have a VFD its best to use a switch.

Paul T.

"KD" wrote in message
om...
I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

In article ,
what says...
On Tue, 22 Jun 2004 12:35:19 -0400, the renowned Jeff Wisnia
wrote:

KD wrote:
I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

Ask your electrical supply store for a "manual double throw three phase
transfer switch" with sufficient ampacity for the heavier of the two
loads. Wire it in where you can easily reach it to throw the handle.

Lots of companies make them.

If cost is a factor and you've got a well stocked electrical junk pile,
but no transfer switches in it...... You could use a couple of three
phase disconnect switches (fused or unfused) and rig some kind of a
mechanical interlock between them so that they won't both be "on" at the
same time. It shouldn't take much more than appropriate mounting
locations and some sort of center pivoted lever to accomplish that. (No
warranty from me on an electrical or insurance inspector "buying" it
though. G)

Good Luck,

Jeff

I'd probably wire the two up and just remember not to switch both on
at once... but that would be wrong.


That's what I do with my 3 phase machines that do not have
VFDs. As long as the wiring is adequate, in most case
there's no problem starting another machine when another is
already running, with either a static or rotary converter.
In other words, I don't understand why the OP feels it's
necessary to have only one machine connected at a time.

I do have a pair of 30A motor starting switches wired as
Jeff describes above to select either the rotary or static
converter. One switch is mounted upside down and a bar
between the handles prevents both from being on at the same
time.

Ned Simmons

Ned Simmons wrote:

snipped

I do have a pair of 30A motor starting switches wired as
Jeff describes above to select either the rotary or static
converter. One switch is mounted upside down and a bar
between the handles prevents both from being on at the same
time.

Ned Simmons


Hey, thanks Ned! I thought I was going to get all sorts of jazz from
folks for that "interlock" suggestion.

My first thought was to recommend your "upside down" (and I presume
offset by one width.) trick, but I wasn't sure how much an upside down
disconnect switch would agitate an inspector. G

That reminds of what some critic called Laurel and Hardy...."Two minds
without a single thought.."

Jeff

--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"My luck is so bad that if I bought a cemetery, people would stop dying."

Use two disconnects, side-by-side, one upside-down, with the handles
duct-taped together...untill you make a bracket from metal.

--

"KD" wrote in message
om...
I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

Hey KD,

Not sure I follow EXACTLY what you mean, but what I have done is
gang-mount three sockets for clothes dryers (6 bucks Canadian each)
side by side on the wall, all inter-connected as three phase ( instead
of two hots and a neutral). The 220 circuit breaker feeds two of
these legs. Then for my purposes, I've scrounged up five used plugs
from old clothes dryers (new = 15 bucks each.......at garage sale, a
buck or two). I've hooked each individual motor's leads for the
machines to the individual dryer plugs, including the rotary phase
convertor. For two of them, the cord set itself is long enough, and
for the other three I just joined the motor cab-tire to the cord set
with wire-nuts and taped them all up. Bit lumpy, but not bad if
you're neat. So I just plug in as required. Very simple, and I can
have just 220 single phase for a welder or whatever, by not wiring the
neutral on the plug.

Sorry if I've mis-understood, and this isn't what you meant.

Take care.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXX
On 22 Jun 2004 08:51:47 -0700, (KD) wrote:

I have 2 machine tools both 3 phase. I have a phase converter. I have
been in the past, just pulling the 3 wires from the motor off of the
converter, and plugging in the motor wires from the other machine.
Its a bigger pain that it sounds. I am looking for some kind of swith
to just switch between the two without having to pull wires. ANybody
know what I should be looking for? Thanks for the help. if trying to
email me direct, email
Thanks

In article ,
says...
Ned Simmons wrote:

snipped

I do have a pair of 30A motor starting switches wired as
Jeff describes above to select either the rotary or static
converter. One switch is mounted upside down and a bar
between the handles prevents both from being on at the same
time.

Ned Simmons


Hey, thanks Ned! I thought I was going to get all sorts of jazz from
folks for that "interlock" suggestion.

My first thought was to recommend your "upside down" (and I presume
offset by one width.) trick, but I wasn't sure how much an upside down
disconnect switch would agitate an inspector. G

Inspector? You need a code before you can have an
inspector. This is a town with no shortage of multi-million
dollar waterfront homes with no building code or electrical
code. The State of Maine does require towns to have a
plumbing code and shoreland zoning, but that's about it.

Here's a photo of the switches...
http://www.suscom-maine.net/~nsimmons/XferSw.JPG

If anyone wants to do something like this I have quite a
few of those switches, 3 pole 30A @ 600VAC, 7.5/15/20 HP @
240/480/600 VAC 3 phase.


That reminds of what some critic called Laurel and Hardy...."Two minds
without a single thought.."


Speak for yourself, I thought it was pretty clever g.

Ned Simmons

"Jeff Wisnia" wrote in message
...
Ned Simmons wrote:

snipped

I do have a pair of 30A motor starting switches wired as
Jeff describes above to select either the rotary or static
converter. One switch is mounted upside down and a bar
between the handles prevents both from being on at the same
time.

Ned Simmons


Hey, thanks Ned! I thought I was going to get all sorts of jazz from
folks for that "interlock" suggestion.

My first thought was to recommend your "upside down" (and I presume
offset by one width.) trick, but I wasn't sure how much an upside down
disconnect switch would agitate an inspector. G

My commercially made MTS transfer panel works that way. It is impossible
to have our generator connected to the panel and still be connected to the
service. It's a slick way, and perfectly acceptable by code. They use a
Square D panel and add the interlock. Real slick system.

Harold

Hey Harold,

I'd be surprised if there isn't a short delay in the transfer from
generator to utility, and not just an inter-lock. Except on very
expensive systems that do phase monitoring. In fact, even from
utility to generator during routine test. Actually, part of this is
occurs naturally as the switch gear is "centre-off" and not
centre-shorted. Common "timing" on emergency power is 13 seconds from
loss of utility, and at least two cycles for strictly resisitive
loads, but we required a 15 second advance warning of transfer to
shut-down to keep from damaging our MG sets.

They are pretty much gone now-a-days in favour of Robonic transfer
switches, but there were lots of fair size systems that had emergency
(called "auxiliary" today) systems where individual circuits were
hand-switched with three-pole-double-throw disconnect, where Up was
ON, Centred was OFF, and Down was ON. I've seen them from as small as
60 Amp up to 500 Amp. Mind you, I would not be too hasty to have to
throw the 500 myself!! With this system, the "load" is connected to
the "centre" or moving poles, and the "up" was normal or utility, and
"down" was the auxiliary. I even recall quite an elaborate system of
chains and pulleys, connected to various of these disconnects, to
"force" the operator to "do" the switching in a required sequence.

Take care.

Brian Lawson,
Bothwell,, Ontario.
XXXXXXXXXXXXXXXXXXXXX
On Tue, 22 Jun 2004 21:59:33 -0700, "Harold & Susan Vordos"
wrote:


"Jeff Wisnia" wrote in message
...
Ned Simmons wrote:

snipped

I do have a pair of 30A motor starting switches wired as
Jeff describes above to select either the rotary or static
converter. One switch is mounted upside down and a bar
between the handles prevents both from being on at the same
time.

Ned Simmons


Hey, thanks Ned! I thought I was going to get all sorts of jazz from
folks for that "interlock" suggestion.

My first thought was to recommend your "upside down" (and I presume
offset by one width.) trick, but I wasn't sure how much an upside down
disconnect switch would agitate an inspector. G

My commercially made MTS transfer panel works that way. It is impossible
to have our generator connected to the panel and still be connected to the
service. It's a slick way, and perfectly acceptable by code. They use a
Square D panel and add the interlock. Real slick system.

Harold

"Brian Lawson" wrote in message
...
Hey Harold,

I'd be surprised if there isn't a short delay in the transfer from
generator to utility, and not just an inter-lock. Except on very
expensive systems that do phase monitoring. In fact, even from
utility to generator during routine test. Actually, part of this is
occurs naturally as the switch gear is "centre-off" and not
centre-shorted. Common "timing" on emergency power is 13 seconds from
loss of utility, and at least two cycles for strictly resisitive
loads, but we required a 15 second advance warning of transfer to
shut-down to keep from damaging our MG sets.

They are pretty much gone now-a-days in favour of Robonic transfer
switches, but there were lots of fair size systems that had emergency
(called "auxiliary" today) systems where individual circuits were
hand-switched with three-pole-double-throw disconnect, where Up was
ON, Centred was OFF, and Down was ON. I've seen them from as small as
60 Amp up to 500 Amp. Mind you, I would not be too hasty to have to
throw the 500 myself!! With this system, the "load" is connected to
the "centre" or moving poles, and the "up" was normal or utility, and
"down" was the auxiliary. I even recall quite an elaborate system of
chains and pulleys, connected to various of these disconnects, to
"force" the operator to "do" the switching in a required sequence.

Take care.

Brian Lawson,


Hey Brian,

I probably should have been a little more specific when I talked about my
panel. We have just a small (5 Kw) single phase generator that we can use
in an emergency, enough to power our boiler and a few other things. I've
wired enough things through the panel that I can, by selective switching,
run our well, heat, alarm system, freezer, refrigerator, and water heater,
just not all at the same time. While we've not been through it yet, I've
been told that power is known to be off for a few days in our area when we
have severs freezing rain storms. So far we've dodged that bullet, including
last January when Portland got slammed. It started out freezing here, but
about an hour later it changed. We were high enough that the inversion held
the cold air at a lower level. Very lucky, at least that time.

The panel of which I spoke is a real simple device, must be switched
manually, and I even have to plug in the generator, although it would be
left plugged in and in position if desired. It has a couple breakers
mounted back to back with a slide that doesn't permit both the generator and
the line to be connected to the structure at the same time. That way it
can't back feed into the entire grid system.

By the way, you're making me drool with the idea of having a large one that
switches as you describe, especially if it was 3 phase. I came very close
to buying a 15 Kw 3 phase generator while I was still in Utah. There are
times when I wish I had. It was a surplus military unit with sound
proofing enclosure, diesel powered. Appeared to be in excellent condition.

Harold

On Wed, 23 Jun 2004 22:31:15 -0700, "Harold & Susan Vordos"
wrote:

The panel of which I spoke is a real simple device, must be switched
manually, and I even have to plug in the generator, although it would be
left plugged in and in position if desired. It has a couple breakers
mounted back to back with a slide that doesn't permit both the generator and
the line to be connected to the structure at the same time. That way it
can't back feed into the entire grid system.

Harold,

Does that switch transfer BOTH the hot and
neutral wires? If not, there are circumstances
where you COULD send power back into the grid.

Any method you use to connect a generator MUST
transfer all wires except the ground off the
grid. You might work something up with switches
intended for 3-phase that would allow a proper
transfer.

Here is something I wrote in rec.boats in Sept 99:

[I asserted that it was possible to feed power back
into the grid if only the hot lead was transferred.
Another reader said the breaker would trip first.]

A short of that magnitude would trip the breaker on the generator,
but perhaps not quickly enough to prevent someone getting a nasty
shock.

As I pointed out earlier, breakers don't trip all that fast if
the overload is not great. Resistance in the local "loop" is
one way that the overload may be fairly low.

The 60V at the transformer "neutral" (and anywhere between the
transformer and the house) could be a problem if a few things
failed simultaneously. But there is no 2nd wire to return current
(if the mains are disconnected at the "hots"), so there could be
no step-up at the transformer. As far as I know, the transformer
secondary has windings only between hot and neutral, and there is
no winding between neutral and earth, as that would impress a
voltage on neutral with respect to ground. The neutral is
connected to a stiff earth ground somewhere, either at the breaker
panel itself, or somewhere closer to the transformer. This stiff
ground would have to fail before any significant voltage would be
seen at the neutral up at the transformer.

Neutral-to-ground (N2G) bonding is not always a good connection.
When it is made at the breaker box, it is usually made with a single
screw from the neutral buss-bar to the shell of the breaker enclosure.
If the screw is loose or has failed to cut through the paint in the
pre-tapped hole (common, in my experience), then the N2G bond may
have fairly high resistance.

The local (demand side of transformer) loop can take many paths.
When a generator is connected across neutral and disconnected
hot leads, a hot to ground connection (short in an appliance,
damaged insulation, etc) will try to raise the neutral to 120v
against whatever bonding exists. A high-resistance bond (or low
current-carrying capacity such as a tiny bit of thread cutting
through paint) can make this possible without overloading the
breaker. Now, all that is needed is a path to ground on the
hot lead between the transformer and the disconnected mains
OR ON ANY HOT LEAD STILL CONNECTED TO THE TRANSFORMER. If there
is another dwelling on the same transformer, then any appliance
or load that is still connected provides a path to ground through
the neutral-to-ground bonding in THAT dwelling. Other paths to
ground could include fallen drops (transformer to house wires)
that let the hot lead connect to ground, fallen branches or
other power lines across the drop -- anything that connects
the transformer side of the hot wire (before the disconnected
main breakers) to ground.

The loop then becomes: generator-hot - hot wire on load side of
breaker - damaged appliance - ground - (say) fallen drop hot
wire - hot terminal of transformer - transformer secondary
winding - neutral terminal of transformer - neutral buss in
breaker box - generator-neutral. There are plenty of places in
this loop likely to be high enough resistance that the breaker
does not trip immediately (or even at all). These things will
all tend to reduce the current in the secondary and thus the
current induced in the primary which is being fed back into
the transmission lines. Nonetheless, with a step-up of 120v
to 4000v or more, the induced voltage is going to be quite
high. Even 12 volts across the secondary can make 400 volts
on the primary.

If the transmission grid was all in working order, it wouldn't
be enough to cause a dangerous voltage on the transmission lines,
but the nature of storm damage is that many sections of the
transmission lines are isolated either deliberately or by
automatic disconnections with little or no load on them.
It is precisely these sections that are likely to have a
water-soaked lineman working on them.

No quibbling -- it is just extremely bad practice to connect a
generator to a dwelling that is not COMPLETELY isolated from
the transformer by a transfer switch that is designed to
do exactly that job with no failure modes that can bypass it.

Here is a google-groups url that will take you
to the original post; you can get to the whole 47
message thread from the
http://www.google.com/groups?q=hot+n...n.com& rnum=1
If you have trouble cutting and pasting that long
line try searching google groups using advanced
search for:
all these words: hot neutral generator
author: peter meek


--
--Pete
"Peter W. Meek"
http://www.msen.com/~pwmeek/