If your connections are 3 phase, it shouldn't matter, except for direction
on motors. If the motor spins the wrong way, transpose any two wires. If you
want to connect to something single phase on a high leg delta, you need to
determine which is the wild leg, which you can do with a volt meter.
When I install 3 phase refrigeration or HVAC equipment, I also install
or order the factory option of a 3 phase protection module which shuts
down the control voltage if there is any problem with the power. The
cheap simple unit doesn't care about which direction a motor is turning
in relation to incoming power but there is a more elaborate unit that I
install on high end gear that will not operate if the 3 phase is not
exactly L1 L2 L3 as seen on an oscilloscope.
Years ago we use to have a mechanical phase tester. We were supposed to use
it when connecting 3 phase service equipment. When connecting a 3 phase
motor, it doesn't help to know the phase rotation of the power supply, but
not know the phase rotation of the motor leads. Ultimately, trial and error
is probably the quickest method
I use my phase tester even when the power company crew is there hooking
up the drop. The linemen around here are OK with it and will make sure
the sequence is right before making a permanent connection. Southern
Company Power wires L2 as the high leg in a Wye secondary 3 phase. If
I'm lucky, I can get Delta-Delta then everybody's happy. :-)
I've had a Sperry rotating disk phase sequence tester for many years. I
believe Ideal bought Sperry out according to this picture.
If you are particular go to the panel and put a toner on A phase then go
to the wire end with the detector. Same for B phase, last one must be C.
It really doesn't matter except for three phase motors motors.
ANd if the panel or the power company is wrong? After the panel it's tough to
screw up the color coding.
Many moons ago (over 35 years) I designed a power phase detector that found
its way into every IBM mainframe of the time. They didn't like the blowers
running backwards, but the phase-controlled regulators really got pissed with
reversed phase rotation. Before the three-phase contactors kicked in the
service system would sense the phase rotation and lock up with an error if
they were bad. It *did* change at times, particularly after major power
changes and bad storms. Relying on the installers to test the rotation didn't
On Sun, 23 Jan 2011 11:37:16 -0600, The Daring Dufas
Sure, they used M-G sets to get the 400Hz. The M-G sets were also used as the
power-backup to do checkpointing or switchover to secondary power, on power
failure. IIRC, all of the phase controlled regulators used 400Hz. It's been
a long time, but I believe the blowers were all 50/60Hz (they could take a
brown-out on power change).
On 1/23/2011 11:53 AM, email@example.com wrote:
When I was out at the Kwajalein Missile Range, now The Reagan Test Site,
back in 1987-88, There were computer systems on Roi Namur that
had MG sets with big flywheels for UPS type power. The island power
plant used big old EMD diesel generators putting out 4,161 volts
into the island power grid. I suppose the flywheels could keep things up
until another EMD was started but during a mission, I believe a
backup was kept warmed up anyway. I was working for a contractor who
built the new mission control center that housed a Cray X-MP super
computer (high tech back then) and an atomic clock. I don't think the
Cray used any special power because we only ran conventional 60hz
electrical power and wiring.
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