Fluke 9040 Service Guide

Don’t run it backwards

Phase rotation testing in

utility power distribution systems

Testing Functions

Case Study

Tools: 9040 Phase Rotation Indicator

Operator: Municipal electric utilities

Measurements: Phase rotation, tests

during installation, maintenance, and
troubleshooting

There’s an old saying that the first time you hook up a
three-phase motor it will run backwards. If you’re lucky,
it will only make you look foolish. If you’re not, it could
severely damage expensive equipment and cost you or
your employer substantial money.

Ruining compressors

Here’s an example of what can
go wrong. A public utility in the
Northwest was installing a new
piece of computerized switch­gear. It was intended to service a
rather large area that comprised
both industrial customers and
some miscellaneous commercial
facilities. The crew doing the
installation was experienced, but
the piece of equipment was new
to them. The foreman, who was
responsible for specifying which
leads were connected where,
inadvertently reversed phases.

Once the utility had finished
its work, it turned the power
back on.

Down the road, at a major
manufacturer, a whole set of
screw compressors for the HVAC
system—ranging from 25 to
50 hp—started running back­wards. Screw compressors are
lubricated by internal oil pumps,
“and if they run backwards, they
don’t pump oil,” said the manu­facturer’s maintenance chief. In
a few seconds, all the compres­sors were toast. “Thank God our
chillers didn’t come on before we
discovered the problem,” said the
maintenance chief, “because that
would have been really bad.”

The utility ended up paying
for all new compressors, plus
the rent on units brought in on
a temporary basis. While it also
did energy studies and set up a

Application Note

new, more efficient system for
the customer, it still was left with
egg on its face—and a large bill.

All of this could have been
prevented, if the utility crew had
better understood the instruc­tions on the new equipment
and had used a phase rotation
indicator like the Fluke 9040 to
check the phase rotation at the
480 volt output of the transform­ers that fed the compressors.
Those few minutes would have
saved the customer considerable
downtime and the utility a pile of
money.

Doing it right

A different utility, after many
years of using the old-style
rotating-disc units, changed out
to Fluke 9040s instead. They
use them most commonly after a
meter base or transformer bank
has been changed out, to make
sure the rotation is correct before
connecting the load. Interest­ingly, this isn’t a consideration in
a new installation, because then
the responsibility falls on the
customer’s electrician to make
sure the rotation is right before
hooking up the motors. If he’s
wise, he’ll have his own 9040.

The utility has now been
using the 9040s for about three
years. They were initially drawn
to the tool because it was the
only Category IV unit they could
find. The need for this was made

F r o m t h e F l u k e D i g i t a l L i b r a r y @ w w w . f l u k e . c o m / l i b r a r y

abundantly clear when customer
electricians went to check the
phase rotation on a transformer
whose nameplate read 240
V a using rotating-disc phase
unit. Unfortunately for them,
the system voltage was actually
2400 V, and they smoked their
phase rotation indicator. This
got the utility people to think­ing: “If it happened to them, and
we have 2400 V secondaries in
our system, there’s a possibility

that someone might misread a
nameplate in our system. Let’s go
ahead and get a Category IV in
case someone messes up.”

So the utility bought 9040s.
Some of the older technicians
resisted at first, insisting they
were more comfortable with the
old rotating dots, but the younger
ones are used to electronic
devices. And what could be sim­pler: It’s marked L1, L2, L3, red,
white blue, so you can’t easily go
wrong.

Let’s get a CAT IV tool in case someone messes up

More ruined equipment

Of course you have to actu­ally use the 9040. One time the
utility bought a new motor and
relocated an existing meter base
to power it, but the electrician
didn’t hook it up the way it had
been, and while the meter base
said red white and blue coun­terclockwise, it was actually
clockwise. A technician checked
rotation at another meter base,
found it correct, and apparently
assumed that this one would
be the same. They plugged in a
meter, threw the breaker, and
ruined the motor.

Another time the job was to
replace a bank of transform­ers with heavier units with
heavier wire. Despite the fact
that everyone on the job was
experienced, for some reason no
one took a rotation reading. They
finished hooking everything up,
plugged it in, turned it on….. and
then bought all new rotational
equipment for the customer
downstream. The amount that
incident cost doesn’t even com­pare to the cost for a new 9040
for everyone on the crew.

Standardizing on the
Fluke 9040

Another utility had been using
the old mechanical rotation
devices that had been the indus­try standard for years, but they

had started breaking down and
even cross-phasing internally,
and the manufacturer didn’t
respond quickly or even seem to
take the safety issue as seriously
as they might.

The meter technicians and
linemen now use the 9040s to
verify phase rotation on new
installations and mark breaker
panels with the existing rotation.
Later, if they’re troubleshoot­ing an outage or do a routine
swap, the crews will verify
rotation both before and after,
using those markings and the

9040. Tthe idea is to make sure
to leave the customer with the
same phase rotation. This check
occurs inside transformers, at
disconnects on meter panels,
on the pole to verify overhead
service, on overhead transformer
banks, and in vaults to verify at
the last disconnect point prior
to feeding that source to the
customer.

The utility maintenance chief
has developed a fondness for
Fluke equipment, and says it
has proven its product over the
years. The equipment, he says,
is “made tough for this industry.
These things are going to be
dropped, get wet, get beat up,
dropped from poles and out of
pockets.” And it’s simple to use,
with a yes or no answer. “It’s
about time we got something
other than this mechanical stuff,”
he concludes.

2 Fluke Corporation Don’t run it backwards - Phase rotation testing in utility power distribution systems

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©2010 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 5/2010 3799717A AW-EN-N

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