Application Note

5 Fluke Corporation Seven ways to use your troubleshooting superpowers for good
#6 Diagnosing a three-phase motor
without suiting up
If you have a big motor you need to diagnose, such
as a 408 V AC 200 HP motor with a wye-delta, you
can use the CNX wireless system to test without
needing personal protective equipment (PPE). Dis-
connect power before you open the motor control
center (MCC) cabinet. Then connect three hard jaw
clamp CNX current modules—one per phase—to
measure three-phase current. Or, connect three
CNX voltage modules or use a combination of both.
Close the MCC cabinet, re-apply power and start
the motor. Now you can take all the measure-
ments without PPE. These tests will show you if
the motor is working too hard electrically. If it is,
you still need to find out why. The 805 will show
you mechanical problems. The VT02 will reveal
hot spots. Heat with no vibration could help verify
internal electrical faults.
#7 Pump occasionally blows a fuse
You have a pump motor that occasionally blows a
fuse, and you can’t find an obvious cause. Set up
a CNX current module, securing it to an electrica l
disconnect and feeding the module wires through
a ½ inch knockout. Now you can monitor the amps
wirelessly and discover what’s causing the fuse
to blow—or at least you’ll know the timing of the
event. By the next morning, you’ll know the exact
time when the event occurs.
You may find that at the time of the fault,
multiple processes start up, creating an excessive
load on a branch circuit, causing a nuisance trip.
Resizing the breaker or redistributing the loads
may solve this type of problem. It could also be
a loose connection. The VT02 is helpful for finding
those. Check for hot spots that signal loose con-
nections in the circuit, possibly at one of the loads.
Fluke. Keeping your world
up and running.
®
Fluke Corporation
PO Box 9090, Everett, WA 98206 U.S.A.
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The Netherlands
For more information call:
In the U.S.A. [phone] or
Fax [phone]
In Europe/M-East/Africa [phone] or
Fax [phone]
In Canada (800)-36-FLUKE or
Fax [phone]
From other countries [phone] or
Fax [phone]
Web access: http://www.fluke.com
©2013 Fluke Corporation.
Specifications subject to change without notice.
Printed in U.S.A. 03/2013 4331701A A-EN
Modification of this document is not permitted
without written permission from Fluke Corporation.
0.0
32.2
23.5
29.4
V AC
A AC
A AC
A AC
Auto
1
2
3
INRUSH
Hz
L1 L2 L3
L1
DMM
L2
L3
Motor power
Cabinet
INRUSH
Hz
INRUSH
Hz
INRUSH
Hz
0.0
32.2
23.5
29.4
V AC
A AC
A AC
A AC
Auto
1
2
3
Determining current unbalance