Fluke 377 User manual

September 2020
©2020 Fluke Corporation. All rights reserved.
All product names are trademarks of their respective companies.
377/377 FC
378/378 FC
Clamp Meter
Users Manual
Test Equipment Depot - 800.517.8431 - 99 Washington Street Melrose, MA 02176 - TestEquipmentDepot.com

LIMITED WARRANTY AND LIMITATION OF LIABILITY
Each Fluke product is warranted to be free from defects in material and workmanship under normal use and service. The warranty period is three
years and begins on the date of shipment. Parts, product repairs, and services are warranted for 90 days. This warranty extends only to the
original buyer or end-user customer of a Fluke authorized reseller, and does not apply to fuses, disposable batteries, or to any product which, in
Fluke's opinion, has been misused, altered, neglected, contaminated, or damaged by accident or abnormal conditions of operation or handling.
Fluke warrants that software will operate substantially in accordance with its functional specifications for 90 days and that it has been properly
recorded on non-defective media. Fluke does not warrant that software will be error free or operate without interruption.
Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers only but have no authority to extend a
greater or different warranty on behalf of Fluke. Warranty support is available only if product is purchased through a Fluke authorized sales outlet
or Buyer has paid the applicable international price. Fluke reserves the right to invoice Buyer for importation costs of repair/replacement parts
when product purchased in one country is submitted for repair in another country.
Fluke's warranty obligation is limited, at Fluke's option, to refund of the purchase price, free of charge repair, or replacement of a defective product
which is returned to a Fluke authorized service center within the warranty period.
To obtain warranty service, contact your nearest Fluke authorized service center to obtain return authorization information, then send the product
to that service center, with a description of the difficulty, postage and insurance prepaid (FOB Destination). Fluke assumes no risk for damage in
transit. Following warranty repair, the product will be returned to Buyer, transportation prepaid (FOB Destination). If Fluke determines that failure
was caused by neglect, misuse, contamination, alteration, accident, or abnormal condition of operation or handling, including overvoltage failures
caused by use outside the product’s specified rating, or normal wear and tear of mechanical components, Fluke will provide an estimate of repair
costs and obtain authorization before commencing the work. Following repair, the product will be returned to the Buyer transportation prepaid and
the Buyer will be billed for the repair and return transportation charges (FOB Shipping Point).
THIS WARRANTY IS BUYER'S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
FLUKE SHALL NOT BE LIABLE FOR ANY SPECIAL, INDIRECT, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSSES, INCLUDING
LOSS OF DATA, ARISING FROM ANY CAUSE OR THEORY.
Since some countries or states do not allow limitation of the term of an implied warranty, or exclusion or limitation of incidental or consequential
damages, the limitations and exclusions of this warranty may not apply to every buyer. If any provision of this Warranty is held invalid or
unenforceable by a court or other decision-maker of competent jurisdiction, such holding will not affect the validity or enforceability of any other
provision.
11/99
Fluke Corporation
P.O. Box 9090
Everett, WA 98206-9090
U.S.A.

i
Title Page
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Contact Fluke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Safety Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Before You Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Terms to Know. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Fluke Connect™ (377 FC/378 FC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Radio Frequency Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Fluke Connect™ App . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Features/Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Auto Power Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Backlight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Power-On Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Maintenance Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Basic Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Hazardous Voltage Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Field Sense Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Field Sense AC Current, Voltage, and Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
L1-L2-L3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Power Health Indicator (378/378 FC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Table of Contents

377/377 FC/378/378 FC
Users Manual
ii
AC/DC Voltage Measurement with Test Leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Resistance/Continuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Capacitance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
DC Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
iFlex Probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Measurement Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Display Hold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
MIN/MAX/AVG Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Inrush Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Data Logging (377 FC/378 FC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Clear Memory (377 FC/378 FC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Firmware Update (377 FC/378 FC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Firmware Version . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
How to Clean the Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1
Introduction
The Fluke 377, 377 FC, 378, and 378 FC Current Clamp (the
Clamp or Product) provides:
• display with two simultaneous measurements (current and
voltage)
• grounding with a single lead
• live measurements with no circuit downtime
• non-contact voltage technology (measurement for Power
Health Indicator, power factor, and real power)
• wireless connectivity to smartphone for work-orders and
reporting integration with Fluke Connect™
The Clamp measures true-rms ac current and voltage, dc current
and voltage, inrush current, resistance, capacitance, frequency,
and dc millivolts.
The included iFlex (detachable, flexible current-probe) expands
the measurement range to 2500 A ac. The iFlex allows
measurements of awkward sized conductors and improved wire
access.
The illustrations in this manual show the 378 FC.
Table 1 is a list of features available for each model.
Table 1. Features by Model
Model 377 378 377 FC 378 FC
BLE for FC ••
Power Heath Indicator ••
Phase Rotation App Only App Only
Sequential phase - NC voltage
measurement ••••
Phase-to-phase voltage calculation ••••
True RMS ••••
Logging ••

377/377 FC/378/378 FC
Users Manual
2

Clamp Meter
Before You Start
3
Before You Start
Table 2 is a list of items included with the Product. Use Table 3 to
order additional accessories.
Table 2. Standard Equipment
Item Model Number Description
varies Clamp Meter
i2500-18 iFlex Flexible Current Probe 18 in (48 cm)
TPAK Hanging Kit
AC285 Alligator Clips (one pair, red and black)
TL224 Insulated Test Leads
TP220 Industrial Test Probes
1
2
3
4
5
6

377/377 FC/378/378 FC
Users Manual
4
Table 3. Accessories
Item Model Number Description
C550 Tool Bag
AC87 Heavy-Duty Bus Bar Clip Set (one pair: red and black)
AC89 Heavy-Duty Insulation Piercing Test Clip
LVD1 Volt Light
L206 LED Hat Light
TL75 Hard Point Test Lead Set (one pair: red and black)

Clamp Meter
Before You Start
5
Terms to Know
Use this section to familiarize yourself with these terms that are
unique to this Product.
Field Sense/Non-contact voltage (NCV) measurement. Voltage
measurements by capacitive sensing technology complete
galvanic isolation. This technology uses capacitive sensors for
measuring AC voltages via non-galvanic contact, coupled with a
Hall Effect jaw that allows simultaneous current measurements. It
enables minimizing voltage probes connections, therefore
reducing hazardous situations and saving setup-up time, and
circuit or machine downtime. Fluke-developed icon for Field Sense
is U.
L1-L2-L3. L1, L2, and L3 (or Line 1, Line 2, and Line 3) is a
common naming convention for the wires in three-phase
alternating current (ac) systems. The Clamp features a sequential
line-to-ground measurement that results in a calculated voltage
measurement. This voltage measurement is an indication that the
three-phase system is, or is not, working as expected.
Fluke Connect™. Fluke Connect is a system that wirelessly
connects your Clamp with an app on your smartphone or tablet.
THD. The total harmonic distortion is a measurement of the
harmonic distortion present in a signal and is defined as the ratio
of the sum of the powers of all harmonic components to the power
of the fundamental frequency.
Fluke Connect™ (377 FC/378 FC)
The Clamp supports the Fluke Connect™ Wireless System (may not
be available in all regions). Fluke Connect is a system that wirelessly
connects your Clamp with an app on your smartphone or tablet. The
app shows the measurements and calculations on your smartphone
or tablet display. You can save these measurements, calculations, and
images to Fluke Connect™ Cloud storage and share with your team.
Fluke Connect™ uses low-power 802.15.4 wireless radio
technology to connect the Clamp with an app on your smartphone
or tablet. The wireless radio does not cause interference with
Clamp measurements.
Radio Frequency Data
Note
Changes or modifications to the wireless 2.4 GHz
radio not expressly approved by Fluke Corporation
could void the user’s authority to operate the
equipment.
SIMPLIFIED EU DECLARATION OF CONFORMITY
Hereby, Fluke declares that the radio equipment contained inthis
Product is in compliance with Directive 2014/53/EU.
Fluke Connect™ App
The Fluke Connect™ app works with Apple and Android mobile
products. The app is available for download to your smart device
from the Apple App Store and Google Play.
To use Fluke Connect:
1. Turn on the Clamp. See Figure XXX.
2. Push Fto activate the radio on the Clamp. Eshows on the
display.
3. On your smartphone, go to Settings > Bluetooth.
4. Verify that Bluetooth is turned on.
5. Go to the Fluke Connect App and in the list of connected
Fluke tools, select 377 FC/378 FC.

377/377 FC/378/378 FC
Users Manual
6
Battery
XW Warning
To prevent personal injury and for safe operation
of the Product:
• The battery door must be closed and locked
before you operate the Product.
• Remove all probes, test leads, and accessories
before the battery door is opened.
• Replace the batteries when the low battery
indicator shows to prevent incorrect
measurements.
• When batteries are changed, ensure that the
calibration seal in the battery compartment is
not damaged. If damaged, the Product may not
be safe to use. Return the Product to Fluke for
replacement of the seal.
WCaution
To prevent damage to the battery:
• Repair the Product before use if the battery
leaks.
• Do not expose battery to heat sources or high-
temperature environments such as an
unattended vehicle in the sun.
• Always operate in the specified temperature
range.
• Do not incinerate the Product and/or battery.
To install the batteries:
1. Open the battery door. See Figure 1.
2. Insert the batteries.
3. Close the battery door. Make sure the door is firmly closed.
Figure 1. Battery
AA

Clamp Meter
Before You Start
7
Features/Buttons
Table 4 is a list of features and controls.
Table 4. Feature/Control Descriptions
Item Description
Jaw with Field Sense U
Tactile Barrier
Hold
Control Knob
Display
Function Shift: extends the function selection to yellow items on the
Control Knob. Push >2 s. to turn on/turn off the backlight.
Volts/Ohm input terminal
Common terminal
Min/Max/Av for current, voltage, and frequency measurement functions.
Push >2 s. to turn on/turn off the Phase-to-Phase measurement function

INRUSH: push to enter inrush mode. Push a second time to exit inrush mode.
Integration time is 100 ms.
Push >2 s. to start data logging function with the Fluke Connect mobile
app.

Turn on/turn off Fluke Connect. The button turns blue and flashes when
paired with the Fluke Connect mobile phone app.
Push >2 s. to save a measurement to the Fluke Connect mobile app.
Jaw release
1
2
3
4
5
6
9
10
11
12
7
8

377/377 FC/378/378 FC
Users Manual
8
Display
Table 5 is a list of the display annunciators.
Table 5. Display
Item Description
Clamp senses a voltage ±30 V or a voltage overload (OL)
L1, L2, L3 mode is active
Clamp requires a ground connection
Jaw measurement
Fluke Connect is on
iFlex measurement
Field Sense measurement
Remaining memory (377 FC/378 FC)
Inrush measurement
Log mode is active (377 FC/378 FC)
Hold mode is active
MinMax mode is active
Battery status
Min, Max, or Avg measurement indication
Continuity indication
Power Health indication
Current measurement
Line calculation
Voltage measurement
1
2
3
4
789
610
14
11 12 13
15
16
17
18
19
5

Clamp Meter
Power
9
Power
Two AA batteries supply power to the Clamp.
To turn on the Clamp, rotate the control knob to a function.
To turn off the Clamp, rotate the control knob to OFF.
Auto Power Off
The Clamp automatically powers off after 20 minutes of no use. If
the Clamp automatically powers off, turn the Control Knob to OFF
and then to a function.
To disable auto power off, see Power-On Options.
Note
Auto power off is always disabled when you use the
Min/Max/Avg function.
Backlight
The display on the Clamp includes a backlight that improves the
readability in dim work areas.
To turn on the backlight, hold Bfor >2 seconds.
To turn off the backlight, hold Bfor >2 seconds.
The backlight has an auto off feature that turns off the backlight
after 2 minutes of no use. To disable the auto off backlight feature,
see Power-On Options.

377/377 FC/378/378 FC
Users Manual
10
Power-On Options
Power-on options allow you to customize the controls:
• Turn off/turn on audible beeper
• Turn off/turn on auto backlight
• Turn on/turn off auto power shutoff
• Clear Logging Memory
•SetPQLevel
To select a power-on option:
1. Turn off the Clamp.
2. Push and hold eas you turn the control knob to V.
The Clamp goes into the option mode.
Note
Anytime you release ethe Clamp exits the option
mode but retains any changes to the settings.
3. Push Bto go through the options.
4. Push Mto change a setting.
5. Release eto exit the options mode.
All power-on options are canceled when you turn off the
Clamp with the exception of PQ Level setting.
Option Display
Beeper Enabled bEEP On
Beeper Disabled bEEP OFF
Auto Backlight On
(Backlight turns off after 2 minutes of no use) 8CLt On
Auto Backlight Off
(Backlight stays on) 8CLt OFF
Auto Power On
(Clamp powers off after 20 minutes of no use)
AUtO On
Auto Power Off
(Auto Power Off is disabled)
AUtO OFF
Clear Logging Memory CLr
Maintenance Mode: set PQ Power Level nmAt nm0d
PQ Level
LEU HI
LEU nmEd
LEU L0

Clamp Meter
Power
11
Maintenance Mode
In Maintenance Mode you can check:
• LCD segments
•Firmwareversion
• Battery status annunciators
• Fluke Connect LED
• Backlight
To enter Maintenance Mode:
1. Turn off the Clamp.
2. Push and hold eas you turn the control knob to V.
The Clamp goes into the option mode.
3. Push Buntil nmAt nm0d shows on the display.
All LCD segments turn on and the backlight turns off.
4. Release e.
All LCD segments continue to show on the display.
5. Press eagain to show the firmware version.
6. Continue to press eto cycle through:
• Empty battery annunciator
• 25 % battery annunciator
• 50 % battery annunciator
• 75% battery annunciator
• Blue LED + live battery annunciator (for FC model only,
step is skipped for non-FC model)
• White backlight + live battery annunciator
• Green backlight + live battery annunciator
7. Press eagain to show CAL on the display.
For more information about calibration, see the
377/377 FC/378/378 FC Calibration Manual.
8. Press eagain to loop back to show all LCD segments
(step 4).
To exit Maintenance Mode at any time, turn off the Meter.

377/377 FC/378/378 FC
Users Manual
12
Basic Measurements
Before you use the Clamp for the first time, remove the battery
isolator between the batteries and battery contacts.
XW Warning
To prevent possible electrical shock, fire, or
personal injury:
• Hold the Product behind the tactile barrier.
• Do not measure current while the test leads are
in the input jacks.
Hazardous Voltage Indicator
When the Clamp senses a voltage ±30 V or a voltage overload
(OL), Zshows on the display to tell you a hazardous voltage is at
the Clamp input.
Field Sense Measurement
Field Sense, or Non-contact voltage (NCV) measurement, is ac
voltage, current, and frequency measurement with no electrical
contact to live voltage. The Clamp display shows the voltage and
current measurements at the same time.
Note
All Field Sense measurements require a ground lead
connection.
Field Sense AC Current, Voltage, and Frequency
To make the measurement:
1. Insert the ground lead into the COM input and attach the
alligator clip to ground.
2. Rotate the control knob to U.
The display shows the Uicon.
3. Use the jaw release to open the jaw and position the Clamp
around the conductor. Close the jaw and make sure the wire
position is correct. See Figure 2.
Figure 2. Wire Placement
The display shows Cto indicate that the measurement is
from the jaw. When the current measurement is <0.5 A, the
center dot in the icon flashes. For current measurements
>0.5 A, the center dot in the icon is steady.
Note
Use Bto toggle on/off the Hz function shown in
yellow at the control knob position.
34 mm Ø
8.2 mm Ø
3.3 mm Ø
L1 L2 L3

Clamp Meter
Basic Measurements
13
L1-L2-L3
Three-phase alternating current (ac) systems are universally used
to distribute electrical power and to supply electricity directly to
high-power equipment. Use the Clamp to make a sequential line-
to-ground measurement that results in a calculated voltage
measurement. This voltage measurement is an indication that the
three-phase system is, or is not, working as expected.
The Clamp also indicates the phase rotation as 1-2-3 or 3-2-1 in
the three-phase system.
To setup:
1. Turn the control knob to U.
2. Connect the Clamp to ground with the ground lead.
3. Push Mfor >2 seconds. The Clamp is in the line-to-line
mode and x-y-z shows on the display.
To test:
1. Position the Clamp jaw around the first conductor.
Wait for the measurement on the display to settle. xshows
on the display.
2. Move the Clamp jaw to the second conductor within
10 seconds.
Wait for the measurement on the display to settle. yshows
on the display.
3. Move the Clamp jaw to the next conductor within 10 seconds.
Wait for the measurement on the display to settle. zshows
on the display.
When the x-y-z measurements are complete, use the Clamp to
calculate the total voltage between each pair of conductors:
1. Push M. The displays shows the total voltage between L1
and L2.
2. Push Magain to show the total voltage between L2 and
L3.
3. Push Magain to show the total voltage between L3 and
L1.
While in the line-to-line mode, you can review each line-to-ground
measurement:
1. Push Magain to show the L1 measurement.
2. Push Magain to show the L2 measurement.
3. Push Magain to show the L3 measurement.
To review L1-L2-L3 measurements, continue to push Mand
scroll through the measurements.
To exit the phase-to-phase mode, push Mfor >2 seconds.

377/377 FC/378/378 FC
Users Manual
14
Power Health Indicator (378/378 FC)
The Power Health indicator shows that the ratio of the real power
compared to the apparent power or harmonic distortion is outside
the optimal range.
To setup:
1. Turn the control knob to U.
2. Connect the Clamp to ground with the ground lead.
If THD for PQ volts or PQ current or the power factor (PQ PF)
is outside the optimal range, the related indicator shows on
the display.
Fluke Connect supports the Power Health indicator.
AC/DC Voltage Measurement with Test Leads
To measure ac or dc voltage:
1. Turn control knob to Vor N.
2. Connect the black test lead to the COM terminal and the red
test lead to the VXterminal. See Figure XX.
3. Touch the probes to the test points of the circuit.
The display shows the measurement.
Note
Use Bto toggle on/off the mV function shown in
yellow at the control knob position.
Resistance/Continuity
To measure resistance or continuity:
1. Turn the control knob to D.
2. Remove power from the circuit to test.
3. Connect the black test lead to the COM terminal and the red
test lead to the VXterminal.
4. Touch the probes to the test points of the circuit.
The display shows the measurement.
If the resistance is <30 Ω, the beeper sounds continuously to
indicate continuity. If the display shows OL, the circuit is open.
To disable the beeper, see Power-On Options.

Clamp Meter
Basic Measurements
15
Capacitance
The Clamp determines capacitance by charging a capacitor with a
known current, measuring the resulting voltage, then calculating
the capacitance.
Note
A good capacitor stores an electrical charge and may
remain energized after power is removed. Before you
touch the capacitor or make a measurement, turn all
power OFF, use the Clamp to confirm that power is
OFF, and carefully discharge the capacitor by
connecting a resistor across the leads. Be sure to wear
appropriate personal protective equipment.
To test capacitance:
1. Turn the control knob to D.
2. Push Bto shift to the tfunction.
3. Remove the capacitor from the circuit and discharge the
capacitor.
4. Connect the black test lead to the COM terminal and the red
test lead to the VXterminal.
5. Touch the probes to the capacitor leads.
The display shows the measurement.
OL indicates the capacitor is faulty or the capacitance value is
higher then the measurement range. diSc indicates the
capacitor does not properly discharge.
DC Current
To measure dc current:
1. Turn control knob to Y.
The display shows Cto indicate that the measurement is
from the jaw. When the current measurement is <0.5 A, the
center dot in the icon flashes. For current measurements
>0.5 A, the center dot in the icon is steady.
iFlex Probe
XW Warning
To avoid electrical shock, do not apply or remove
from live hazardous conductors.
The high-performance AC Flexible Current Probe uses the
Rogowski principle for accurate, non-intrusive measurement of
sinusoidal, pulsed, and other complex waveforms. The flexible and
lightweight measuring head allows quick and easy installation in
hard-to-reach areas and works well with large conductors.
To use the iFlex Probe:
1. Connect the iFlex Probe to the Clamp. See Figure 3.
2. Connect the flexible part of the iFlex Probe around the
conductor. If you open the end of the iFlex Probe to make the
connection, make sure that you close and latch the coupling.
See the detail in Figure 3. You should be able to hear and feel
the lock snap into place.
Note
When you measure current, center the conductor in
the iFlex Probe. Avoid measurements close to other
current-carrying conductors.

377/377 FC/378/378 FC
Users Manual
16
3. Keep the probe coupling >2.5 cm (1 inch) away from the
conductor.
4. Turn the control knob to K.
The display shows Jto indicate that the measurements are
from the iFlex Probe. When the current measurement is
<0.5 A, the center dot in the icon flashes. For current
measurements >0.5 A, the center dot is steady.
The display shows the measurement.
If the iFlex Probe does not work as expected:
• Make sure that the coupling system is connected and closed
correctly or look for any damage. If any foreign material is
present, the coupling system will not close properly.
• Inspect the cable between the iFlex Probe and the Clamp for
any damage.
• Check that the control knob is in the correct position (K).
Figure 3. iFlex Probe Setup
<0.5 A >0.5 A
1 2 3 4
>2.5 cm
>1 in