Bypass Diode Tester
FT4310
and Shorts in Broad Daylight Without
Covering Panels

Traditionally, bypass diodes can only be inspected for good working condition at night or when power is not being generated by the solar panels in order to verify that any applied current is guided past the solar cells. With the FT4310 Bypass Diode Tester, you can detect for open faults even when the sun is out without covering the panels. Also test for short-circuit faults and cell string losses.
| Model No. (Order Code)
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How to use the Hioki Bypass Diode Tester FT4310 The FT4310, a bypass diode tester for maintaining solar power systems, can detect open faults and short faults during daylight hours without the need to cover the solar panels. Watch this video to see how it can be easily and convenient used in the field. |
• Test for open or short-circuit bypass diodes even during the day *1
• Easily test using the strings in the junction boxes *2
• Save time – simultaneously measure all electrical parameters *3
• Automatically transfer data wirelessly (Available for Android and IOS devices *4)
*1: Testing can also be performed at night. Testing for short-circuit faults can only be performed during the day
*2: There is no need to climb onto the roof and dramatically improving work efficiency.
*3: Measure open-circuit voltage, short-circuit current, and bypass route resistance and display all three values at once.
*4: Automatically transfer data with Bluetooth® wireless technology
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Test for bypass diode open faults and other malfunctions using the strings in junction boxes
Easily test using the strings in the junction boxes, eliminating the need to climb onto the roof and dramatically improving work efficiency.
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Save time - simultaneously measure all electrical parameters
Simply set the rotary knob to “BPD TEST” and press the “Measure”button to measure and display all parameters necessary for fault identification (open-circuit voltage, short-circuit current, and bypass route resistance). Measurement takes 2 sec. or less per string! |
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Instantly create reports by a free app (GENNECT Cross)
GENNECT Cross, a free app designed specifically for use with Hioki measuring instruments, lets you check and manage measurement results and create reports. |
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Be alerted to faults with an audible warning and by the instrument’s backlight
Red backlight and audible warning alert the user to possible faults. |
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High-precision voltmeter ideal for detecting short-circuit faults
When a bypass diode experiences a short-circuit fault, the output voltage decreases (by about 10 V) because the corresponding solar panels are not contributing to the array’s generated power. |
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Convenient accessories
• Bundled case with neck strap
Leave both hands free so you can precisely position test probes without worrying about dropping the instrument. |
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[Reference] Issues caused by faulty bypass diodes
Normal reading: |
The impact of measurement on strings has been investigated thoroughly since even if bypass diode open faults can be detected while solar panels are exposed to sunlight, the endeavor would be pointless if the panels were damaged in the process.
When the FT4310’s measurement button is pressed, the instrument first measures ISC (the short-circuit current) and then applies a voltage such that a current that is 1 A greater than ISC flows.
Because bypass diodes are required by the JIS to function without issue even if a current equal to 1.25 times the module’s rated short-circuit current flows for a period of one hour, because the FT4310 performs constant-current control, and because the time of application is 5 ms or less, the FT4310’s impact on strings does not differ from that of I-V curve measurement or insulation resistance measurement.
The FT4310 can be used with confidence that it will not damage solar panels.
Note: The FT4310 cannot measure strings installed in parallel. Please contact your authorized Hioki distributor or reseller for more information. *Android, Google Play and the Google Play logo are trademarks of Google Inc. *iOS is a registered trademark of Cisco Technology, Inc. and/or its affiliates in the United States and certain other countries. *iPhone, iPad, iPad mini, iPad Pro and iPod touch are trademarks of Apple Inc. *Apple and the Apple logo are trademarks of Apple Inc. App Store is a service mark of Apple Inc. *Microsoft, Windows, Windows Vista, and Excel are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries. *The Bluetooth® word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of such marks by HIOKI E.E. CORPORATION is under license. *For the latest information about countries and regions where wireless operation is currently supported, please visit the Hioki website.
Basic specifications (Accuracy guaranteed: 1 year, Accuracy guarantee period after adjustment made by Hioki: 1 year)
[BPD TEST mode]
Measurement items | Bypass diode comparator judgment, Bypass route resistor, Open-circuit voltage, Short-circuit current, Measurement (applied) current |
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Measurement object |
Crystal system string
Open-circuit voltage: 1000 V DC or less, Rated current: 2 A to 12 A DC |
Measurement method | Short-circuit and pulse voltage application |
Measurement accuracy |
Open-circuit voltage: ±0.2% rdg. ±3 dgt. (at 0 to ±1000 V) Short-circuit current: ±3% rdg. ±3 dgt. (at 0.0 to 15.0 A) Bypass route resistance: ±5% rdg. ±5 dgt. (at 0.0 to 15.0 Ω, During pure resistance measurement) |
Measurement time | 2 s or less (3 seconds or less when measurement voltage is 10 V or less) |
Possible number of measurements |
3000 times (Comparator, backlight, Bluetooth® OFF) LR6 Alkaline battery × 6 |
[Voc mode]
Measurement items | Open-circuit voltage |
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Measurement range | 0 V to 1000 V DC (Displayed up to 1200 V DC), Accuracy: ±0.2% rdg. ±3 dgt. |
Response time | Within 1 sec. |
[General]
Dustproof and waterproof | IP40 (EN60529) |
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Functions |
Displays the number of bypass diode measurements, Automatic polarity judgment function, Comparison display, Auto hold, Live circuit indicator, Buzzer sounds, Backlight, Comparator, Battery indicator, Auto power off, Bluetooth® Smart |
Interface | Bluetooth® 4.0LE, Supports devices: iOS, Android TM smartphone/ tablet |
Power supply |
LR6 (AA) alkaline battery×6, Maximum rated power 18 VA Continuous operating time: 45 hours (Comparator, backlight, Bluetooth® OFF) |
Dimensions and mass |
152W×92H×69D mm (5.98 W × 3.62 H × 2.72 D in) 650 g (22.9 oz) (including batteries, excluding test leads) |
Countries and regions where wireless operation is currently supported (FT4310)
Last update: May 7, 2021
Countries and regions where wireless operation is currently supported | Australia, Austria, Belgium, Bulgaria, Canada, Chile, China, Colombia, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hong Kong, Hungary, Iceland, Ireland, Israel, Italy, Japan, Kenya, Latvia, Liechtenstein, Lithuania, Luxembourg, Macao, Malta, Myanmar, Netherlands, Norway, Peru, Poland, Portugal, Romania, Singapore, Slovakia, Slovenia, Spain, Sweden, Switzerland, Thailand, Turkey, United Kingdom, United States, Viet Nam |
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Note | Use of devices that emit radio radiation requires approval in the country of use. Thus, use of the instrument in a country or region where they have not been approved may be subject to penalty as a violation of law. |
Catalog: Bypass Diode Tester FT4310 | Download PDF | English |
Catalog: GENNECT CROSS SF4071, SF4072 | Download PDF | English |
The L9788-11 is bundled, others are exclusive options for L9788-11

Bundled with Test Lead with Remote Switch L9788-10/ Earth lead, alligator clip, 1.2 m (3.94 ft) length

For checking breaker terminal, Detachable for tip of the L9788-10, 65 mm (2.56 in) length, φ 2.6 mm (0.10 in)

Lighting LED lamp & comparator indicator (Operate only when main unit provides a comparator function), 1.2 m (3.94 ft) length

Spare parts for tip of the L9788/ L9788-10, Tip length 35 mm (1.38 in)/φ 3.2 mm (0.13 in)
Other option
*The C0206 is bundled

PC peripherals

• Mobile app for iOS, Android
• Improve efficiency of operations that repeat measurement and recording
• Analyze correlated data during issues and generate quick reports