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Fluke 1555 FC Insulation Resistance Tester Review: Specs, Features & 10kV Testing Guide
Testing medium-voltage switchgear, transformers, cables and large motors needs more than a 1 kV handheld megger. In humid conditions, surface leakage across bushings and cable ends can also make healthy insulation look bad. The Fluke 1555 FC is a 10 kV insulation tester built for exactly this work. To evaluate every class of testing hardware available for your facility, review our complete fleet of industrial insulation resistance testers. In this review we cover the Fluke 1555 FC specifications, accuracy at each test voltage, the guard terminal, PI/DAR testing, what comes in the box, and how it compares with the Fluke 1550C and the Megger MIT1525.
⚡ Key Takeaways: Fluke 1555 FC Evaluation
- Wide Voltage Output: Selectable test voltages up to 10 kV in 50 V steps (up to 1 kV) and 100 V steps (above 1 kV).
- Measurement Ceiling: Measures insulation resistance up to 2 TΩ, plus leakage current (1 nA to 2 mA) and capacitance.
- Active Guard Technology: The guard terminal removes the effect of surface leakage on dirty or humid cable terminations and bushings.
- Automated Diagnostics: Automatic Polarization Index (PI) and Dielectric Absorption Ratio (DAR) with no extra setup; covers the full range of test voltages in IEEE 43-2000.
- Safety Architecture: Rated CAT IV 600 V / CAT III 1000 V, with a live circuit warning from 30 V to 660 V AC/DC.
What Is the Fluke 1555 FC Insulation Resistance Tester?
The Fluke 1555 FC is a heavy-duty 10 kV digital insulation tester engineered for acceptance testing, preventive maintenance, and fault diagnostics on high-voltage apparatus. It measures resistance up to 2 TΩ, calculates PI and DAR automatically, and works with the Fluke Connect® app so you can start and stop tests and watch a live trend graph on your phone from a safe distance.
A 1 kV tester does not stress the insulation of 6.6 kV or 11 kV equipment at a meaningful level. The 1555 FC lets you choose test voltages from 250 V to 10 kV, so you can test at the level your standard or procedure asks for and find moisture, contamination and ageing before the insulation fails in service.
How the Guard Terminal Removes Surface Leakage Errors
In humid, dusty or coastal sites, the surface of insulators picks up moisture and contamination. When test voltage is applied across a bushing or cable insulation, current flows along two paths:
- Bulk Conduction Current (I_v): The true leakage current passing directly through the internal dielectric structure.
- Surface Leakage Current (I_s): Current traveling across airborne salt, moisture, and dust deposits on the outer surface of the insulator.
Engineering Alert: Why Unguarded Tests Fail Inspection
Without an active guard connection, the meter measures total current (I_{total} = I_v + I_s). Because surface current can be much larger than the current through the insulation, the calculated resistance (R = V / I_{total}) drops drastically, condemning perfectly healthy equipment. Connecting the Fluke 1555 FC Guard Lead to a bare copper wire wrapped around the cable insulation routes surface currents straight back to the power supply, bypassing the measuring shunt.
Fluke 1555 FC Technical Specifications
| Test voltage | 250 V to 10,000 V DC; 50 V steps from 250 V to 1000 V, 100 V steps above 1000 V |
| Resistance range | Up to 2 TΩ (bar graph 0 to 2 TΩ) |
| Test voltage accuracy | -0%, +10% at 1 mA load current |
| Induced AC current rejection | 2 mA maximum |
| Charge / discharge rate | 5 s per µF charge; 1.5 s per µF discharge |
| Leakage current | 1 nA to 2 mA, ±(5% + 2 nA) |
| Capacitance | 0.01 µF to 15.00 µF, ±(15% rdg + 0.03 µF) |
| Timer | 0 to 99 minutes (1 minute setting, 1 second indication) |
| Live circuit warning | 30 V to 660 V AC/DC, 50/60 Hz, ±(15% + 2 V) |
| Test functions | Insulation resistance, PI, DAR, ramp (breakdown) test, timed test, guard |
| Memory | 99 locations with user labels |
| Wireless | Fluke Connect® via the infrared adapter (ir3000 FC) |
| Display | Digital/analog LCD, 75 × 105 mm |
| Power | 12 V lead-acid rechargeable battery (Yuasa NP2.8-12), over 750 tests per charge; charger input 85 to 250 V AC, 50/60 Hz |
| Operating / storage temperature | -20 °C to 50 °C / -20 °C to 65 °C |
| Humidity | 80% up to 31 °C, falling linearly to 50% at 50 °C |
| Enclosure | IP40; Class II (double insulated) |
| Safety | IEC 61010-1, IEC 61010-2-030: CAT IV 600 V / CAT III 1000 V; IEC 61557-1, IEC 61557-2; EMC EN 61326 |
| Size / weight | 269 × 277 × 160 mm; 3.7 kg |
| Warranty | 3 years |
Insulation resistance accuracy by test voltage
| 250 V | 5% from 250 kΩ to 5 GΩ; 20% from 5 GΩ to 50 GΩ |
| 500 V | 5% from 500 kΩ to 10 GΩ; 20% from 10 GΩ to 100 GΩ |
| 1000 V | 5% from 1 MΩ to 20 GΩ; 20% from 20 GΩ to 200 GΩ |
| 2500 V | 5% from 2.5 MΩ to 50 GΩ; 20% from 50 GΩ to 500 GΩ |
| 5000 V | 5% from 5 MΩ to 100 GΩ; 20% from 100 GΩ to 1 TΩ |
| 10000 V | 5% from 10 MΩ to 200 GΩ; 20% from 200 GΩ to 2 TΩ |
Below the lowest band and above the highest band the reading is unspecified. Outside 0 °C to 35 °C, add ±0.25% per °C (±1% per °C on the 20% bands).
Fluke 1555 FC vs Fluke 1550C FC
| Maximum test voltage | 1555 FC: 10 kV | 1550C FC: 5 kV |
| Resistance range | 1555 FC: up to 2 TΩ | 1550C FC: up to 1 TΩ |
| Shared features | PI/DAR, ramp test, guard, timer to 99 min, 99 memories, live circuit warning, Fluke Connect, CAT IV 600 V / CAT III 1000 V, 3.7 kg |
If you only test equipment rated up to about 3.3 kV, the Fluke 1550C FC 5 kV tester is the lighter-budget choice. For 6.6 kV and 11 kV switchgear, cables, motors and generators, the Fluke 1555 FC gives you the extra voltage. Our 5 kV vs 10 kV vs 15 kV insulation tester guide explains how to choose.
Fluke 1555 FC vs. Megger MIT1525: Which High-Voltage Tester Fits Your Fleet?
While the Fluke 1555 FC serves as a versatile workhorse for general industrial 10 kV acceptance testing, commissioning engineers operating on heavy grid interconnects or large turbo-generators often evaluate higher voltage thresholds. If your testing regime requires 15 kV stress capability along with high-noise immunity rejection, see our Megger MIT1525 15kV insulation tester review.
| Feature | Fluke 1555 FC | Megger MIT1525 |
|---|---|---|
| Maximum Voltage | 10,000 V (10 kV) | 15,000 V (15 kV) |
| Maximum Resistance | 2 TΩ | 30 TΩ |
| Wireless / Cloud Sync | Native Fluke Connect® App | USB and Bluetooth; PowerDB Lite software |
| Safety rating | CAT IV 600 V / CAT III 1000 V | CAT IV 1000 V |
| Test modes | IR, PI, DAR, ramp, timed | IR, IR(t), DAR, PI, SV, DD, PDC, ramp |
| Target Application | Industrial plants, MV switchgear, motors, generators, cables | Utilities and substations needing 15 kV and advanced diagnostics |
What Is in the Box?
| Fluke 1555 FC | Test cables with alligator clips (red, black, green), heavy-duty alligator clip leads, infrared adapter with interface cable, AC power cord, soft carrying case, quick reference card, USB-IR cable installation guide |
| Fluke 1555 FC Kit | Same as above, but with an IP67 hard case instead of the soft case, plus a certificate of calibration |
See the Fluke 1555 FC Kit and the Fluke 1555 FC 10 kV Insulation Tester Kit. For long cable runs, add the Fluke TL1550EXT 25 ft extended test leads.
How to Run a PI or DAR Test
- Isolate, lock out and prove the equipment dead. Discharge it before connecting.
- Connect + and − across the insulation under test, and the guard lead to a bare wire wrapped around the insulation surface if surface leakage is a concern.
- Select the test voltage (for example per IEEE 43-2000 for rotating machines) and choose PI or DAR.
- Start the test locally or from the Fluke Connect app. The 1555 calculates DAR (1 min / 30 s) and PI (10 min / 1 min) automatically.
- Let the tester discharge the load at the end (1.5 s per µF) before removing the leads, and save the result to memory.
Pros and Cons
Pros: 10 kV in fine steps, 2 TΩ range, guard terminal, automatic PI/DAR, ramp test, remote control and live trend with Fluke Connect, CAT IV 600 V rating, over 750 tests per charge, 3-year warranty.
Cons: 3.7 kg is heavy compared with 5 kV testers, the enclosure is IP40 (keep it dry on site), wireless needs the infrared adapter, and the top range of 2 TΩ is below 15 kV testers such as the Megger MIT1525.
Who Should Buy the Fluke 1555 FC?
- Electrical contractors commissioning MV switchgear, transformers and cables
- Maintenance teams trending motor and generator insulation with PI/DAR
- Utilities and testing companies who want remote operation and simple reports
Browse all insulation resistance testers, more Fluke products, or read our guide to electrical safety standards and CAT ratings.
Fluke 1555 FC FAQ
What is the maximum test voltage of the Fluke 1555 FC?
10 kV DC. You can select from 250 V to 1000 V in 50 V steps and above 1000 V in 100 V steps.
How high can the Fluke 1555 FC measure insulation resistance?
Up to 2 TΩ. At 10 kV it is ±5% from 10 MΩ to 200 GΩ and ±20% from 200 GΩ to 2 TΩ.
Does the Fluke 1555 FC calculate PI and DAR?
Yes. It calculates the Polarization Index and Dielectric Absorption Ratio automatically with no extra setup.
What is the difference between the Fluke 1555 and 1550C?
The 1555 tests up to 10 kV and 2 TΩ. The 1550C tests up to 5 kV and 1 TΩ. Other features and the safety rating are the same.
What is the safety rating of the Fluke 1555 FC?
CAT IV 600 V and CAT III 1000 V to IEC 61010-2-030, and it meets IEC 61557-1 and -2.
How does Fluke Connect work with the 1555?
Through the infrared adapter. With the Fluke Connect app you can start and stop tests remotely, see a live trend graph and save results to the cloud.
How long does the battery last?
The 12 V rechargeable lead-acid battery gives over 750 tests per charge.
ملخص مهني: جهاز فحص عزل الكابلات والمحولات Fluke 1555 FC
يُعد جهاز Fluke 1555 FC الحل المثالي لاختبارات الجهد العالي حتى 10 كيلوفولت وقياس مقاومة عزل تصل إلى 2 تيراأوم. يساعد نظام طرف الحماية (Guard System) على عزل تيارات التسرب السطحي ويضمن دقة نتائج مؤشر الاستقطاب (PI) ونسبة الامتصاص العازل (DAR).
الجهاز معتمد بتصنيف أمان CAT IV 600V ومتوافق مع تطبيق Fluke Connect لتشغيل الاختبارات ومتابعتها عن بُعد.
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