Fluke 1507 Insulation Tester Megger: Working, Buying Guide
The Fluke 1507 Insulation Tester is a compact insulation resistance tester designed to check the condition of electrical insulation in motors, cables, switchgear, panels, and other low-voltage equipment. It applies a controlled DC test voltage and measures the resistance of insulation, helping electricians identify leakage paths, moisture, contamination, and insulation deterioration.
Although electricians often call an insulation resistance tester a “Megger,” Megger is actually a well-known test equipment brand. The Fluke 1507 performs the same general type of insulation resistance test, with selectable test voltages and a digital resistance reading.
For electrical maintenance teams, the important point is not simply getting a high megohm value. The test voltage, equipment rating, temperature, test duration, and condition of the installation all affect the result.
Fluke 1507 Insulation Tester Specifications at a Glance
The following table summarizes the main features relevant to insulation resistance testing.
| Feature | Fluke 1507 Detail |
|---|---|
| Instrument type | Insulation resistance tester |
| Insulation test voltages | 50 V, 100 V, 250 V, 500 V, 1000 V DC |
| Insulation resistance range | Up to 10 GΩ |
| AC/DC voltage measurement | Yes |
| Continuity testing | Yes |
| Resistance testing | Yes |
| Auto discharge | Yes |
| Test lock | Yes |
| Display | Digital LCD |
| Min/max recording | Available for relevant measurements |
| Typical applications | Motors, cables, panels, switchgear and electrical installations |
| Power source | Battery operated |
| Safety category | CAT IV 600 V / CAT III 1000 V |
The selectable voltage range makes the instrument useful for different electrical systems. A technician can select a lower test voltage for sensitive equipment or use a higher voltage when the insulation system is designed for it.
If you are comparing different instruments before purchasing, our guide to best insulation resistance testers can help you compare insulation testers, test voltage ranges, measurement capabilities, and practical applications.
How Does Fluke 1507 Insulation Tester Work?
The basic operating principle is straightforward.
The tester generates a DC voltage and applies it between the conductor being tested and its insulation reference point, usually earth, another conductor, or the equipment frame. The instrument measures the resulting leakage current and calculates insulation resistance using Ohm's law.
The basic relationship is:
Insulation Resistance = Test Voltage ÷ Leakage Current
For example, if a 500 V test produces only 0.5 µA of leakage current:
R = 500 ÷ 0.0000005 = 1,000,000,000 Ω
That equals 1 GΩ.
A healthy insulation system generally allows very little current to pass through it. If insulation has absorbed moisture or developed a damaged path, leakage current increases and the measured resistance decreases.
What Happens During an Insulation Test?
| Step | What Happens |
|---|---|
| 1 | Technician isolates the circuit |
| 2 | Appropriate test voltage is selected |
| 3 | Test leads are connected |
| 4 | DC test voltage is applied |
| 5 | Leakage current flows through the insulation |
| 6 | Tester calculates resistance |
| 7 | Resistance is displayed |
| 8 | Test voltage is removed |
| 9 | Stored charge is discharged |
The Fluke 1507 includes automatic discharge capability, which is important because cables and other electrical equipment can retain charge after an insulation resistance test.
Never assume a circuit is safe simply because the test button has been released. Follow the equipment manufacturer's procedure and verify the circuit is discharged before handling conductors.
Fluke 1507 Insulation Resistance Test Voltages
Selecting the correct test voltage is one of the most important parts of insulation testing.
The available test levels are 50 V, 100 V, 250 V, 500 V, and 1000 V DC. The correct selection depends on the equipment under test and the applicable standard or manufacturer's instructions.
| Test Voltage | Typical Use |
|---|---|
| 50 V | Sensitive or low-voltage electronic equipment where permitted |
| 100 V | Low-voltage circuits and selected control applications |
| 250 V | Certain low-voltage equipment and control circuits |
| 500 V | Common LV cable, motor and installation testing |
| 1000 V | Equipment and circuits where the insulation system is suitable for the higher test voltage |
These are general applications, not universal rules. Some electronic devices contain components that can be damaged by insulation testing. Disconnect sensitive equipment before testing whenever the manufacturer's instructions require it.
How to Use Fluke 1507 Insulation Tester
Before connecting the instrument, switch off the circuit and isolate it from all sources of electrical energy. Lockout/tagout procedures should be followed where applicable.
A practical test sequence is:
- Confirm the equipment is de-energized.
- Isolate the equipment from external circuits.
- Check the tester and test leads for damage.
- Select the required insulation test voltage.
- Connect one lead to the conductor.
- Connect the other lead to earth, the motor frame, or the specified reference point.
- Press and hold the TEST button.
- Allow the reading to stabilize.
- Record the resistance value.
- Release the test and allow the instrument to discharge the circuit.
- Verify the equipment is safe before reconnecting it.
For three-phase motors, insulation resistance can be checked between each phase and the motor frame. Phase-to-phase testing can also be performed when the applicable procedure calls for it.
Motor Insulation Testing Example
Suppose a three-phase motor has been removed from service for maintenance.
A technician may test:
| Test | Connection |
|---|---|
| Phase A to earth | A → Motor frame |
| Phase B to earth | B → Motor frame |
| Phase C to earth | C → Motor frame |
| Phase A to B | A → B |
| Phase B to C | B → C |
| Phase A to C | A → C |
The readings should be recorded rather than relying on memory.
A single reading can provide useful information, but a trend is often more valuable. If a motor previously measured several hundred megohms and later drops significantly, the change deserves investigation even if the new reading still appears acceptable.
Temperature also affects insulation resistance. Therefore, maintenance records should include test conditions whenever practical.
Understanding Megohm Readings
A higher insulation resistance reading generally means less leakage through the insulation. A low reading can indicate moisture, dirt, carbon tracking, aging insulation, mechanical damage, or another leakage path.
However, there is no single resistance value that automatically determines whether every electrical system is safe.
| Reading Trend | Possible Interpretation |
|---|---|
| Very high resistance | Generally indicates low leakage |
| Stable high reading | Often indicates consistent insulation condition |
| Gradually decreasing | May indicate aging or environmental effects |
| Sudden reduction | Requires investigation |
| Very low resistance | Possible insulation fault or leakage path |
| Unstable reading | Moisture, contamination, connections, or equipment characteristics may be involved |
Always compare the result with the applicable standard, equipment manufacturer's requirements, previous maintenance records, and the rated voltage of the equipment.
For a broader comparison of instruments used for this type of maintenance, see our guide to best insulation resistance testers.
Common Applications
The Fluke 1507 Insulation Tester can be used in several electrical maintenance situations.
Motors
Motor windings can be tested against the frame to identify deteriorated insulation. Regular readings can also help maintenance teams track insulation condition over time.
Power and Control Cables
Insulation testing can help identify damaged or contaminated cable insulation before energization. Both individual conductors and conductor-to-earth tests may be required depending on the installation.
Electrical Panels
Panels and associated circuits can be checked during commissioning or maintenance, provided sensitive electronic components are properly isolated.
Switchgear
Insulation resistance testing can form part of preventive maintenance programs for suitable switchgear and electrical assemblies.
Generators
Generator windings can require insulation resistance testing during maintenance. The manufacturer's testing procedure should always be followed because generator construction and connected components vary.
Fluke 1507 vs Other Insulation Testers
A compact insulation tester is useful when the main requirement is insulation resistance testing rather than advanced diagnostic functions.
For example, technicians who also need temperature measurements, capacitance, polarization index, or more advanced motor diagnostics may consider a different instrument.
For a detailed comparison of the two Fluke instruments, read our guide on fluke 1587 vs 1507.
| Requirement | Suitable Instrument Type |
|---|---|
| Basic insulation resistance testing | Dedicated insulation tester |
| Cable maintenance | Insulation tester |
| Motor maintenance | Insulation tester with suitable voltage range |
| Insulation plus general electrical measurements | Multifunction insulation multimeter |
| Advanced diagnostic testing | Advanced insulation analyzer |
The Fluke 1507 is particularly useful when straightforward insulation resistance testing is the main requirement.
Safety Precautions Before Testing
Insulation resistance testing involves applying DC voltage to equipment. The procedure must therefore be treated as a live electrical hazard even when the original circuit supply has been switched off.
Important precautions include:
- Disconnect the equipment from all power sources.
- Follow lockout/tagout procedures.
- Verify absence of voltage before testing.
- Disconnect sensitive electronic equipment when required.
- Never touch test leads during an active test.
- Use properly rated test leads and PPE.
- Allow capacitive equipment to discharge.
- Follow the manufacturer's instructions.
- Follow applicable electrical safety standards.
- Record unusual readings for further investigation.
If you need more functionality than a dedicated insulation tester provides, our comparison of the fluke 1587 insulation multimeter explains how a multifunction instrument differs from a dedicated insulation resistance tester.
Factors That Affect Insulation Resistance Readings
A resistance reading should always be interpreted in context.
| Factor | Effect on Reading |
|---|---|
| Temperature | Resistance can change significantly with temperature |
| Moisture | Can reduce insulation resistance |
| Dirt and contamination | May create leakage paths |
| Cable length | Longer insulation systems can show different readings |
| Equipment age | Aging can gradually reduce resistance |
| Surface condition | Contamination can cause surface leakage |
| Test voltage | Results can vary with applied voltage |
| Test duration | Resistance may change while voltage remains applied |
This is why maintenance teams should avoid judging equipment from one number alone.
Fluke 1507 Insulation Tester Testing Tips
Good testing technique improves the quality of maintenance records.
First, keep test conditions consistent where possible. Testing the same motor at different temperatures can produce noticeably different results.
Second, record the exact test voltage. A 250 V reading and a 1000 V reading should not be treated as directly interchangeable.
Third, compare readings with historical results. Trend analysis can reveal deterioration before a complete insulation failure occurs.
Finally, investigate unexpected changes rather than immediately assuming the equipment has failed. Check connections, moisture, contamination, temperature, and whether all connected components were properly isolated.
Frequently Asked Questions
1. What is the Fluke 1507 used for?
The Fluke 1507 is primarily used to measure insulation resistance in electrical equipment such as motors, cables, panels, and suitable electrical installations. It applies selectable DC test voltages and measures the resulting insulation resistance.
2. Is the Fluke 1507 a Megger?
The Fluke 1507 is an insulation resistance tester, while Megger is a separate test equipment brand. In everyday electrical work, “megger” is often used as a generic term for an insulation resistance tester.
3. What test voltages does the Fluke 1507 have?
It provides selectable insulation test voltages of 50 V, 100 V, 250 V, 500 V, and 1000 V DC. The correct voltage depends on the equipment and applicable testing requirements.
4. What is a good insulation resistance reading?
There is no universal “good” reading for every piece of equipment. The acceptable value depends on the equipment rating, applicable standards, manufacturer requirements, temperature, and previous test results. In general, higher resistance means lower leakage, but the trend and test conditions are also important.
5. Can the Fluke 1507 test motor insulation?
Yes. It can be used for suitable motor insulation tests, including winding-to-frame testing. The motor should be isolated and prepared according to the manufacturer's maintenance procedure before applying the insulation test voltage.
Final Thoughts
The Fluke 1507 Insulation Tester is designed around a practical maintenance task: applying a controlled DC voltage and measuring how well an electrical insulation system resists leakage current. Its selectable test voltages make it suitable for a range of electrical maintenance and troubleshooting applications.
The most useful approach is to treat insulation resistance testing as a diagnostic process rather than simply looking for a large megohm number. Record the test voltage, temperature, equipment condition, and historical readings. Consistent testing makes changes easier to identify and investigate.
For technicians building a test kit, comparing the available insulation resistance testers and understanding where dedicated testers differ from multifunction instruments can help match the equipment to the actual maintenance work.
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