Pacific Sensor Tech supplies CENTER insulation resistance testers — also called megohmmeters or IR testers — for verifying the condition of electrical insulation in cables, motors, transformers and switchgear. Three instruments cover the range: routine 250–1000 V testing, measurement to 20 GΩ, and a CAT III 1000 V unit rated for higher-energy installations. All three include the 500 V DC range used for low-voltage insulation resistance verification.
Pacific Sensor Tech supplies CENTER insulation resistance testers — also called megohmmeters or...
Below you will find guidance on selecting a test voltage and range, what AS/NZS 3000 requires for insulation resistance verification, how to interpret a reading against previous results, and a side-by-side comparison of the three instruments.
If you are replacing an ageing megger and are not sure which model matches it, send us the model number and we will confirm the closest equivalent.
Four things decide which instrument suits the work: the test voltage, the resistance range, whether you also need continuity testing, and the safety category of the installation.
Match it to the rated voltage of the equipment. Testing a 230Â V circuit at 1000Â V tells you little; testing 1000Â V switchgear at 250Â V will not expose a weakness that only appears under stress. The 250, 500 and 1000Â V steps cover most fixed-wiring work. Lower 50 and 100Â V steps matter only where electronics cannot tolerate a higher test voltage.
Healthy insulation often measures in gigaohms. An instrument that tops out at a few thousand megaohms simply reports “over range” — confirming the insulation is sound, but giving you no number to trend against at the next inspection.
A dedicated low-Ω range confirms earthing and bonding conductors with a meaningful test current, which a discharge buzzer cannot. If one instrument has to cover both jobs, look for an insulation and continuity tester.
The CAT rating describes the transient energy the instrument is built to survive, not the voltage it can measure. CAT III 1000 V is the appropriate rating for fixed installation work — distribution boards, busbars, fixed motors and switchgear.
The CENTER C360 covers 250–1000 V to 4,000 MΩ, with a 40-segment analogue bargraph for watching a reading settle. The CENTER C365 adds 50 and 100 V steps, extends to 20 GΩ, and includes live circuit detection and a low-Ω range. The CENTER C366 matches the C365 and adds an IEC CAT III 1000 V rating for higher-energy installations.
AS/NZS 3000, the Wiring Rules, requires insulation resistance to be verified on new electrical installations and on alterations, as part of the mandatory testing and verification process. For typical low-voltage circuits, insulation resistance testing is generally performed at 500 V DC with a minimum acceptable insulation resistance of 1 MΩ, subject to the applicable exceptions and requirements of AS/NZS 3000.
The reading is only meaningful if the test voltage sees insulation and nothing else. Isolate, prove dead and discharge the circuit, then disconnect anything the test voltage could damage or that would load the result — electronic control gear, surge protection devices, dimmers and equipment containing power electronics. Devices left connected are the most common reason a sound installation returns a poor reading.
Results are also sensitive to temperature and moisture, so the same circuit can read differently on different days. Record the test voltage, the value and the conditions alongside each result, and treat a single low reading as a prompt to investigate rather than a conclusion.
Higher is better, but the absolute figure matters less than the trend. A motor reading 80 MΩ is not necessarily healthier than one reading 40 MΩ — what matters is what each read last year. A winding that has fallen from 400 MΩ to 80 MΩ over two inspections is deteriorating far faster than one that has sat at 40 MΩ for a decade. The bands below are a starting point for low-voltage installations, not an acceptance standard.
| Reading | Condition | What to do |
|---|---|---|
| Above 100 MΩ | Excellent | Record the value and conditions. |
| 10–100 MΩ | Good | Normal in service. Compare with the last result. |
| 1–10 MΩ | Investigate | Check for connected equipment or moisture first. |
| Below 1 MΩ | Failed or failing | Do not return to service. Locate the fault and re-test. |
Allow the value to stabilise before recording it — typically around 60 seconds, as the dielectric charges. A reading that will not settle usually means something is still connected, the circuit has not fully discharged, or moisture is present.
The same device goes by several names, which makes it harder to search for than it should be:
Pacific Sensor Tech supplies CENTER megohmmeters; we do not stock Megger-branded instruments. Note also that a megohmmeter is not an insulation monitoring device (IMD) — an IMD is permanently installed to monitor an IT earthing system continuously, whereas these are portable test instruments.
| Specification | CENTER C360 | CENTER C365 | CENTER C366 |
|---|---|---|---|
| Insulation test voltages | 250Â V / 500Â V / 1000Â V | 50Â V / 100Â V / 250Â V / 500Â V / 1000Â V | 50Â V / 100Â V / 250Â V / 500Â V / 1000Â V |
| Maximum insulation range | 4,000 MΩ | 20.0 GΩ | 20.0 GΩ |
| Safety rating | 600Â V rms protection | 600Â V rms protection | IEC CATÂ III 1000Â V |
| Voltage measurement | 600Â V AC / 600Â V DC | 60Â V / 600Â V, AC and DC | 60Â V / 600Â V / 1000Â V, AC and DC |
| Resistance ranges | 400 Ω – 4,000 Ω, auto-ranging | 600 Ω / 6 kΩ / 60 kΩ / 600 kΩ | 600 Ω / 6 kΩ / 60 kΩ / 600 kΩ |
| Low-Ω continuity test | Discharge indication beeper, ≤ 40 Ω | LoΩ range 6 Ω / 60 Ω, >200 mA | LoΩ range 6 Ω / 60 Ω, >200 mA |
| Live circuit detection | — | Yes | Yes |
| Best suited to | Routine 250–1000 V testing where the 40-segment analogue bargraph helps judge a trending reading | Most users: full 50–1000 V range, live-circuit detection, in stock now | Higher-energy installations where a CAT III 1000 V rating is required |
| More information | View C360 specifications | View C365 specifications | View C366 specifications |
An insulation resistance tester — also known as a megohmmeter, IR tester or megger — applies a high DC test voltage across de-energised wiring and measures the leakage current passing through the insulation. It is used to find cracked, damp, contaminated or ageing insulation in cables, motors, transformers and switchgear before it causes a fault.
Isolate and lock off the circuit, discharge any stored energy, and confirm the circuit is dead. Disconnect sensitive electronics that the test voltage could damage. Connect the test leads between the conductor and earth, select a test voltage appropriate to the circuit rating, and apply it for approximately 60 seconds. Read the resistance in MΩ or GΩ once the value stabilises.
AS/NZS 3000 (the Wiring Rules) requires insulation resistance to be verified for new electrical installations and alterations as part of the mandatory testing and verification process.
For typical low-voltage circuits, insulation resistance testing is generally performed at 500 V DC, with a minimum acceptable insulation resistance of 1 MΩ, subject to the applicable exceptions and requirements of AS/NZS 3000.
The CENTER 360, CENTER 365 and CENTER 366 insulation resistance testers all provide a 500 V DC test range, making them suitable for applications requiring this test voltage.
Higher is better. As a general guide for low-voltage installations, a reading above 100 MΩ is excellent, 10–100 MΩ is good, and 1–10 MΩ warrants investigation. Below 1 MΩ indicates insulation that has failed or is failing and should not be returned to service. Always apply the acceptance value set by the relevant standard.
Match the test voltage to the rated voltage of the equipment. 250 V suits low-voltage circuits up to around 100 V, including SELV and PELV; 500 V is standard for general 230/400 V installations; 1000 V is used for higher-rated equipment, motors and switchgear. The CENTER 365 and CENTER 366 offer 50, 100, 250, 500 and 1000 V; the CENTER 360 offers 250, 500 and 1000 V. The CENTER 366 adds an IEC CAT III 1000 V safety rating for higher-energy installations.
