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The Extech MG300 is a CAT IV 600V rated insulation tester and True RMS digital multimeter combined into a single rugged, IP67-rated handheld instrument. It replaces the two separate tools an electrician or maintenance technician would otherwise carry — a dedicated megohmmeter for insulation work and a professional DMM for general electrical troubleshooting — in one double-molded housing designed for field use.
Per the datasheet, the MG300 is used to measure the insulation resistance of transformer windings and to make True RMS measurements of distorted waveforms where average-responding meters produce inaccurate readings. The insulation tester provides selectable 125V, 250V, 500V, and 1000V test voltages with a measurement range from 0.001 MΩ up to 4000 MΩ, supporting routine insulation verification on motors, transformers, cables, and electrical apparatus.
ValueTronics International stocks, tests, and ships the Extech MG300 and MG302 from our 20,000 square foot secure warehouse at 1675 Cambridge Drive in Elgin, Illinois. Every unit moves through our in-house verification process before shipment, and our team is available by phone at 800-552-8258 or through valuetronics.com to confirm configuration details, radio variant, calibration status, and accessory completeness before you place an order — a level of pre-sale visibility that drop-shipping resellers and online marketplaces cannot match.
Extech Instruments was acquired by FLIR Systems in 2007 and operates as part of the broader FLIR / Teledyne family following Teledyne Technologies' 2021 acquisition of FLIR. The Extech brand and product lines, including the MG300 series, continue under this ownership.
The MG300 series is offered in two model variants that differ only in the wireless transmitter frequency used to communicate with the included PC receiver. Both share identical insulation tester ranges, identical True RMS multimeter capabilities, identical IP67 mechanical construction, and identical CAT IV 600V safety ratings per EN 61010-1.
Per the datasheet, the MG300 uses a 915 MHz wireless link and is intended for use in the USA, Mexico, and Canada, while the MG302 uses a 433 MHz wireless link and is intended for the majority of other countries. Selection between the two is determined by the regulatory environment of the country in which the meter will be operated, not by measurement capability.
Each new model below is its own dedicated product page with condition-matched pricing and availability. Use the comparison table to confirm the radio frequency variant required for your country, then visit the matching product page for the specific configuration you need.
The functional difference between the MG300 and MG302 is the wireless transmitter frequency — 915 MHz on the MG300 and 433 MHz on the MG302. All insulation tester specifications, multimeter ranges, accuracies, accessory contents, and the IP67 housing are common to both models per the datasheet.
Each model is also available with the suffix -NIST, indicating that the unit ships with a Certificate of Calibration Traceable to NIST. The comparison table that follows lists the four configurations covered by this datasheet so you can match the right radio variant and calibration documentation level to your application.
| Model | Wireless Frequency | Insulation Test Voltages | Insulation Resistance Range |
|---|---|---|---|
| MG302 | 433 MHz | 125V, 250V, 500V, 1000V | 0.001 MΩ to 4000 MΩ |
| MG300 | 915 MHz | 125V, 250V, 500V, 1000V | 0.001 MΩ to 4000 MΩ |
| MG300-NIST | 915 MHz | 125V, 250V, 500V, 1000V | 0.001 MΩ to 4000 MΩ |
| MG302-NIST | 433 MHz | 125V, 250V, 500V, 1000V | 0.001 MΩ to 4000 MΩ |
Additional differences in specifications beyond the few shown above are not listed here — see each model's full specifications below.
| Specifications | Range | Resolution | Accuracy |
|---|---|---|---|
| Insulation Tester | |||
| Insulation Resistance | 4MΩ, 40MΩ, 400MΩ, 4000MΩ | 0.001MΩ | ±3% |
| Insulation Test Voltages | 125V, 250V, 500V, 1000V | — | — |
| Multimeter | |||
| AC Voltage | 1000V | 0.1mV | ±1% |
| DC Voltage | 1000V | 0.01mV | ±0.06% |
| AC Current | 10A | 0.1µA | ±1.5% |
| DC Current | 10A | 0.01µA | ±1.0% |
| Resistance | 40MΩ | 0.01Ω | ±0.3% |
| Capacitance | 40mF | 0.001nF | ±3.5% |
| Frequency | 100MHZ | 0.001HZ | ±0.1% |
| Duty Cycle | 0.1 to 99.9% | 0.01 | ±1.2% |
| Temperature | -58 to 1832°F -50 to 1000°C |
0.1°F 0.1°C |
±1% + 4.5°F ±1% + 2.5°C |
| 4-20mA% | -25 to 125% | 0.01% | — |
| Continuity/Diode | Yes | — | — |
| Power source | 6 x AA batteries | ||
| Dimensions | 7.8 x 3.6 x 1.9" (200 x 92 x 50mm) | ||
| Weight | 20.5oz (582g) | ||
| Safety Ratings | EN 61010-1, CAT IV 600V, IP67 Waterproof/Dustproof, UL listed on MG300 only |
Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.
Model No
Extech
Condition
New
Manufacturer
Extech
30+ Years in Business
Secure Payments
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30+ Years in Business
Secure Payments
Sell Test Equipments
Knowledgeable Staff
On-site Lab
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