Insulation Resistance Tester (Megohmmeter): The KYORITSU KEW 3431, Explained
Searching for an insulation resistance tester usually means wading through a wall of unfamiliar model numbers before you even know what you're comparing. Here's a straightforward one: the KYORITSU KEW 3431, a 3-range analog megohmmeter built by a company that's been making electrical test equipment in Japan since 1940. It's small enough to hold and read one-handed, and it's built around a design standard — JIS C 1302 — that most North American electricians have never had reason to look up, but that governs how Japanese insulation testers are built and calibrated.
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Three Ranges Covers Most Panel and Cable Work
The KEW 3431 tests at 250V, 500V, and 1000V, which covers the rated voltages you'll actually run into on low-voltage building wiring, motor circuits, and cable insulation checks. Effective measuring range runs from 0.1MΩ up to 1000MΩ depending on the range selected, with accuracy of ±5% of reading on the primary scale. A color-coded LED backs up the analog needle — green for high resistance (good insulation), red for low resistance (a problem) — so you don't have to squint at scale markings to get a fast pass/fail read in the field.
Auto Voltage Detection and a Safety Discharge Function
Before you connect test leads to a circuit, the meter automatically detects and displays any live AC or DC voltage present (0–600V), which is exactly the check you want to run before applying a test voltage to something that turns out to still be live. After a measurement, an auto-discharge function bleeds off the charge the test itself puts into the circuit, rather than leaving that for you to manage manually.
Meant to Be Carried, Not Just Stored
At 97 × 156 × 46mm and roughly 430g with batteries, it's genuinely a one-hand tool — you can hold the meter and the remote-switch probe in the same hand and trigger the test without setting anything down. It ships with a carrying case built for quick in-and-out rather than a foam-cutout box you have to fully unpack.
About KYORITSU
KYORITSU Electrical Instruments Works, Ltd. was founded in Tokyo in May 1940 and has focused on field-use electrical test equipment ever since — multimeters, clamp meters, insulation testers, earth resistance testers, phase indicators, and power quality analyzers. In 1965 the company developed Japan's first clamp meter, a product line it still leads domestically. Exports to the US and Europe began in 1955, and KYORITSU now sells in roughly 120 countries through local offices in Thailand, the UK, China, and Singapore. In Japan, its meters are widely used by utility companies, major electrical contractors, and electrical safety inspection associations.
Full Specifications
| Model | KYORITSU KEW 3431 |
| Rated test voltage | 250V / 500V / 1000V (3 ranges) |
| Max scale reading | 200MΩ (250V/500V) / 2000MΩ (1000V) |
| Effective measuring range | 0.1–100MΩ (250V/500V) / 1–1000MΩ (1000V) |
| Accuracy (primary range) | ±5% of reading |
| Accuracy (secondary range) | ±10% of reading |
| Open-circuit voltage | Max 1.2× rated test voltage |
| Short-circuit current | 1.5mA or less |
| LED green/red threshold | 0.25MΩ (250V) / 0.5MΩ (500V) / 1MΩ (1000V) |
| Voltmeter range | AC 0–600V (45–65Hz) / DC 0–600V, ±5% of full scale |
| Standards | JIS C 1302:2018, JIS C 1010-1 CAT III 600V, IP40 |
| Power | AA (LR6/R6) ×4 |
| Dimensions | 97(L) × 156(W) × 46(D)mm |
| Weight | Approx. 430g (with batteries) |
| Included | Remote-switch test probe (7260), alligator clip lead set (7261A), carrying case (9173), long tip fitting (8017A), shoulder strap (9121), AA batteries ×4, instruction manual |
| JAN | 4560187065644 |
Why Buy This From Us
We specialize in Japanese-market professional tools and measuring instruments — this isn't a general reseller storefront. If you're ordering multiple items, we offer combined shipping discounts, so it's worth checking our other KYORITSU listings before checking out.
Questions about which voltage range fits your work, or what's included in the case? Message us before ordering and we'll help you confirm.
View on eBay: yourtoolboxJP →Specifications sourced from KYORITSU's official product data. Availability and stock reflect current listings and may change.