An insulation tester — also called a megohmmeter or megger — measures the resistance of electrical insulation in cables, motors, transformers, switchgear, and wiring systems. A high insulation resistance reading means healthy insulation; a low reading indicates deterioration, moisture ingress, or damage that could lead to equipment failure or electric shock. This guide explains how to choose the right model for your needs.

 

What test voltage do you need?

This is the most important selection criterion. The test voltage must be appropriate for the voltage rating of the equipment being tested.

500V test voltage— suitable for testing low-voltage cables, single-phase and three-phase wiring (up to 1000V systems), domestic and commercial electrical installations. Recommended models: KEW 3131A (analogue), KEW 3551 (digital).

1000V test voltage — the most commonly used for industrial electrical maintenance, motors, LV switchgear, and cables rated up to 1000V. Recommended models: KEW 3552 and KEW 3552BT (digital with Bluetooth), KEW 3132A (analogue).

2.5kV to 5kV test voltage— for high-voltage motors (HV), transformers, HV cables, and switchgear. Recommended models: KEW 3121B (2.5kV), KEW 3122B (5kV), KEW 3025A (5kV).

10kV test voltage — for EHV cables, large power transformers, and utility-grade switchgear. Recommended models: KEW 3123A (10kV), KEW 3124A (10kV), KEW 3125B (12kV), KEW 3127 (10kV analogue).

 

Analogue or digital?

Analogue insulation testers use a moving-coil meter display. They are preferred by experienced engineers who like the visual "drift" of the pointer to judge the quality of insulation as it charges — a pointer moving steadily to a high value indicates good insulation; one that drifts and fluctuates suggests a problem. Models like the KEW 3131A and KEW 3132A are popular for this reason in Indian utilities and industrial sites.

Digital insulation testers give precise numerical readings, often with automatic discharge, data hold, buzzer alarms, and — in advanced models — Bluetooth connectivity for data logging on a smartphone. The KEW 3552BT is the most popular digital model in India, offering 1000V testing, Bluetooth data transfer, and a live circuit warning for safety.

 

Special features to consider

Bluetooth connectivity (KEW 3552BT): connects to a smartphone app for data recording and report generation — valuable for maintenance teams that need to document results.

Live circuit warning: present in most Kyoritsu digital models — alerts you if the circuit under test is still live, preventing dangerous testing errors.

PI and DAR testing: Polarisation Index and Dielectric Absorption Ratio tests are available in advanced models (KEW 3552BT, KEW 3552) — used for assessing the condition of motor windings and cable insulation over time.

PV insulation testing (KEW 6024PV): a specialist model for testing insulation in solar PV arrays, with live voltage detection and positive/negative pole selection.

 

Quick selection guide Domestic / commercial wiring contractor: KEW 3131A (500V analogue) or KEW 3551 (500V digital)

Industrial electrical maintenance: KEW 3552BT (1000V digital, Bluetooth)

HV motor and cable testing: KEW 3121B or KEW 3122B

Utility / substation engineer: KEW 3125B or KEW 3127 (10kV+)

Solar PV installer: KEW 6024PV

 

All models are supplied with a 3-year warranty by KEW India — India's official Kyoritsu distributor.