Leroy-Somer — Checking the insulation
Testing & diagnosis · Stator winding / motor insulation
From a Leroy-Somer service manual — check it applies to your exact model before use.
Before you start
- Do not use a magnetoelectric system megohmmeter
- If repeating the factory high voltage test use half the standard voltage: 1/2 (2U+1000V)
Procedure
- Check insulation between phases and earth, and between phases
- Carry out an initial test at 30 or 50 volts
- If insulation is greater than 1 megohm, carry out a second test at 500 volts for 60 seconds
- The insulation value must be at least 10 megohms in cold state
- If value cannot be achieved, dry the stator 24 hours in a drying oven at 110°C to 120°C
- If no oven is available, run the motor with the rotor locked at 3-phase A.C. reduced to approx. 10% of rated voltage for 12 hours
- Or supply the 3 phases in series with D.C. current at 1 to 2% of the rated voltage
- Monitor A.C. current with a clamp ammeter and D.C. current with a shunt ammeter; must not exceed 60% of rated current
- Place a thermometer on the housing; if temperature exceeds 70°C reduce voltage/current by 5% for every 10° difference
- While drying, all motor orifices (terminal box) must be open
Tools required
- Megohmmeter 500 V DC Amazon
- Clamp ammeter Amazon
- Shunt ammeter Amazon
- Thermometer Amazon
- Drying oven Amazon
- Induction regulator or reduction transformer Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 500 V DC
- 10 megohms cold state
- 110°C to 120°C for 24 h
- 60% rated current
- 70°C housing limit
Source: Leroy-Somer service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.