What is the recommended voltage when doing an insulation resistance test on NW breakers when breaker is in the closed position?

500-1000Vdc is acceptable as per the Masterpact field testing and maintenance guide, page 46 document 0613IB1202 R08/15

https://www.se.com/us/en/download/document/0613IB1202/?searchSource=guided

Insulation Resistance Test Severe environmental conditions can reduce the dielectric strength of molded case circuit breakers. Check insulation resistance during electrical system testing. To check the insulation resistance, perform the following steps:
1. De-energize and isolate the circuit breaker:
2. Clean the circuit breaker as described earlier.
3. Using a megohmmeter with a capacity of 500–1000 Vdc, apply voltage from: a. Each phase-to-ground with the circuit breaker on (circuit breaker contacts closed). b. Phase-to-phase with the circuit breaker on (circuit breaker contacts closed). c. Between each line and load terminal with the circuit breaker off (circuit breaker contacts open).
4. Record resistance values. Resistance values of less than one megohm (1,000,000 ohm) should be investigated.

Released for: Schneider Electric UK