Alternative or Additional Test Methods

Load bank testing will typically normalize pole resistance as it gives the circuit breaker rated current and voltage which allows the contacts to reach their normal operating temperature and potentially burn away resistive oxides and it simulates service conditions. Acceptable thermal performance during load bank testing demonstrates that the circuit breaker is usable regardless of initial pole resistance test results. If load bank testing is not feasible, placing the circuit breaker in service and monitoring for thermal issues will accomplish the same results. Refer to Schneider Electric document 0600DB1603 titled “Circuit Breaker Operating Temperatures” for UL recognized thermal limits.

Contact conditioning is a reasonable alternative to load bank testing as it will burn through resistive oxides. To condition the contacts, primary inject the circuit breaker with 300% of the circuit breaker’s rated current for 75% of the circuit breaker’s minimum tripping time (per the trip curve), allow the circuit breaker to cool, and then measure contact resistance again without toggling the circuit breaker. If one or the other of these methods do not give acceptable results, circuit breaker replacement may be in order.