Two common inspections of circuit breaker contacts are visual inspection and contact resistance inspection.

1. Visual inspection The inspection includes checking the contacts of the circuit breaker for any signs of pitting caused by arc discharge and worn or deformed contacts.

2. The second check is the contact resistance measurement. This involves injecting a fixed current through the contact, usually around 100A, 200A, and 300A, and measuring the voltage drop across it. The test is done using a special contact resistance measuring instrument. Then, the resistance value is calculated using Ohm's law. The resistance value needs to be compared with the value given by the manufacturer. This value should also be compared with the previous record.

Both tests need to be completed together. Due to the fact that the contact has good contact resistance but is still in a damaged state. Therefore, for a certified healthy contact, it needs to have good contact resistance and the visual inspection test should be cleared.

There are generally two types of catheter testers:

1. The series ohmmeter has 4 resistors, the internal battery voltage -E and output terminals A and B. When the A and B terminals are connected with the R1 and R2 resistors, the battery forms a simple series circuit.

2. Shunt ohmmeter, used to measure the resistance value of small current. When the A and B terminals are closed, the needle reads zero because current only flows through resistor RX. When these two terminals are disconnected, no current flows through the RX resistance, so the reading on the conductor tester is marked as infinite.