What is Contact Resistance, Where It Occurs, How Is It Tested?
What is Contact (Contact) Resistance?
The term contact (contact) resistance refers to the contribution to the total resistance of a system, which can be attributed to the contacting interfaces of electrical cables and connections, as opposed to internal resistance. There are two main determinants of contact resistance:
- Geometry between contacting surfaces
- Insulation layers
The resistance of a contact is inversely proportional to its area, which in turn depends on the force holding the two surfaces.
Where Does Contact (Contact) Resistance Occur?
- Cutters
- Contactors
- Relays
- Keys
- Connectors
- Other Switching Devices
What Problems Does the Contact (Contact) Resistance Test Detect?
- It is used to measure resistance in different applications of electrical testing. Consisting of a DC ammeter and several other components, this tester detects the following issues;
- Loose connections
- Sufficient tension on bolted connections
- Worn contact surfaces
- Dirty or worn contacts
Why is Contact (Contact) Resistance Test Necessary?
The contacts in the circuit breaker need to be checked periodically to ensure that the breaker is healthy and functional. Poorly maintained or damaged contacts can cause sparks, loss of phase or even fire. Measuring contact resistance helps identify corrosive corrosion of contacts and allows diagnosis and prevention of contact corrosion. An increase in contact resistance can cause a high voltage drop in the system and this needs to be controlled.
What is done during the contact (contact) resistance test?
Two common checks performed on the contacts of a circuit breaker are visual inspection check and contact resistance check.
Visual inspection check includes inspecting the contacts of the circuit breaker for any signs of pitting due to arcing and worn or deformed contacts.
The second check is the contact resistance measurement. This involves injecting a constant current, usually around 100A, through the contacts and measuring the voltage drop across it. This test is done with a special contact resistance measuring device. Then the tester calculates the resistance value. The resistance value read on the device should be compared with the value given by the manufacturer. The value should also be compared with previous records.
Both of these tests need to be done together. Because the contacts have good contact resistance and can also be damaged. Therefore, to be considered reliable, a contact must have good contact resistance and pass a visual inspection test.
