Primary injection testing of a circuit breaker. Photo: YouTube
Periodic inspection and testing of power circuit breakers almost always includes a visual inspection, calibrating the overcurrent protection, contact resistance and insulation tests, but how often do you perform these other important, and often overlooked, checks and tests?
The contacts of the auxiliary switch are designed to open or close external control circuits as the breaker operates. The circuit breaker operating mechanism controls opening or closing of the switches.
As the operating mechanism rises to the “open” position (breaker tripping), the switch is forced to “make” or “break” contacts. When the mechanism is pulled closed (breaker ON), the switch resets and returns the contacts to their de-activated position.
To ensure good circuit establishment, you can use a flash light test circuit, or any other desirable test circuit, wired in series with switch contacts, and operate the circuit breaker manually. The test circuit should show proper and positive switch contact operation (consult manufacturers literature for typical lead connections).
Secondary disconnects connect the circuit breaker to the control circuits. Photo: YouTube
With the circuit breaker disconnected from all voltage sources and the main contacts open, test for continuity between the common and B terminals.
Verify that the common and A terminals show an open circuit.
Close the breaker then verify continuity between the common and A terminals.
Verify that the common and B terminals show an open circuit.
When a circuit breaker closes, all three contacts should make at about the same time. If they are too far off, the arcing contacts will suffer accelerated wear, leading to failure of the main contacts. Most manufacturers of low-voltage power circuit breakers recommend that all contacts touch within 0.032" (1/8") of each other.
The easiest method for determining contact sequence is to use a simple light circuit across the circuit breaker contacts. A different color light is used for each phase and is powered by a battery. The breaker is slow closed until the first contact touches, then the other two phases are measured. There should be no more than the 1/8" or whatever the manufacturer’s specification is.
Light Circuit for Contact Sequence. Photo: TestGuy
The anti-pump relay is connected so that it seals in as long as the close signal is maintained. When an electrical closing command is issued, only a single closing operation results. The anti-pump relay is energized when the close signal is applied. The anti-pump relay, when sealed in, opens a contact in the close circuit.
Verify the anti-pump function after closing the circuit breaker electrically by maintaining the close signal and observing that the close circuit has an open contact in the circuit, preventing further close operations as long as the close signal is maintained. This prevents the circuit breaker from trying to close immediately after being tripped open (pumping) on concurrent close and trip signals.
The Anti-Pump Relay (Y-Relay) prevents the circuit breaker from trying to close immediately after being tripped open.
Verify trip free functionality by ensuring that the circuit breaker does not reclose unless properly reset after tripping, per manufacturers procedure. Also verify circuit breaker will not close if locked out.
Trip-free is an important safety feature, as it assures that the decision to open a circuit breaker dominates over the command to close.
Solid state trip units are fitted with long-life batteries. Without the battery, the Cause of Trip indications will not be displayed if auxiliary power is lost to the trip unit. Check the status of the battery at any time by pressing the Battery/Test push button and observing the battery test LED.
If the Battery Test LED does not light, replace the battery. The condition of the battery has no effect on the protection function of the trip unit. Even with the battery removed, the unit will still trip the circuit breaker in accordance with its settings.