Troubleshooting
46 Check for Incoming Power
Whenever equipment or circuits are not working, always start by confirming that there is voltage available. If there is voltage at the source of supply, then you have confirmed that the problem is downstream from that point.
If the main overcurrent protection is provided by a circuit breaker, check that the handle is in the “On” position, and not the “Off” or “Tripped” position. A circuit breaker indicates that it has tripped when the handle is in the centre position. To reset, push the handle fully off, then on. If the handle “trips” again suddenly, then there is likely a short circuit somewhere bypassing a load.
If the main overcurrent protection is provided by a fusible disconnect, the status of the fuses will determine if voltage is present. There are two tests that can confirm if a fuse link is intact: an ohmmeter continuity test and the crisscross voltmeter method.
The difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points. It is measured in volts (V).
A sharp and fast rise in current over a short period of time (fractions of a second) where the value of current is far greater than the nominal line current.
An automatic device that is designed to safely disconnect circuits under fault conditions. Most circuit breakers provide Overload and Overcurrent protection, and are rated in Volts, Amps and Horsepower.
An insulated tube containing a strip of conductive metal that has a lower melting point than either copper or aluminum. It protects a circuit from damage because it will melt in overload or overcurrent situations and break the connection with the rest of the circuit.
A device used to measure the resistance of a circuit. Ohmmeters must not be used on live circuits. Ohmmeters connect a small internal voltage source to the circuit that is being measured or tested, and determine the value of resistance or continuity by measuring what value of current flows through the meter.
Can be either digital or analogue.
The crisscross voltmeter method is used to troubleshoot fuses on a live circuit. It involves checking the potential difference between the line and load sides of fuses connected to different phases in a three-phase fusible disconnect.
