Two Useful Functions of Digital Multimeters
This method can check whether the power cord of household appliances is broken, and also locate the breakpoints of internal heating wires in electric blankets, electric irons and other household appliances.
① Locating Broken Cores in Wires Method: Connect one end of the insulated wire with broken core to the live wire of the 220 V AC power supply, and leave the other end open. Set the digital multimeter to the 2 V range. Starting from the end connected to the live wire, slide the red test lead along the outer insulation of the wire. The displayed voltage value will fluctuate around a few tenths of a volt. When the red test lead moves to a certain point and the voltage suddenly drops to several hundredths of a volt, this position is the breakpoint of the wire core.
Thanks to the high sensitivity of the AC range on digital multimeters, you can identify the live wire accurately just by touching the outer sheath of the power cords without contacting the internal copper conductors. The operation method is the same as described above. Since the probe tip does not touch the inner copper wire, the induced voltage is relatively low, so a small measurement range should be selected.
② Distinguishing Live Wire from Neutral Wire of Mains Supply Set the multimeter to the AC 20 V range. Remove the black test lead. Hold the insulated handle of the red test lead, and touch the two holes of the power socket with the probe tip one by one. The socket hole with a larger reading is the live wire, and the one with a smaller reading is the neutral wire.
When using the 20 V AC range of a digital multimeter, if the two readings are 6.01 V and 0.4 V respectively, the terminal showing 6.01 V is the live wire, and 0.4 V corresponds to the neutral wire.
