1, the multimeter ohm gear, range to 1000 ohms can be adjusted to directly measure the ends of the electric heating tube, if there are dozens or hundreds of ohms of resistance, indicating that the internal electric heating wire is normal. If there is no reading on the multimeter, the internal has been burned off, such as the multimeter reading is small and tends to be close to zero, then the internal short circuit.

2, electric heating tube is a seamless metal (carbon steel, titanium, stainless steel, copper tube) loaded with electric heating wire, through a good thermal conductivity and insulation materials, isolation, and then processed into a variety of shapes of electrical parts. So the piece of insulation, but also to measure. With a shaking table to measure the insulation between the electric heating wire and the shell, there may be readings, readings in a few megohms or more for safety.

Two same power with the same type of 110V electric heater, can be used in series to access the 220V power supply, the principle is series voltage division. The voltage on each load is 110V, and if one of them is damaged, the other will not work properly.

If the working voltage of the electric heating tube is matched with the power supply used, we can use parallel connection, connect multiple loads in parallel, the working voltage on each load is equal. If one of the heating tubes is damaged, the loads on the other branches can work normally.

If it is a three-phase, three-wire power supply, in the absence of a zero line, you can connect three 220V heating tubes to a 380V power supply by star connection. Star connection requires that the three loads have the same power, the voltage at the neutral point is 0, the voltage loaded on each load is 220V, and the three loads work normally. One of the load is damaged, the other two become series connection, 380V series voltage divider, the operating voltage on each load becomes 190V, two heating tubes can work, but the power decay.