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It is well known that the power supply for high and low temperature test chambers is 380V, but due to constraints in the customers’ locations, the power supply for some of these chambers can be changed to 220V. This raises the question: why is a single-phase three-pin socket required in such cases? In our country, electricity is in short supply, especially during peak usage times, when the voltage tends to **drop**. In some areas or during off-peak electricity usage, voltages that are high or even higher may also occur. The electrical components of the test chamber, such as the compressor motor, have specific requirements regarding their operating voltage range; exceeding this range can cause the compressor to operate abnormally or even burn out. Actual operation shows that most cases of compressor burnout are related to voltage abnormalities. Reasons for using a single-phase three-pin socket in high and low temperature test chambers: 1. The three pins of a single-phase three-pin socket are the live wire L, the neutral wire N, and the ground wire E. Among these, E is connected to the ground through the power supply and distribution circuit, and its potential is equal to that of the ground, i.e., zero. 2. When the insulation of the electrical components in the test chamber deteriorates or fails, it can cause the metal enclosure of the constant temperature and humidity test chamber to become charged; touching it may result in an electric shock hazard. Therefore, in the design of high and low temperature test chambers, the metal enclosure is connected to the E terminal on the power cord plug; once the enclosure becomes charged, electricity is conducted to the ground through the E terminal, keeping the enclosure at a zero potential at all times and thus preventing any harm to humans. Some users of constant temperature and humidity test chambers, although they use three-prong plugs, have the E prong left unconnected, which does not meet safety requirements; a ground wire should be installed instead. The emphasis on grounding in the instructions for high and low temperature test chambers is based on safety considerations.