In my experience, there are essentially two possibilities regarding servo motor leakage. One is leakage caused by electromagnetic induction. This occurs when testing servo motors supplied with LUSTservoc. All three phase wires of the servo motor are connected to the driver, but the ground wire is not connected to the driver. Touching the servo motor while it's running causes an electric shock because the motor casing is induced with a relatively high voltage. This is actually quite normal. Connecting the servo motor's ground wire and the driver casing together to the ground or neutral wire will eliminate the electric shock problem.
I haven't specifically tested the electric shock issue with Japanese servo motors because people usually unconsciously connect the servo motor's ground wire and the driver's housing to the neutral wire, but I suspect the same problem exists. Another issue compared to Japanese servo motors is that European servo motors have an additional shielding wire in their power cable. If this shielding wire is accidentally touched while the motor is running, electric shock will still occur, so this shielding wire also needs to be connected to the driver's housing. Another type of leakage is caused by damage to the insulation of the phase wire.
A bending machine in Chuzhou, Anhui Province, presented a similar problem: customers reported electric shocks upon touching the control panel immediately after powering on and starting the machine. This electric shock was essentially caused by a short circuit to ground in a phase of the servo motor. After disassembling the servo motor, it was discovered that the bearing on the side closest to the device was damaged, and the retaining ring was broken into several pieces. These broken pieces scraped off the insulating varnish of the servo motor's stator windings, leading to leakage. Further inspection revealed severe wear on the keyway on the servo motor's shaft. Checking the reducer of the servo motor revealed no output when rotating at a 30-degree angle, indicating a reducer malfunction that caused the servo motor damage and the electric shock. Given this issue, it's advisable to install a residual current device (RCD) in the bending machine's electrical control system to prevent safety problems. Furthermore, the cause of electric shock is a crucial question for those working in electrical fields. Simply put, electric shock occurs when current flows through the human body; when the current reaches 10mA, the person will experience a shock.
Most electric shocks occur when a person is standing on the ground and touches a live conductor or a phase voltage source. Sometimes, it's necessary to touch a live conductor. In such cases, it's best to use the back of your right hand. Using the right hand is because the heart is generally located on the left, which helps prevent the current from passing through the heart. Using the back of the hand makes it easier to quickly remove oneself from the live conductor. Another minor question arises: when a person touches a live conductor, they will get an electric shock, and the current flows from the fingers to the feet and then to the ground. But why do only the fingers feel the pain, while other parts of the body don't? This is because fingers are thinner, and the current passing through a unit area is larger, hence the sensation. In contrast, the cross-sectional area of the body is much larger than that of the fingers, and the current flowing through a unit area is smaller, so the body doesn't feel the shock.
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