Repeated grounding means that in a system where the neutral point is directly grounded, a metal wire is used to connect the grounding device at one or more places on the neutral main line. In the low-voltage three-phase four-wire neutral point directly grounded line, the construction unit should ground the neutral main line and the terminal of the branch line of the distribution line during installation, and ground the zero main line every 1 km. For power distribution lines that are more than 50 meters away from the grounding point, the neutral line connected to the user should still be grounded repeatedly, and the repeated grounding resistance should not be greater than 10 ohms. Repeated grounding of the neutral wire can shorten the duration of the fault, reduce the voltage drop loss on the neutral wire, and reduce the risk of reverse connection of the phase and neutral wires.
After the protection of the neutral line breaks, when the insulation of the electrical equipment is damaged or the phase line touches the shell, repeated grounding of the neutral line can also reduce the voltage to the ground of the faulty electrical equipment and reduce the risk of electric shock accidents. Therefore, repeated grounding of the neutral line plays a very important role in the power supply network, but this role is often overlooked.
In the residential power supply line, the repeated grounding of A and B is set by the power supply bureau.
The circuit breaker in the main distribution box is a single air switch.
In the low-voltage three-phase four-wire system using protective zero connection, in order to strengthen the safety of zero connection, one or more places of the zero line are connected to the earth again through a grounding device, which is called repeated grounding, as shown in the figure.
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