Abstract: We all know that the billboards on the bus sations are full of various wires. Due to the wind and sun, and lack of maintenance, some of the lights do not turn on directly, and some of them are leaking. The power supply lines are always used outdoors for a long time, the operating environment is harsh, and the safety level and protection level standards adopted in the design or construction are not so high, the power supply circuit are ofen too aging, become invalid and leakage. For an island system such as a single bus station or a bus guard post, if the power supply system adopts a distribution box for centralized power supply, it is appropriate to install a residual current monitor in the main control box to monitor the leakage of each circuit in real time and distribution circuit, configuration 30mA relay of residual current with no delay in action current and or 30mA leakage protect switch for protection.

Keywords: landscape fountain; fountain; personal electric shock; ground fault; electric shock protection

0  Industry background

    On the afternoon of May 26, 2019, two girls were found lying in the stagnant water on the scenic trail in the Hushan Dijingwan Community, Yuhang Street, Hangzhou, and never woke up again. According to reports from Yuhang Street and news medias, it’s preliminarily judged that this tragedy may be caused by an electric shock.

    This is not the first time that happened. During the recent years, there had many cases that children were electrocuted in the community, especially near the fountain pool. On the afternoon of August 9, 2013, in Kudi Pet Park in Beijing Chaoyang Park,two pet dogs died because of the electric shock in the fountain where dogs swim,not only that the owner of the dogs also being electrocuted when he went into the water to save his pet dog,and died at last. Every time when these things appears, it marks a deep hole in the conscience of society.

    For some fountains or landscape fountains that are not allowed to enter during using,people are safer, but there are still some fountains and landscape fountains that peple can enter, It has greater risk of electric shock when the crowd enters, the impedance of the human body decreases, and the impedance of the contact path drops to a small value.,and usually,there are especially more children in these places.

    In order to protect lives of people,in Article 4.6.5: of 《General specification for building electrical and intelligent》(draft for approval),it clearly defined that:

    When a residual current device (RCD) is used as an additional protective measure for electric shock protection, the following requirements shall be met:

    1. The rated residual current action value should not be greater than 30mA;

    2. The following circuits that under 32A should be equipped with a residual current device (RCD);

        2.1 Circuit of electric supply socket for general personnel;

        2.2 Mobile electrical equipment indoor;

        2.3 Electrical equipment outdoor that people can touch;

    3 Residual current device (RCD) should be used as one of the protection measures;

    4 When using residual current device (RCD), a protective earthing conductor (PE) should be installed.

    The standard of residual current operated relay in GB/T22387-2016 clearly stipulate,

    Residual current operated relay should be equipped as a means of protection on equipments installed in water,such as electrical equipments in swimming pools, fountains, bathrooms, and baths.

2 Product introduction

    The ASJ series residual current operated relays and multi-circuit residual current monitors can be made up into a residual current device with low-voltage circuit breaker and low-voltage contactor,that mainly suitable for AC 50Hz, rated voltage 400V and below TT and TN system power distribution lines.It can be used to protect electrical circuits from ground faults,prevent the damage of equipment and electrical fire accidents by fault of currents,and it can also provide indirect contact protection against personal electric shock hazards.

ASJ10/20 series residual current operated relays

ASJ60 series residual current monitor

3 Function introduction

    The ASJ10/20 series residual current operated relays have the following functions: A-type or AC-type residual current measurement, while the alarm of the residual current over-limit instruct, rated residual operating current can be set,limit non-driving time can be set, two sets of relay outputs, with on-site, remote "test" and "reset" functions;

The ASJ60 series residual current monitor has the following functions: 16 residual current monitoring, 1 warning relay output, 16 alarm relay output, 2 DI input, automatic reclosing function, remote communication function, remote opening and closing function.

4 Technical index

ASJ10/20 series residual current action relay technical indicators

5 Selection instructions

    We should pay attention to the type of low-voltage system when the residual current operated relay is use.

System form	System wiring	Directions
System  of TT		ASJ is recommended,because when the accident of single-phase grounding happens, the fault current is very small and it is difficult to estimate,and a dangerous voltage will occur on the outer covering when the operating current of the switch is not reached.
System  of TN-S		ASJ can be used,the fault can be cut off quickly and sensitively,so that safety and reliability can be improved.At this time,the PE wire can’t pass through the transformer,and the P wire must pass through the transformer,and it can’t be grounded repeatedly.

    Other remaining wiring types need to be transformed into the two types above to prevent misoperation or failure of the outlet.

    The selection of residual current transformer should be based on the rated current of the main circuit as a reference.

    Actually, as shown in the figure, the transformer is installed on the main circuit or branch,and judge whether to drive the circuit breaker by measuring the residual current.

6 Conclusion

    For electric shock accidents of fountains or landscape fountains, these problems are management problem largely. If you work hard on fine management, it can indeed be solved. If the landscape fountain cannot be touched by ordinary people, there will be no electric shock accidents. Ordinary fountains can also be equipped with fences. If there is no fence or you can enter the fountain area at any time, there is still a safety hazard.

    For such problems, it can be controlled by technology . 24 volts or even 12 volts of safety electricity must be used in landscape fountains, landscape lights, underground lights, and light strips in public areas. All lights are disconnected during the day and only open at night, using relay control. At the same time, it is mandatory to install a leakage protection device to cut off the power automaticly in case of emergency.

    At the same time, supervision should be done well. On one hand, doing a good job of normalized supervision,and on the other hand, relevant units should conduct inspections from time to time to prevent line aging and damage.

References

    [1] Acrel Enterprise Microgrid Design and Application Manual. 2019.11 Edition

About the author:

    Xiang Teng, male, currently works at Acrel Co., Ltd., and his main research direction is in the field of low-voltage power distribution and safe use of electricity. Mobile: 18702113830, Email: 381392761@qq.com