Switches are very familiar to us as electrical practitioners. But are you really using the right switches and options?
Tn-s is the power supply mode for the site construction. There are three levels of power distribution and two levels of protection. One machine, one gate, one leak and one box are required. PE line is prohibited to install switches, it is forbidden to connect multiple electrical equipment above a switch. And the space between the primary box, the secondary box and the tertiary box is 30 meters.
When we choose the switch of the three-stage distribution cabinet, we should pay attention to such a problem, that is, in the setting of the rated leakage protection of the two-stage leakage current and rated leakage action time should be reasonable, to avoid the phenomenon of skipping.
Normally when we install the tertiary distribution in selection of the three is to set up the leakage protector in the distribution box, the total distribution of leakage rating of the leakage protector action rated leakage current is less than or equal to 150 ma action time is not greater than 0.2 seconds, the secondary rated leakage current action is not more than 75 ma, rated leakage action time not greater than 0.1 seconds, The leakage operating current in the switch box shall not exceed 30 ma, and the rated operating time shall not exceed 0.1 seconds. In humid places, the leakage action current in well-conductive places is not more than 15 ma, and the time is not more than 0.1 seconds.
When dealing with problems why must we force the use of transparent circuit breakers and leakage circuit breakers. Later, I consulted relevant information and learned that we must leave obvious disconnect points on the line when we receive electricity at the scene, so as to avoid the situation that the line is not disconnected from live operation. Using transparent circuit breakers and leakage protectors can intuitively check whether the line or switch is disconnected, so as to avoid the risk of electric shock.
There is also the use of a 3P circuit breaker why also in its lower end to install a 3P+N leakage circuit breaker. The role of the circuit breaker is to be on and off and overload, short circuit protection. Leakage circuit breaker has a leakage protection function in addition to the overload short circuit on and off. Because of more mud and water on the site, the construction environment is complex and the installation of leakage protector has become an essential safety measure.