断路器
低压断路器又称为自动空气开关，可手动开关，又能用来分配电能、不频繁启动异步电机，对电源线、电机等实行保护，当它们发生严重过载、短路或欠压等故障时能自动切断电路。
断路器文字符号为：qf
断路器图形符号为：
接触器
接触器辅助常开触点，后面那个应为常闭触点
接触器由电磁机构和触头系统两部分组成，接触器最常见线圈电压有ac220v、ac380v和dc220v几种。
接触器电磁机构由线圈、动铁心(衔铁)和静铁心组成;接触器触头系统由主触头和辅助触头两部分组成，主触头用于通断主电路，辅助触头用于控制电路中。
接触器文字符号为：km
接触器图形符号为：
热继电器
热继电器是利用电流通过元件所产生的热效应原理而反时限动作的继电器。
热继电器文字符号：fr
热继电器图形符号：
中间继电器
中间继电器的原理是将一个输入信号变成多个输出信号或将信号放大(即增大继电器触头容量)的继电器。其实质是电压继电器，但它的触头较多(可多达8对)、触头容量可达5-10a、动作灵敏。
当其他电器的触头对数不够时，可借助中间继电器来扩展他们的触头对数，也有通过中间继电器实现触电通电容量的扩展。
中间继电器文字符号：ka
中间继电器图形符号：
button
in practical applications, buttons are usually selected based on the required number of contacts, usage scenarios, and colors. the commonly used la18, la19, la20 and other series buttons are suitable for control circuits with ac500v, dc440v, rated current of 5a, and control power of ac300w, dc70w.
button text symbol: sb
button graphic symbol:
button color requirements:
(1) "stop" buttons and "emergency stop" buttons must be red. pressing the red button must stop the operation of the equipment or cut off the power.
(2) the color of the "start" button is green.
(3) buttons for alternating actions between "start" and "stop" must be black, white, or gray, and cannot use red or green buttons.
(4) "jog" buttons must be black.
(5) the "reset" button (if there is a reset button for a protective relay) must be blue. if the reset button also has a stop function, it must be red.
indicator lamps
the functions of indicator lamps are:
(1) indicate the running or stop status of the equipment.
(2) monitor whether the power supply of control devices is normal.
(3) use a red light to monitor whether the tripping circuit is normal, and use a green light to monitor whether the closing circuit is normal.
toggle switch
a universal toggle switch consists of operating mechanism, panel, handle, and several contact bases.
the text symbol for a universal toggle switch is:sa
the graphic symbol for a universal toggle switch is:
the on/off states of each contact at different positions of the handle are represented by black dots. a black dot indicates closed contact, while no black dot represents open contact.
limit switch
a limit switch, also known as a position switch, is a commonly used low-current main command device. it uses the collision of moving parts of production machinery to make the contact action and achieve the purpose of circuit connection or disconnection control.
行程开关文字符号为：
sq
行程开关图形符号为：
电机接触器、控制方式示意图
