The symbol for a contact break is normally open, and the symbol for a contact closure is normally closed.
This is how normally open and normally closed symbols are identified within an electrical circuit diagram. Give you a picture
Identification method
The general method of looking at an electrical control circuit diagram is to look at the main circuit first, then look at the auxiliary circuits, and use the loops of the auxiliary circuits to study the control program of the main circuit.
1. Look at the steps of the main circuit
The first step: look at the main circuit in the electrical equipment. Electrical equipment refers to the consumption of electrical appliances or electrical equipment, look at the map first of all to see how many electrical appliances, their categories, uses, wiring and some different requirements.
The second step: to figure out what electrical equipment is controlled by what electrical components. There are many ways to control electrical equipment, some are controlled directly by switches, some are controlled by various starters, and some are controlled by contactors.
The third step: to understand the main circuit used in the control appliances and protective appliances. The former refers to other control elements in addition to conventional contactors, such as power switches (transfer switches and air circuit breakers), universal transfer switches. The latter refers to short-circuit protection devices and overload protection devices, such as air circuit breakers in the electromagnetic release and thermal overload release specifications, fuses, thermal relays and overcurrent relays and other components of the use and specifications. Generally speaking, the main circuit for the above content of the analysis, you can analyze the auxiliary circuit.
The fourth step: look at the power supply. To understand the power supply voltage level, is 380V or 220V, from the busbar busbar power supply or distribution screen power supply, or from the generator set connected out.
2. Steps to look at auxiliary circuits
Auxiliary circuits contain control circuits, signal circuits and lighting circuits.
Analyze the control circuit. According to the main circuit of the motor and the control requirements of the executive appliances, one by one to find out the control circuit of the other control links, the control line "into zero", according to the different functions into a number of local control lines to analyze. If the control line is more complex, you can first exclude the lighting, display and other control of the circuit is not close, in order to focus on the analysis.
The first step: look at the power supply. First look at the type of power supply. Is AC or DC. Secondly. To see the auxiliary circuit of the power supply is connected from somewhere, and its voltage level. The power supply is generally from the main circuit of the two phase lines, the voltage is 380 V. There is also a phase line from the main circuit and a zero line from a single-phase 220 V voltage; in addition, it can also be from the special isolation of the power transformer, the voltage of 140, 127, 36, 6.3 V and so on. Auxiliary circuits for DC, DC power supply can be connected from the rectifier, generator set or amplifier, its voltage is generally 24, 12, 6, 4.5, 3V, etc.. The rated voltage of the coil of all electrical components in the auxiliary circuit must be the same as the auxiliary circuit supply voltage. Otherwise, when the voltage is low, the circuit components do not act; when the voltage is high, the electrical component coil will burn out.
The second step: to understand the control circuit used in a variety of relays, contactors, such as the use of a number of special structure of the relay, should also be aware of their principle of action.
Step 3: Study the action of the main circuit in the light of the auxiliary circuit.
After analyzing these contents above and then combined with the requirements in the main circuit, you can analyze the action process of the auxiliary circuit.
Control circuits are always drawn between two horizontal power lines or two vertical power lines in order of action. Therefore, they can also be analyzed from left to right or from top to bottom. For complex auxiliary circuits, the entire auxiliary circuit in the circuit constitutes a large circuit, in which the large circuit is divided into several independent small circuits, each of which controls an appliance or an action. When a small circuit to form a closed loop of current flow, in the circuit of electrical components (contactors or relays) is action, the power equipment connected to the power supply or removal. In auxiliary circuits, the circuit is generally connected by a pushbutton or transfer switch. For the analysis of the control circuit must be readily combined with the action of the main circuit requirements to carry out, only after a comprehensive understanding of the main circuit of the control circuit requirements, in order to truly grasp the principle of the action of the control circuit, can not be viewed in isolation of the principle of the action of the various parts of the action should pay attention to the action of whether or not there is a mutually restraining relationship, such as the motor positive and reverse rotation should be equipped with interlocks and so on.
The fourth step: the study of the interrelationship between electrical components. All electrical components in the circuit are not isolated but interconnected, mutual constraints. This mutual control relationship is sometimes expressed in a circuit, sometimes in several circuits.
Step 5: study other electrical equipment and electrical components. Such as rectifier equipment, lighting, etc.? [1]?
Information reference: electrical circuit diagram identification method Baidu Encyclopedia