A few days ago, a customer purchased the HD13 series knife switch, and the model was confirmed at the beginning. However, it was found in the final determination with the engineer that the rated current of the model was smaller than that in the design. Fortunately, even if the product was found and replaced, Reduced a lot of unnecessary trouble. After this incident, and considering that some people asked us about some models and choices of the knife switch in the mail, I have summarized it a bit and referred to the comments on the Internet. Here are some suggestions to help everyone understand how to understand Select the knife switch .
Knife switch is an important product of low-voltage electrical appliances. Its main function is to isolate the power supply to ensure the safety of the circuit during maintenance, and to break the load, such as infrequently switching off small-capacity low-voltage circuits. At the same time, the knife switch is easy to operate because of its simple structure and convenient operation. Especially, the breaking and closing state is obvious and easy to observe, which can ensure the safety and the correctness of judgment.
First of all, the classification of the lower knife switch is discussed in general. In terms of the number of stages, mainstream products include single pole knife switches, bipolar knife switches and three pole knife switches. From the model number, the commonly used knife switches include HD single-throwing switch, HS double-throwing switch, HR fuse-type knife switch (also known as knife-melt switch), and HK-type knife switch.
Next, I will talk about how to choose the knife switch. I personally think that I mainly consider two aspects:
1. structure type
The structural form is determined on the basis of the action of the knife switch in the line or the mounting position in the complete power distribution unit. For example, when only for isolating the power supply, you only need to select the product without the arc extinguishing cover; if it is used to break the load, you should choose the product with the arc extinguishing cover and the lever operated; for example, the central handle type The knife switch cannot cut off the load current. Other forms can cut off a certain load current, but the knife switch with the arc extinguishing cover must be selected. In addition, it should be based on whether it is a frontal operation or a side operation. It is a direct operation or a lever drive. It is a front-panel wiring or a post-board wiring to select a structural form (all cases should be explained in design and price asking). I use the HD and HS series knife switches of Shanghai People's Electric Switch Factory to explain:
HD11, HS11 is mainly used for magnetic stations, can not cut off the circuit with load, only for isolation current;
HD12, HS12 is mainly used in the front side of the front to operate the switchgear in the maintenance, in which the knife switch of the arc extinguishing device can cut off the load circuit below the rated current;
HD13, HS13 is mainly used in the switch cabinet with front operation and rear maintenance. The knife switch with arc extinguishing device can cut off the load circuit below the rated current;
The HD14 can be used in a power Distribution Box where a knife switch with an arc extinguishing device can be operated with a load.
2. Rated current
The rated current of the knife switch should generally be no less than the sum of the rated current of each load in the circuit being disconnected. If the load is a motor, it must be considered whether the maximum short-circuit peak current that may appear in the circuit is below the motor stability peak current corresponding to the rated current level (Note 1). If there is more than one, you should choose a knife switch with a higher rated current!
Note 1: The so-called electric stability peak current means that when a short-circuit accident occurs, if the knife switch can pass a certain maximum short-circuit current, it will not be deformed, damaged or automatically touched by the action of the huge electric power generated by it. The phenomenon that pops up. Then the short-circuit peak current is the electric stability peak current of the knife switch
These are some of the most important aspects of the choice of knife switch, the number of stages, model, structure and current rating. I hope that these will help you choose the right knife switch. If there is something wrong or unclear, please communicate with us.
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