Any electrical equipment needs protection from disruption in the operation of the electrical network: voltage surges, overloads and other negative influences. For these purposes, a huge number of automatic protective devices and equipment have been created. Some of them are technically complex and expensive, while others are affordable and simple. One such simple device is a surge protector.
Content
What is a surge protector and what does it protect against?
Network filter - this is an electrical device designed to connect various household equipment and is able to protect it from the negative impact power surges.
Electric networks of any purpose are not ideal in terms of the quality of the transmitted energy.Uneven load on the electrical network, accidents and the influence of various factors can cause voltage drops in the network, which in turn can lead to malfunction or failure of household appliances.
Surge protectors are used to protect home devices from surges above the nominal voltage. Also, such devices are used to reduce the influence of radio and electromagnetic on the operation of household appliances (for example, this is noticeable with acoustic and television, video equipment).
Operating principle
The principle of operation of network filters is quite simple and consists in filtering interference and limiting voltage. 
Protection against radio and electromagnetic noise is carried out using inductive elements (toroidal inductors) and capacitors, which help to reduce the high frequency components to the normal frequency of 50 Hz. This is due to the fact that the resistance of an inductor increases with increasing frequency, and that of a capacitor decreases.
The voltage limitation is carried out using a metal oxide varistor, which diverts additional voltage, forming a connection between the phase and the ground conductor. If the voltage is below a certain value (equal to or less than nominal), then the varistor creates a significant resistance, and if the voltage exceeds the nominal value, then this electronic component, on the contrary, reduces the resistance. The main overvoltage protection is in the form of a fuse and/or a bimetal fuse.
What it consists of and how it is arranged
Externally, the surge protector looks like a standard extension cable with a cable of various lengths and several sockets for connecting household appliances. But the internal circuit is fundamentally different from ordinary household extension cords. Inside the surge protector, in addition to the pads, there is a protective microcircuit and a fuse. Also, the surge protector has a power button.
Expensive and well-made line filters have a capacitor bank and several chokes and additional protection systems, but inexpensive devices (often made in China) are devoid of such components, but still contain varistor.
Varieties of network filters
Surge protectors, like any household appliances, are produced in huge quantities and have different characteristics and appearance. There are basic, advanced and professional options.
Basic surge protectors are affordable devices and are often used to connect unpretentious home appliances. They have a very simple design, protect against voltage surges, but may not protect against interference.
Advanced devices are used for any household appliances. They are made more complicated than the basic options, they are of better quality and more reliable devices.
Professional filters are used for highly sensitive and expensive equipment. Such devices are made very high quality, their circuit is complex and reliable. 
There are also various additions to the standard network filter device, for example, the ability to control the switching on and off of devices remotely (via Wi-Fi or Bluetooth interfaces). Also, surge protectors can have any cable length and the number of connection points in the socket group from 1 to 10 pieces.
How to choose a surge protector for household appliances
The choice of a surge protector largely depends on the budget and equipment that this filter must protect. You need to understand that the more sensitive the household appliance to voltage drops, the more difficult the device and the more expensive it is to purchase a surge protector. It is also important to consider how many electrical appliances this filter will be designed for: this affects the size of the outlet group and the permissible load.
Some surge protectors may be directly indicated for their purpose: for computers, acoustic devices, washing machines or other equipment.
Additional functions of network filters are: lightning protection, the presence of overheating sensors, USB ports, indication, as well as the possibility of "smart" control.
It is also best to purchase devices from trusted well-known manufacturers, as they have extensive experience in the production of such devices, as well as many service centers, certification and warranty.
Also, do not forget in which country you live in order to buy or order a surge protector in the online store with exactly the type of sockets that are used in your territory.
What is the difference between a surge protector and an extension cord
At first glance, it may seem that the power strip and surge protector are exactly the same devices. Often people confuse them, counting on protection, which is not in the extension cord. The extension cord is designed to connect devices and devices remote from stationary sockets, while not providing their protection.Surge protectors perform all the functions of an extension cord, but they also have a special microcircuit that allows you to protect household equipment.
For very sensitive devices, surge protectors may also not be suitable, as they turn off the power abruptly (the fuse snaps off or melts). But Surge Protectors can smoothly turn off or equalize the voltage without shutting down, but these are more complex and expensive devices that allow protection at several levels.
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