Dahua Technology DH-XVR42 AN-I Series, User Manual

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User’s Manual
371
Earthing
Appendix 7.1 What is the Surge
Surge is a short current or voltage change during a very short time. In the circuit, it lasts for
microsecond. In a 220 V circuit, the 5KV or 10KV voltage change during a very short time (about
microseconds) can be called a surge. The surge comes from two ways: external surge and internal
surge.

The external surge: The external surge mainly comes from the thunder lightning. Or it comes from
the voltage change during the on/off operation in the electric power cable.

The internal surge: The research finds 88% of the surge from the low voltage comes from the
internal of the building such as the air conditioning, elevator, electric welding, air compressor,
water pump, power button, duplicating machine and other device of inductive load.
The lightning surge is far above the load level the PC or the micro devices can support. In most cases,
the surge can result in electric device chip damage, PC error code, accelerating the part aging, data
loss and etc. Even when a small 20 horsepower inductive engine boots up or stops, the surge can reach
3000 V to 5000 V, which can adversely affect the electronic devices that use the same distribution box.
To protect the device, you need to evaluate its environment, the lightning affection degree objectively.
Because surge has close relationship with the voltage amplitude, frequency, network structure, device
voltage-resistance, protection level, ground and etc. The thunder proof work shall be a systematic
project, emphasizing the all-round protection (including building, transmission cable, device, ground
and etc.). There shall be comprehensive management and the measures shall be scientific, reliable,
practical and economic. Considering the high voltage during the inductive thundering, the
International Electrotechnical Commission (IEC) standard on the energy absorbing step by step theory
and magnitude classification in the protection zone, you need to prepare multiple precaution levels.
You can use the lightning rod, lightning strap or the lightning net to reduce the damage to the building,
personal injury or the property.
The lightning protection device can be divided into three types:

Power lightning arrester: There are 220 V single-phrase lightning arrester and 380 V three-phrase
lightning arrester (mainly in parallel connection, sometimes use series connection) You can
parallel connect the power lightning arrester in the electric cable to reduce the short-time voltage
change and release the surge current. From the BUS to the device, there are usually three levels
so that system can reduce the voltage and release the current step by step to remove the
thunderstorm energy and guarantee the device safety. You can select the replaceable module
type, the terminal connection type and portable socket according to your requirement.

Signal lightning arrester: This device is mainly used in the PC network, communication system.
The connection type is serial connection. Once you connected the signal lightning arrestor with
the signal port, it can cut the channel of the thunderstorm to the device, and on the other hand,
it can discharge the current to the ground to guarantee the device proper work. The signal
lightning arrester has many specifications, and widely used in many devices such as telephone,
network, analog communication, digital communication, cable TV and satellite antenna. For all
the input port, especially those from the outdoor, you need to install the signal lightning arrester.