DVR systems DVRxx04HF-A Series - Manual (Page 176)

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Appendix G Earthing
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 220V 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.
z
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.
z 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 3000V to 50000V, which can adversely affect the electronic devices that use
the same distribution box.
To protect the device, you need to evaluate its environment, the lighting 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 Committee (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,
z
The lightning protection device can be divided into three types:
Power lightning arrester: There are 220V single-phrase lightning arrester and 380V three-
phrase lightening 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.
z 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