AGI Security SYS-HC0451 HDCVI DVR User Manual - Manual (Page 279)

HDCVI Standalone DVR User’s Manual
270
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.
 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 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,
 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.