61
APPENDIX III CABLE DIAMETER CALCULATION AND
LIGHTNING & SURGE PROTECTION
Relation between 24VAC Cable Diameter and Transmission Distance
In general, the maximum allowable voltage loss rate is 10% for AC-powered devices. The table below
shows the relationship between transmission power and maximum transmission distance under a certain
specified cable diameter, on condition that the 24VAC voltage loss rate is below 10%. According to the
table, if a device rated at 50W is installed 17-meter away from the transformer, the minimum cable
diameter shall be 0.8000mm. A lower diameter value tends to cause voltage loss and even system
instability.
0.8000
1.000
1.250
2.000
10
283 (86)
451 (137)
716 (218)
1811 (551)
20
141 (42)
225 (68)
358 (109)
905 (275)
30 94
(28)
150 (45)
238 (72)
603 (183)
40
70 (21)
112 (34)
179 (54)
452 (137)
50
56 (17)
90 (27)
143 (43)
362 (110)
60
47 (14)
75 (22)
119 (36)
301 (91)
70
40 (12)
64 (19)
102 (31)
258 (78)
80
35 (10)
56 (17)
89 (27)
226 (68)
90
31 (9)
50 (15)
79 (24)
201 (61)
100
28 (8)
45 (13)
71 (21)
181 (55)
110
25 (7)
41 (12)
65 (19)
164 (49)
120
23 (7)
37 (11)
59 (17)
150 (45)
130
21 (6)
34 (10)
55 (16)
139 (42)
140
20 (6)
32 (9)
51 (15)
129 (39)
150
18 (5)
30 (9)
47 (14)
120 (36)
160
17 (5)
28 (8)
44 (13)
113 (34)
170
16 (4)
26 (7)
42 (12)
106 (32)
180
15 (4)
25 (7)
39 (11)
100 (30)
190
14 (4)
23 (7)
37 (11)
95 (28)
200
14 (4)
22 (6)
35 (10)
90 (27)
Power (W)
Diameter (mm)
Distance (ft / m)
62
Lightning & Surge Protection
The product adopts multi-level anti-lightning and anti-surge technology integrated with gas discharge tube,
power resistor and TVS tube. The powerful lightning and surge protection barrier effectively avoids
product damage caused by various pulse signals with power below 4kV, including instantaneous lightning,
surge and static. However, for complicated outdoor environment, refer to instruction below for lightning
and surge protection:
The product features with dedicated earth wire, which must be firmly grounded. As for surveillance
sites beyond the effective protection scope, it’s necessary to erect independent lightening rods to
protect the security devices. It’s recommended to separate the lightning rod from the mounting pole,
placing the rod on an independent pole, as shown in the figure below. If the product has to be installed
on the same pole or pedestal for lightning rod, there should be strict insulation between the video cable
BNC terminal, power cable, control cable and the standing pole of the lightning rod.
For suburb and rural areas, it’s recommended to adopt direct burial for the transmission cables.
Overhead wiring is prohibited, because it’s more likely to encounter lightning strike. Use shielded
cables or thread the cables through metal tubes for burial, thus to ensure the electric connection to the
metal tube. In case it’s difficult to thread the cable through the tube all the way, it’s acceptable to use
tube-threaded cables only at both ends of the transmission line, yet the length in burial should be no
less than 15 meters. The cable sheath and the tube should be connected to the lightning -proof
grounding device.
Additional high-power lightning-proof equipment and lightning rods should be installed for strong
thunderstorm or high induced voltage areas (such as high-voltage substation).
The lightning protection and grounding for outdoor devices and wires should be designed in line with
the actual protection requirement, national standards and industrial standards.
The system should perform equipotential grounding by streaming, shielding, clamping and earthing.
The grounding device must meet anti-interference and electric safety requirements. There should be no
short-circuiting or hybrid junction between the device and the strong grid. Make sure there’s a reliable
grounding system, with grounding resistance below 4
Ω
(below 10
Ω
for high soil resistivity regions).
The cross-sectional area of the earthing conductor should be no less than 25mm².
Lightning rod
Front device
for surveillance
system
Separated layout for the lightning
rod and the standing pole
LPZO
B
LPZO
A
Mounting
pole for
front device
30°
30°
Infinova
51 Stouts Lane,
Monmouth Junction, NJ 08852, U.S.A.
Tel: 1-888-685-2002 (USA only)
1-732-355-9100
Fax: 1-732-355-9101
V1.3 1506
