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APPENDIX I 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.
Diameter (mm)
Distance (ft / m)
Power (W)
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
0.8000
1.000
283 (86)
451 (137)
141 (42)
225 (68)
94 (28)
150 (45)
70 (21)
112 (34)
56 (17)
90 (27)
47 (14)
75 (22)
40 (12)
64 (19)
35 (10)
56 (17)
31 (9)
50 (15)
28 (8)
45 (13)
25 (7)
41 (12)
23 (7)
37 (11)
21 (6)
34 (10)
20 (6)
32 (9)
18 (5)
30 (9)
17 (5)
28 (8)
16 (4)
26 (7)
15 (4)
25 (7)
14 (4)
23 (7)
14 (4)
22 (6)
10
1.250
2.000
716 (218)
1811 (551)
358 (109)
905 (275)
238 (72)
603 (183)
179 (54)
452 (137)
143 (43)
362 (110)
119 (36)
301 (91)
102 (31)
258 (78)
89 (27)
226 (68)
79 (24)
201 (61)
71 (21)
181 (55)
65 (19)
164 (49)
59 (17)
150 (45)
55 (16)
139 (42)
51 (15)
129 (39)
47 (14)
120 (36)
44 (13)
113 (34)
42 (12)
106 (32)
39 (11)
100 (30)
37 (11)
95 (28)
35 (10)
90 (27)
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