45
Appendix VI 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)
Distance
(ft / m)
Power (W)
Diameter (mm)
