Dc Power Connection Wire Gauge Calculations For Hpd; Table 34: Dc Power Connection Wire Gauge Maximum Distances For An Iv And D Site; Table 35: Power Connection Wire Gauge Maximum Distances For Hpd - Motorola ASTRO 25 GTR 8000 Manual

MN003286A01-E
Chapter 3: GTR 8000 Base Radio Installation
• Length (m/ft) = V/I/R
where:
• V = voltage drop in one leg of the loop (max = 0.5 V)
• I = current the base radio draws during DC operation
• R = resistance of the wire being considered (in Ohms per ft)
For common wire sizes, the maximum distances shown in
Gauge Maximum Distances for an IV and D Site on page 102

Table 34: DC Power Connection Wire Gauge Maximum Distances for an IV and D Site

AWG Resistance (ohm/304.8 meter/ 1000 ft)
2 0.1563
3 0.1970
4 0.2485
5 0.3133
6 0.3951
3.4.4.3

DC Power Connection Wire Gauge Calculations for HPD

Since the power supply disconnects itself from the DC input when it senses that DC voltage has
dropped to 42 VDC, it is important to minimize the voltage drop in the DC power supply loop (the total
length of the 48 VDC hot wire and the DC return wire) to no more than 1 V total. Minimizing the voltage
drop ensures that the maximum energy is removed from the battery before disconnecting the power
supply from the DC input line.
A base radio transmitting at 50 W draws up to 7.4 A current when operating from a 54 V source
(nominal 48 VDC system). As voltage decreases (due to the standby battery discharging) the current
increases proportionally (since the base radio appears to be a constant power load). At the low voltage
disconnect point (42 V for a nominal 48 VDC system), the current will be up to 9.5 A. Use of smaller
gauge wire would reduce this length depending on the resistance of the wire. To determine the
maximum length of wire for wire other than 2 AWG, the following relationship can be used:
• Length (ft) = V/I/R
where:
• V = voltage drop in one leg of the loop (max = 0.5 V)
• I = current drawn by the base radio during DC operation (9.5A)
• R = resistance of the wire being considered (in Ohms per ft)
For common wire sizes, the maximum distances shown in
Maximum Distances for HPD on page 102

Table 35: Power Connection Wire Gauge Maximum Distances for HPD

AWG Resistance (ohm/1000 ft)
2
3
4
102
apply.
0.1563
0.1970
0.2485
Table 34: DC Power Connection Wire
apply.
Maximum Distance (for 13A)
75 m (245 ft)
60 m (195 ft)
47 m (155 ft)
37 m (120 ft)
30 m (95 ft)
Table 35: Power Connection Wire Gauge
Maximum Distance
102m (335 ft)
81m (265 ft)
64m (210 ft)