Technical Data Wire Sizing
Method of Wire Sizing for
Electrical Components of an
Automatic Irrigation System
Minimum Operating Voltages at
Various Static Pressures (standard
24 V ac solenoid)
The accompanying charts are useful for
quick and easy selection of wire sizes for
valves with standard and optional solenoids. Optional Low-voltage Solenoids
Multiplier Factor for Various
Controller Output Voltages and
Chart #3 is set up to provide maximum wire
runs given a standard 24 V ac valve with a
minimum operating voltage of 20 volts and
a controller output of 24 V ac Chart #4 is a
multiplier factor for determining maximum
wire runs for other controller output
Chart4
Chart1
Data Needed
Controller
Output
Voltage
24‑Volt Solenoids
•
•
•
Maximum current draw of the electrical
unit (valve or controller) in amperes (I)
Distance in feet (one way) to the
electrical unit (F)
The allowable voltage drop in the
wire without affecting functions of the
electrical unit (Vd)
Minimum Solenoid
Operating Voltage
24 V ac
24 V ac‑D 24 VDC
Under Various Line Pressure
28
27
26
25
24
23
22
2.00
1.75
1.50
1.25
1.00
.75
5.77
5.05
4.33
3.61
2.88
2.16
1.44
5.45
4.77
4.09
3.41
2.73
2.05
1.36
Voltage
Voltage
Line Pressure
(Internal Bleed
(External Bleed
voltages and optional solenoids.
Configurations)
Configurations)
Example:Determinemaximumwirerunto
avalvewithmodel24Vac‑Dsolenoidand
controlleroutputvoltageof26voltsand
#14controlandgroundwire.
200
psi (13,8 Bar)
21.1
20.2
19.1
18.2
17.1
16.1
16.0
Steps
175 psi (12,1 Bar)
1
.Calculate the maximum allowable
wire resistance per 1000 feet with the
following formula:
150
125
100
75
psi (10,3 Bar)
psi (8,6 Bar)
psi (6,9 Bar)
psi (5,2 Bar)
20.0
19.1
18.2
17.3
16.4
From Chart #3 we find a length of 2590 ft.
with #14 ground and control wire. From
Chart #4 the multiplier factor at 26 V ac
controller output with a model 24 V ac‑D
solenoid is 4.33. Therefore, the maximum
wire distance to the valve is: 4.33 x 2590
feet = 11,215 feet.
.50
Chart5
R = *500 x Vd
F x I
Controller
Output
Voltage
12‑Volt Solenoids
50 psi (3,4 Bar)
12
V.a.c.
12 V ac‑D 12 VDC
where R = allowable wire resistance per
1000 feet.
16
15
14
13
12
11
.58
.50
.41
.33
.25
.17
2.50
2.08
1.67
1.25
.83
1.96
1.63
1.30
.98
Chart2
2.
Select the wire size from Chart #2 which
has a resistance less than that calculated
in the above formula.
Copper Wire Resistance of
Various Sizes
* This assumes control wire and ground wire are the same size.
Sizes
AWG
Resistance at 20°C
Ohms per 1000 ft.
Example: A valve with a minimum
operating voltage of 20 volts and inrush
current of .30 amps is to be located
.65
4
.25
.40
.42
.33
6
2680
ft. from a controller. The controller
Chart3
8
.64
minimum output voltage is 24 V ac.
Maximum One-way Distance (ft.) Between Controller and Valve
(standard 24 VAC solenoid) †
10
12
14
16
18
1.02
1.62
2.57
4.10
6.51
The allowable voltage drop
(Vd) = 24 – 20 = 4 volts
Valve Wire Sizing
Ground Wire
Control Wire
The distance to valve (F) = 2680 ft.
The current draw (I) = .3 amps
18
16
14
12
10
8
6
18
16
14
12
10
8
1020
1260
1470
1640
1770
1860
1930
1260
1630
2000
2330
2610
2810
2960
1470
2000
2590
3180
3710
4150
4480
1640
2330
3180
4120
5050
5900
6590
1770
2610
3710
5050
6540
8030
9380
1860
2810
4150
5900
8030
10400
12770
1930
2960
4480
6590
9380
12770
16540
R = 500 x 4 = 2.49 ohm/1000 ft.
2680
x .3
From Chart #2 we find that #14 AWG wire
has slightly too much resistance. Therefore,
choose #12 AWG copper wire.
6
†SolenoidModel:24VacPressure:150psiVoltageDrop:4VMin.Op.Voltage:20VAmperage(peak):0.3A
90
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