Control Valve
Application
Guide
Nelson Irrigation Corp. 848 Airport Rd. Walla Walla, WA 99362-2271 USA Tel: 509.525.7660 Fax: 509.525.7907 E-mail: [email protected] Web site: www.nelsonirrigation.com
In the event that the controller has a higher voltage output than 24 VAC, longer wire runs can be made. See Table 5 for the multiplier
which can be used in conjunction with Table 4 to give the maximum length of run for controllers with higher voltage output.
EXAMPLE: If the controller voltage output is 27 VAC, the lengths in Table 4 can all be increased by
a multiplier factor of 1.8.
In the event that there are two valves which must turn on per station; and they are both at approximately the same location,
a multiplier factor of 0.46 applied to lengths shown in Table 4 will find the maximum length of run for the wires. The controller
current output must be at least 1 amp for both valves per station to work.
Multiplier Factors for Various Controller output Voltages and Optional Solenoids:
6.2.2 WIRE SIZING WITH FORMULAS
When the wire run distances exceed those given in the tables or for more complicated systems, the wire sizing must be
calculated using formulas.
Data needed to size wire is:
(1) the maximum current draw of the valve in amps (Iinrush).
(2) distance in feet (one way) to the valve from the controller (L).
(3) maximum expected line pressure on the valve solenoid.
(4) the allowable voltage loss (AVL) in the wire without affecting function of the solenoid .
(5) controller output voltage (obtained from manufacturer)
The formula for resistance is:
Rw = AVL * 1000
Eq. 1
L * 2 * Iinrush
in which Rw is resistance of the wire (ohms). The "2" in the formula is used to double the length to include the common and
power wire of equal length.
EXAMPLE FOR SELECTING WIRE SIZE WITH FORMULAS (ONE VALVE):
STEP 1. Find AVL by subtracting the valve operating voltage (20.4 VAC) from the controller output voltage.
24 VAC - 20.4 VAC = 3.6 VAC.
STEP 2. Determine the inrush current from Table 6. At 100 PSI line pressure it is 0.278 amps.
STEP 3. As an example for 3000 feet wire run calculate Rw =
(3.6 * 1000) = 2.16
3000 * 2 * .278
STEP 4. The wire resistance must not exceed 2.16 ohms per 1000 feet. Select the proper wire size from Table 7.
Since #14 has resistance of 2.63 and this exceeds the 2.16 ohms allowable, select the #12 wire size which is only 1.65.
ELECTRICAL APPLICATIONS
Table 5
Table 6
Table 7
Controller
Output
Voltage
28
27
26
25
24
23
22
24
VAC
(low
power)
2.1
1.8
1.5
1.28
1.0
0.7
0.44
24
VDC
2.1
1.8
1.5
1.28
1.0
0.7
0.44
Maximum
Line Pressure
50 PSI
100 PSI
150 PSI
24V AC & DC
Iinrush
current
.248 amps
.278 amps
.312 amps
Wire
Size
AWG
18
16
14
12
10
8
6
Specific
Resistance*
Ohms/1000ft
6.64
4.18
2.63
1.65
1.03
0.64
0.41 *85° F
15
