CIT - Certified Irrigation Technician Electrical Systems and Wiring 2 — Questions and Answers

Question 1: An irrigation technician measures 28 VAC at the controller's zone terminal but only 18 VAC at the solenoid in the field. What is the most likely cause?

The transformer is failing
Excessive voltage drop due to long wire runs or undersized wire (Correct answer)
The solenoid is drawing too much current
The controller is set to a low-voltage mode

Correct answer: Excessive voltage drop due to long wire runs or undersized wire

A 10 VAC drop between the controller and the field solenoid indicates excessive voltage drop in the field wiring. This is typically caused by wire runs that are too long for the gauge of wire used, poor splice connections, or corroded wire.

Voltage drop in irrigation wiring follows Ohm's law: V = I x R. As wire length increases or wire gauge decreases, resistance increases and more voltage is lost along the wire. Most solenoids require a minimum of 22-24 VAC to reliably operate. The 18 VAC measured at the solenoid may cause intermittent valve operation. Solutions include: upgrading to larger gauge wire, reducing wire run length, improving splice connections (using waterproof connectors), or adding a separate common wire for distant valves. Wire sizing charts based on distance and number of solenoids should always be consulted during design.

Question 2: What is the standard operating voltage for residential and commercial irrigation solenoid valves in North America?

12 VAC
24 VAC (Correct answer)
120 VAC
48 VDC

Correct answer: 24 VAC

Standard irrigation solenoid valves operate on 24 VAC (volts alternating current), supplied by a transformer in the controller that steps down 120 VAC household power to 24 VAC. This low voltage is safe for direct burial wiring.

The 24 VAC standard has been used in irrigation since the 1960s because it provides enough power to reliably operate solenoid valves while being classified as low voltage (Class 2) under the National Electrical Code. This means irrigation field wiring does not require conduit and can be directly buried. The controller contains a transformer that converts 120 VAC (or 240 VAC in some commercial units) to 24 VAC. The solenoid's inrush current is typically 0.3-0.5 amps, dropping to 0.15-0.25 amps holding current after the valve opens.

Question 3: When using a multimeter to test an irrigation solenoid, a reading of OL (overload/infinity) on the ohms scale indicates:

The solenoid is functioning normally
An open circuit — the solenoid coil is broken (Correct answer)
A short circuit in the solenoid
The multimeter battery is dead

Correct answer: An open circuit — the solenoid coil is broken

An OL or infinity reading on the resistance (ohms) scale means there is no electrical path through the solenoid coil — it has an open circuit. The coil wire inside the solenoid has broken, and the solenoid must be replaced.

A healthy irrigation solenoid typically reads 20-60 ohms of resistance. OL (open loop/overload) means infinite resistance — no current can flow through the coil. This occurs when the fine copper wire inside the solenoid coil breaks, often due to a power surge, water intrusion, or manufacturing defect. In contrast, a reading near 0 ohms would indicate a short circuit (insulation breakdown between coil windings). When testing, disconnect the solenoid wires from the field wiring first to ensure you're testing only the solenoid and not the entire circuit including wire resistance.

Question 4: The common wire (often white) in an irrigation system serves what purpose?

It carries the signal to activate specific zones
It provides the return path for electrical current from all solenoids back to the controller (Correct answer)
It connects to the rain sensor only
It powers the controller's display panel

Correct answer: It provides the return path for electrical current from all solenoids back to the controller

The common wire provides the return electrical path from all solenoid valves back to the controller. It is shared by all zones, while each zone has its own individual wire from the controller to its solenoid.

In a standard irrigation wiring configuration, each valve solenoid requires two connections: one from its dedicated zone wire (carrying 24 VAC from the specific zone terminal) and one from the common wire (shared return path to the controller's C or COM terminal). When a zone is activated, current flows from the zone terminal, through the zone wire, through the solenoid coil, and returns via the common wire to the controller. Since the common wire carries current for whichever zone is active, it should be the same gauge as the zone wires. On long runs, installing two common wires in parallel reduces voltage drop.

Question 5: What type of wire splice connection is recommended for direct burial irrigation applications?

Standard wire nuts with electrical tape
Waterproof grease-filled wire connectors (gel-filled) (Correct answer)
Soldered connections left exposed
Push-in connectors designed for indoor use

Correct answer: Waterproof grease-filled wire connectors (gel-filled)

Waterproof grease-filled (gel-filled) wire connectors are the standard for direct burial irrigation splices. The dielectric grease seals out moisture and prevents corrosion, ensuring reliable long-term connections in wet soil conditions.

Gel-filled connectors (such as 3M DBY/DBR or King Safety Connectors) are specifically designed for direct burial applications. The silicone-based dielectric grease fills the connector, sealing out water and preventing oxidation of the copper conductors. Standard wire nuts, even with tape, will eventually allow moisture intrusion and corrode the connection. Solder connections without waterproof encapsulation will also corrode. Failed splices are one of the most common causes of irrigation system malfunctions, especially in zones with intermittent operation problems. All splices should be placed in valve boxes for future access.

Question 6: A technician is wiring a new controller and notices the transformer has two primary voltage taps: 120V and 240V. The building has 240V service only at the controller location. What should the technician do?

Use only the 120V tap and add a step-down transformer
Connect the primary wires to the 240V tap to match the building's supply voltage (Correct answer)
Connect the 240V supply to the 120V tap for higher solenoid output
Advise the client that the controller cannot be used with 240V

Correct answer: Connect the primary wires to the 240V tap to match the building's supply voltage

Multi-tap transformers are designed to accept different input voltages while producing the same 24 VAC output. The technician should connect the building's 240V supply to the 240V primary tap, which will produce the correct 24 VAC secondary output for the solenoids.

Commercial irrigation controllers often include multi-tap transformers because commercial buildings may have 120V, 208V, 240V, or 277V service available at the controller mounting location. Each tap has a different number of primary windings calculated to produce 24 VAC output from that specific input voltage. Connecting 240V to the 120V tap would produce approximately 48 VAC — double the intended output — which would burn out solenoids and potentially create a fire hazard. Always verify the supply voltage with a multimeter before making connections, and ensure the transformer's VA (volt-ampere) rating is sufficient for the number of solenoids.

CIT - Certified Irrigation Technician Electrical Systems and Wiring 2

An irrigation technician measures 28 VAC at the controller's zone terminal but only 18 VAC at the solenoid in the field.
What is the most likely cause?