If you need a wiring diagram for a Square D Pumptrol FSG2 pressure switch, the core rule is simple: 240V line power from your double-pole breaker enters Terminals 1 and 2, load power to the pump motor exits Terminals 3 and 4, and the bare copper equipment ground bonds directly to the green grounding screw on the metal baseplate. The FSG2 is a double-pole, single-throw (DPST) switch, meaning it breaks both hot legs simultaneously when the water pressure reaches your cut-out threshold (typically 40/60 PSI or 30/50 PSI).
Decoding the FSG2 Diagram Symbols and Physical Terminals
When looking at the schematic printed on the inside of the FSG2 cover, you will see two distinct single-pole switches drawn in parallel. This is the standard electrical symbol for a DPST (Double-Pole, Single-Throw) switch. In reality, the physical device uses a single plastic rocker mechanism actuated by a metal diaphragm to push two separate metal contact bridges down onto the terminals simultaneously.
Here is how the physical device maps to the diagram:
- Terminals 1 & 2 (Line Side): Located on the left side of the switch base. These are the incoming power terminals. The diagram symbols show the line source feeding into the stationary contacts here.
- Terminals 3 & 4 (Load Side): Located on the right side. These feed the pump motor. The schematic shows the movable contacts bridging the gap between the line and load sides.
- Ground Symbol (⏚): The diagram shows a ground symbol attached to the switch enclosure. Physically, this is the green machine screw threaded directly into the steel baseplate, not the plastic terminal block.
- Springs and Adjustment Nuts: While prominent on the physical switch, the large and small springs with their adjustment nuts are purely mechanical. They do not appear on the electrical wiring diagram because they carry no current; they only dictate the hydraulic PSI thresholds for the contacts to open and close.
Node-by-Node Trace: Panel to Pump Motor
To wire this correctly, follow this exact textual trace from the source to the load. This assumes a standard 240V, single-phase, 3-wire setup (Black Hot, Red Hot, Bare Ground) with no neutral required.
- Source (Main/Subpanel): A 240V double-pole breaker provides two hot legs. Black and Red THHN wires are terminated to the breaker lugs; the bare copper ground is terminated to the panel ground bar.
- Conduit Run: The three wires (Black, Red, Bare) travel through liquid-tight flexible metallic conduit (LFMC) or rigid PVC from the panel to the pressure switch's 1/2" knockout.
- Line Connection (Terminals 1 & 2): The Black wire from the panel lands on Terminal 1. The Red wire from the panel lands on Terminal 2. (Polarity between 1 and 2 does not matter for 240V, but keeping colors consistent aids troubleshooting).
- Internal Switching: When water pressure drops below the cut-in point (e.g., 40 PSI), the diaphragm releases, and the internal contacts drop, bridging Terminal 1 to Terminal 3, and Terminal 2 to Terminal 4.
- Load Connection (Terminals 3 & 4): A second set of Black and Red wires (or Black and White if using 2-conductor NM-B cable to the pump) connects to Terminals 3 and 4. These run out through the opposite knockout to the pump motor terminal box.
- The Ground Path: The bare copper ground wire from the panel is pigtailed (if necessary) or looped under the green ground screw on the FSG2 baseplate. The ground wire must make direct metal-to-metal contact with the baseplate. It then continues out to the pump motor chassis. This ensures that if a hot wire chafes against the pump casing, the breaker trips instantly rather than electrifying the well casing.
Terminal Mapping and Multimeter Verification
Before energizing the circuit, use this spec-sheet table to verify your physical connections and test the switch logic with a digital multimeter (DMM).
| Terminal / Point | Physical Location | Wire Function (240V) | Multimeter Verification Step |
|---|---|---|---|
| Terminal 1 | Left side, top screw | Line Hot 1 (Black) | Voltage: Read 120V to ground. Continuity: Read < 1Ω to Terminal 3 when switch is manually closed. |
| Terminal 2 | Left side, bottom screw | Line Hot 2 (Red) | Voltage: Read 120V to ground, 240V across Term 1 & 2. Continuity: Read < 1Ω to Terminal 4 when closed. |
| Terminal 3 | Right side, top screw | Load Hot 1 (Black/White) | Voltage: Read 0V when switch is open. Read 120V to ground when closed. |
| Terminal 4 | Right side, bottom screw | Load Hot 2 (Black/White) | Voltage: Read 0V when open. Read 240V across Term 3 & 4 when closed. |
| Ground Screw | Steel baseplate, green screw | Equipment Ground (Bare) | Continuity: Read < 0.5Ω to the main panel ground bar and to the pump motor chassis. |
Sizing Decision Tree: Breaker, Wire, and Conduit
Well pump wiring is governed by NFPA 70 (NEC) Article 430, which requires motor circuits to be sized based on Full Load Amps (FLA), not just horsepower. Use this decision table to terminate your material choices. Do not guess; match your pump's nameplate FLA to the row below.
| Pump Motor HP | Voltage | Typical FLA | Required Wire (THHN in Conduit) | Required 2-Pole Breaker |
|---|---|---|---|---|
| 1/2 HP | 240V | ~ 4.0A | 14 AWG (Min 15A ampacity) | 15A |
| 3/4 HP | 240V | ~ 6.9A | 14 AWG | 15A or 20A |
| 1.0 HP | 240V | ~ 8.0A | 12 AWG (Min 20A ampacity) | 20A |
| 1.5 HP | 240V | ~ 10.0A | 12 AWG | 20A |
| 2.0 HP | 240V | ~ 12.0A | 10 AWG (Min 30A ampacity) | 25A or 30A |
| 3.0 HP | 240V | ~ 17.0A | 10 AWG | 30A |
The Concrete Pick: For the vast majority of residential shallow and deep well setups running a 1.5 HP, 240V submersible pump, your default material list is: 12 AWG THHN wire (Black, Red, Green), a 20A double-pole breaker, and 1/2" liquid-tight conduit. The Square D FSG2 switch is rated for up to 2 HP at 230V (roughly 16A), making it perfectly matched to this 1.5 HP / 20A breaker configuration. If you are running a 2 HP or 3 HP pump, you must upgrade to the heavier-duty Square D Pumptrol FSG2J24M4 or a heavy-duty contactor setup to handle the increased inrush current without pitting the contacts.
Mains Safety and Final Torque Checks
Once your wires are landed according to the node trace and decision tree, the final step before re-energizing is mechanical verification. The FSG2 terminal screws are relatively small and prone to stripping if over-torqued, but loose connections will cause high resistance, localized heating, and eventual melting of the plastic terminal block.
- Torque Specification: For 10 AWG to 14 AWG solid copper wire, torque the terminal screws to 14 in-lbs. If you do not have an inch-pound torque screwdriver, the practical rule is to tighten the screw until the wire is snug, then give it exactly one-quarter (90-degree) turn more.
- Strand Check: Ensure no stray strands of the bare ground wire are splaying out and touching Terminals 3 or 4. A single stray ground strand touching a load terminal will cause a dead short and a violent breaker trip the moment the switch closes.
- Conduit Locknuts: Verify that the locknuts on your conduit knockouts are tight. The ground path relies on the metal-to-metal connection between the conduit fitting, the locknut, and the switch baseplate if you are using metallic conduit as your equipment grounding conductor (though pulling a dedicated bare wire is always best practice).
Replace the gray plastic cover, ensuring the small rubber gasket is seated to prevent moisture ingress, turn on the double-pole breaker, and open a faucet to drain the pressure tank. You should hear the distinct, sharp click of the FSG2 contacts closing as the pressure drops below 40 PSI, followed by the hum of your well pump kicking on.
