Single-Phase 5 HP Motor Capacitor Wiring Guide
Most 5 HP single-phase motors use a two-capacitor setup. You have a run capacitor that stays in the circuit the whole time, and a start capacitor that only kicks in when you first flip the switch. Getting the wiring wrong usually means the motor won't start, or worse, it will burn out something inside a minute or two. Here is how a standard motor with a start capacitor and a run capacitor connects. This is for a 230V supply. If yours is rated for 115/230V dual voltage, the internal winding connections shift, and you need a different diagram. Terminals (standard T-code):
T1: Line Hot L1
T2: Common (neutral side of run winding)
T4: Run winding output
T5: Start winding output
T7: Line Hot L2 (on 230V single-phase, this is just the other leg) The run capacitor connects between T2 and T4. The start capacitor connects between T4 and T5, but only through the centrifugal switch, which opens once the motor reaches about 75 percent of rated speed. The hot line connects to T1 and T7 depending on your specific motor terminal layout. Basic connection flow:
Line L1 goes to T1. Line L2 goes to T2 (or T7, depending on your motor). The run capacitor bridges T2 to T4. The start capacitor and centrifugal switch bridge T4 to T5. The start winding returns to line through T5. I wired a 5 HP air compressor motor last month for a guy who'd been replacing the run capacitor every three weeks. The old diagram he found online had the start capacitor permanently connected across the run capacitor instead of going through the centrifugal switch. The start cap was getting full system voltage continuously, heating up until the electrolyte boiled off. Re-wired it through the switch contacts and it has run fine for six months since.
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Component Specifications
A 5 HP motor at 230V draws roughly 28 to 32 amps full load. The run capacitor is usually in the 30 to 50 microfarad range at 370 or 440 volts AC. The start capacitor runs larger, often 100 to 200 microfarads, but only for a few seconds at a time. These are not the same thing. Putting a run cap in the start position or vice versa will get you nowhere fast. The voltage rating on the capacitor matters more than people give it credit for. A motor generating back EMF on a 230V system can push the voltage across the capacitor well above the line voltage. A 250V rated cap on a 230V motor will fail, sometimes explosively. Always use at least a 370V or 440V rated capacitor for this size motor.
Dual Voltage Wiring Note
Many 5 HP motors are dual voltage, meaning you can wire them for either 115V or 230V. The difference is in how the two halves of the run winding connect. For 230V, the two winding halves are in series. For 115V, they are in parallel. The start winding connection changes too. If you wire a dual voltage motor for 115V but feed it 230V, you will destroy the windings quickly. Always check the nameplate before closing the terminal box. The most frequent mistake I see is treating the run and start capacitors as interchangeable. They are built differently. Run capacitors use metallized polypropylene film. Start capacitors use electrolytic construction. A start capacitor will overheat and fail if left in the circuit. A run capacitor will not provide enough starting torque if substituted for a start capacitor. The motor will hum and stall. Another issue is the centrifugal switch itself. On older motors, these switches get coated in carbon and oil residue over the years. The contacts stick open, and the motor never starts. Or they stick closed, and the start capacitor runs continuously until it fails. I once pulled a 20-year-old motor apart and the switch mechanism was fused shut with what looked like hardened syrup. Cleaned the contacts and replaced the switch assembly, motor ran fine after that.
Also check your wiring gauge. A 5 HP motor at 230V pulling 30 amps needs at least 10 AWG copper on a dedicated circuit. Running it on lighter wire and expecting it to run cool is a recipe for insulation breakdown. I sized the branch circuit and added a proper overload relay because the existing thermal protector on this particular motor had been bypassed by the previous owner. That alone probably explains why two start capacitors burned out in the span of four months.
Wiring Diagram Summary
The actual 5 Hp Motor Capacitor Wiring Diagram you need depends on your motor's terminal markings and nameplate. Here is the most common configuration for a conventional capacitor-start, capacitor-run 5 HP motor on 230V: T1 connects to Line L1
T2 connects to Line L2 and one side of the run capacitor
T4 connects to the other side of the run capacitor and one side of the start capacitor
T5 connects to the other side of the start capacitor and one side of the centrifugal switch
The centrifugal switch closes when the motor is stopped, completing the start circuit, and opens at speed to disconnect the start capacitor Always verify against your motor's nameplate and the manufacturer's diagram before applying power. Generic wiring diagrams cover the majority of cases, but they are not universal. If the terminal designation on your motor uses a different numbering system, cross-reference with the manufacturer's documentation. The general principles remain the same, but getting the specific terminals wrong can cause immediate damage.
