How to Wire a Century Single-Phase Motor for 115 or 230 Volts
Most people buying a Century motor end up confused when they look at the terminal box. There are six leads, sometimes four, sometimes more, and the diagram on the nameplate is small enough that you need a flashlight and steady hands to read it. I've been doing this since the mid-2000s and I still get occasional calls from people who wired their motor backwards because they mixed up the main and auxiliary windings. The basic principle is straightforward once you see it done. A typical Century 115/230V single-phase motor has six leads: L1, L2, L3, T1, T2, T3, plus a ground. The numbering varies by model, so don't assume every Century motor uses the same lettering. Some are marked with numbers only. Always check the actual label on the motor before you touch a wire.
Century Ac Motor Wiring Diagram 115 230 Volts
For 230-volt connections, you tie L1 and L3 together and apply power to L2 and the tied pair. For 115 volts, you apply one hot to L2 and the other hot to both L1 and L3 tied together. The capacitor always stays across the same two points regardless of voltage, which is the part most people miss. They move the capacitor taps thinking they need to rewire it, but the capacitor connection is fixed. Only the line voltage taps change. I worked on a job last year where someone had a Century 5HP pump motor that would not start. The previous electrician had connected it for 115 volts instead of 230, pulling nearly 45 amps and tripping the breaker every time. Once I rewired it properly for 230 and verified the capacitor was seated correctly, it pulled about 22 amps and ran quiet. That kind of mistake costs hours and a blown breaker. The run capacitor connection point is critical. On most Century motors, the capacitor goes between the start winding terminal and the common line terminal. If you swap those, the motor will hum and not turn, or worse, it will burn out the start winding within seconds. I always double-check the capacitor leads with a multimeter before applying power. A quick resistance check across the windings tells you immediately if something is wrong.
For 230V single-phase, the current draw should roughly halve compared to 115V. A motor rated at 28 amps on 115V should draw around 14 amps on 230V. If your ammeter reads significantly higher than the nameplate rating, stop immediately and check your wiring. Something is wrong, usually a crossed connection between the main and auxiliary windings. One thing the manuals don't always make clear: the order of T1, T2, and T3 matters for rotation direction. If you wire it correctly and the motor spins the wrong way, swap any two of the three line leads and try again. Don't swap the capacitor leads—that won't fix rotation and may damage the capacitor. Also worth noting: if your Century motor has a thermal overload protector built in, it may trip during initial testing if the windings are hot from a previous attempt. Let it cool for fifteen minutes and try again. Don't keep cycling power repeatedly, or you'll cook the windings faster than any wiring mistake would.
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Common Mistakes to Avoid
Connecting both line voltages to the same terminal block point. This creates a dead short across the transformer winding and will blow fuses or trip breakers instantly. Assuming the white wire is always neutral. In a 230V single-phase setup, both wires are hot. The color coding on motor leads does not follow residential wiring conventions. Treat every lead as live until you verify otherwise. Using undersized wire because "it's only 115 volts." A 5HP motor on 115V draws close to 50 amps at full load. That requires at least 6 AWG copper, preferably 4 AWG, depending on run length and local code. Running it on 10 AWG wire will heat the conductors to dangerous temperatures over a sustained run.
Skipping the ground. Century motors have a green ground terminal inside the junction box. Connect it. I have seen too many people skip this because "the motor is already grounded through the mounting frame," which is not a reliable grounding path and violates NEC requirements.
What You Need Before Starting
A digital multimeter capable of measuring resistance and AC voltage. Clamp-on ammeter if you have one. Basic hand tools: screwdrivers, wire strippers, and cable cutters. Wire nuts or terminal lugs rated for the wire gauge you are using. Heat-shrink tubing for any splices. And the actual wiring diagram from your motor's nameplate, not a generic diagram you found online. The diagram on the Century Motors website is useful but you need your specific model number. A TEFC (totally enclosed fan cooled) motor may have a different terminal arrangement than an open drip-proof version of the same horsepower. I learned this the hard way on a 3HP replacement job where the old motor and new one had different terminal layouts despite being the same frame size. Verify your voltage before connecting anything. Measure at the source, not just at the motor. If you're running a long distance from the panel, voltage drop can be significant. A 100-foot run on 115V with a 5HP motor might deliver only 100 volts at the motor terminals, causing it to draw excessive current and overheat.
If you are working with a three-phase Century motor, this guide does not apply. Three-phase wiring is completely different and requires a phase sequence meter to verify correct rotation. Mixing up the two systems will destroy the motor quickly. The whole process, from opening the terminal box to confirming correct operation, should take about 30 to 45 minutes for someone who has done it a few times. If it is taking longer, you are probably second-guessing a connection. Stop, verify with the multimeter, and proceed methodically. Rushing this wiring job is the single biggest cause of motor failures in the field.
