US Motors D60P1GS & D20P1G FLA, SG90 Servo Specs, and Arduino Stepper FAQ

I've been specifying motors for about seven years now—industrial AC motors, little hobby servos, steppers, you name it. I've personally made and documented over $4,000 in mistakes, and this FAQ is the list I wish someone handed me before I ordered my first replacement motor. My experience is mostly with US Motors (the Nidec brand) and common Arduino components, so if you're working with something else, your numbers might differ. This was accurate as of February 2025; verify current specs before you buy.

Questions this FAQ answers

• US Motors D60P1GS 575V FLA: what's the full load amp rating for this 60 HP motor?
• US Motors D20P1G 575V full load amps for the 20 HP model
• Why the nameplate FLA beats a NEC table value
• Why 575V current is lower than 460V current
• SG90 servo motor datasheet specs worth remembering
• Can an Arduino run an SG90 servo?
• What's a stepper motor?
• Which stepper driver should an Arduino project use?

1. What's the full load amp rating for a US Motors D60P1GS at 575V?

The short answer is around 62A. According to NEC 430.250, a three-phase 60 HP induction motor at 575V has a full load current of 62A. The D60P1GS nameplates I've handled were right around that number—one said 62.0 FLA, if I remember correctly. Don't hold me to that exact decimal, because the same model number can appear with different enclosures, service factors, or efficiency classes. The S in D60P1GS has a specific meaning, but I don't trust suffix memory for official work. Use the nameplate.

NEC 430.250, three-phase induction motor, 60 HP at 575V: 62A full load current.

If you're working with a NEMA MG-1 Design B motor, this value is a solid starting point. If your motor is inverter-duty, high-efficiency, or runs in a hot environment, the real FLA can shift. I recommend photographing the nameplate before you trust any table.

2. What about the US Motors D20P1G at 575V?

A 20 HP, 575V motor from the same NEC table is 22A full load current. The D20P1G units I've seen had nameplate FLA around 21.8–22.0A. That's not a large spread, but it's enough to matter for overload relay selection. If you use the NEC table value, you're probably fine. If you use a value from the motor's actual nameplate, you're even better. On a 20 HP motor, 0.2A is not a rounding error—it can be the difference between a nuisance trip and running too hot on a continuous load.

3. Why does FLA matter more than horsepower?

Horsepower is the output rating. FLA is what the motor draws at full load. That's the number that dictates wire gauge, breaker size, overload relay setting, and starter contacts. I once sized overloads from a horsepower chart instead of the nameplate. The control panel was ordered that way—$3,200 in materials. The controls engineer caught it during commissioning. We spent $900 on rework and lost a week. The lesson: FLA is not a suggestion. It's a specification.

This is also where the honest limitation kicks in. If you're dealing with a rewound motor, a special torque motor, or a vertical motor, don't assume the table value is close. Look at the plate.

4. Why is 575V FLA lower than 460V FLA?

For the same horsepower, current drops as voltage increases. Power is roughly voltage × current × power factor × efficiency. A 20 HP motor at 460V is around 27A on the NEC table; at 575V it's around 22A. So if someone gives you a FLA for 460V and you apply it to a 575V motor, you'll set the overloads too high. That's a real failure mode. I've opened a starter panel where someone had done exactly that, and the motor windings were beautifully discolored. The motor survived, barely.

If you're swapping voltage, always recalculate or read the dual-voltage nameplate.

5. SG90 servo motor datasheet: what should you actually remember?

The SG90 is a 9g analog micro servo, not a precision positioning instrument. The common datasheet values are roughly:

• Operating voltage: 4.8–6V
• No-load speed: about 0.1s per 60° at 4.8V
• Stall torque: about 1.8 kg·cm
• PWM signal: 50Hz, 1–2ms pulse
• Current: maybe 150–200mA no load, 600–700mA stalled

The 1–2ms pulse range is the standard story. Some clones use 0.5–2.5ms, so the same servo library code can move 120° when you expected 90°. I bought clones to save a few dollars once. Saved $12, spent four hours debugging a robotic arm. (Which, honestly, was cheap entertainment compared to a dead motor.)

Take this with a grain of salt: SG90 clones vary. If you're using a clone, your experience might differ.

6. Can an Arduino run an SG90 servo?

Yes, but don't power it from the Arduino's 5V pin if you actually want the arm to move. The signal wire goes to an Arduino digital pin, ground connects to Arduino ground, but the motor's current should come from an external 5V supply. A stalled SG90 can pull 600+ mA, which is enough to make an Arduino running from USB reset. I've seen that exact failure: first move, green LED flickers, board resets, serial monitor says 'kaboom' in a happy font. Use a separate supply and a common ground.

I recommend this setup for light loads. If your project stalls often, an MG90 or a small stepper is a better fit. The SG90 is for doors, camera tilt, and things that don't fight back.

7. What's a stepper motor?

A stepper motor is a brushless electric motor that moves in fixed steps by energizing its coils in sequence. For example, a common NEMA 17 motor has 200 steps per revolution, or 1.8° per step. The motor doesn't need an encoder to hold a position—the controller counts steps, so you get open-loop positioning. That's why a stepper is a stepper: it literally steps.

The catch is open-loop. If you overload a stepper, it skips steps, and the controller still thinks it's where it should be. A servo system, on the other hand, closes the loop with feedback and corrects position. For a 3D printer or Arduino project, steppers are usually the right tool because they're simple and cheap. For a robot arm that needs to know where it is when the power comes back, a servo might be worth it.

8. Arduino stepper motor: which driver should I use?

For common Arduino projects, you'll see two combos:

• 28BYJ-48 with ULN2003 driver for small, slow, cheap positioning
• NEMA 17 with A4988 or DRV8825 driver for faster and stronger motion

The 28BYJ-48 is a unipolar stepper with a gearbox, so it's slow and noisy but fine for a little valve or vent actuator. The NEMA 17 is a bipolar stepper, common in 3D printers, and needs a chopper driver with adjustable current. Whichever you use, don't connect the motor coils directly to Arduino pins. You'll fry the pin or the whole board. I burned my first A4988 by setting the current limit too high—it got hot enough to skip steps. The driver was under $5, but the lesson stuck.

Use the Stepper or AccelStepper library and check your motor's rated current before touching the driver's current pot. If you're outside the hobby sizes, stop guessing and read the datasheet. That's the same advice I give myself before I spend money.