The full load amps (FLA) for a D20P1G-class 20 HP motor on a 575V three-phase system is nominally 22 amps according to standard code tables, representing the maximum continuous current drawn at rated mechanical output. When sizing conductors and overcurrent protection for this 600V-class equipment, you must multiply this base FLA by 125% for wire ampacity and apply specific inverse-time breaker multipliers, shifting your design from a raw 22A draw to a 27.5A minimum wire capacity and a 60A maximum standard breaker. Whether D20P1G refers to your specific motor catalog number, a compressor frame, or the NEMA starter assembly driving it, the 575V circuit math and code requirements remain identical.
The Core Data: 575V Full Load Amps Reference Table
Before you pull wire or set a dial, you need the baseline code-book values. The table below provides the nominal Full Load Current (FLC) for standard 3-phase motors operating on a 575V system, derived directly from NEC Table 430.250 (and CEC Table 44). We have included the calculated minimum conductor ampacity and maximum standard inverse-time breaker sizes to save you the math on the jobsite.
| Motor HP | 575V FLC (NEC 430.250) | Min Conductor Ampacity (125% of FLC) | Max Inverse-Time Breaker (250% of FLC) | Standard Breaker Size (Next Size Up) |
|---|---|---|---|---|
| 15 HP | 17A | 21.25A | 42.5A | 45A |
| 20 HP (D20P1G Baseline) | 22A | 27.5A | 55A | 60A |
| 25 HP | 27A | 33.75A | 67.5A | 70A |
| 30 HP | 32A | 40.0A | 80A | 80A |
| 40 HP | 41A | 51.25A | 102.5A | 110A |
Note: Breaker sizing assumes standard inverse-time thermal-magnetic breakers per NEC 430.52. If using a motor circuit protector (MCP) with instantaneous trips, the multiplier drops to 1300% of FLC, but standard thermal-magnetic is most common for general branch circuits.
What 575V Changes in a Real Circuit Installation
Moving from a standard 480V or 240V system up to 575V (the standard utilization voltage for 600V distribution networks, heavily used in Canada and heavy US industry) fundamentally changes three things in your installation:
- Insulation Rating and Dielectric Stress: You cannot use standard 300V residential wire. All conductors must be rated for at least 600V. While THHN/THWN-2 is rated for 600V, many industrial facilities mandate XHHW-2 or 1000V-rated tray cable for 575V feeders to handle the increased dielectric stress and transient voltage spikes from VFDs.
- Current Reduction and Wire Downsizing: Because Power = √3 × V × I × PF, pushing the voltage up to 575V drops the current. A 20 HP motor pulls roughly 27A at 480V, but only 22A at 575V. This lower current reduces I²R heating, allowing for smaller conductors and smaller physical contactor frames (like a NEMA Size 2 instead of Size 3).
- Arc Flash and Clearing Times: The incident energy at 575V is substantially higher than at 480V for the same fault current. This dictates stricter PPE categories and often requires you to specify current-limiting fuses (like Class J or RK1) instead of standard breakers to reduce the let-through current and protect the starter assembly.
Where You Meet This in Practice (With Worked Math)
You will typically encounter D20P1G-class 575V loads in commercial rooftop HVAC units (RTUs), industrial air compressors, and Canadian manufacturing plants running 600V delta or wye service. Let’s walk through a complete, code-compliant branch circuit sizing for our 20 HP, 575V motor baseline.
Step 1: Sizing the Conductors
Per NEC 430.22, conductors must be sized at 125% of the motor FLC.
Calculation: 22A × 1.25 = 27.5A.
Looking at the 75°C column of NEC Table 310.16 (assuming THHN in a standard 30°C ambient environment), 12 AWG is only good for 25A. We must step up to 10 AWG, which provides 35A of ampacity. If this is a long run (over 100 feet), you must also calculate voltage drop; at 575V, a 3% drop allows for 17.25V of loss, which usually permits much longer runs on 10 AWG than you'd get at 240V.
Step 2: Sizing the Short-Circuit / Ground-Fault Breaker
Per NEC 430.52, the maximum rating for an inverse-time breaker is 250% of the FLC.
Calculation: 22A × 2.50 = 55A.
Because 55A is not a standard breaker size (standard sizes per 240.6 are 50A, 60A, 70A), the code permits you to round up to the next standard size. Therefore, you install a 60A 3-pole breaker. (Do not use a 50A breaker, or the motor's inrush current will nuisance-trip the magnetic element on startup).
Step 3: Setting the Overload Relay
The overload relay protects the motor from burning out under continuous mechanical strain. Here, you ignore the code book and look at the physical metal nameplate on the D20P1G motor. If the nameplate FLA is 21.2A and the service factor (SF) is 1.15, you dial the bimetallic or electronic overload relay precisely to 21.2A. Modern electronic overloads (like the Eaton C440 or Allen-Bradley E300) will auto-calibrate if you input the nameplate data via their front panel or software.
Common Confusions: FLA vs. FLC vs. LRA
The most common way installations fail inspection—or worse, burn up a motor—is by confusing the three distinct "amp" ratings associated with 575V industrial loads.
- FLC (Full Load Current): This is the theoretical, code-book value found in NEC Table 430.250 (22A for 20HP at 575V). It is a standardized number used strictly for sizing wires and breakers so that inspectors have a uniform baseline.
- FLA (Full Load Amps): This is the actual, measured value printed on the manufacturer's nameplate (e.g., 21.2A). It accounts for the specific efficiency and power factor of that exact motor model. You use this number only to set the overload protection.
- LRA (Locked Rotor Amps): The massive surge of current drawn when the motor is energized but the shaft is physically prevented from turning (or during the first milliseconds of startup). For a 20 HP 575V motor, LRA is typically 6 to 7 times the FLA (roughly 130A - 150A). Your 60A breaker's magnetic trip is designed to ignore this brief LRA spike, whereas a standard thermal breaker might trip instantly if not sized correctly.
Frequently Asked Questions
Can I use a 50A breaker instead of 60A if my wire is 10 AWG?
While 10 AWG wire is protected by a 50A breaker under standard feeder rules, motor branch circuits are an exception. The breaker is sized to allow motor starting inrush, not just to protect the wire. If a 50A breaker nuisance-trips during the 575V motor's startup sequence, NEC 430.52 explicitly allows the 60A next-size-up. The wire is still protected from sustained overloads by the overload relay inside the starter, not the breaker.
Does 575V require a neutral wire?
No. A standard D20P1G 3-phase motor load only requires three phase conductors (L1, L2, L3) and an equipment grounding conductor (EGC). 575V is typically derived from a 600V delta or ungrounded wye system, and motor loads do not utilize a neutral. If your control circuit requires 120V, you must use a separate control transformer stepped down from 575V, not a neutral.
Where can I verify the official code tables for my region?
For US installations, refer to the NFPA 70 (National Electrical Code), specifically Article 430. For Canadian installations, the Canadian Electrical Code (CEC) Part I, Section 28 and Table 44 provide the exact equivalent metrics for 575V systems.
Sizing for 575V full load amps requires shifting your mindset from standard residential voltage drop rules to industrial motor-starting tolerances. By anchoring your wire size to the 125% FLC multiplier and your breaker to the 250% inverse-time limit, you ensure the D20P1G assembly starts reliably under load without tripping the panel or melting the terminal lugs. Always verify your final settings with a true-RMS clamp meter during the commissioning phase under actual mechanical load.
