How-To Guide  ·  Allen-Bradley PowerFlex 525  ·  Fuse & Circuit Breaker Sizing

PowerFlex 525 Fuse & Circuit Breaker Sizing: Branch Circuit Protection for Every Model

25B-D2P3N104 · 1 HP, 480V AC, 3-Phase · Frame A · Example Drive

1. Why Branch Circuit Protection Is Required

Variable frequency drives like the PowerFlex 525 contain input rectifier diodes and DC bus capacitors, but they do not include branch short circuit protection. If a short circuit occurs on the input power wiring between the branch circuit panel and the drive, there is no internal mechanism to interrupt the fault current. This is why the NEC, IEC, and local codes require external protection—either fuses or a circuit breaker—installed upstream of the drive.

What Protection Does

2. How to Size Fuses — 25B-D2P3N104 Example

We’ll walk through the fuse sizing process using the 25B-D2P3N104—a 1 HP (0.75 kW) PowerFlex 525 for 380–480V, 3-phase input.

Step 1: Find the Drive’s Input Current Rating

From the 520-TD001 technical data (page 29), the 25B-D2P3N104 has:

Step 2: Determine the Recommended Fuse Range

Rockwell provides a minimum and maximum fuse rating for each drive. For the 25B-D2P3N104:

Step 3: Select a Specific Fuse

For the 25B-D2P3N104, any of these fuses will work:

Step 4: Allen-Bradley Protection Devices (Optional)

Rockwell recommends their own protection devices for coordinated protection. For the 25B-D2P3N104:

3. Complete Fuse Sizing Table — 380–480V 3-Phase

The table below covers every PowerFlex 525 model at 380–480V, 3-phase input. Models with suffix N114 (built-in EMC filter) use the same fuse ratings as their N104 counterparts. All data from Rockwell publication 520-TD001, Table “380…480V 3-phase Input Protection Devices.”

IEC (Non-UL) Fuse Ratings

UL 61800-5-1 Fuse Ratings

4. Circuit Breaker Sizing Table

As an alternative to fuses, you can install a circuit breaker upstream of the drive. Rockwell recommends their Bulletin 140M (IEC) or 140MT (UL) motor circuit protectors for coordinated protection. The 140M/140MT can be used upstream from the drive without the need for fuses when used as a self-protected (Type E) combination motor controller.

5. Fuse Types Explained

The PowerFlex 525 accepts several fuse classes for UL-listed installations. Each class has different physical dimensions, interrupting capacity, and speed characteristics. All of the following are acceptable per Rockwell’s technical data.

IEC Fuse Types

For IEC (non-UL) installations, Rockwell recommends:

• IEC BS88 (British Standard) Parts 1 & 2 — equivalent to UL Class J performance
• EN60269-1 Parts 1 & 2, type gG (general purpose, full range) — the standard European industrial fuse

6. Installation Best Practices

Fuse Installation Checklist

1. Verify voltage rating: All fuses must be rated for at least 480V AC (or 600V for future flexibility). Never use a 250V-rated fuse on a 480V circuit.
2. Match the fuse class to the holder: Class J fuses only fit Class J holders. Class CC fuses only fit Class CC holders. This rejection feature prevents incorrect substitution.
3. Install a fused disconnect switch: Mount the fused disconnect within sight of the drive (NEC 430.102). This provides lockout/tagout capability for maintenance.
4. Use time-delay fuses: The PowerFlex 525 draws a brief inrush current during power-up as the DC bus capacitors charge. Standard fast-acting fuses may nuisance-trip. Time-delay (dual-element) fuses tolerate this inrush.
5. Size wire to the fuse, not the drive: Per NEC 240.4, conductor ampacity must be ≥ the fuse rating. For a 10 A fuse, use at least 14 AWG copper (THHN/THWN).
6. Ground the drive enclosure: Connect the drive ground terminal (PE) to the equipment grounding conductor. This is critical for both safety and drive operation.

Circuit Breaker Installation Notes

1. If using a Bulletin 140M/140MT, it can serve as both the branch circuit protection and the disconnect, eliminating the need for a separate fused disconnect switch.
2. Set the adjustable current trip to the lowest setting that does not trip during normal drive operation, including startup inrush.
3. The 140M/140MT provides Type E self-protected combination motor controller per UL 508, which satisfies NEC branch circuit protection requirements.

7. PowerFlex 525 Models — 380–480V 3-Phase Quick Reference

All PowerFlex 525 models available from PLC Exchange. Every drive ships with a 2.5-year warranty and free shipping.

8. Related Guides

Reference Documentation

The following Rockwell Automation publications were used as references for this guide. All fuse and circuit breaker data comes directly from these publications.