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 Current Ratings

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 rating at 380–480V, 3-phase input, Frames A–E. Models with suffix N114 (built-in EMC filter) use the same fuse ratings as their N104 counterparts; the 25 HP and 30 HP Frame E ratings are listed only as N114. 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 lists Bulletin 140M/140MT self-protected combination motor controllers for each rating. The 140M/140MT can be used upstream from the drive without fuses when used as a self-protected (Type E) combination motor controller, with one restriction: Per 520-TD001, the 140M/140MT used this way is a Manual Self-protected (Type E) Combination Motor Controller that is UL Listed only for 208V Wye or Delta, 240V Wye or Delta, 480Y/277V, and 600Y/347V systems. It is not UL Listed for 480V or 600V Delta/Delta, corner-ground, or high-resistance-ground systems; on those systems use the listed fuses instead.

5. Fuse Types Explained

For UL installations, the 520-TD001 UL 61800-5-1 table lists Class CC, J, or T for every 380–480V PowerFlex 525 rating. (The general fusing text in 520-TD001 also names Class RK1, but the rating tables for these drives list only CC, J, or T.) Interrupting ratings and time-current characteristics vary by fuse manufacturer; check the fuse maker’s data.

IEC Fuse Types

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

• IEC BS88 (British Standard) Parts 1 & 2
• EN60269-1 Parts 1 & 2, type gG, or equivalent

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: Locate the disconnecting means as required by NEC/local code. This provides lockout/tagout capability for maintenance.
4. Use a listed fuse class: Use any of the fuse classes listed for your rating in 520-TD001 (Class CC, J, or T for UL; BS88 or EN60269-1 type gG for IEC).
5. Size wire to the overcurrent device: Size input conductors per NEC/local code for the installed fuse or breaker. The Frame A power terminal block accepts 18–10 AWG (520-UM001); those are terminal limits, not recommendations.
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 as a Type E self-protected combination motor controller, it can serve as both the branch circuit protection and the disconnect, eliminating the need for a separate fused disconnect switch. This applies only on the system types for which it is UL Listed (see item 3).
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 is a Type E self-protected combination motor controller. Per 520-TD001, the 140M/140MT used this way is a Manual Self-protected (Type E) Combination Motor Controller that is UL Listed only for 208V Wye or Delta, 240V Wye or Delta, 480Y/277V, and 600Y/347V systems. It is not UL Listed for 480V or 600V Delta/Delta, corner-ground, or high-resistance-ground systems; on those systems use the listed fuses instead.

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.