SCHRACK Motor protection circuit-breakers

schrack motor protection circuit breakers selection and coordination

Use these manual motor circuit breakers at the head of each feeder when you need combined short-circuit and overload protection with a visible isolating function. Frames typically cover 0.1…32 A in compact bodies and up to 63…80 A in larger sizes; adjustable thermal dials match motor FLA, while magnetic trips (often 10–14× In) clear bolted faults within milliseconds. Utilization categories and making/breaking are stated for 230/400/690 V; type plates list Ui to 690 V and Uimp 6–8 kV. Lockable operators and trip-free mechanisms support LOTO at the machine.

Frames, trip curves, and dial ranges

Two envelope sizes solve most cabinet layouts: a 45-mm wide body for fractional to ~32 A motors and a taller frame for feeders up to 63/80 A. Closely spaced dial steps (e.g., 2.5–4–6.3–10–16–25–32 A) keep you near nameplate FLA without over-derating. Phase-loss sensitivity is built in on thermal elements, so single-phasing trips before windings overheat. For high inrush or star-delta starts, confirm the magnetic pickup band vs the motor’s actual start profile.

Schrack MPCB accessories and mounting

Snap-on OF/SD auxiliaries report ON/OFF and TRIP; shunt trip and undervoltage releases enable monitored shutdown from the PLC or safety relay. Rotary door handles (red/yellow or black/grey) use shaft kits 100–320 mm to suit door depth; optional door-defeater tools support set-up while interlocks prevent opening in ON. Comb busbars feed rows quickly, end-feed blocks clean up copper work, and phase barriers maintain creepage in dense boards. Terminal cages accept ferruled fine-strand; follow the molded torque table for warm rails.

Thermal behavior, Icu/Ics, and derating tables

Datasheets state Icu/Ics per grid (e.g., 6–15 kA at 400 V on compact frames; higher on reinforced sizes). Select Ics above calculated fault level at the mounting point, or use cascading with the upstream MCCB to raise the effective withstand. Ratings assume Ta 40 °C; clustered rows or sealed enclosures require derating. Document dial settings and final magnetic band on the schematic and nameplate—FAT goes faster and later troubleshooting is unambiguous.

Schrack wiring practice and panel layout

Place the breaker directly above the contactor; keep line tails short and neutral bars mirrored to row order. On VFD panels, the device typically sits upstream of the drive sized to the drive’s input current; let the drive handle thermal while the breaker covers short-circuit and isolation. Bond shields at the gland plate, keep VFD outputs away from control wiring, and record auxiliary contact mappings in the HMI for quick diagnosis.

Schrack coordination with contactors, soft starters, and VFDs

Apply manufacturer Type 1/Type 2 tables so the contactor remains serviceable after a short-circuit. Electronic overloads add selectable trip class (10/20/30), ground-fault sensitivity, and unbalance alarms to a dry contact—useful on conveyors and pumps where you want to stop only one branch. For emergency stops, UVR on the breaker and EDM on the contactor give positive feedback before reset.

Schrack selection workflow for OEMs and facility teams

1. Network fault level: choose Icu/Ics (or a cascading set) above the calculated kA at the board.
   
    
2. Motor FLA/duty: set the dial to nameplate, consider service factor and ambient.
   
    
3. Starting profile: magnetic pickup must ride through inrush yet clear bolted faults quickly.
   
    
4. Interfaces: auxiliaries, shunt/UVR, and door handle style per your panel standard.
   
    
5. Environment: IP/IK for enclosed versions; stainless hardware in damp rooms.
   This is also where many specs call out schrack thermal magnetic breakers to keep device families consistent across frames and rows.
   
    

Procurement and kitting with Schrack assemblies

Standardize three frames (≤32 A, ≤63/80 A, and the largest size you actually use), two handle colours, and two shaft lengths. Pre-kit comb busbars, end-feeds, auxiliaries, hasps, and legend plates per panel section. Record dial settings and accessory stacks in the CAD article so service swaps are tool-predictable. If your BOM includes starters, pair frames with contactors and overloads under one code to reduce picking errors and MTTR.