Technical Resources · Selection Guide
MPCB Selection Guide: Motor Current, Trip Range and Breaking Capacity
A motor protection circuit breaker is selected against one motor circuit, not by choosing the nearest ampere label. The buyer must define the motor, supply, starting behavior, prospective fault current and the exact functions expected from the device. The proposed MPCB must then be checked in its own manufacturer tables.
This article owns MPCB selection inputs. It does not replace the published comparison of MPCBs, thermal overload relays and MCBs, and it does not claim a coordinated starter combination for GYMP7.
Buying Decision at a Glance
| Decision input | Buyer must confirm | Evidence required |
|---|---|---|
| Motor record | Rated voltage, full-load current, phase and starting method | Exact adjustment band and motor-duty data |
| Fault duty | Prospective short-circuit current at the device location | Breaking-capacity row at the same voltage |
| Trip behavior | Required overload and magnetic response | Exact trip information and tolerances |
| Control scope | Manual operation, isolation and auxiliary requirements | Documented functions and supported accessories |
| Coordination | Contactor, upstream and downstream device identities | Exact manufacturer combination table when a claim is made |
Start With the Motor and Circuit
Record the motor nameplate, supply voltage and frequency, full-load current, phase arrangement and starting method. Add the expected start frequency, acceleration conditions and any duty that can create prolonged current. These inputs explain why a setting band cannot be selected from motor power alone.
Record the prospective short-circuit current at the intended MPCB position separately from normal motor current. The breaker must have documented interruption performance at the project voltage. If the fault level is unknown, stop the selection and request the calculation rather than treating the magnetic release setting as a substitute.
Read the Adjustment Band Correctly
The motor current should fall within the exact model adjustment range, but range inclusion is only the first gate. Ask how the manufacturer instructs the setting to be established and which ambient or enclosure conditions apply. Do not transfer a setting rule from another series.
GYMP7 is published as multiple documented current bands across two frame groups. A buyer should identify the proposed order code and band, then confirm the corresponding voltage and breaking data. The family maximum does not describe every band at every voltage.
Separate Protection Functions
An MPCB can combine overload and short-circuit protective functions when those functions are documented for the exact device. That does not mean every motor-control requirement is included. Control coils, remote operation, contactor switching, undervoltage behavior and process interlocks remain separate unless the exact configuration states otherwise.
When a supplier describes a manual motor starter, ask whether the term refers to the breaker alone or to a documented combination. ABB catalogs organize manual motor starters, contactors and overload components as distinct records and publish coordination data for exact combinations. The principle is evidence discipline, not compatibility with GYMP7.
Compare Quotations on the Same Basis
Normalize each offer to the same motor, voltage and fault-current record. Compare the adjustment band, exact breaking-capacity row, trip information, operator and isolation functions, mounting, terminals and accessories. A lower price for a breaker-only offer is not comparable with a quoted assembled starter.
Reject combined best-case comparisons. Do not take the widest current range from one variant, the highest breaking figure from another voltage and an accessory image from a third. One orderable code and its supporting documents must satisfy the project record.
Build an Evidence File Before Approval
Create one review sheet for the proposed MPCB order code. Put the application inputs in the left column and the supplier evidence in the right column. At minimum, preserve the records for motor record, fault duty, trip behavior and control scope and coordination. This makes it clear which information comes from the project and which statement comes from the manufacturer.
Attach the exact datasheet pages, drawings and tables used in the decision. Record their revision or retrieval date and highlight the row for the quoted model. A sales email can clarify scope, but it should not silently replace a technical document when the decision depends on a rating, connection, trip characteristic, thermal limit or tested combination.
Check that every linked value describes the same orderable configuration. Similar model names often share a housing while differing in control supply, current band, poles, terminals, accessories or environmental limits. If a document covers several variants, mark the selected row rather than treating the broadest range on the page as the capability of every variant.
Control Changes During Sourcing
Keep the application record frozen while suppliers prepare quotations. If voltage, load, duty, fault level, enclosure or operating method changes, issue a revised record and ask each supplier to reconfirm the candidate. Otherwise procurement may compare responses that were prepared for different requirements even though the email subject and product family are unchanged.
Apply the same rule to substitutions. A replacement proposed because of price or availability returns to the technical gate with its own order code and evidence. Do not approve it solely because the nominal current, product shape or mounting method resembles the original candidate. The substitution is complete only when the required functions and conditions are rechecked.
Common Procurement Errors
- Selecting MPCB from one headline rating while leaving the application context undefined.
- Using a diagram, curve or accessory table from a neighboring model without confirming scope.
- Treating a product-category page or marketing image as exact-model evidence.
- Comparing a device-only quotation with an assembled or accessory-inclusive quotation.
- Allowing an unresolved technical field to disappear when the commercial offer is revised.
Resolve these errors before commercial comparison. The technical reviewer should be able to trace each accepted statement to the project record or to the exact candidate document without relying on memory. Procurement can then compare price, quantity, destination and lead time against a stable technical baseline instead of reopening the selection after order placement.
How to Compare Supplier Offers
Compare every MPCB offer against one frozen application record. Do not combine the best figures from several variants or accept a family maximum as the rating of the quoted order code. Keep the document revision, test conditions and unresolved fields beside each value so procurement can see whether two offers are genuinely equivalent.
| Comparison point | Required evidence | Do not accept |
|---|---|---|
| Adjustment | Exact band contains motor current; setting method supplied | Only family current range |
| Interruption | Breaking capacity at project voltage and configuration | Single kA figure without conditions |
| Functions | Trip and operator functions documented | Assumed from the name MPCB |
| Combination | Exact tested combination record when claimed | Shared brand or matching ampere range |
A quotation can remain commercially interesting while technically incomplete. Mark missing data as an open action and ask the supplier for the exact page, drawing or combination table. Price and lead time should be compared only after the technical scope is normalized. This prevents a lower-cost but narrower offer from appearing equivalent to a complete documented solution.
Decision Workflow
- Freeze motor nameplate and operating-duty information.
- Obtain the prospective fault current at the MPCB location.
- Select a candidate adjustment band without crossing model boundaries.
- Verify voltage, breaking capacity and trip behavior for the exact order code.
- Check terminals, mounting, accessories and environmental limits.
- Request exact coordination evidence for any proposed contactor or starter combination.
At each step, preserve the boundary between project inputs and supplier evidence. The project team defines the application and required functions; the supplier identifies an exact product and provides its documents. Neither side should fill an evidence gap by inference from appearance, a nearby model or a shared headline rating.
RFQ Preparation Checklist
A useful RFQ for motor protection circuit breaker selection guide should be concise enough to answer but complete enough to prevent silent assumptions. Attach the available project record and identify unknown values as questions. Ask the supplier to answer with an exact orderable code rather than a generic product-family recommendation.
- Motor power and nameplate voltage/current
- Supply frequency, phase and starting method
- Prospective short-circuit current
- Required adjustment range and protection functions
- Mounting, enclosure and environment
- Exact model code and documentation revision
- Quantity and destination
Request the current datasheet revision and identify the scope of any certification, coordination or compatibility claim. If the response proposes a substitute, require the same evidence set for that substitute. Record quantity and destination after the technical inputs so commercial terms do not obscure unresolved engineering questions.
Stop Conditions Before Order Release
Do not release the order while a publication-critical input is unknown, the quoted model is ambiguous, or a required rating is supported only by another manufacturer’s document. Stop as well when a combination claim lacks exact component codes or when a diagram is being reused across product families. These are evidence gaps, not editorial details.
The final approval record should state what the selected item does, what remains outside its scope and which exact documents support the decision. If the application, duty, environment or proposed model changes, reopen the relevant checks rather than carrying the previous conclusion forward.
Frequently Asked Questions
Can I size an MPCB from motor kW alone?
No. Voltage, current, starting duty, fault level and exact manufacturer data are also required.
Does an MPCB eliminate the need for a contactor?
Not automatically. Switching and control scope must be defined separately from the protective functions.
Can matching current ranges prove coordination?
No. Coordination claims require an exact manufacturer-tested combination record.
Related RITOKS Products and Guidance
Use these links as separate category, product and educational records. A contextual link does not claim interchangeability, compatibility or a coordinated combination.
GYMP7 motor protection circuit breakers
MPCB vs thermal overload relay vs MCB
Technical References
The following authoritative sources support only the general concepts stated below. Their product values, diagrams, combinations and approvals do not transfer to RITOKS products.
ABB, Control Catalog: IEC Manual Motor Starters
Supports the distinction between manual motor starters, contactors and overload relays, and the need to use exact coordination tables. ABB model data does not transfer to GYMP7.
ABB, Contactors and Overload Relays Guide
Supports separate overload, short-circuit protective-device and coordination decisions. Its combinations are ABB-only.
Request an Exact-Model Review
Send the recorded application requirements, exact documentation questions, quantity and destination through the RITOKS contact form. An RFQ requests an exact-model review; this guide does not approve a wiring design, installation or automatic substitute.