What this is
What is motor current signature analysis (MCSA)?
What is motor current signature analysis (MCSA)?
Motor current signature analysis is a predictive maintenance technique that reads the frequency spectrum of a motor's supply current while it runs, rather than stopping it to inspect it. Characteristic sidebands around the line frequency reveal broken rotor bars, air gap eccentricity and some winding and bearing faults. It is run from the switchgear or a clamp at the terminals, so no disassembly and no downtime are needed to collect the data.
What faults does MCSA detect that vibration analysis misses?
Vibration analysis is mechanical: it sees forces transmitted through the frame and bearings. MCSA is electromagnetic: it sees the effect of a fault on the current the motor draws, which shows up long before it produces enough mechanical vibration to register. Broken or cracked rotor bars are the classic example, along with early eccentric air gaps, both of which can sit undetected by a vibration route for months.
Why does load percentage at test matter for MCSA results?
Rotor bar related sidebands scale with slip, and slip only exists under load. A motor tested unloaded or lightly loaded produces a current spectrum that looks clean regardless of the rotor's actual condition, because there is not enough slip frequency to generate a visible sideband. A result recorded at low load cannot be trusted as a clean bill of health.
Scope
When is a motor current signature analysis required?
This record is one step in a larger reliability programme. Using it for work that belongs to a neighbouring template produces records that are hard to report on later.
Use this template when
- A motor on the condition monitoring route is due its scheduled current signature test
- A vibration or thermal alert has raised suspicion of an electrical fault that vibration alone cannot confirm
- A baseline needs to be established for a motor newly added to the monitoring route
- A retest is required after a repair, rewind or bearing replacement to confirm the fault has cleared
- A linked record needs this one to exist: links condition monitoring, work orders
Do not use it for
- Alignment and Balance Record, which records shaft alignment or rotor balancing work, with before and after readings, not current spectrum data.
- Lubrication Route Record, which records the lubrication round, with what was applied where, how much, and any condition observed.
- Condition Monitoring Route Plan, which sets which assets are monitored, by which technique, at what interval and against which alarm limits, rather than recording a single test.
- Sensor and IoT Data Review, which reviews continuous online sensor trends rather than a discrete manual MCSA test event.
- Anything outside KnowMaintain, which belongs in the workspace that owns that process
Compliance mapping
Which ISO 55001 cl.8.1 requirements does this satisfy?
ISO 55001 cl.8.1 requires operational controls that keep asset performance within acceptable limits; the fields below are how this record produces evidence against that clause.
| Clause | Requirement | Where it lands |
|---|---|---|
| ISO 55001 cl.8.1 – operational planning and control | Asset condition data must be collected under controlled, repeatable conditions so it can be relied on for a decision. | Conditions |
| ISO 55001 cl.8.1 – operational planning and control | The asset and its identity must be traceable to the register before any condition data is attached to it. | Header |
| ISO 55001 cl.9.1 – monitoring, measurement, analysis and evaluation | Condition indicators must be interpreted against a defined severity scale, not left as raw readings. | Findings |
| ISO 55001 cl.9.1 – monitoring, measurement, analysis and evaluation | A trend judgement (deteriorating, stable, improved) must be recorded against the asset's own history, not just the current snapshot. | Assessment |
| ISO 55001 cl.10.2 – nonconformity and corrective action | Where the finding indicates a fault, an action must be raised and traceable back to this record. | Assessment |
| ISO 55001 cl.8.1 – operational planning and control | Completion and analyst sign-off must be captured so the record can be relied on as controlled evidence. | Result |
What it does not cover
- Load Percent At Test, which if left low or unrecorded means a Normal rotor bar finding cannot be trusted regardless of what the spectrum showed.
- Baseline Available, which if answered No turns Overall Severity into a first observation rather than a trend judgement, however the field is filled in.
- Supply Voltage Balanced, which if significant imbalance is present means findings should be reviewed for a site electrical cause before the motor is condemned.
- Same Test Point As Baseline, which if answered No breaks the comparison the whole Change Since Last Test judgement depends on.
- Action Recommended, which if left at Continue monitoring against an Alert or Alarm severity contradicts its own Overall Severity finding.
Global
Motor Current Signature Analysis requirements by country
MCSA itself is a technique, not a licensed inspection, so its legal weight comes from the asset management and electrical equipment frameworks it feeds evidence into.
ISO 55001
An asset management system standard requiring operational controls that keep asset performance within defined limits, supported by monitoring and measurement.
MCSA results are only useful under ISO 55001 if they feed a documented decision trail: severity, trend, and action, held against the asset record, not left as a standalone test report.
NFPA 70B, Recommended Practice for Electrical Equipment Maintenance
Recommends predictive electrical testing, including current signature analysis, as part of an electrical preventive maintenance programme for motors and switchgear.
Where a site's EPM programme cites NFPA 70B, this record is the documentary evidence that the recommended predictive test was actually performed and interpreted, not just scheduled.
IEC 60034 series, rotating electrical machines
Defines the performance, rating and testing parameters for the class of motor under test, against which baseline current and vibration levels are ultimately judged.
Retest tolerances and what counts as a meaningful change from baseline should trace back to the motor's IEC 60034 rating, not an arbitrary percentage.
How to complete it
How to complete a motor current signature analysis, step by step
Filling in every field correctly still leaves four judgement calls that decide whether the record is defensible if the motor fails later.
A non-zero Load Percent At Test is not the same as a representative load. An analyst who accepts a brief, atypical loading window to get the test done quickly is producing a record that will not stand up if a rotor fault is missed and the motor fails weeks later under normal duty.
Driven By Variable Speed Drive changes what the current spectrum should look like at baseline. A finding of elevated sidebands on a VSD-fed motor needs the analyst to judge whether the drive's own switching frequency, not the rotor, produced the pattern, before recommending intervention.
Same Test Point As Baseline being No does not automatically invalidate the test, but it does mean the analyst must judge how much of any apparent change is down to measurement location rather than motor condition, and say so in the assessment.
Voltage imbalance and harmonic distortion can themselves produce current sidebands that look like rotor or winding faults. Where Supply Quality Issue Found is anything other than None, the analyst has to judge whether the electrical finding explains the mechanical-looking indication before recommending work on the motor itself.
What auditors find
Most common motor current signature analysis findings
The patterns that repeat across MCSA records tend to sit at the boundary between a genuine motor fault and a supply or test-condition artefact.
| Finding | Clause | What fixes it |
|---|---|---|
| Rotor Bar Condition marked Broken bars indicated with Load Percent At Test left blank | ISO 55001 cl.9.1 | Require Load Percent At Test before Rotor Bar Condition can be recorded as anything other than Good, so a positive finding always carries the evidence that made it valid. |
| Steady State Achieved marked No but Overall Severity still recorded as Normal | ISO 55001 cl.8.1 | Route any test where steady state was not achieved to a mandatory retest before the severity band is accepted into the asset record. |
| Change Since Last Test marked Stable when Baseline Available is No | ISO 55001 cl.9.1 | Grey out the Change Since Last Test field, or force it to a Not applicable state, whenever no baseline exists to compare against. |
| Supply Quality Issue Found marked Significant with no note pointing to a work order against the site supply, only the motor | ISO 55001 cl.10.2 | Add a required linked action specifically for supply-side findings, separate from the motor's own Action Recommended field. |
| Action Recommended left at Continue monitoring against an Alarm severity rating | ISO 55001 cl.10.2 | Add a validation rule that blocks Continue monitoring whenever Overall Severity is Alert or Alarm. |
| Driven By Variable Speed Drive marked Yes with no note on which sidebands were attributed to drive switching versus the rotor | ISO 55001 cl.9.1 | Add a free-text field capturing the drive's fundamental switching frequency whenever this option is Yes, so the analyst's reasoning is auditable later. |
Case in point
Case in point: the fan motor that passed twice before it failed
A cooling tower fan motor was tested on the standard six-month route and came back Normal both times, current spectrum flat, no action recommended. Three weeks after the second test it seized in service. The retrieved records showed Load Percent At Test recorded at 22 and 18 percent on both occasions; the fan had been running against a partially closed damper for months, well below its rated duty.
The rotor bar fault was there throughout, invisible at that load because the slip frequency never rose high enough to generate a detectable sideband. Once the site started rejecting any MCSA test recorded under 40 percent load as inconclusive rather than filing it as Normal, the same motor class began surfacing genuine rotor faults on the very next scheduled route.
The template
The template, field by field
The form exactly as it installs. Every field, option, score and conditional rule is editable, and the links to other templates come with it.
5 sections
- Reference
- MNT-085
- Archetype
- Record
- Record ID
- MCSA-2026-000
- Scoring
- Severity
- Direction
- Low is good
- Singleton
- Yes
- Basis
- ISO 55001 cl.8.1
- Links
- Links Condition monitoring, Work orders
- Tags
- Predictive
- Sections
- 5
- Fields
- 45
- Follow up fields
- 3
- Repeating sections
- 0
- Links out
- 4
Header
12 fieldsRecord ID*
Auto sequence. Format MCSA-2026-000.
The record's own ID. Other templates point at this value.
Status*
Drives who this goes to next.
- Planned2 pts
- In progress2 pts
- Complete3 pts
- Deferred0 pts
- Open0 pts
- Closed3 pts
- Overdue0 pts
Date and Time*
Completed By*
Site*
Site ID*
Format SITE-000.
Links to FDN-001 Site ID
Asset*
Asset ID*
Format AST-0000.
Links to FDN-002 Asset ID
It Sees What Vibration Cannot
Broken rotor bars, eccentric air gaps and winding faults show in the current spectrum long before they produce enough vibration to notice.
Motor Rating
Motor Type
Analyst*
Conditions
6 fieldsLoad Percent At Test*
The test needs meaningful load. A motor running unloaded hides rotor faults completely.
Steady State Achieved*
- Yes3 pts
- Marginal1 pt
- No0 pts
Supply Voltage Balanced*
- Yes3 pts
- Slight imbalance1 pt
- Significant0 pts
Driven By Variable Speed Drive
- No3 pts
- Yes1 pt
Baseline Available*
- Yes3 pts
- No0 pts
Same Test Point As Baseline*
- Yes3 pts
- No0 pts
Findings
8 fieldsRotor Bar Condition*
- Good3 pts
- Marginal1 pt
- Broken bars indicated0 pts
Sideband Amplitude
Air Gap Eccentricity*
- None3 pts
- Slight1 pt
- Significant0 pts
Stator Winding Indication*
- None3 pts
- Early1 pt
- Significant0 pts
Bearing Indication*
- None3 pts
- Early1 pt
- Advanced0 pts
Load Related Indication
- None3 pts
- Some1 pt
- Significant0 pts
Supply Quality Issue Found*
Voltage imbalance damages motors continuously and is usually a site problem, not a motor problem.
- None3 pts
- Some1 pt
- Significant0 pts
Harmonic Distortion Noted
- Within limits3 pts
- Elevated1 pt
- Excessive0 pts
Assessment
6 fieldsOverall Severity*
- Normal4 pts
- Watch3 pts
- Alert1 pt
- Alarm0 pts
Change Since Last Test*
- Improved3 pts
- Stable3 pts
- Deteriorating0 pts
Estimated Time To Failure
- Over 12 months4 pts
- 6 to 12 months3 pts
- 1 to 6 months1 pt
- Under a month0 pts
Action Recommended*
- Continue monitoring3 pts
- Plan intervention2 pts
- Schedule urgently1 pt
- Remove from service0 pts
Work Order ID
Links to MNT-002 Work Order ID
Retest Interval*
- Extended3 pts
- Unchanged3 pts
- Shortened1 pt
- Continuous2 pts
Result
13 fieldsItems Assessed*
Excludes anything marked N/A.
Items Failed*
Score Percent*
Calculated on submission. High is good. N/A items leave the denominator.
Result Band*
- Pass3 pts
- Caution1 pt
- Fail0 pts
Completeness Percent*
How much of the template was actually answered. A high score on a half completed form is not a high score.
Action Required*
Raise the action record, then enter its reference here.
- No2 pts
- Yes0 pts
Priority
- High0 pts
- Medium1 pt
- Low3 pts
CAPA ID
Format CAPA-2026-00000.
Links to FDN-014 CAPA ID
Action Owner
Analyst*
Signature*
Reliability*
Second Signature*
MNT-085 · record IDs look like MCSA-2026-000 · Links Condition monitoring, Work orders
Open in KnowellaRun it with agents
From a document you fill in to a programme that runs itself
The form is the easy part. Keeping it current, routing it to the right owner and holding the evidence together is the work that actually slips.
Holds the MCSA library against your asset register, tracks which motors are due their next test on the condition monitoring route, and keeps the baseline trail together.
Turns an Alert or Alarm severity finding into a scheduled outage window before the motor reaches Estimated Time To Failure, coordinating with production rather than surprising it.
Keeps the ISO 55001 evidence trail intact across every asset, so an audit can trace a severity finding back to the test conditions that produced it.
Coordinates the crew, rolls completion and exceptions into one view, and holds every write for your approval before it touches a record.
This template lives in KnowMaintain — asset maintenance. Work orders, planned maintenance, calibration, reliability and shutdowns.
Meet KnowMaintain→Glossary
Motor Current Signature Analysis definitions and key terms
- Sideband
- A pair of small frequency peaks either side of the main supply frequency in the current spectrum, produced by a periodic disturbance such as a broken rotor bar. Their spacing and amplitude are what an analyst reads to judge fault severity.
- Slip
- The difference between the rotating magnetic field's speed and the rotor's actual speed under load. Rotor bar fault sidebands are spaced at a frequency proportional to slip, so slip must be present, meaning the motor must be loaded, for the fault to show.
- Air gap eccentricity
- An uneven gap between the stator and rotor caused by bearing wear, a bent shaft or a manufacturing defect. It produces its own characteristic current sidebands and, left uncorrected, accelerates bearing and winding wear.
- Steady state
- A test condition where the motor's speed, load and temperature have stabilised rather than still changing from a recent start or load step. MCSA readings taken before steady state is reached are not comparable to a stored baseline.
- Baseline
- The first trusted MCSA reading taken for a given motor at a known test point and load, against which every later test is compared to judge change over time rather than an absolute pass or fail.
FAQ
Frequently asked questions about motor current signature analysis
What is the motor current signature analysis template based on?+
It is built against ISO 55001 cl.8.1, the asset management systems standard's requirement for operational controls that keep asset performance within acceptable limits, supported by monitoring and measurement under cl.9.1.
What sections does the motor current signature analysis contain?+
There are five sections: Header, Conditions, Findings, Assessment and Result. Together they hold 45 fields, most of which are required, covering test setup, test validity, the electrical findings themselves, and the resulting action.
How many motor current signature analysis records should we have?+
This is a singleton per asset in practical terms: one live record set up per monitored motor and updated at every scheduled test, rather than a fresh unrelated record each time with no link back to the baseline.
How is a motor current signature analysis scored?+
Scoring is severity, where low is good: Normal, Watch, Alert and Alarm bands drive the recommended action, from continued monitoring through to removal from service.
Can MCSA replace vibration monitoring on a motor?+
No. The two techniques see different fault mechanisms; MCSA is strong on rotor bar and air gap faults but weaker on general bearing wear than a dedicated vibration route. Most reliability programmes run both, not one instead of the other.
Why does the template ask whether the motor is fed by a variable speed drive?+
A VSD changes the current waveform the motor draws, which can introduce its own sidebands unrelated to any mechanical fault. Recording drive presence lets the analyst separate a drive artefact from a genuine rotor or winding indication.
Keep going
Related templates and programmes
Industries this is written for
Programmes this belongs to
Used together in Reliability and Predictive Maintenance
Root Cause Analysis
Finds out why something happened rather than who was involved
Equipment Failure Report
Records that an asset has failed and stopped or degraded production
Failure Mode Record
Records how an asset failed, using standard failure mode codes rather than free text
Repair Record
Records what was actually done to fix the asset, including parts replaced and settings changed
Temporary Repair Record
Records a repair that is not permanent, with an expiry date and a plan for the proper fix
Repeat Failure Review
Reviews an asset that has failed the same way more than once
More in Predictive Maintenance
Alignment and Balance Record
Records shaft alignment or rotor balancing work, with before and after readings
Lubrication Route Record
Records the lubrication round, with what was applied where, how much, and any condition observed
Condition Monitoring Route Plan
Sets which assets are monitored, by which technique, at what interval and against which alarm limits
Sensor and IoT Data Review
Reviews continuous sensor data for drift, alarms and anomalies, and whether anybody acted on them
Written and reviewed by
Siddarth Singh
Founder & Chief Executive Officer, Knowella
Certified Safety Professional and industrial and systems engineer with more than a decade inside food supply chain, freight and manufacturing operations. This page was written against the current text of the standards it cites, not against secondary summaries of them.
- Certified Safety Professional (CSP), Board of Certified Safety Professionals
- MBA, University of Chicago Booth School of Business
- MS and BS, The Ohio State University, Industrial and Systems Engineering
- Six Sigma Black Belt
Sources and last review. Reviewed 16 August 2026 against:
- ISO 55001 cl.8.1, cl.9.1, cl.10.2 — Asset management systems
- NFPA 70B — Recommended Practice for Electrical Equipment Maintenance
- IEC 60034-1 — Rotating electrical machines, rating and performance
- IEEE Std 1068 — Recommended Practice for the Repair and Rewinding of Motors
This page is general guidance, not legal advice. Confirm requirements with your jurisdiction’s regulator.