Pump Reliability & Predictive Maintenance (PlusSmart) · 10 min read · Updated November 2026
Electrical Signature Analysis at the MCC: Submersible, Remote and Ex-Area Motors
A third of the motors in a typical plant cannot carry a vibration sensor: they are under water, on top of a cooling tower, inside a hazardous area or simply never visited. Their current and voltage, however, pass through a switchboard that someone opens every month. Electrical signature analysis reads the motor — and the pump behind it — from there.
An induction motor is a sensor as well as a machine. Any periodic variation in the air gap between rotor and stator, or in the load torque, modulates the stator current. In the current spectrum those modulations appear as sidebands around the supply frequency at frequencies characteristic of each fault. Motor current signature analysis (MCSA) reads the current; electrical signature analysis (ESA) adds voltage so that supply-side problems can be separated from motor and load problems. ElectroSine implements ESA with hardware installed in the motor control centre — current transformers and voltage taps — and software that converts the spectra into diagnoses. Nothing is mounted on the machine.
Worked example: a cracked rotor bar
Broken or cracked rotor bars produce sidebands at f × (1 ± 2s), where f is the supply frequency and s the slip. A 4-pole 50 Hz motor running at 1,470 rpm has synchronous speed 1,500 rpm and slip s = (1,500 − 1,470)/1,500 = 0.02, so the sidebands sit at 48 Hz and 52 Hz. Their amplitude relative to the 50 Hz line, in dB, grades the severity — roughly, above −45 dB is healthy, −45 to −35 dB warrants watching, above −35 dB indicates developing bar damage. Vibration analysis finds this fault only with difficulty; ESA finds it routinely, which is why it is the first technology for large motors with many starts.
What ESA detects
| Group | Faults | Signature |
|---|---|---|
| Rotor | Cracked/broken bars, end-ring faults, static/dynamic/mixed eccentricity | Slip sidebands; rotational-speed sidebands around slot harmonics |
| Stator | Turn-to-turn and coil shorts, insulation degradation | Changes in current unbalance, specific harmonics, negative-sequence current |
| Bearings | Outer/inner race, rolling elements, lubrication (DE and NDE) | Bearing-defect frequencies as current sidebands; requires high resolution and good signal-to-noise |
| Mechanical | Misalignment, unbalance, looseness, gear mesh, belt tension, coupling wear | 1×, 2× and gear-mesh modulation of current |
| Load / pump | Cavitation, impeller anomalies, torque oscillation, overload, no-load running | Broadband and vane-pass modulation; load-current trends |
| Supply | Voltage unbalance, harmonics, frequency deviation, VFD harmonics, poor connections, sags and swells | Voltage spectrum and symmetrical components |
Voltage unbalance: the fault the plant already has
A few percent of voltage unbalance creates a disproportionate negative-sequence current and extra winding heating; NEMA MG-1 derates motors to about 0.98 at 1 % unbalance, 0.95 at 2 %, 0.88 at 3 %, 0.82 at 4 % and 0.75 at 5 %, and advises against running above 5 %. Plants with long feeders, single-phase loads on motor buses or loose connections run motors at 2–4 % unbalance for years, shortening winding life and wasting energy. ESine4 performs full three-phase analysis — voltage and current unbalance, negative sequence, phase loss, true active and reactive power, NEMA/IEC derating — so the first report from an ESA installation is often an electrical-supply correction that benefits every motor on the bus.
Where ESA is the only option
- Submersible and borehole pumps — wastewater lift stations, deep wells, dewatering: the motor is under water, the current is in the panel.
- Cooling-tower and roof-mounted fans — accessible only by scaffold.
- Hazardous-area motors — no field work, no permits.
- Motors in hot or dusty enclosures — cement fans, kiln drives, furnace blowers.
- Large MV motors — where rotor and stator faults are the dominant risk and the CTs already exist.
ESine3 versus ESine4
ESine3 is the monitoring-at-scale product: continuous current and voltage analysis for many motors with lower installation cost, intended to cover a fleet. ESine4 is the high-resolution, real-time instrument for complex and critical systems: full three-phase analysis, phase-to-phase fault location, zero-sequence ground faults, phase sequence, and the derating calculations. A plant typically installs ESine3 on the general-service motors and ESine4 on the MV drives, large pumps and anything with a history. Both feed PlusSmart engineers who measure a baseline for each motor and turn later changes into actions, combining the results with vibration, oil and drive data in one ranking.
Installation and safety
Installation is electrical work in the MCC under the plant's lockout and arc-flash procedures, usually during a scheduled panel maintenance; split-core CTs and fused voltage taps minimise the intervention. Motors on VFDs are supported — the analysis separates drive harmonics from fault signatures — and reports the harmonic distortion the drive produces. The deliverable is not a spectrum but a per-motor baseline and, from then on, a change report with cause and recommended action.
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Quick answers
Can ESA detect bearing faults as well as vibration does?
It detects them, typically later and with less precision on location than a well-mounted accelerometer. For accessible machines use both; for inaccessible motors ESA is the practical way to see bearings at all.
Does it work on VFD-driven motors?
Yes. ESine analyses the drive-induced harmonics and separates them from mechanical and electrical fault signatures, and also reports the power quality on the motor side of the drive.
Does the motor have to stop for installation?
Installation is in the MCC and follows electrical safety procedures; it is usually done during routine panel maintenance or a scheduled outage of the feeder, not of the whole plant.