Lovato PMF20A240 self-powered minimum and maximum frequency monitoring relay for 220–240 V AC single-phase systems, with selectable 50 or 60 Hz frequency and adjustable trip delay.
£462.83
The Lovato PMF20A240 is a reliable minimum and maximum frequency monitoring relay designed to supervise the frequency of 220–240 V AC electrical supplies. As part of the established Lovato Electric PMF20 monitoring relay range, it helps protect machinery, control systems and electrical equipment against potentially damaging underfrequency and overfrequency conditions.
The relay is self-powered directly from the monitored circuit and supports selectable nominal frequencies of 50 or 60 Hz. Adjustable minimum and maximum frequency thresholds allow engineers to define an acceptable operating window around the selected rated frequency, making the PMF20A240 suitable for generator systems, industrial machinery and power-quality supervision.
Adjustable tripping and resetting times from 0.1 to 20 seconds help prevent nuisance operation during short-duration frequency fluctuations. Its normally energised changeover output, automatic reset and clear LED indication provide dependable fault signalling in compact DIN rail control panels where stable frequency is essential for equipment performance.
Abnormal supply frequency can affect motor speed, transformer performance, timing functions and the stability of sensitive electronic equipment. The Lovato PMF20A240 continuously compares the measured frequency with the configured minimum and maximum limits, providing a clear fault response whenever the frequency moves outside the permitted range.
When an abnormal frequency remains present beyond the selected tripping delay, the normally energised relay output de-energises. This output can stop machinery, activate an alarm or send a fault signal to a PLC or control system. Automatic resetting restores the output once the frequency returns within the acceptable range for the configured resetting time.
| Phase | Single Phase |
|---|---|
| Manufacturer | Lovato Electric |
| Series | PMF20 |
| Model | PMF20A240 |
| Product type | Frequency monitoring relay |
| Monitoring function | Minimum and maximum frequency |
| System type | Single-phase |
| Rated monitored voltage | 220–240 V AC |
| Power supply | Self-powered |
| Operating voltage range | 0.85–1.1 × Ue |
| Selectable rated frequency | 50 or 60 Hz |
| Frequency measurement range | 40–70 Hz |
| Minimum frequency set-point | 90–99% of rated frequency |
| Maximum frequency set-point | 101–110% of rated frequency |
| Tripping delay | 0.1–20 seconds |
| Resetting time | 0.1–20 seconds |
| Reset hysteresis | 0.5% |
| Reset mode | Automatic |
| Repeat accuracy | Better than ±0.1% |
| Maximum power consumption | 10 VA |
| Maximum power dissipation | 1.5 W |
| Relay outputs | 1 |
| Contact arrangement | 1 changeover SPDT |
| Relay operating mode | Normally energised, de-energises on trip |
| Rated operational voltage | 250 V AC |
| Maximum switching voltage | 400 V AC |
| Conventional thermal current | 8 A at up to 40°C |
| Electrical life | 100,000 operations at rated load |
| Mechanical life | 30,000,000 operations |
| Programming method | Front potentiometers |
| Terminal type | Screw terminals |
| Maximum terminal torque | 0.8 N·m |
| Conductor capacity | 0.2–4 mm² |
| Rated insulation voltage | 575 V |
| Rated impulse withstand voltage | 6 kV |
| Mounting type | 35 mm DIN rail |
| Modular width | 2 modules |
| Protection rating | IP40 front, IP20 terminals |
| Operating temperature | -20°C to +60°C |
| Storage temperature | -30°C to +80°C |
| Dimensions (W × H × D) | 35.8 × 104.7 × 64.9 mm |
| Weight | Approx. 125 g |
| Compliance | IEC/EN 60255-5, IEC/EN 61000-6-2, IEC/EN 61000-6-3, UL 508, CSA C22.2 No. 14 and IEC/EN 60335-2-89 |
| HS Code | 85364900 |
The PMF20A240 monitors the frequency of a 220–240 V AC supply and detects both underfrequency and overfrequency conditions.
Yes. The rated operating frequency can be selected as either 50 or 60 Hz.
The minimum threshold can be adjusted from 90% to 99% of the selected rated frequency, while the maximum threshold can be adjusted from 101% to 110%.
No. The relay is self-powered directly from the monitored 220–240 V AC circuit.
Yes. Both the tripping delay and resetting time can be independently adjusted from approximately 0.1 to 20 seconds.
The normally energised changeover relay de-energises after the configured delay, allowing machinery to be stopped or an alarm signal to be generated.
Lovato Electric monitoring relays are used by panel builders, machine manufacturers and automation engineers to detect abnormal electrical conditions and improve the safety and reliability of industrial control systems.
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2025 has been a big year for LED Controls, and our blog has expanded accordingly. We've covered a wide range of topics across industrial control and factory automation this year. From core technology explainers and new product releases to panel building best practice...