# Does 50 Hz or 60 Hz matter for an oxygen plant?

**Does the mains frequency (50 Hz or 60 Hz) and its fluctuation affect an oxygen plant and its spare parts?**

Yes: WHO's 2020 interim PSA specifications (superseded in 2024) asked for a plant's electrical requirements to be locally compatible, with frequency, voltage and plug type specified, and Assist International warns that power frequency fluctuation can, over time, damage the large motors that are a very expensive part of PSA plants.

WHO's Technical specifications for PSA oxygen plants (interim guidance, 8 June 2020) gave as power requirements 380 VAC ± 15%, three-phase, 50 Hz for plant operations and 220 VAC ± 15%, single-phase, 50 Hz for the control system, with a note on voltage, frequency and plug variations across countries, and asked for the product label to state the electrical input requirements (voltage, frequency and socket type). WHO's Foundations of medical oxygen systems (2023) repeats that electrical elements must be compatible with the power source. The PATH and CHAI brief (July 2021) describes the ideal supply as 230 V single-phase for VSA and valve operations and 380 to 400 V three-phase at 50 Hz for PSA and compressor and dryer operations.

## Frequency and voltage on site

- Frequency fluctuation: Assist International, answering on Open Critical Care, says power frequency fluctuation over time can damage the large motors, which are a very expensive part of PSA plants.
- Voltage fluctuation: WHO (2023) states that voltage fluctuation will cause damage to the unit, and that voltage stabilisers or diesel generators with stable voltage can be installed where needed.
- Balanced phases: Global Fund sustainability guidance (22 August 2024) asks for properly balanced three-phase power, reliably sized cables and appropriately sized protection from voltage fluctuation.
- Backup power: Global Fund commissioning guidelines (28 August 2024) ask for the supply voltage on all phases to be measured at start-up and in normal operation, and for the backup supply to meet start-up and running loads with the same phase rotation as the primary supply.
- Unstable supply: a USAID RISE operating procedure, written for hospitals in India, tells operators not to run the plant when the voltage supply is unstable and to verify that the incoming voltage matches the plant manual.

## Spare parts

WHO's 2020 specifications asked for a 3-year spare parts kit that identifies brand and model specifics, for example for the circuit breaker, printed circuit board, compressor components and motor capacitor. Global Fund commissioning guidelines ask for photos or details of the nameplates of all supplier-provided equipment, including voltage regulators, to be kept for the hospital's future use.

In the ULTRAOX 2022 datasheet, the ULTRASCREW compressors have high efficiency 400 V, three-phase, 50 Hz, IE3 IP55 motors with class F insulation. The ULTRASEC refrigeration dryer table lists single-phase 230 V supplies at 50 or 60 Hz for models USL 1 to USL 5, single-phase 230 V at 50 Hz for USL 6 to USL 15, and three-phase 400 V at 50 Hz from USL 16. The customer provides the three-phase supply, and the plant can be connected to a diesel-electric generator.

### Should a PSA plant also have a UPS?

Assist International advises a small 1 kW uninterruptible power supply feeding the control circuit and PLC, in addition to generators.

### What should a diesel generator for a PSA plant have?

WHO (2023) prefers an electronically controlled engine and, where the generator is the primary source, features such as shunt excitation and an integrated automatic voltage regulator.

## Sources

- [WHO, Technical specifications for PSA oxygen plants, interim guidance (8 June 2020), power supply and labelling](https://www.who.int/publications/i/item/WHO-2019-nCoV-PSA_Specifications-2020.1)
- [Open Critical Care FAQ (Assist International): How do power frequency fluctuations affect an oxygen plant, in terms of spare parts?](https://opencriticalcare.org/faq/how-do-power-frequency-fluctuations-affect-an-oxygen-plant-in-terms-of-spare-parts/)
- [Open Critical Care FAQ (Assist International): Is it advisable to have UPS as well as generators for a PSA plant?](https://opencriticalcare.org/faq/is-it-advisable-to-have-ups-as-well-as-generators/)
- [WHO, Foundations of medical oxygen systems (17 February 2023), sections 2.2.3 and 3.5.3](https://www.who.int/publications/i/item/WHO-2019-nCoV-Clinical-Oxygen-2023.1)
- [PATH and CHAI, Oxygen Generation and Storage: Pressure/Vacuum Swing Adsorption Plant (July 2021)](https://media.path.org/documents/O2_generation_and_storage_PSA_VSA_v1.pdf)
- [Global Fund / Build Health International, Overview: Sustainability Guidance for PSA Oxygen Plants (22 August 2024)](https://resources.theglobalfund.org/media/bwrp43cm/cr_c19rm-psa-oxygen-plant-sustainability_overview_en.pdf)
- [Global Fund / Build Health International, Overview: PSA Oxygen Plant Commissioning Guidelines (28 August 2024)](https://resources.theglobalfund.org/media/qp3h1vxo/cr_c19rm-psa-oxygen-plant-commissioning_overview_en.pdf)
- [USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [ULTRAOX datasheet 2022, p. 9, p. 10 and p. 13](https://www.ultracontrolo.com/ultraox)
- [ULTRASEC datasheet (model table)](https://www.ultracontrolo.com/products/ultrasec)
- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/does-50-or-60-hz-matter-for-an-oxygen-plant/