What power feed and cabling does a PSA plant need?

What the supplier must state

WHO's Foundations of medical oxygen systems (2023) asks the supplier for an electrical requirements chart, including the starting current, minimum protection current and load curve, to determine total power needs and configure the power source, such as a diesel generator, voltage stabiliser or grid connection with transformer. The power load differs with the configuration, single or multiplex, with or without a cylinder filling station. UNDP's 2025 requirements ask suppliers for the same chart.

The 2020 WHO interim specification for PSA plants (superseded by WHO's technical specifications of 31 December 2024), issued on 8 June 2020 and stating that it would expire two years after publication, gave 380 VAC ±15%, three-phase, 50 Hz for plant operation and 220 VAC ±15%, single-phase, 50 Hz for the control system, and asked for electrical requirements to be locally compatible, with frequency, voltage and plug type specified.

Feeder and cables

• A feeder from the main distribution panel. The Global Fund site readiness overview (11 April 2025) asks for an electrical infrastructure assessment by a qualified professional, a stable and sufficiently sized connection from the utility (such as a transformer upgrade, when required), trenches of about 20 cm x 60 cm for the feeder cables from the metering panel, and a new feeder from the main distribution panel to the plant location agreed with the supplier.
• A cable to each component. WHO (2023) and UNDP (2025) ask for appropriately sized cables to the air compressor, dryer, oxygen generator and booster compressor, with a power cabinet that has surge and earth protection and a built-in phase controller for three-phase devices.
• Aluminium or copper. Assist International (Open Critical Care) suggests aluminium from the electricity meter to the generator control panel, and copper from the control panel to the compressor for sizes of 22 kW and above.
• Balanced phases and earthing. Global Fund sustainability guidance (2024) asks for properly balanced three-phase power, reliably sized distribution cables and appropriately sized protection from voltage fluctuation; WHO (2023) asks for power from an armoured, grounded outlet with an earth cable.
• Protection devices. The 2020 WHO interim specification asked for resettable circuit breakers or replaceable fuses in both neutral and live lines.

Stability and backup

• Voltage. WHO (2023) states that voltage fluctuation will cause damage to the unit, and the USAID RISE operating procedures (2022), written for hospitals in India, say not to operate the plant when the voltage supply is unstable.
• Frequency. Assist International (Open Critical Care) notes that power frequency fluctuation can, over time, damage the large motors of a PSA plant.
• Transfer switch. WHO (2023) says the primary and secondary supplies should connect to the power cabinet through a transfer switch: an automatic one reduces the transfer delay, a manual one needs less maintenance. The Global Fund commissioning guideline (2024) checks that backup power meets the start-up and running loads and has the same phase rotation as the primary supply.
• Control circuit. Assist International advises a small 1 kW UPS feeding the control circuit and PLC.

ULTRAOX plants

For an ULTRAOX plant, the customer provides the three-phase electrical supply, and the plant can be connected to a diesel-electric generator (ULTRAOX datasheet 2022). The ULTRASCREW compressors used in ULTRAOX ST plants have 400 V, three-phase, 50 Hz IE3 IP55 motors with star-delta starting. Compressor power per model is listed in the datasheet tables, from 2.2 kW (model 3) to 97.5 kW per unit (model 560) for the ULTRAOX SC and from 2.2 kW to 220 kW (model 1640) for the ULTRAOX ST, whose datasheet adds that compressor power and pressure can vary with the service conditions of the facility.