Running commercial refrigeration through power cuts: generators and inverters

The starting current problem

When a compressor starts, it draws a short burst of current several times higher than its running current. A generator or inverter must supply that surge without its voltage collapsing. If it cannot, the compressor stalls, hums and trips on overload, and repeated attempts damage it.

Ask the refrigeration supplier for each unit's running current and starting current, or the recommended backup capacity. Size the backup for the starting surge of the largest unit plus the running load of everything else on the same supply.

Generators

• Size for starting current, not just total running watts; your generator supplier can advise with the motor data.
• Voltage and frequency should be stable under load; poorly regulated sets can damage compressors and controllers.
• Use a proper change-over switch installed by a licensed electrician, so the generator can never feed back into the grid supply.
• Earth the generator system correctly.
• Place the generator so its exhaust and heat do not reach refrigeration condensers.

Inverters and UPS

Inverters suit smaller loads such as a single visi cooler or a pharmacy refrigerator. Choose a pure sine wave output; motors run hotter and noisier on modified or square wave output. The inverter's surge rating must handle compressor start, and battery capacity decides how long it lasts.

Running a compressor continuously for hours drains batteries quickly. Calculate backup duration from the unit's actual energy use in your conditions rather than from the label on a cool day.

Keep inverter batteries in a ventilated spot, away from the refrigeration condenser and out of direct sun. Battery life falls in hot rooms, and a backup system that worked in winter may run short in the summer months when outages and refrigeration load are both at their worst. Test the backup under real load before you rely on it.

Staggered restart

When power returns, or when the generator takes over, every unit tries to start at once. The combined surge can trip breakers, stall the generator or overload the inverter. Controllers often include a start delay; your electrician or technician can set different delays on different units so they start one after another. Some stabilisers and protection devices also add a delay.

Do not switch units on and off repeatedly during fluctuating supply. Each restart before pressures equalise stresses the compressor.

Decide priorities in advance

Backup capacity is rarely enough for everything. Decide which units matter most — freezers with high-value stock, pharma refrigerators, the cold room — and put those on backup first. Display coolers holding bottled drinks may be able to wait.

Write the plan down and train staff, so during an outage nobody improvises with extension leads.

During an outage

• Keep doors closed. Every opening lets cold air out and warm air in.
• Note the time the outage began and check temperatures with a thermometer at intervals.
• Move critical stock to the units on backup if needed, quickly and in one trip.
• After power returns, check that every unit restarted and is pulling down.

Food safety after a long outage

Common guidance holds chilled food at 5 °C or below and frozen food at −18 °C or below. If a cabinet was above these limits for a significant time, follow your food safety plan and FSSAI guidance on whether stock can be used. A temperature logger that records through the outage takes guesswork out of the decision.

Safety note

Change-over switches, generator connections and inverter wiring must be installed by a licensed electrician. Never backfeed a generator into a socket, and never run a generator indoors or where exhaust can enter the building.