Generator & ATS Backup Power

Where the generator fits

A standby diesel generator does a different job from a UPS. The UPS bridges 10 to 30 seconds while the set starts, then the generator carries the site for hours. For most offices under 50 people we would back up the server rack, switches, CCTV recorder and a few lights only, because adding every air conditioner doubles the set size for little benefit. Remote sites often add a hybrid solar and battery system so the generator runs fewer hours per day.

Sizing and switching done properly

Sizing starts from a measured load list, not the main breaker rating. We record kW and power factor, convert to kVA, then add margin for motor starting current, which reaches 5 to 7 times running current on pumps and compressors. UPS input on a generator needs care: distorted UPS input current can force an oversize of about 1.5 to 2 times the UPS kVA, or the UPS may reject the supply when frequency drifts. The ATS sits between utility, generator and load:

• Open-transition ATS with adjustable delay, so voltage and frequency settle before loading
• Correct poles: 3-pole where the neutral stays common, 4-pole where it is switched and earthed once
• Monthly test under load, because an unloaded run hides fuel faults and flat starter batteries

Details that decide reliability

What we usually see on sites is small: a flat starter battery, an ATS left in manual after maintenance, or a set that never ran under load. We size cables for voltage drop, set one clean earthing point, route exhaust away from intakes, and ventilate for hot-season heat. Fuel planning counts too: a 40 kVA set at half load burns roughly 5 to 6 litres an hour, so a 100-litre tank lasts about 16 to 20 hours. Send us a photo of your main panel, your load list and the generator nameplate if one exists on WhatsApp and we will suggest a size and ATS arrangement.