Short answer: for CNC machines, servers, medical equipment and anything that cannot tolerate even a 5–10 ms break, choose an online (double-conversion) UPS. For basic office PCs and lighting, a line-interactive or offline UPS is usually enough.
How each type works
- Offline (standby) UPS: passes mains straight to the load and switches to battery only when power fails. Transfer takes a few milliseconds and the output during normal operation is whatever the mains supply is.
- Line-interactive UPS: adds automatic voltage regulation to smooth moderate high/low voltage, but still switches to battery during a cut.
- Online (double-conversion) UPS: converts AC to DC and back to a fresh, regulated sine wave all the time. There is no transfer time, and spikes, sags and frequency variation never reach the load.
Which one does a factory need?
In Indian industrial estates, the supply often fluctuates through the day and DG changeovers are common. Machine controllers, PLCs and drives can trip or reset during a switchover. An online UPS keeps them running through outages and through poor-quality mains, which is why it is the standard for:
- CNC, VMC and automation lines
- Server rooms, bank branches and ATMs
- Hospitals, diagnostic labs and imaging
- Process control and instrumentation
Comparison at a glance
| Feature | Offline | Line-interactive | Online |
|---|---|---|---|
| Transfer time | Few ms | Few ms | Zero |
| Voltage regulation | None | Moderate | Full, continuous |
| Output waveform | Mains / stepped | Mains / sine | Pure sine |
| Best for | Home PCs | Small offices | Industrial & critical loads |
What to check before buying
- Running load in kVA and future expansion (keep 20–25% headroom)
- Required backup time – this decides the battery bank, not the UPS rating
- Single-phase or three-phase input and output
- Output THD (look for under 3%) and efficiency
- Local service support, AMC and battery replacement
Unitech has manufactured online UPS systems in India since 1991, in ratings from 1 to 60 kVA. See specifications or send us your load list for a recommendation.