UPS for a Factory: Load Classification, Runtime and Cost Drivers

A factory UPS should be sized from the loads that cannot stop, not from the whole plant. Sort loads into no-break, short-break and can-stop, add up their measured kW and kVA, and set battery runtime to the time the DG or a controlled shutdown needs. The cost then follows five drivers: kVA rating, redundancy, battery chemistry and autonomy, the room and cooling, and service.

Which factory loads belong on the UPS?

Most oversized UPS projects start with a list of everything that has a plug. Start instead from what each load does when the supply drops for a few seconds. The table is a classification you can fill in per machine and per panel.

Our guide to UPS planning for critical factory and office loads goes deeper on topology and bypass. This article is about what the answer costs.

How do you work out the runtime?

Ask what the UPS is bridging. With a DG set, the bridge is the DG's measured start and transfer time with a margin, plus any controlled shutdown for loads that cannot restart on their own. Without a DG, the runtime is the time needed to bring the process to a safe stop. A round number such as one hour "to be safe" multiplies the battery, its space, its cooling and its cost.

On an energy balance, runtime is usable battery energy divided by load. Usable energy is the nominal battery energy multiplied by the usable fraction, the inverter efficiency and an ageing fraction. Our UPS runtime calculator uses an ageing fraction of 0.8, which treats the battery as at end of life at 80% of rated capacity. In its worked example, a 1,000 W load on a 48 V, 100 Ah bank with a usable fraction of 0.8 and inverter efficiency of 0.9 gives about 2 hours 46 minutes, which is 14 minutes short of a 3-hour target. The same bank new gives about 25% more, which is why you check runtime at end of life, not on installation day.

That is a screening method. The battery maker's constant-power discharge data, at the actual end voltage and the lowest temperature expected, decides the runtime you can rely on.

What drives the cost of a factory UPS?

We quote no price here, because the figure depends on the drivers below and on the make. What we can show is what moves it and which question exposes each driver.

How do battery choice and room design change the budget?

Valve-regulated lead-acid batteries cost less per unit of energy at purchase, need more space and are replaced more often. Lithium-ion packs usually cost more at purchase, take less space and last longer between replacements, and they bring fire-safety conditions for the room. We have not compared specific products, so ask each bidder for the replacement interval, the warranty basis and the fire safety arrangement in writing. The compliance side is in our note on lithium-ion UPS room fire safety, and the ventilation duty for charging areas is in battery charging room ventilation.

Room design is the cost most buyers discover late. A UPS and its batteries turn losses into heat, so the room needs cooling that the UPS quotation may not include. Put cooling, ventilation, the earth connection and cable entries into the same budget line as the UPS, or the comparison between quotes is false.

UPS, DG and solar: keep the roles separate

A UPS covers seconds to minutes. A DG covers hours. Solar cuts daytime grid units but does not ride through a grid failure on its own. Do not size the UPS to replace the DG. For the longer-duration question see DG versus battery storage for factory backup. The DG must be sized to start the UPS rectifier along with the other loads, and the UPS input power factor and harmonics belong in the DG selection.

Whole-life cost, not purchase price

Compare bids on purchase price, plus battery replacements over the planning period, plus service, plus the energy lost in the UPS and the cooling that removes the heat. A UPS at light load runs at lower efficiency, so a unit sized for loads that never arrive wastes energy every hour. Ask for efficiency at 25%, 50% and 100% load on the datasheet, and a battery replacement price, so the whole-life view can be built.

How Secured Engineers helps

We design electrical systems in-house, including UPS and DG integration, and take electrical, HVAC, fire fighting and plumbing under one contract. CEIG and DISCOM filings are done in-house. Our offices are in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. See electrical infrastructure for the scope.

If you have a UPS budget or quotation, send it with the load list, single-line diagram and DG details, and we will review it for the drivers above: what was measured, what is missing and what a revised scope would change. Reach us on WhatsApp, call +91 70099 85817, or ask for a free proposal.