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ITGlossary · Electrical units
Load
Any device or system connected to a power source and drawing electrical current.
Technical level:Basic
When choosing a UPS, the load is the total of all devices connected to its outputs: computers, monitors, routers, servers, cameras or a boiler. It is measured in watts (W) or volt-amperes (VA), and the relationship between the two depends on the power factor.
The load determines two things: the size of the UPS and the runtime. A UPS at 50% of its rated load usually runs more than twice as long as at 100%, because batteries perform better at lower currents.
Work out the actual consumption in watts, ideally by measuring it, since labels usually show the maximum value, and allow a margin of about 20–30%. Do not connect laser printers or heaters to the UPS; they have large consumption peaks and drain the battery for no good reason.
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Related terms
- Noise (Electrical)Unwanted high-frequency disturbances on the supply voltage, e.g. from motors or power supplies, which UPS systems and line conditioners filter out.
- ATS (Automatic Transfer Switch)A device that automatically moves the load from the grid to a generator during an outage and back again when grid power returns.
- Transfer SwitchA manual or automatic switch that connects the load to one of two sources, such as the grid and a generator, never both at once.
- Zero Transfer TimeA feature of online UPS systems, where the inverter feeds the load continuously so a power cut causes no gap at all.
- Capacity SystemParallel UPS units that share the load with no spare unit (N configuration), so the failure of one unit overloads the rest.
- Double Conversion EfficiencyThe share of input power that an online UPS delivers to its output, lower at light load and highest at medium to high load.