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ITGlossary · UPS technology
Capacity System
Parallel UPS units that share the load with no spare unit (N configuration), so the failure of one unit overloads the rest.
Technical level:Advanced
In a capacity system, also known as an N configuration, two or more UPS units or modules run in parallel and share the load, with no spare unit. For example, two 10 kVA UPS units together supply an 18 kVA load: the total power is sufficient, but no unit is left over.
This setup is used mainly when more power is needed than a single unit provides. However, if one unit fails, the others become overloaded and the system goes to bypass or shuts down. That is the difference from a redundant N+1 configuration, where one extra unit covers the loss.
If continuity is critical, as in a data centre or hospital, a capacity system is not enough. Size the system so that the load is still covered with one unit missing.
Related terms
- OverloadA condition where the connected load exceeds the UPS’s rated output in VA or W.
- ScalabilityThe ability of a UPS system to expand capacity by adding additional modules or batteries.
- BypassA path that feeds the load directly from the mains, without protection, when the UPS is overloaded, faulty or under maintenance.
- 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.
- Offline (Standby) UPSA UPS that leaves the load on the mains and switches to battery only when the mains fails, with a short transfer time; the simplest and cheapest topology.
- Online (Double Conversion) UPSA UPS that continuously converts incoming AC to DC and back to AC, so the load is always fed by the inverter with clean, stable power.