Transformers may come semi-wired, where the installer completes the last internal connections to have the unit perform the amount of buck or boost needed. Units may have multiple taps on both the primary and secondary coils to achieve this flexibility. They may be designed for hard-wired installations (no plugs) or with plug and receptacle to allow the same transformer to be used in several different applications. The same transformer can be rewired to raise or lower voltage by 5%, 10% or 15%. The primary may have wiring combinations for dual voltage usage: example for either 120 V AC or 240 V AC applications, depending on the final wiring done by the electrician.