Voltage or voltages. The API call is
void EmonLibDB_set_pInput(uint8_t _input_I, uint8_t _inputV1 [, uint8_t _inputV2])
Sets the relationship between voltage and current inputs to enable the calculation of real
power. For single-phase, one leg of a split-phase and 3-phase 4-wire measurements,
voltage and current sensor must be on the same phase/leg. The second voltage is needed
only for the line-line power calculation in split-phase and 3-phase systems; i.e. when the
current measured is line-line.