The Helios BSX is a surface-mounted speed controller equipped with a reversing switch, ideal for controlling reversible fans in both intake and extract modes. Housed in a durable white polymer casing, it is compatible only with fans that support double pole switch reversal, such as the HVR 150/2 RE and REW 150 and 200 models. The controller operates within a minimum load of 0.15 A and a maximum load of 1.0 A, providing efficient and reliable fan speed adjustment for ventilation systems requiring reversible airflow.