Mercury step down voltage converter enables a 110 120vac device from the usa to be powered from a 230 240vac uk mains outlet allows use of us electrical equipment with 2 or 3 pin plugs in the uk this transformer is not suitable for constant use and cannot be used for more than an hour at a time and is not silent as it makes a slight humming noise simply plug in the wall step down transformer ideal for radios hi fi systems and other small appliances allows 110 120 vac devi