Xtralis Test Transformer VTT-10000 (previously known as the Hot Wire Test – Power Supply Unit (PSU)) is a tool used to test very early warning aspirated smoke detection equipment. The unit generates a high current that passes through a test cable in order to heat it, which in turn causes its insulation to burn giving off smoke. The maximum operating time for the unit is three minutes and then it must be left immediately to cool it off for a period of at least seven minutes.