There exists within the power distribution world two different types of 110V supply system. Care must be taken to ensure the correct transformer is chosen for the application. Otherwise there is the possibility of creating a short circuit when connecting equipment specified for the alternate system and causing damage.
Type 1 (110V Mains System)
This is the 110V live, neutral and earth system used for electrical distribution in the United States and other countries. It is a similar to our UK 240V mains system merely operating at a lower voltage. The transformer coil has two output leads, Live and Neutral, The neutral lead may be connected to the supply earth.
Type 2 (110V Site Safety System)
This is the 110V CTE or 55-0-55V system. In this system the 110V output coil has a centre tap in addition to the two leads at the ends of the coil. The centre tap is electrically wired directly to the system earth. With this system a lead must not be connected to one of the ends of the secondary coil to define the neutral as this will create a short circuit within the winding.
This type of system is used for power tool operation throughout Europe. The environment in which these items are used is generally considered to be hazardous with the potential for damage to the equipment that could expose live internal wiring. The centre tap of the system being earthed limits the magnitude of an electrical shock under such circumstances to 55V instead of the full system voltage of 110V.