Why is 110v used on a construction site?

For personal safety reasons. In the UK the line voltage is 230 volts and this voltage can be lethal in a wet construction site. The step down transformer used has a centre tapped secondary winding of 55v+ 55v make 110 volts.The centre tap is earthed to the power tool etc, thus making the maximum potential for electric shock at 55 volts:-sub lethal. <><><> Supplies of 110 volts are recommended for use on construction sites for personal safety reasons, on the basis that, if any wiring or equipment casings become "hot" or "live", the danger of electrocution is greatly reduced compared to the certain dangers that would exist if supplies at higher voltages, such as 230 volts ac, were used. In countries running a 50 Hz power supply service, 230 volts ac is the common voltage supplied for use for normal lighting, appliances and small electrical tools and equipment - except on construction sites, where the use of equipment running on 110 volts is now mandatory to meet the requirements of Health & Safety laws.