The normal practice in the UK in building sites is to power portable lighting from an isolating transformer.
Two principle types exist, the smaller ones have a single phase primary winding to suit the normal single phase supply of 230/240 volts. The secondary winding is single phase 110 volt nominal with an earthed center tap.
This ensures that the maximum voltage to earth is only 55 volts, thus almost eliminating the risk of dangerous electric shock.
Such transformers are generaly portable and fitted with a short length of cable and a 240 volt plug. Common ratings are from 500 watts up to 3,000 watts, though larger units exist.
The second type has a three phase primary winding to suit the UK 400/415 volt supply.
The secondary winding is three phase Y (or star as we say in the UK) with the neutral earthed, the voltage 110 volts from phase to phase, and 62 volts phase to neutral. The neutral point is earthed, and the 110 volt loads are connected from phase to phase. This limits the voltage to earth to about 62 volts, and therefore greatly reduces the risk of dangerous shock.
Such transformers are sometimes fitted with a length of supply cord and a three phase plug, but are more commonly hard wired via armoured cable.
The most common ratings are from 6,000 up to 12,000 watts, though other sizes exist.
Sometimes a three phase 110 volt output is provided, but the main use of these transformers is to supply a number of single phase 110 volt lamps or tools etc.
110 volt lighting or power tools are normally connected to either type of transformer via extension cords with suitable plugs, dedicated to 110 volt use.
Such transformers are sometimes used to supply fixed wireing in workshops etc. but they are commonly used on building sites.
Suitable transformers, complete and ready for use may be purchased from any large wholesaler in the UK.
Note that the manufacturers rating often assumes only intermitant use for hand tools etc. For continous loads such as lighting the size of the transformer often has to be doubled.
