It is not always possible to know what surface you should excavate, or what cabling is located in the ground. Therefore, there are a lot of things you have to keep track of. In the case of larger machinery, you also have to be aware of whether there are any overhead lines which the excavator may ram. Before starting work, you must ensure, among other things:

• That an excavation permit has been acquired
• That information on cabling has been acquired
• That installations in the earth have been marked up
• That drawings show the actual surroundings, with cabling and drains
• That there is information on any contamination
• That there is a delineation plan in public places
• That safe distances are maintained to overhead cables

Find out lots more here:
Manual for the safety group (pages 78-86)