The power supply system provided with a safety or insulating transformer allows the use of electric equipments even in narrow conducting spaces, that is narrow rooms generally delimited by metal or conducting surfaces, where it is very likely that the human body may get in touch with these walls while it is almost impossible to break off this contact.
Narrow conducting spaces within building yards are, for instance, little metal tanks, the inner part of metal pipe systems, damp underground passages, narrow ground excavations and trestles.