I can think of two solutions:
"The purpose of the inspection is to identify defects on the electrical installation in the area, that may represent a risk..."
Adding the comma will create a pause, separating the words area and that. Compare this to "identify defects on the electrical installation, in the area that may represent a risk..."
"The purpose of the inspection is to identify defects on the electrical installation that may represent a risk..."
Remove the confusion by taking out in the area. This, however, does remove a detail which may be important in the context that you are using it in.
EDIT:
"The purpose of the inspection is to identify defects, on the electrical installation in the area, that may represent a risk..."
This is also grammatically correct. In this instance, on the electrical installation in the area is inserted into the sentence "The purpose of the inspection is to identify defects that may represent a risk..." as a piece of additional information. This makes it obvious that it is the defects that represent a risk, since "defects" and "risk" are in the same clause.