A marking tape that is positioned underground above utility lines wherein the marking tape carries a pair of closely spaced, parallel, insulated conductors that extend the length of the tape and at least one other insulated conductor extending the length of the tape which is separated from the pair of...http://www.google.es/patents/US4767237?utm_source=gb-gplus-sharePatente US4767237 - Marking tape with wire conductors and methods for use
Marking tape with wire conductors and methods for use
