Underground Utility Locating Fiber Lines
A local excavator was installing a water pipe along I-80 in Truckee, CA. He needed to trench under an overpass and needed a utility locate from Encompass Inspections to avoid damaging CalTrans streetlight and fiber optic lines. He had already located the electric lines, but was unable to locate the fiber optic line. The excavator had exposed some conduit by hand-digging, but wanted to be sure he did not damage any conduits or wires within them.
How We Responded
Encompass dispatched a technician to Truckee to locate the fiber optic line. The technician accessed the line at a manhole near the overpass, and attempted to use the RD 7000 to clamp the fiber loop contained within. The fiber optic line did not carry a signal, so the technician direct connected to a ground wire going into the conduit. After pinpointing this signal for a couple hundred feet the signal split and it was unclear whether the fiber optic ground wire was grounded to the electric and therefore simply bleeding off onto the electric or whether the ground wire ran the entire length of the conduit. The technician then rodded the conduit with a conductive line, and similar results to the locate with the ground wire were uncovered. Unfortunately, the rodder did not extend the entire length of the locate, and no other access point could be used to rod backward toward the manhole. The technician then used the nonmetal-to-metal induction mode on the transmitter (known as “dropping the box”) to verify the previous marks from the manhole with the rodder still extended, then moved the transmitter to a location down the line, set it on its side on top of the electric locate marks so that the magnetic field would not transmit to the electric line, but would carry a signal to the rodder and ground wire, and located from that point forward to where the signal had originally split. In this way, the false signal was eliminated. The locator then verified that the streetlight wires were not carrying a signal by following the path of the electric line locate marks and verifying that no signal was present on the receiver where the electric marks split off from the fiber optic marks all the way to a known point of origin for the streetlight wires, a pull box on the other side of the street from the manhole.
Results We Delivered
The technician successfully located the fiber optic line using multiple techniques as described above, and marked the fiber lines in orange paint. The excavator was cautioned that the locate was facilitated using the ground wire at the point where the rodder stopped, so it was important to hand dig these areas, and make sure that he exposed the fiber optic conduit carefully.
Thanks to Encompass Inspections, the contractor was able to perform their work safely without damaging any underground utilities. Encompass also provided sketch of where the utilities are located for future reference at the contractors request.
Contact Us To Learn More
Encompass Inspections offers Ground Penetrating Radar/Concrete X-ray, Underground Utility Locating, Video Camera Inspection, Leak Detection, and Utility Mapping services for all of Northern California including: San Francisco, San Jose, Oakland, Sacramento, Truckee, and surrounding cities. For more information on our equipment and services, refer to our equipment page.
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