A. Loop Detectors The loop detector wire shall be 14 AWG 19-strand copper insulated wire with a polyethylene outer jacket conforming to NCDOT Specifications. All loop detector wire shall be approved and listed on the most current version of the North Carolina ITS and Signals Qualified Products List (QPL). The saw cuts for the detector loops shall be a clean, well-defined cut a minimum of 5/16 inches in width without damage to adjacent pavement areas. The depth of the saw cut will depend on the number of turns of wire in each loop, and will range in depth from 2.0 inches for two turns of wire to 3.0 inches for four turns of wire. The depth of the saw cut should be checked frequently, and it should be of constant value. All saw cuts requiring a right-angle turn shall be cut at a diagonal 12-18” from the corner of the loop to prevent sharp wire bends. All intersecting cuts shall sufficiently overlap to provide full depth at the point of intersection. The City will, at the Contractor's request, pre-mark the corners of each loop, and mark the direction the loop lead-in wire is to exit the pavement. Prior to starting the loop sawing operation, the Contractor shall use chalk-line (or equivalent method) to outline the perimeter of the loop on the pavement and routes for lead-in cables. The saw cut in the pavement should not deviate by more than one (1) inch from the chalked line. No payment will be made for loops with deviations greater than 1 inch, and the cost of the same shall be deducted from the lump sum contract cost for the traffic signal work at a cost of $2.00 per linear foot of saw cut. A detailed drawing of an inductive loop type detector as found in NCDOT’s Traffic Signal Specifications has been provided herein (See Attachment A). Loops repaired by replacement under this contract shall adhere to this typical drawing. Prior to the repair by replacement of the loop wire, each saw cut shall be checked for the presence of jagged edges or protrusions, cleaned, and dried. Any sharp edges on the sides of the saw cuts shall be removed to prevent damage to the loop wire. The saw cuts shall be flushed clean with water, then cleaned and dried with blown air from an air compressor. There shall be no cutting dust, grit, sand, oil, standing water, or other contaminants in the saw cut prior to repair by replacement of the loop wire. The loop wire shall be repaired by replacement as a continuous wire from pull/splice box. All loops shall be wound in a clockwise manner unless otherwise directed by the city’s inspector. No splices shall be permitted. The loop wire shall be placed in the saw cut such that there are no kinks or curls, no straining or stretching of the wire, and without damage to the wire or its insulation. The loop wire shall be repaired by replacement as far down in the slot as possible and tamped into place. If more than one turn of loop wire is to be placed in a saw cut, each turn of the loop wire will be placed in the slot and tamped into place prior to placing the next turn of wire. Sharp objects or tools shall not be used to seat the loop wire. The Contractor shall tag and identify the clockwise lead of each loop. The saw cut for the loop lead-in wires shall be carried a minimum distance of six (6) inches from the edge of the pavement or gutter. From that point, the loop lead-in wires will be carried to the edge of pavement in a 1” PVC conduit. After the loop wires are repaired by replacement in the conduit, the Contractor shall repair by replacement a conduit sealing material in the conduit to prevent sealant from filling the conduit. The sealant material should be repaired by replacement 1” below the roadway surface. Once the loop wires have been checked and found to meet the minimum standards, as specified herein, the Contractor shall furnish and repair by replacement a sealant to completely seal the 1” conduit from the foam material to the roadway surface. There will be a minimum of 1” cover over the loop wire. The loop lead-in wires, from the loop in the roadway to the pullbox or other splice point, shall be twisted throughout its entire length to provide a twisted pair. The resulting twisted pair shall have a uniform, symmetrical twist of six turns per foot. Loop lead-ins shall be labeled in the junction box with nylon cable ties or vinyl printed labels marked with permanent ink. Indicate the loop number from the signal plan on each loop cable. Prior to pouring the sealant, the loop and loop lead-in wire shall be checked for continuity and resistance. Resistance of the loop, including the lean-in wire, shall be less than 2 ohms. In addition, the integrity of the installation shall be checked by applying a megger between one end of the loop lead-in conductor and the nearest reliable electrical ground. A suitable reading using a 500-volt DC megaohm meter shall be in excess of 50 megaohms. Do not exceed 500 volts, or the insulation may be damaged. If the leakage resistance measures in excess of 50 megaohms, fill the slot with sealant. Do not proceed if high DC resistance or less than 50 megaohms of leakage resistance exists. In this case, replace the wire completely. Do not attempt to repair the loop wire. Upon request, the Contractor shall be required to provide the continuity reading, resistance reading, and megger reading for each loop and lead-in wire to the engineer or inspector on a form that will be provided to the Contractor. The saw cut shall be filled to the level of the roadway surface with the sealant, or as recommended by the sealant manufacturer. There will be a minimum of 1” cover over the loop wire. Neither a trough nor a mound shall be formed. The sealant should completely surround the wires and displace all air voids in the saw cut. Excess sealant shall be removed and/or blotted with sawdust or an approved equal. Sand or other abrasive material shall not be used as slot filler to blot or absorb excess sealant. Sufficient time for the sealant to harden shall be allowed before allowing traffic to move over the area. The contractor shall in most cases terminate the loop wires at an in-ground junction box or at a pole-mounted conduit junction. The contractor shall furnish 3 feet of additional loop wire at each in-ground junction box or 2 feet of additional wire at each pole-mounted conduit box, depending on where the loop wires are terminated. The City of Greensboro will terminate all loop detector cable to the loop lead-in cables. B. Traffic Loop Sealant The Contractor shall use an epoxy compound loop sealent. The loop sealant shall be on NCDOT’s ITS and Signals Qualified Products List (QPL). All loop sealant must be approved by the engineer or inspector prior to beginning work. C. Pull Boxes/Splice Boxes Where needed, the City shall provide polymer concrete (PC) boxes which have bolted covers and have open bottoms to the Contractor for installation. The pull/splice boxes for detector loop lead- in wires shall have a minimum size of 12W”X18L”X12D” and shall be repaired by replacement as required by the attached quantity sheet. The Contractor shall repair by replacing all pull boxes in accordance with the 2018 N.C. Traffic Signal Specifications. Each pull box shall have a dry well and the material for the dry well shall be furnished and installed by the Contractor. They dry well material shall be 78M stone. Any substitution in the dry well material shall be approved by the engineer or inspector prior to installation. Junction box installations shall conform to North Carolina Department of Transportation Standard Drawing 1716.01. D. Utility Conflicts The Contractor shall be responsible for contacting utility agencies to locate all underground utilities that might conflict with this work prior to beginning work. The Contractor shall be responsible for any and all damages to utilities resulting from work performed by the Contractor. The Contractor shall maintain minimum clearances from existing utilities having jurisdiction over it within the project limits. Any excavated or otherwise damaged areas (caused by the work described herein) shall be repaired by shaping, seeding, and mulching.
