Perform a Cable Take Off for Traffic Signal Installation
Before we get started with the steps on how to perform a "take-off" there are two definitions that are vital. Definitions:Take-off: A set of counts or measurements of materials, based on drawings, which quantify the materials needed to build a project. Scale: The dimensional conversion a set of plans are drawn to. Even though these steps are for cable take-offs specifically, the principle of using a scaled drawing to measure items for a construction project can be applied to many other types of materials, including but not limited to, soils, bricks, paint, lumber, to almost anything that can be measured.
Steps
- Identify the installation page..
- Identify the one-line wire diagram. These diagrams are for the intersection you wish to find the cable lengths for.
- Set your “Scale Master®” to the correct scale. This is annotated typically on the bottom of the installation plan sheet.
- Verify the scale. On the installation page, verify that the scale shown on the plan sheet is correct. To verify that the scale is correct, find on the plan sheet an item where a dimension is noted on the drawing (example circled in green). If no dimensions for any items are noted, highway stations are always 100 ft. apart and traffic lanes are generally 12 ft. wide. Then using your Scale Master®, measure that specified dimension and verify that it is correct. If it is not correct, adjust the scale setting on your Scale Master® until the verified dimension and the length indicated on your Scale Master® match.
- Typically the scales for traffic signal installation plans are 1:30 (meaning that 1 inch is equal to 30 feet on the plans) or 1:40 as circled in red above.
- Put the one-line wiring diagram and the installation plan sheet side by side.
- Find the right cable. Locate on the one-line wiring diagram the first traffic signal that you wish to find a cable length for.
- For instructional purposes we will be using Traffic Signal #1. Traffic Signals are generally labeled “TS #1, TS #2, etc.”
- Find the controller. Locate on the one-line wiring diagram the position “Digital Type Controller and Cabinet”. All cables trace back to the cabinet.
- Take the installation page. Once you have located both those items on the one-line diagram, refer to the installation page and locate the position of the traffic signal.
- Locate the Digital Type Controller Cabinet.
- Follow the cable path. Using your Scale Master®, on the installation page, trace the path of the cable from the traffic signal back to the Digital Type Controller Cabinet. The path of the cable is indicated on the one-line diagram by the dashed lines.
- Don't forget the height. This footage is a “2-dimensional” length and does not account for the height of the pole or and slack needed in manholes or the cabinet. Refer to the project’s specifications for the amount of slack required in manholes and cabinets. If not specified, 10 feet is the general rule. The one-line diagram will show how many manholes the cable passes through
- Slack also needs to be accounted for at the traffic signal itself. 10 feet is also a general rule for this as well.
- Add up all the additional footages. It includes the height of the pole the cable travels down, the slack needed for each manhole, the slack needed for the cabinet, and the slack needed for the traffic signal.
- Add this footage to your “2-dimensional” footage from your Scale Master®.
- The sum of the two footages is the cable needed to power that traffic signal.
- Repeat the steps to find the lengths of all the other traffic signals.
Things You'll Need
- The plans for the project, specifically the installation page and the one-line wiring diagram
- A measuring device (best tool for this is a “Scale Master®” as pictured below).
- Pen or pencil
- Calculator
