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Utility markings accuracy & Locating Underground Pipes

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How Accurate Are Utility Markings?

Have you ever seen strange markings on the pavement, sidewalk or dirt around a site that is about to be excavated? Sometimes they look like colored lines, while other times you’ll see bright symbols and/or colored flags dotting a property. These are utility markings. They are placed after a utility locator discovers the general location of a utility.

Without these symbols, utility lines and structures could be damaged or destroyed during excavation. Even worse, people could be harmed or killed while working in construction if they do not know where underground utilities are located. But can you always trust utility locator markings to be accurate? Here’s what you should know about these markings and what tools you can use to find underground utility structures yourself.

Person Using Pipe Locator

Utility Marking Accuracy

When utilities are properly located and marked, they can generally be found within two feet of the mark (on either side). This means that as a construction worker or homeowner working on a deep dig project, you should maintain at least a 2-foot berth around all markings. If utility markings are not properly located or if they are somehow damaged or removed, the company or person who placed the markings is responsible to pay for any damage caused by their error.

How Are Utilities Located?

There are a variety of materials used in the manufacturing of underground utility lines, so it can be challenging to locate them all. Different methods must be used for different materials. For example, electromagnetic cable locator equipment is used to locate metal cables and pipes, while ground-penetrating radar or other types of pipe locator radiolocation are required to locate concrete or plastic pipes.

Once located, specific color codes must be used to designate what type of utility lies beneath the mark. In the United States, the following colors are used:

  • Red: lighting cables, electric power lines, conduit
  • Yellow: oil, natural gas, petroleum, steam, other flammable or gaseous material
  • Orange: alarm or signal lines, telecommunication cables or conduit
  • Blue: drinking water
  • Green: Sewers and drain lines
  • Pink: Unknown facilities or temporary survey markings
  • Purple: reclaimed water, slurry lines and irrigation
  • White: proposed excavation routes or limits

These color codes follow the American Public Works Association guidelines.

Pipes located and excavated


Get the Right Tools

Whether you’re a homeowner getting ready to install a sprinkler system or a contractor building a home, you may want to double-check all utility locations to keep yourself and others safe. From pipe locators to cable locators, you can find the tools you need at Engineer Supply.

Browse our inventory of cable & pipe locators or call us at 800-591-8907 to get started.

Frequently Asked Questions

What does a utility locator do?

The purpose of a utility locator is to determine where underground utilities should be placed and where existing utilities are located. This consists of items like telephone, gas and power lines. The people that use them often work for utility, consulting and construction companies.

How do you use a utility locator?

There are 3 modes that you can use to help you locate hidden utilities, conductive mode, Inductive Clamp Mode or Inductive mode.

  • The Conductive Mode - Connect directly to the conductor with clips & a ground stake
  • The Inductive Clamp Mode - Use a clamp and place it around the conductor
  • The Inductive Mode - Set the transmitter or antenna over the conductor
The key is applying the proper frequency since the signals dissipate through the ground. Keeping these things in mind will help you better leverage your utility locator.

What is the best underground utility locator?

The best utility locators are designed to withstand the rigors of tough daily field use and a wide range of environmental conditions. In order to do the job right, it needs to be able to transmit a signal through either conductive or inductive means. The receiver should be portable so you can wave it over the areas you believe the utility to be in.

What is a pipe locator?

A pipe locator uses conductive or inductive methods to find pipes that are hidden with a high level of accuracy & reliability. A conductive pipe locator may be used to apply a signal to a coated metallic pipe at a specific access point which could be a valve or meter. The signal's return path can pass through a ground stake or a building grounding system to get back to the transmitter. Conductive pipe locators may also be used to locate tracer wires buried underground with nonmetallic pipes. Pipe locators provide a safe and reliable way to check walls, ceilings, floors and underground for hidden pipes prior to renovation, demolition or digging.

What is a pipe cable locator?

A pipe cable locator is a device that uses electromagnetic induction to find underground cables. Technology has advanced to the point where cable and pipe locators are portable, reliable and accurate. Technicians around the world use them to find underground cables and pipes.

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