One of the most difficult tasks in the utility business is finding the path of an underground conductor (pipe, cable, wire, etc.) in an area congested with other services. Any locator test set works with acceptable accuracy when there are no other utilities in the search area. In areas crowded with other utilities, accurate confident locates can be an all but impossible task.
As telephone plant evolved to underground systems, a better method of cable location became necessary. A method of tracing the magnetic field present in all conductive entities was developed. By placing tone into this magnetic field and tracing its presence with a receiver, the path of an underground conductor could be traced. A locator transmitter is used to provide tracing tone, and its basic setup is the key to a successful locate.
It’s up to you to decide what type of connection to use but here are some tips to optimize your connection whether Direct Connection, Inductive Coupling, or General Induction. Following a look at connection options, we will explore how to optimize for signal.
Option #1. Direct Connection
The Direct Connection must be used to send low frequency tracing tone lower than 1Khz and can be used to send high frequency tracing tone above 1Khz. Low frequency tracing tone is more accurate, but it takes longer to set up. It is the operator’s discretion to select a transmitter frequency for a given locate.
- For Direct Connection, the transmitter cord is connected metallically to ether a conductor in the cable or an isolated shield.
- The conductor or shield must be grounded at the far end in the direction of the locate.
- The transmitter’s ground cord should be placed at a 90 degree angle from the cable path, opposite of any other utilities such as power, gas, water, fiber, or CATV.
- The transmitter output selector should be set to provide adequate locating tone, but don’t overdrive the transmitter.
- The ground should be an independent ground, such as a screw driver or an independent ground rod.
- Do not use common grounds, such as a water pipe; tone will return on other common grounded utilities and cause a mis-locate.
Option #2. Inductive Coupling Connection
Most Locators come with an Inductive coupler that induces high frequency tone on an individual conductor or cable by simply clamping around it. The coupler allows the identity and tracing of one conductor, such as an individual drop or cable in a pedestal. Even though all conductors will carry tone, the one with the coupler will carry significantly more tone.
The coupler can also be used on the receiver for conductor and cable identification. For example, to identify a specific drop at an endcap splice, apply tone at the NID with a Direct Connection. Plug the coupler into the receiver and couple around each drop-in turn. The drop with the most tone is yours. As always, don’t overdrive the receiver.
Inductive Coupling works best for separating conductors in areas (such as subdivisions) where there are multiple facilities because it concentrates the tone. The coupler should not be used on conduit runs with multiple cables; locate signal travels to the next manhole and returns back to the transmitter canceling the signal. Instead use general induction.
We realize that many manufacturers advocate using the coupler in a conduit run, and have supplied accessory equipment (long poles that attach to the coupler) to make attachment without venting or entering the manhole. Unfortunately, with this practice, your chances of a mis-locate are great.
- The coupler should be placed around the cable below the bond where the cable enters the earth.
- Coupling around an individual bonding ribbon is also acceptable.
- Do not disconnect the bond when using the coupler.
- Be sure that the coupler jaws are completely closed.
Option #3. General Induction Connection
Some locators have a transmitting coil in the bottom of the transmitter that will inject high frequency tracing tone into the cable that is re-radiated by the cable or conductor, which then can be traced with the locator receiver.
This method should be used only when there are no other conductive entities in the area of the locate as tone will appear proportionately on every conductor or cable in the vicinity, which may cause a mis-locate.
- To use General Induction, set the transmitter over the suspected cable path and proceed with the locate.
- To locate conduit runs place the transmitter on top of the cables inside the manhole where they enter the duct.
- Do not use General Induction in congested areas. unless you are locating a conduit run. All conductors or cables in the area will reradiate the signal, causing a mislocate.
- Use the receiver to optimize the transmitter when using the General Induction method. Place the transmitter on the ground in the vicinity of the conductor.
- Set a reference on the receiver.
- Move the transmitter back and forth over the suspected cable path. Induced tone should be loudest in the receiver when the transmitter is directly over the cable.
- Rotate the transmitter back and forth over the cable site path. Maximum signal is induced when the transmitter is parallel with the cable path.
OPTIMIZING THE LOCATE SIGNAL
Whatever method you use, the purpose is to optimize the locate signal — and this is challenging in congested areas. When setting up a locate in congested areas, the object is to get maximum current flow on the cable or conductor that you are attempting to locate, and minimum current flow on all other cables or conductors.
Use the receiver to determine the amount of current flow on any cable or conductor to be located.
When you hook up the transmitter at a pedestal, try whatever you think might be best — whether Direct Connection, Inductive Coupling Connection, or General Induction Connection.
YOU MAY NEED TO TRY OTHER OPTIONS
- Attach the coupler to the cable and turn on the transmitter.
- Place the receiver on the ground near cable to be located in the direction of the locate.
- Place the receiver in a position so the receiving coil is in the peak position.
- Adjust the receiver gain to an acceptable level.
- Next, couple around the bonding ribbon. If more tone is received, use the coupler around the bonding ribbon.
When using the coupler, you decide to either couple around the cable or bonding ribbon; however, there are a few more steps to take if you are using a Direct Connection:
- First, connect to a vacant pair or the cable shield.
- Use an independent ground.
- Set the receiver gain with the receiving coil in the peak position.
- Ground the pair at the far end.
You should see an increase in tone, but don’t be surprised if the tone decreases when using a high-frequency transmitting signal.
- In this case, reset the receiver reference.
- Next, disconnect the bond.
- Again, you should see an increase in tone.
- Remember to adjust the gain control on the receiver each time you try a different hookup.
- Don’t overdrive the receiver.
TRY DIFFERENT GROUNDING TECHNIQUES
- Again, do not use common utility grounds.
- The receiver indicates acceptable hookups to the operator.
- Using your receiver helps you to optimize your transmitter.
- Properly adjusted, the receiver also indicates the relative strength of transmitted signals on other cables that may interfere with your conductor locate.
By following these procedures outlined here, you optimize the signal on your conductor and minimize the chance of a mislocate. When setting in the locate frequency, remember the Golden Locate Rule: Set high frequency for convenience, set low frequency for accuracy.
The best method of any transmitter hookup must be determined by the technician at the locate. We encourage trying each of the hookups to find optimum tracing signal for the conditions.
If you have any insights on this topic or want to share something you struggle with or have tips you’d like to share, I’d love to hear from you. Send me an email: email@example.com, or call 831.818.3930. Thank you for taking the time to read my columns!