- Published 13 Nov 2024
- Last Modified 13 Nov 2024
- 7 min
Avoiding Underground Cables
Avoiding buried cables and pipes is essential for safe excavation work. Learn here about how cable avoidance tools help you map a site’s underground utilities and avoid the extreme hazards of underground cable strikes.
Reviewed by Peter Kendall, Technical Support Engineer (October 2024)
‘Call before you dig’ is a good practice for avoiding disastrous contact with buried cables and pipes, but you can also locate them yourself with the right instruments. This guide explains what cable avoidance tools (CATs) are, their important role in site excavation, and how to use a cable avoidance tool.
Cable Avoidance Importance
Underground cable strikes are an ongoing serious problem for worksite safety: around 60,000 cable strikes per year in the UK. All digging work carries risks of contacting previously routed and buried cables and pipes. This is because the infrastructure enabling the comforts of our lives largely runs below our feet:
- Electrical cables
- Telecommunications cables
- Water supply pipes
- Sewage pipes
- Natural gas pipes
These all need to be installed and occasionally serviced, which requires excavation work. This in turn means working around all the other adjacent buried utilities, which means an ever-present need to be aware of all buried cables and pipes before you do any digging.
Safety Hazards
The number one reason for cable avoidance is keeping your workers and the general public safe. Underground cable strikes and pipe strikes can mean:
- Serious electric shock from contacting live wires by hand or with metallic tools
- Exposure to blowouts of pressurised water or natural gas
- Inhaling natural gas
- Fires or explosions from igniting leaking natural gas
- Exposure to the health hazards of leaking sewage
These apply chiefly to excavation workers, but extreme hazards like leaking natural gas can affect your whole worksite’s staff or even the nearby general public.
Financial Risks
Avoiding underground cables and pipes also avoids serious financial setbacks. When these incidents happen, so can:
- Damage to tools and heavy equipment
- Repair costs to the damaged utilities
- Cleanup of large amounts of leaked water and sewage
- Nearby homes and businesses losing their utilities
- Regulators investigating the incident and potentially imposing fines or revoking permits
- Damage to your company’s reputation due to these cost and time overruns
Each of these alone is reason enough to make pipe and cable avoidance an essential early step for any excavation work your business does.
Cable Avoidance Practices
Pipe and cable avoidance can seem daunting and inescapably dangerous, but it can be safely done with the right techniques. Good cable avoidance and CAT and Genny scanning practices include:
- Providing cable avoidance training for your staff doing excavation and those supervising and planning their work.
- Practising cable avoidance tool calibration to ensure accuracy of what you find.
- Researching and requesting existing utility layout plans from utility providers.
- Assessing the risk of the excavation task and planning mitigation measures accordingly.
- Knowing which emergency services to call if an underground cable strike does happen.
- Using a CAT and Genny tool to locate cables and wires and mark their routes as you find them.
- Logging and saving the data for use later. Use your CAT’s datalogging features if it has them.
- Assuming wires are live and pipes are pressurised.
- When uncovering the utilities you discover, start gradually with hand tools to confirm what’s there before using heavier equipment.
- Record the locations of any new utility routes you lay so that others can safely avoid them later.
Cable Avoidance Tools
Just what is a cable avoidance tool? Cable avoidance tools are testing instruments for finding underground pipes and wires. They help you avoid underground cable strikes and their resultant injuries and financial setbacks. CATs are handheld, though substantial in size: They’re typically waist-high and can be easily held as you walk around scanning a site.
How do cable avoidance tools work? They locate underground utilities by exploiting their ability to conduct electricity or transmit electromagnetic signals. Instruments in the CAT detect wires’ electrical current, nearby radio waves travelling through pipes, or signals deliberately created and sent through these utilities. As the user walks around a site with an active CAT, it alerts them to the presence of utilities.
What does a CAT and Genny detect? Underground pipes, tubes, cables, wires, valves and couplings, as long as they’re metallic.
Using a CAT and Genny has some limitations, though. What can a cable avoidance tool not detect?
- Non-metallic utilities, though cable avoidance tools come with flexible conductive rod accessories for feeding into plastic pipes to help trace their path
- Cables and pipes below the CAT’s depth limit
- Abandoned or disconnected cables
- Whether pipes have anything flowing through them, such as water or natural gas
Modes of Cable Avoidance
Cable avoidance tools have three main modes for detecting cables and pipes. Many of these tools are capable of all three:
- Power mode: This detects the electromagnetic fields of live wires and cables—but not dead ones. Detecting wires this way requires them to be actively sending electricity to a device.
- Radio mode: This detects local radio signals, which tend to pass through buried metal pipes and cables.
- Genny mode: While the power and radio modes detect pre-existing signals, in this mode the tool uses a separate signal generator (a ‘Genny’) to send a signal through buried utilities and then detect it.
- Avoidance mode: This applies all three of the above modes at once, giving you a general idea of the area’s utilities setup so you can begin planning your work.
Signal Generators (Gennies)
This guide’s been mentioning Gennies, but just what is a Genny? That term refers to the generation of signals that some cable avoidance tools can do. These instruments use a separate signal generator (the ‘Genny’) to emit a signal that the CAT can reliably detect. When the signal reflects off underground cables and pipes, the CAT picks this up and informs the user. That is the induction Genny method, though Gennies can also apply a controlled, detectable signal directly to a valve or junction box connected to an underground utility. This is more accurate.
Are there CAT and Genny differences? Yes, using a Genny gives you the following capabilities the power and radio modes lack:
- Detecting non-live wires
- Estimating the depth of utilities
The Genny mode requires setting up two pieces of equipment, though, rather than using just the CAT.
Using Cable Avoidance Tools
Using a CAT and Genny involves the following steps:
- Hold the CAT upright and don’t let it swing as you walk.
- Set the CAT to the desired mode.
- Squeeze the trigger switch in the handle to make the CAT detect signals.
- Walk around the planned area in a sweeping pattern.
- When the CAT detects something and emits a sound, stop walking.
- Move the CAT around this area (while keeping it vertical) and reduce the sensitivity until you’ve found the ‘sweet spot’ where you’re sure you’re detecting only the discovered utility.
- Mark the spot, gradually move the CAT to find the utility’s trajectory, and walk in that direction to map that route.
- Regularly move the CAT from side to side to ensure you haven’t lost the route, and keep placing marks.
Finally, ensure you perform regular CAT and Genny calibration to maintain reliability of the data these instruments pick up.
RS can also help you look beneath surfaces indoors. Browse our stud finders to locate the inner structures of walls and ceilings and then work around them comfortably.
