Digging into the ground without checking for underground services is one of the most dangerous mistakes a homeowner can make. Buried power cables, gas lines, water mains, and telecommunications conduits can all be lurking just below the surface — sometimes shallower than you'd expect. Taking the time to locate these services before you pick up a spade or hire an excavator could save your life and spare you a very expensive repair bill.
Why It Matters: The Risks of Uninformed Digging
Striking a live electrical cable can cause electrocution, fire, or widespread power outages. Cutting a gas line creates an immediate explosion and asphyxiation risk. Damaging a water main or sewer can flood your property and result in costly repairs — and you may be liable for the damage. Beyond your own section, you could disrupt services to your neighbours or the wider street. WorkSafe NZ treats excavation near services as a significant hazard, and contractors are legally required to manage it.
Step 1: Use Dial Before You Dig (DBYD)
The first thing to do — before any digging, no matter how small the job — is submit a request through Dial Before You Dig (DBYD). In New Zealand, this free service is available at beforeudig.co.nz. You enter your site address and the nature of your work, and utility asset owners (power, gas, water, telecoms) are notified. They then send you plans showing the approximate location of their assets in your area.
Allow several working days for responses to come back. Keep in mind that plans are indicative only — they show approximate routes and depths based on records, which may not be perfectly accurate, especially for older infrastructure.
Step 2: Check Your Own Property Records
Council-issued LIM reports (Land Information Memoranda) and your property's title documents may show easements and service routes crossing your section. Your local council's GIS mapping tool (most councils have one online) can also reveal stormwater drains, sewer lines, and other council-owned assets. Ring your council's infrastructure team if you're unsure — they're usually happy to help.
Step 3: Use a Cable and Pipe Locator
Once you have the plans, use a cable and pipe locator (also called a service locator or CAT scanner — short for Cable Avoidance Tool) to physically trace services on the ground. These devices detect electromagnetic signals from buried cables and metallic pipes. Many hire centres, including Bunnings and Mitre 10, offer tool hire, and specialist hire companies carry professional-grade locators.
Tips for using a locator:
- Walk a grid pattern over the area, not just a single line
- Use the locator in both passive mode (picks up live cables) and active mode (with a signal generator for non-energised pipes)
- Mark located services on the ground with spray paint or flags before digging begins
- Remember that plastic pipes and non-metallic conduits may not be detectable with standard locators — a ground-penetrating radar (GPR) unit or a professional locating service may be needed
Step 4: Understand Safe Dig Zones
Even with accurate plans and a locator, you must follow safe digging practices once you start:
| Distance from marked service | Recommended method |
|---|---|
| More than 500 mm away | Mechanical excavation may be used with care |
| Within 500 mm | Hand dig only (spade or trowel) |
| Within 300 mm | Expose by hand; no mechanical tools |
These are general industry guidelines — always follow any specific requirements from the asset owner's plans or your local council. Vacuum excavation (hydrovac or suction excavation) is an increasingly popular option that removes soil without risking damage to services and is worth considering for complex sites.
Step 5: Mark and Protect Before You Dig
Once you've located and marked all services, photograph the markings and keep a copy of the DBYD plans on site. If you're hiring an excavator operator, brief them thoroughly and ensure the marked lines are clearly visible. Never assume the operator has done their own checks.
Common Underground Services in NZ Homes
- Electrical cables — often 450–600 mm deep, but can be shallower in older properties
- Gas lines — typically polyethylene (yellow or black) pipe; not detectable by standard CAT tools without a tracer wire
- Water supply pipes — copper, PVC, or polyethylene
- Sewer and stormwater drains — clay, concrete, or PVC
- Telecommunications — copper or fibre optic conduits
- Irrigation systems — often installed by homeowners with no formal records
BRANZ research has highlighted that service depths in New Zealand can vary significantly, particularly in older suburbs where records are incomplete.
When to Call a Professional
If your project is large, complex, or near known high-pressure gas or high-voltage electricity assets, hire a professional locating service. Licensed locating technicians use GPR and advanced electromagnetic equipment to produce accurate service maps. This is especially important for:
- Any excavation near the property boundary where street assets may be close
- Projects involving trenching longer than a few metres
- Sites with no or incomplete service records
- Work near substations, gas mains, or fibre trunk lines
For any work that involves connecting to or altering electrical, gas, plumbing, or drainage services, you must use a licensed tradesperson. Electrical work is restricted work under the Electricity Act and must be carried out by a registered electrician (EWRB). Gas and plumbing/drainlaying work is regulated by the Plumbers, Gasfitters and Drainlayers Board. Unlicensed work on these services is illegal and can void your insurance.
You can find qualified local excavators, locating specialists, and other tradespeople on tradedirectory.co.nz.