Before you break ground on any digging project — whether it's a garden bed, fence post, or major excavation — you must locate and mark all underground services on your property. Striking a buried power cable, gas line, or water main can cause serious injury, death, and expensive repairs. In New Zealand, taking the time to identify underground services isn't just good practice — it's a legal and moral obligation.
Why Locating Underground Services Matters
Underground services can include electrical cables, gas pipes, water mains, stormwater and wastewater drains, telecommunications lines, and fibre optic cables. These are often buried at varying depths and don't always follow predictable paths. Even shallow digging with a spade can be enough to strike a live cable or rupture a gas line.
WorkSafe NZ treats underground service strikes as a serious workplace hazard, and the same risks apply to homeowners doing DIY excavation. Damage to a network utility operator's assets can also result in significant financial liability.
Step 1: Check Your Property Documents
Start by gathering any as-built drawings or LIM (Land Information Memorandum) reports for your property. These can be requested from your local council and often show the location of drainage, water supply, and other services. However, as-builts can be inaccurate or out of date, so never rely on them alone.
Step 2: Contact Dial Before You Dig
The most important step is to contact Dial Before You Dig (DBYD). In New Zealand, this free service connects you with network utility operators who can provide plans showing where their assets are located on or near your property.
- Visit beforeudig.co.nz or call 0800 248 344
- Submit a request with your site address and the nature of your work
- Operators will respond (usually within 2 business days) with plans showing their assets
- Always allow enough lead time — don't leave this until the day before digging
Note that DBYD covers network utility assets (power, gas, telecoms, water mains), but private drains and cables on your own property may not be registered. You'll need to investigate these separately.
Step 3: Use a Cable and Pipe Locator
Once you have the plans, use a cable and pipe locator (also called a CAT scanner — Cable Avoidance Tool) to physically detect buried services on site. These can be hired from most equipment hire companies. A CAT tool detects electromagnetic signals from live cables and can also be used with a signal generator (genny) to trace non-live services.
Tips for Using a Locator:
- Sweep the area in a grid pattern, both horizontally and vertically
- Mark detected services with spray paint or marker flags as you go
- Use different colours for different service types (see the table below)
- Don't assume a service runs in a straight line between two known points
Step 4: Mark Services Clearly on the Ground
Use marking paint or coloured flags to indicate the path of each service. The internationally recognised colour coding used in New Zealand is:
| Colour | Service Type |
|---|---|
| Red | Electrical power |
| Yellow | Gas |
| Blue | Water (potable) |
| Green | Sewer / wastewater |
| Orange | Telecommunications / fibre |
| White | Proposed excavation area |
| Purple | Reclaimed water / irrigation |
Keep markings visible throughout the project and refresh them if they fade or are disturbed.
Step 5: Hand Dig Around Marked Services
Once services are marked, never use mechanical equipment directly over or near a marked line. The standard practice is to hand dig (using a spade or shovel) within 500mm either side of a marked service until you have visually confirmed its exact location and depth. Only then can you carefully continue with machinery, keeping a safe clearance.
This process is sometimes called potholing or trial holes, and it's considered best practice on any professional excavation site.
Building Consent and NZ Building Code Considerations
Depending on the scale of your excavation, a building consent may be required. Under the New Zealand Building Code and the Building Act 2004, some earthworks are exempt under Schedule 1, but this depends on depth, proximity to boundaries, and other factors. Always check with your local council before starting significant earthworks. MBIE Building Performance has useful guidance on when consents are needed.
For work near public infrastructure, you may also need a corridor access request (CAR) from your local council or road controlling authority.
When to Call a Professional
If your project involves significant excavation, is near known high-pressure gas mains, high-voltage cables, or public infrastructure, you should engage a licensed earthmoving contractor rather than attempting the work yourself. Professionals have access to better detection equipment, carry appropriate insurance, and understand their legal obligations under the Health and Safety at Work Act 2015.
For any work that exposes or requires connection to electrical cables, you must use a registered electrician (EWRB). Work on gas pipes must be carried out by a licensed gasfitter, and plumbing and drainlaying connections require a licensed tradesperson registered with the PGDB. These are legally restricted work categories — homeowners cannot perform them.
You can find qualified, local earthmoving contractors and other tradespeople on tradedirectory.co.nz.
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