Digging into the ground without checking for underground services first is one of the most dangerous mistakes a homeowner or fencer can make. In New Zealand, buried electrical cables, gas pipes, water mains, and drainlines can all be lurking just below the surface — and striking one can cause serious injury, costly repairs, or even death. The good news is that there are straightforward steps you can take before a single post hole is dug.
Why Underground Services Are a Serious Hazard
Underground services include electrical cables, gas pipes, water supply lines, stormwater and wastewater drains, and telecommunications cables. These can be found at varying depths — sometimes surprisingly shallow, especially on older properties or after landscaping work has changed ground levels.
Striking a live electrical cable can cause electrocution. Damaging a gas line can lead to fire or explosion. Cutting through a water main can flood your property and result in a large repair bill. Under the Health and Safety at Work Act 2015, you have a duty of care to manage these risks before any ground disturbance begins.
Step 1 — Contact Before You Dig (CBYD)
The first and most important step is to use the Before U Dig service (also known as CBYD — Contact Before You Dig). This is a free national service in New Zealand that notifies utility asset owners (power, gas, water, telco) about your planned excavation. They will respond with plans showing the location of their assets near your site.
- Visit beforeudig.co.nz or call 0800 248 344 to submit a request
- Allow at least 3 working days for responses
- Keep records of all responses you receive
Note that not all private services (such as older drainage runs or privately installed cables) will appear on these plans, so CBYD is a starting point — not a complete guarantee.
Step 2 — Check Your Property Documents
Gather any as-built drawings, LIM reports (Land Information Memoranda), or building consent documentation for your property. These can show the location of drainage, water supply, and other services installed as part of consented work. Your local council can provide a LIM report, and MBIE Building Performance has guidance on what these documents cover.
Also check with your neighbours if the fence line runs along a boundary — they may have knowledge of services on their side.
Step 3 — Visual Inspection of the Site
Before digging, walk the fence line carefully and look for:
- Meter boxes, inspection covers, and manholes — these indicate services nearby
- Toby (water shutoff) boxes — usually found near the boundary
- Gas meter locations — trace the likely pipe route back from the meter
- Electrical conduit entering the ground near the house
- Soft or disturbed ground that may indicate a previous excavation
- Irrigation systems or outdoor taps — these have supply lines
Step 4 — Use a Cable and Pipe Locator
A cable and pipe locator (also called a CAT scanner — Cable Avoidance Tool) is a handheld electronic device that detects buried metallic services. These can be hired from most equipment hire companies, including outlets at Bunnings or Mitre 10.
For best results, use the locator in both passive mode (detects signals already present on cables) and active mode (uses a signal generator to trace specific services). Be aware that:
- CAT scanners cannot reliably detect non-metallic pipes (such as PVC drains or poly water pipes)
- Results depend on operator skill — if you're unsure, hire a professional locator
- Ground penetrating radar (GPR) is a more advanced option used by professional locating services for complex sites
Step 5 — Hand Dig or Pot Hole First
Once you've done your checks, hand dig a trial hole (also called pot-holing or hand potholing) along the fence line before using a post-hole borer or mechanical auger. This is especially important:
- Within 600mm of any marked service
- In areas where you're uncertain about service locations
- Near older homes where records may be incomplete
Use a spade or hand auger carefully, and stop immediately if you encounter anything unexpected.
Depth Guidelines to Be Aware Of
While depths vary, here are general minimums you may encounter in NZ (always verify with asset owners):
| Service Type | Typical Minimum Depth |
|---|---|
| Electrical cables (LV) | 450–600 mm |
| Gas pipes | 450–600 mm |
| Water supply | 450 mm |
| Telecommunications | 300–450 mm |
| Stormwater/wastewater | Varies widely |
These are guides only — actual depths can be much shallower, particularly on older properties.
Do You Need a Building Consent?
Most residential fences don't require a building consent under Schedule 1 of the Building Act 2004, but there are exceptions (height limits, retaining walls, proximity to boundaries). Always confirm with your local council before starting, as rules vary by district. MBIE Building Performance has useful guidance on consent exemptions.
When to Call a Professional
You should engage a professional underground service locator if:
- Your site is complex or has a history of multiple owners and modifications
- CBYD responses indicate services are close to your fence line
- You're working near high-voltage infrastructure
- You're unsure how to interpret locator results
For any electrical or gas work that may be disturbed, you must engage a licensed electrician (registered with the EWRB) or a licensed gasfitter (registered with the PGDB) — this is restricted work under NZ law and cannot be done by homeowners.
A qualified local fencer will also be familiar with these checks and can manage the process on your behalf. You can find experienced fencing contractors in your area on tradedirectory.co.nz.
