Underground Cable Plans and Site Marks: What to Check Before Excavation

An underground cable plan and a set of painted marks are two parts of a safety handover. Treat neither one as a promise that every cable is shown. The line is not exact, and the depth beside one mark does not apply along the whole route.

The person controlling excavation needs to know where the information came from, where it applies, what is still uncertain, and what must be checked before plant moves. Use the checks below to reconcile the plans with site evidence and brief the people doing the work.

Jurisdiction and instruction scope

BYDA provides national referral and duty-of-care guidance. The WorkSafe Victoria and Energy Safe Victoria guidance cited here applies to Victorian work. Safe Work Australia publishes a model Code of Practice. Its legal effect depends on local implementation, so check the relevant regulator. In every location, current asset-owner plans, permits, access conditions and instructions take priority for the asset and the proposed work.

Plans and paint do not authorise excavation

A BYDA response, a locator report or a painted line is information for the project’s risk controls. It does not grant permission to excavate. It does not replace an asset-owner permit, remove an exclusion or No Go Zone, or replace the safe system of work. Before work starts, the person controlling the work confirms the applicable permits, owner conditions, clearances, supervision or spotter requirements, excavation method and any physical-exposure hold points.

If the available evidence does not establish the position needed for the proposed activity, keep the work outside the affected area and escalate. Further locating, owner direction or approved physical exposure may be needed. Never use the plan or mark to justify work that its notes or the owner instructions prohibit.

First: make sure the plan pack is complete

A BYDA enquiry produces an enquiry confirmation and responses from affected asset owners. BYDA’s duty-of-care guidance says to check that every owner has responded. Contact an owner if plans have not arrived within the stated period. Follow the duty-of-care information sent with the plans and keep the confirmation sheet on site.

Before using a plan, check:

the enquiry address and mapped enquiry area
the issue date and validity period
the asset owner and service type
the plan number, sheet number and revision
the legend, abbreviations, line styles and scale
any cover letter, permit requirement or special condition
whether the plan says it is schematic, indicative or not to scale
whether private, after-meter or domestic services are excluded
whether the planned excavation sits fully inside the enquiry area

If the work area or scope changes, BYDA says to lodge a new enquiry. A plan for the right street but the wrong side of the property is not the right plan.

Read the line in context

Start with fixed features that can be matched between the plan and the site. These include property boundaries, kerbs, pits, poles, cabinets, hydrants, meters, buildings and maintenance holes. If those features do not align, do not shift the cable route by eye until it “looks right.” Check the plan scale, orientation, revision and any notes about offsets.

Ask what the line represents. Depending on the owner and the drawing, it may be a route, a duct bank, a cable group, a connection or a schematic relationship. The legend controls its meaning. Colour alone is not enough.

BYDA states that owner plans detail the presence of infrastructure rather than its exact location. It also says plans generally do not show the whole domestic connection. Treat the drawing as evidence that directs further investigation. It is not a trench set-out drawing.

The plan-to-ground cross-check

Use a simple reconciliation table before the work is authorised:

Check	Plan evidence	Ground evidence	Action if they disagree
Entry and exit points	Cable route, pit, pole or cabinet shown	Visible pit, riser, pole, switchboard or cable entry	Stop extending the assumed route; inspect records and site again
Number of routes	One or more lines, ducts or groups	Field marks and detected responses	Ask whether routes are bundled, stacked, abandoned or private
Route geometry	Straight line, bend, road crossing	Marks, surface features and field-locate handover	Confirm which parts were detected and which were inferred
Depth information	Typical cover, annotation or no depth	Instrument depth indication or exposed measurement	Keep plan values, instrument indications and physical measurements clearly separated
Work boundary	BYDA enquiry polygon or drawing extent	Proposed trench, bore, pile or excavation footprint	Lodge a new enquiry or extend the investigation if work falls outside it
Validity	Date and owner conditions	Current work date and unchanged site	Refresh expired information or after significant site/scope change

Resolve a disagreement or record how the safe system of work controls it before the affected activity proceeds. Do not average the two routes or depths.

How to read site marks

Paint, flags or pegs indicate the locator’s interpretation within the investigated area. Before relying on them, ask the locator or supervisor to explain:

the meaning of each colour, symbol and abbreviation
whether the mark represents a detected centreline, corridor, duct bank or inferred connection
where the locate started and ended
which routes were directly connected, induced, found passively or supported by GPR
whether depth indicators were recorded and how they were obtained
which expected cables were not found
whether unknown responses or congested areas remain
which surfaces could not be scanned
whether any part of the route was extended by inference between confirmed points

Take dated photographs or a controlled sketch if the marks must be preserved for the project record. Marks can fade, be washed away, be covered by spoil or be transferred incorrectly after surfaces change.

The WorkSafe Victoria and Energy Safe Victoria guide says visual warnings such as signs and marks should be used as warnings and reminders, but should not be the only control. Marks do not cancel exclusion distances, permits, owner conditions, physical exposure requirements or the site’s safe system of work.

What a depth label does and does not mean

A receiver can display an estimated depth to a detected signal. This can help interpretation, but it is not a direct measurement of the cable. Signal distortion, coupling, bends, stacked services and an incorrect conductor can affect it.

An instrument depth reading must not determine how deep machinery digs. Resolve uncertain depths through the agreed investigation and excavation controls.

If depth is critical, ask whether the value came from:

an asset-owner plan or typical installation detail
an EM receiver indication
GPR interpretation
an exposed and measured cable or conduit
a surveyed exposure

These are not interchangeable. Keep the evidence type attached to the number in the handover.

Limits that matter before excavation

Private cables may sit outside the owner plan

Connections after a meter or point of supply, site lighting, gates, pumps, sheds, temporary supplies and later alterations may need private records and a separate field search. Look for switchboards, conduits and cable entries that do not appear in the owner pack.

A mark can represent a signal, not a cable identity

Electromagnetic locating traces a signal on a conductive path. That signal may couple to an adjacent conductor or shared earth. A route that appears under several frequencies or connection setups should be interpreted. Do not accept it solely because it produces a strong tone.

Congested routes may be stacked or bundled

One surface line may not communicate the number or vertical arrangement of cables and conduits. Ask how the corridor was represented. Ask whether the next activity needs a broader exclusion or physical evidence at a crossing.

Out-of-service does not mean safe to strike

The Victorian guide says out-of-service underground cables should be treated as in service unless positively proven otherwise. An unverified abandoned cable still belongs in the site assessment.

Work outside the marks needs a new decision

Do not project a located line beyond the last investigated point, around an unscanned obstruction or into an area outside the enquiry. Change the scope and refresh the evidence.

The supervisor’s pre-excavation handover

The plan pack, marks and locate report should be briefed to the people doing the work. A useful handover covers:

Work footprint: the exact trench, excavation, bore, drilling or piling area.
Plan status: which owners responded, validity periods, missing information and permits.
Field status: methods used, marked routes, investigated boundary and inaccessible areas.
Uncertainty: services not found, unknown responses, inferred sections and ambiguous depths.
Asset-owner conditions: clearances, permissions, supervision or other instructions that apply.
Site controls: how permits, No Go or exclusion zones, the excavation method, physical-exposure requirements and safe work documents address the cable risk.
Escalation: who stops the work and what happens if marks, depth or ground conditions do not match expectations.
Emergency information: current contacts and the project response if an asset is damaged or exposed.

BYDA says it is not an emergency service, and an asset owner must be advised immediately if an underground asset is damaged. A life-threatening emergency requires 000.

Hold points: when the team should stop and reassess

Create a hold point when:

an expected cable cannot be located
a detected route does not connect the expected endpoints
the excavation reveals a cable or conduit outside the marks
depth or route changes unexpectedly
paint or pegs have been lost or disturbed
the work extends outside the enquiry or locate boundary
the plan validity period has expired
a private cable is suspected but not represented
the work method or plant changes
the asset owner’s conditions have not been understood or met
the required permit, permission, spotter, exclusion control or physical exposure is not in place

The Victorian guide presents a process in which changes cause the activity to stop and the safe system of work to be reviewed. The handover should identify who has authority to make that call.

Illustrative example: cable plan and mark disagreement

This example is illustrative. It is not an HR Utilities project record.

A BYDA electricity plan shows a route along the road reserve before turning toward a property boundary. The field marks follow the reserve but continue past the expected turn. A private switchboard on the property also has a conduit entering the ground that does not appear on the owner plan.

The plan line and the painted line require separate checks. The team should:

Confirm the owner-plan legend, sheet and enquiry area.
Ask the locator which marks came from a direct connection and where the route became inferred.
Check whether the marked signal may have continued on another conductor.
Treat the private switchboard feed as a separate investigation target.
Record the unresolved turn and keep excavation out of the affected area until suitable evidence or owner direction is obtained.
Use physical exposure at a selected crossing if the work requires a measured clearance.

A one-page check before plant moves

Plans

Correct site and full work area
Every listed owner response received
Legends, notes, dates and permits reviewed
Private and domestic services considered

Marks and report

Locator explained symbols, methods and boundary
Expected cables not found are recorded
Unknown responses and inaccessible areas are recorded
Depth evidence type is clear
Marks are visible and captured for handover

Work controls

Asset-owner instructions are reflected in the work method
Required permits, permissions and exclusion or No Go Zone controls are in place
Required further locating and physical exposure hold points are complete
The person controlling the work has authorised the planned method
Hold points and stop-work authority are clear
Emergency and damage-reporting contacts are available

For field help, see underground cable locating in Melbourne. For a broader detection scope, review utility locating services. Where a selected crossing needs physical evidence, see non-destructive digging.

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