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How to identify and locate ⚡ Three 3 Phase power cables underground?


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Why do you need to know ⚠️ how to identify and locate 3 phase power?

As a utility locator or property/asset owner, you must be able to identify and locate 3 phase power for numerous reasons, the main reasons being OH&S.

It is your duty of care to safely working with or around high voltage power in any situation.

3 phase power has more wires/cables with a greater power load then single phase residential electricity and has specific dangers associated with it.

Three phase power subsurface locating techniques differ from regular power lines underground, due to nullification which can cancel out signals connected by electromagnetic locators, other factors might include how the utility line lays within a trench, to what material it is within.

This can make it hard to locate for accurate locations via regular utility locating methods. Once you can correctly identify that you have 3 phase present, you can then be more effective at locating protection of the asset to avoid damage and injuries.

3 phase power should be treated as a ⚡ High Voltage HV utility for risk assessments, making the clearance width wider in most cases.

As were single phase might have a 1.5m clearance, HV lines will usually have a 3m clearance for a QLB mark for safe excavations or surface penetration (example, drilling). Clearances vary on asset owners requirements, OH&S regulations and other factors.

Another big consideration for 3 phase is why it is necessary in the first place, ask yourself, what is the power needed for? 🔌 Usually commercial equipment and machinery will be supplied with 3 phase, on sites such as Laundries, restaurants, factories and workshops to name a few.

Now you know the importance of why you need to identify 3 phase power to tell it apart from single phase or other electrical lines, we will go on to information needed to identify and locate these types of lines efficiently, accurately and safely.

The theory 📘 of locating three phase power.

Single phase power cables generally radiate clear signals, but with 3 phase cables, the signal is largely the result of imbalance between the phase loads, as balanced currents tend to cancel their fields. The better the balance, the more difficult detection becomes.

As high voltage cable loadings are generally better balanced, a simple passive search in ‘P’ mode might easily detect a low voltage cable whilst missing both an ⚡ 11kV power cable nearby, and live but unloaded cables, such as street-lighting during the day, which radiate 🪫 no power signal. This is why the availability of the Radio mode and active modes is such a valuable complement to the Power mode.

Very low frequency (long wave) radio energy from distant transmitters is present in the atmosphere world-wide. The ground provides return paths for this radiation, and buried metallic lines form preferred paths.

They then act as aerials re-radiating these signals. The signal strength will vary with coupling to ground, size of line and soil conductivity, the strongest signals emanating from lines with good grounding at each end, or of substantial length so that capacitance coupling is maximized.

📡 Radio frequency signals enable the presence of the conductor to be detected by Radiodetection locators in the Radio mode, which can then find dead power cables or well-balanced high voltage cables which could well be missed by power-frequency-only detectors.

📞 Telecommunication cables and metal pipes also carry these VLF radio signals, so again passive location is effective, but, as with all passive signals, there is no way of identifying the line.


👀 Identify: Using visual, other indicators and other data. QLD


📍  Locate: Use Electromagnetic locating for subsurface locations, Mark, Record, Report Quality Level B (QLB), Use GPR to check depths and other potential targets. All GPR marks are considered Quality Level D (QLD)


🚧 Protect: Here are some common outcomes.

-Ideally the utility locator locates the 3 phase power with Quality Level B (QLB) data, with clearances and permit to dig by asset owners.

-OR another possibility is to pothole for QLA data, which is needed for any construction work area. Potholing specific lines or areas might be recommend by utility locator to confirm assumptions. This is to verify any QLB/QLC/QLD data or to confirm utility position within work area clearances.

How to identify Three Phase power cables?

Here are a few ways to identify 3 phase power while locating on a site.

  1. The easiest way is by previous knowledge 📖

Having prior knowledge of 3 phase power can help speed up identifying 3 phase power, whether through asset/property owner information, old maps, DBYD, or due to other knowledge of specific sites. 🗺️

2. Check the power board or electrical room for type of fuses used on property

Checking the power boards should be on all utility locators work completion ✔️ checklists. This way you can gain alot of information about the power supplied to a property or 🏗️ building.

3. Check for 3 phase cables/plugs or machinery

If you can visually see 3 phase plugs 🔌, cables, machinery or even solar panels, you can probably be sure there is 3 phase power connections on the property.

How to check for three phase power?

Here are four simple ways to check if your home or business has one, two, or three phases connected.

-Service Fuses, Main Switches and Wires/Cables/Plugs, and Appliances/Machines inputs.

What do three phase power Service Fuses look like?

What do three phase power switches look like? 🔄 (Mains Switch)

Having access to the main switchboard/electrical box is important to identify three phase power via the circuit breakers. Three phase power ‘mains switch’ will usually have three consecutive switches as shown below.

What do 3 Phase Plugs 👀 look like?

So what plugs indicate 3 phase power.

  • Look for any indication of plugs that is not a regular standard 3 pin GPOs.
  • Usually 4-5 Pin Plugs and larger outlets
  • 3 phase to 240v Outlets. (heavy duty switches etc.)

What do 3 Phase Wires look like?

For three phase wiring, our AS standard colors are:

  • Phases: Red, White, (dark) Blue
  • Neutral: Black
  • Earth: Green/Yellow


How to 📍 locate three phase power?

Standard Operating Procedure for Locating three phase power.

These steps are in addition to the fundamental utility locating process.

First, Identify what uses three phase power? Large motors/generators , commercial cool rooms fridges, commercial solar etc. Three phase power is commonly used when multiple appliances or electrical devices are being used and where power consumption performance is important. 

Second, Access to check main switchboard or electrical room for.. 1,2,3x (times) connected switches and 1,2,3x service fuses can indicate 1,2,3 phase power.
If 2-3 phase power is present or indicated,

You then clamp (33/66) onto load cable/s available, sweep area, if clear signal, follow to visual indicator and check line signal, milliamps and depths, check wires in/wires out, check lateral. Source to Consumption, pit to pit or cable to cable. Mark/Document/Report, confirm Quality Level B QLB data.

💡 Trouble Shooting Tip: Some 3 phase lines cannot be located due to lack of electrical load, and the 60Htz signal nullifies itself. To solve this, ‘locate’ with a electromagnetic locator by making the line active, and putting a electrical load onto line by turning on power of supplied machine, appliance or equipment etc.

Added Work Completion Checks

✔️ -Electromagnetic Locator Power/Passive/Radio modes Scan
✔️ -Electromagnetic Locator Box Sweep, North to South, East to West.

✔️ -Ground Penetrating Radar GPR Grid Scan

What About  2 Phase Power?

Two phase power supplies are actually also quite common in Australia. Two phase power is best identified using the ‘Service Fuse’ method outlined above. There will be two service fuses present for two phase, rather than one or three.






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