The Radiodection equipment we use allows us to identify and trace underground cables or pipes using the properties of electro-magnetic (EM) fields.
These fields are created when a current flows through a conductor. In the case of an individual cable or pipe the EM field radiates outwards, from the centre of the cable or pipe, decreasing in strength by the square of the distance from the conductor. Similar to the waves created when a stone is dropped into water.
The strength of this field can be measured by the Radiodetection receiver and allows us to give an indication of depth and position.
Where current is flowing in a closed circuit, for example the power supply to a home, the receiver can detect the presence of these cables using the naturally occurring EM field.
However to achieve an accurate locate to AS5488.1:2019 Classification of Subsurface Utility Information we use the receiver in conjunction with the transmitter.
The transmitter allows us to create an EM field at a specific frequency in the desired cable or pipe. By setting the receiver to the same frequency as the transmitter we can then trace the service to a high degree of accuracy.
Our equipment can provide a Quality B locate as per AS5488.1:2019 Classification of Subsurface Utility Information, accurate to +/-0.3m horizontally and +/- 0.5m vertically. Due to environmental variables beyond our control and compliance with the Dial Before You Dig Duty of Care, EM locations can not be used to guarantee the position or depth of any cables or pipes.
It is vital that any underground services identified are located to Quality A by carefully exposing by hand or Non-Destructive Digging (NDD), allowing their position and depth to be visually confirmed before work starts.
The need to generate an EM field is our main limitation. Therefore we can only locate metal cables and pipes. In many situations we can work around this using some of the methods below.
1. Locate the trace wire – modern plastic water or gas pipes are often installed with a metal trace wire. Provided we can directly connect the transmitter to this wire we can create our EM field and locate the service.
2. Other conductive cable – fibre-optic is often installed within existing conduits alongside older copper cables. These copper cables can be used to trace the route of the conduit and therefore the route of the fibre optic.
3. Ducting rods – If no conductive cable is present then we can insert our own. By sliding a ducting rod (containing a copper wire) along the conduit or pipe (ie storm-water) this rod can be located giving us a depth and alignment of the conduit/pipe. This does require access to at least one open end to allow the rod to be inserted.