When you need to undertake any sort of excavation work, avoiding a cable strike is critical. And we are not just talking about electricity cables here, because the term is often used as an overall description of any sort of underground services. This could also be natural gas pipes, water pipes, sewage pipes, telecoms, fibreoptic, and other gas pipes such as LPG.

In order to avoid striking any type of underground service, it is essential to carry out a full survey of the area that needs to be dug, and this needs to be done by an operative who has the correct tools and the training in their use.

Before doing this, you need to obtain any plans that are available from utility companies whose services run in the area. However, you also need to note that the plans can only ever be used as a guide since they are often not accurate, and in some cases do not exist at all.

The problem is that there is no unified system for recording underground services, and also no unified system within the same type of utility. So, for instance, one electricity supplier may keep records in a different manner from another. There can be many reasons why records are not accurate, and we have discussed these elsewhere. It just needs to be understood that plans, or STATS, cannot be taken as gospel, but only used as a starting point, when surveying in order to avoid a cable strike.

When undertaking a survey, the two main tools that are used are the CAT – Cable Avoidance Tool – and the signal generator, or Genny.

A cable avoidance tool such as the Radio Detection RD8000 series can be used to detect in passive, induction, or direct connection modes. When used in passive mode it will pick up a background signal that a utility is giving off, such as an electricity or telecoms cable that emits its’ own power that can be detected at the surface. It needs to be noted that if there is no power, the cable cannot be detected, so if it is dead or has no power running through it, such as a street lighting cable in daylight, then it cannot be detected in this way.

There are also some high voltage, or HV, cables that are the “balanced” type and have been designed so that they do not give off any signal even when live.

If no signals have been detected in this way, then the Genny comes into play, and this is place on the ground and generates a signal into the ground with the purpose of it “attaching” itself to a buried service and then travelling along its’ length which lets the receiver pick up this signal in induction mode.

This May Not Work Either

In some cases, this does not work either, and then the Genny can be directly connected to a service with a clamp or clip leads. This means that access to the service is required through a stop valve, cable riser, inspection chamber, or plant room. It may be that the access point is behind locked gates, for instance, in which case it becomes difficult. This is another reason for having STATS since they may give an indication of where an access point is likely to be.

Another method of detecting the likely whereabouts of underground services is by using ground penetrating radar – GPR – with something such as the Mala Easy Locator. This does not physically locate buried services but detects differences in the ground density in order to give an indication of the possibility of buried services. However, this also has certain limitations because the ground may be uneven or overgrown, or it may be heavy clay or have rubble in it.

All of this is why proper training is needed, such as the courses we provide at Sygma Solutions, in order to fully understand the implications and limitations involved.