24 Aug How Accurate Are Dial Before You Dig Plans?

How Accurate Are Dial Before You Dig Plans?

We recently received an emergency call out to a job in Melbourne where a pile driller had drilled straight into a mains power cable. The auger grabbed onto it, wound it up and snapped it off the power poles at either end of the cable, one was 20m away, the other was a couple of hundred meters away. The driller didn’t know that they’d caught hold of this cable until someone heard the snap of the cable being ripped off the overhead pole 20m away, but at that stage they’d drilled at least another 600mm past where it was first hit. A whole bunch of nearby properties lost their power supplies.

You’d be excused for thinking that these contractors had taken short cuts and this couldn’t happen to you because you’d at least get Dial Before You Dig plans and check if there was a cable nearby. But these guys had done that. They’d planned to drill 7 piles along their rear boundary, but inside their private property, not in the laneway behind their site. So they checked the DBYDs and they showed a power cable was in the laneway, but not in their land. Now this is very easy to believe because the underground power mains are pretty much always in the roadways, and almost never in your private land. So when the power company’s plans say they’re in the laneway, you are inclined to believe them.

Piling auger drilling through power cable

In this particular case, the contractor who installed the power cable on behalf of the power company alledgedly didn’t properly established the boundary between the private land and the laneway! They thought they were installing this cable outside of the private properties boundary and only in the laneway behind it, but it turns out that they bored it through the private property on their way to the laneway. Not ideal.

So to answer the above question how accurate are Dial Before You Dig plans? Not very. They’re a guide to what might be in the area, but you’ll never be able to rely on them to be 100% comprehensive, you’ll also never be able to rely on them to be 100% accurate in the case that they do show a utility is present. To best find out if your request is comprehensive, you need to do a site inspection with a professional contractor who is familiar with underground environments. To best find out if the plans are accurate, you need to trace each underground service individually (then pothole to prove if necessary).

Unfortunately, the contractor will have an argument on their hands to get out of trouble here, despite checking the plans and them not being accurate. The only way to protect yourself, to satisfy your duty of care and therefore not void your professional indemnity insurance, is to do a site inspection with a DBYD certified locator, then follow their recommendations.