Cable Strike on a Domestic Supply
A 2.6 t excavator is cutting a 600 mm deep trench for a new garden supply at an occupied house. Utility drawings, requested the day before, showed no recorded services, and no permit-to-dig has been issued for this job. At 10:20 the bucket teeth score through something hard and the machine jolts; a blue-sheathed cable is severed, and the bucket is now resting against the exposed conductor. The operator is in the cab, the tracks are on damp grass, and there is a smell of hot plastic. The householder is walking down the path toward the machine holding a phone. The supervisor is 25 minutes away and the utility has not been called.
1. Sequence your first actions and give the reason for each. Explain how you decide whether the operator should stay in the cab.
Read the worked answer
1. Keep the operator in the cab and keep the machine exactly as it is. A steel cab on rubber tyres or dry tracks is the best-protected place he can be. The default is: stay put, do not touch the ground and the machine at the same time, do not try to slew the bucket away - moving the bucket may re-strike or arc, and it may also be the only thing keeping the conductor in a predictable position.
2. Stop the householder immediately, before she reaches the machine. She is about to walk into a step-potential gradient on damp grass holding a metal-bodied phone. Get her back, and keep everyone at a distance well beyond the machine (a common working figure is at least 10 m, further in wet conditions).
3. Call the distribution network operator and report a live cable strike. The DNO is the only party who can confirm isolation. Do not accept 'it's only a domestic supply' as reassurance from anyone on site.
4. Call the supervisor and the client, and put a cordon and a person on the cordon. The machine is an unattended hazard if the operator is later moved.
5. Record and preserve. Note the time, depth, position, what was hit and the state of the bucket, before anything is disturbed.
When does he leave the cab? Only if staying is more dangerous than leaving - for example fire, or the machine becoming unstable. If he must leave, he jumps clear with feet together, lands with feet together, and shuffles or hops away without touching the machine and the ground simultaneously. He does not climb down.
2. Decide what must be notified and recorded, and state what has to be true before this trench can be reopened.
Read the worked answer
Notify: the DNO (for isolation and repair), the site supervisor, the client and, if the property has lost supply, the householder. Notify the HSE only if the trigger is met - that is, if someone has been injured, or if the event became a reportable dangerous occurrence such as a fire or explosion. A cable strike with no injury and no fire is not automatically RIDDOR-reportable, so the judgement is to check the actual outcome rather than report reflexively or, worse, not consider it at all.
Record: time, location and depth of the strike, service affected, machine and operator details, who was notified and when, the isolation confirmation, and the corrective actions. Put it in the site diary and the accident book if anyone was affected.
Before reopening the trench, all of the following must be true:
- The DNO has confirmed the cable is isolated and has repaired or rerouted it.
- There is a written permit-to-dig for the remaining work, issued by someone competent, referencing the DNO's records and the position of the cable.
- A cable avoidance tool survey has been done on the line of the trench and the positions marked on the ground.
- The method has changed to safe digging near services: hand-dig trial holes, insulated hand tools, no mechanical digging within the specified clearance of a marked service.
- Everyone on the crew has been briefed on what went wrong and what changed.
3. The supervisor says: 'The drawings showed nothing, so it is not our fault. Move over 2 m and carry on.' Evaluate that instruction.
Read the worked answer
The instruction is wrong on both counts.
'The drawings showed nothing' does not mean there is nothing there. Utility records are indicative: they are often incomplete, out of date or plotted at poor accuracy, and domestic supplies in particular are frequently unrecorded. Records tell you where to expect services; they do not clear the ground. The only way to be reasonably sure is to combine records with locating (a CAT survey, and a signal generator where the CAT alone is inconclusive) and then confirm by careful hand-digging.
'It is not our fault' is not a defence. The duty is to plan the work to avoid danger and to manage it during the work; that duty sits with those in control of the site regardless of what the records said. A strike that was foreseeable from a 600 mm depth in a residential garden, with no permit-to-dig and no locating, is a planning failure, not bad luck.
'Move over 2 m' replaces one unknown with another. The severed cable may run anywhere; the parallel service may be a gas main or a water main. Moving the line of the trench without a fresh survey and a fresh permit is the same mistake repeated.
What you say in reply: the trench line is not moved until the area is surveyed, marked and permitted, and the method is changed to hand-digging near services. If the supervisor insists, escalate - this is exactly the point where an operator's refusal is the correct professional judgement, and it should be recorded.