Mt Horrible Line Rebuild

The challenge

When a section of network approaches end of life, the asset risk is straightforward to describe: unreliable supply, rising fault probability, and customers who can’t be backfed if something fails. What’s harder to describe is the compounding exposure of leaving it unresolved, and harder still is finding a contractor who can actually fix it.

The Mt Horrible line runs across approximately 7km of exposed hill country above Arthur’s Pass (one of the more remote and inaccessible parts of the network), across a mix of DOC conservation land and private leasehold where standard vehicle access disappears long before you reach most of the pole sites. The gradients rule out Elevated Work Platform (EWP) trucks, and the rocky ground on the steeper sections needs specialist breaking techniques rather than conventional excavation. The site also falls within significant native lizard habitat, which meant working up an active management plan with DOC before a shovel went in the ground – a process that shapes the programme schedule, not just the method statements.

The fire risk added another layer. Temperatures on the exposed faces regularly hit 30°C in the Nor’wester, on land where a single ignition could cause damage measured in millions of dollars. And with the line terminating at a true end-of-line position, Orion had no ability to backfeed customers once the outage started. Every day beyond the planned window was a day of customer hardship and regulatory exposure. The programme had to be built around holding that window – not hoping to.

Our approach

Connetics’ crews had been up this line on fault response work over the years, and that history shaped how the job was planned. The team already understood the access constraints and the terrain before the tender was awarded – knowledge that compressed the planning phase in ways that matter on a job with this kind of programme pressure.

Rather than treating the four-week outage window as a target to aim at, the programme was built backwards from it. To hold the window without leaving customers off supply, Orion installed a temporary generator to maintain supply to affected properties throughout the works, freeing the crew to run the full programme without the daily switching complexity that reenergising the line would have added.

Titan FRC poles were specified by Orion for this project – the first time they’d been used on their network. At roughly half the weight of a standard hardwood pole, they can be maneuvered into position on steep ground where heavier poles would create serious handling risk, and their fire-resistance rating made them the right choice for a site where ignition risk was one of the programme’s most significant variables.

Managing fire risk on site went beyond specifying the right pole. Before mobilisation, all hot work gear came off the trucks entirely. Muscle memory is a real risk when crews are used to reaching for a grinder – removing the option removed the exposure. The helicopter was on site every day of the works, rigged with a monsoon bucket so the team could respond to a fire immediately if one started. A water tanker truck with firefighting capability was on the ground as well. Between the two, fire response was a standing operational capability for the duration of the project, not a fallback plan.

Making it happen

At peak, three line crews and five excavators were running across separate work fronts on the hill simultaneously, with the helicopter operating continuously to ferry gear and position equipment on slopes where tracked machines couldn’t reach under their own power.

Getting excavators to the steeper sites meant lifting them in. HGM’s civil crew worked ahead of the lines teams, hand-benching working platforms into the hill before the lines work could start.

The Titan FRC poles, developed in Australia for fire-prone environments, needed a different approach than standard timber. Their lighter weight makes them practical on steep ground, but it also requires careful rigging to get them positioned accurately. That kind of detail doesn’t tend to show up in a progress report, but it does show up in the quality of the finished installation.

The lizard management plan ran throughout construction, not just as a pre-start requirement. At each pole site, the crew cleared scrub and rock formations before breaking ground and managed the cleared material appropriately – all carried out under the supervision and consultation of a trained, experienced herpetologist. That work was built into the programme schedule rather than treated as an interruption to it.

At the end of the project, Connetics carried out a formal land condition review with the leaseholder, walking the full site to confirm the land was left in at least the condition it was found. Where anything needed remediation, it was committed to. That review was on the programme from the start.

The result

Seventy-two poles and 2km of conductor replaced. The four-week works window held. The Titan FRC poles are now in service on the Orion network for the first time, and customers at the end of the line stayed connected throughout, supplied by the temporary generator that had been planned in from the beginning. The DOC land was handed back in good order, and the leaseholder review found nothing that needed remediation.

For Orion’s asset programme, the job cleared a long-standing reliability risk on a section of line that conventional access methods couldn’t efficiently reach – and in doing so demonstrated a repeatable delivery model for similar constrained environments across their network.