BT Openreach and Prysmian invent new system for faster FTTH delivery

BT Openreach and Prysmian invent new system for faster FTTH delivery

Openreach achieves rollouts faster and cost-effectively with fewer application procedures and less disruption: “It is a great bit of kit!”

Prysmian and BT subsidiary Openreach are working on a new fibre installation technique that significantly speeds up FTTH rollouts. The new Karona Overblow System is designed to enable the installation of high density optical fibre cable into pre-existing sub-ducted routes. Karona was announced along with news of a £15bn FTTP rollout that could reach 25 million premises by December 2026. To date, Openreach has purchased more than 100 sets of equipment from Plumettaz. Openreach typically purchases 150km/month of Prysmian Sirocco HD 144f 5.0mm diameter cables.


Prysmian developed the Karona overblow system specifically to allow Openreach to add small diameter cables into low diameter sub-ducts in which legacy cables already in place. Openreach is benefitting from this system to help install its ‘Single Fibre Network’ in major UK cities as well as remote rural areas, where installation is usually more complicated and less efficient. During field tests, the solution has proven to significantly reduce the amount of traffic management and disruption involved in rollout.

Distances of 800m in a single blow are achievable so it 2 km per day is a realistic target when using centre-blowing and other range extending practices. Cascade blowing using two or more installation sets could increase the daily rate even more.

“The overblowing technology my team have been using, and worked with Prysmian to develop, saves us time, when waiting for noticing to dig in roads, and money, as it avoids costly civils like clearing duct blockages,”

says Andy Whale, Chief Engineer, Openreach.

“It is a great bit of kit which we are rolling out across the UK, in rural and urban settings.”


Prysmian Group also provides approved installation training for the Karona Overblow System. Overall, cost savings, overall speed of installation and minimum third party disruption are impressive. By using existing ducts, the process of applications for planning permissions and permits for civil work can be bypassed, saving significant amounts of time to secure. Cable installation using this new method can begin instantly. 


“BT’s sustained partnership with Prysmian means we can benefit from its teams’ skills and innovation to help us build full fibre even further,”

said  Matthew Hemmings, Openreach MD for Fibre and Network Delivery.

Key benefits Karona Overblow System compared to conventional cable installation


  • Cost: civil works costs typically make up approximately 70% of the cost of a new installation; this cost is eliminated
  • Lead Time: generally there is no need to apply for licences for an installation into an existing sub-duct network
  • Speed: when building a new duct network a speed of 50m per day is considered the norm; overblowing is conducted at 40m/min
  • Environmental Impact: huge reduction in energy/greenhouse/ozone affects; no waste products created or to be removed. CO2 reductions typically in excess of 25 tonnes per km
  • End User Satisfaction: installation speed, significantly reduced lead times as well as eliminated civil work drastically reduces end-user disruption



The first trial was conducted at a road crossing under a major dual carriageway (approx. 100m) took less than one hour, without any issues and minimal disruption. Assumed customer cost savings: some £50k.

Subsequently an installation involving cable installation over a bridge, over a major road, for a new housing development brought assumed cost savings of £35k.

A cable was overblown in a 550m sub-ducted route along a minor road, using centre-blow technique involving 250m and 300m installations, taking less than three hours. Assumed cost savings: £25k.

In a trial in Stonehaven Scotland, two Prysmian Sirocco HD 144f 5.0mm diameter cables were overblown along 600m in under 4 hours, increasing route capacity to 432 fibres.

In Bury St Edmunds, two Prysmian Sirocco HD 144f 5.0mm diameter cables were successfully overblown in a 730m route in less than 4 hours.



The Karona Overblow System is a solution comprising overblow cables, installation equipment, connectivity and comprehensive training enabling Installers to use the system. Additional optical fibre cables can be installed, using a range of techniques from ‘Point to Point’ to achieve distances up to 1km, ‘Centre Blowing’ to achieve up to 2km or ‘Fleeting’ to achieve even greater distances. The Karona Overblow System encompasses a range of specifically designed overblow cables from 12 to 576 fibres matched with a range of joint closures to complete installation.