08 Dec A new approach to laying loop cables for National Highways

National Highways manages England’s motorways and major A roads. In 2024 the organisation began relocating to new headquarters in Birmingham.

We were asked to survey the new site in autumn 2024 on behalf of electrical contractor, Impact Building Services.  Three Snow Hill is the city’s largest office building and National highways will occupy three floors.  At this stage in the refurbishment, our engineers could clearly see that the offices and meeting rooms would have raised floors to enable access to services installed beneath. Contacta engineer James Graves wanted to use this underfloor space to host the loop cable installation.

“We planned a low spill phased array design because privacy was very important for this client.  We had to design a layout using our 3D visualisation software that would contain the loop signal within each room. So many cable turns to lay in multiple rooms was a challenge.”

James planned to secure the loop cables to the concrete sub floor.  He chose a round wire cable and carried out a number of initial test loops in situ.  He knew the metal floor tiles would weaken the signal strength of the loop, so tests were vital to ensure the loops would comply with the IEC standard.

“I wanted to be confident that the loop signal would be strong enough, so that all systems met the specification.  This meant powerful V22a-Pro loop drivers were needed.  We ensured the client understood our design logic and the advantages in having the cables protected under the floor tiles.”

Once everything was agreed, James, Dean and new engineer Ryan, installed 16 low spill phased array loops over a period of six months.  They worked around the schedules of multiple contractors, lifting the metal tiles in the rooms, fixing the cabling o nto the sub floor, then relaying the flooring.  This stage also involved installing microphone cables into the ceilings, for delivery of a local sound source in each room.

The team returned to site once the power was live to carry out the ‘go live’ phase.  This involved commissioning the V22a-Pro loop drivers, which were also positioned below the raised access floor, and installing ceiling boundary microphones.

“The client was impressed that the loop signal fades as soon as you step out of the room,” James added, “and we haven’t had any damage to the loop cables!  When we come across similar room layouts in future, we will be able to use the same installation method as it has been a great success.”

The reception desks on each floor were also fitted with an under-the-counter hearing loop to ensure clear conversation for visitors with hearing loss.