Isolated Downconductor System
Modern buildings frequently contain rooftop mounted heating/cooling systems and an array of communication antenna. Traditional methods of lightning protection, such as air terminals (Franklin Lightning Rods) and a network of downconductors connecting to an integrated grounding system, are not well suited to protect these modern devices.
The Isolated Downconductor, part of the ERITECH® line of Facility Electrical Protection products from ERICO®, offers a solution to this problem by applying a high performance insulation around the downconductor. The same isolation as 1,000 mm of air separation can be provided, enabling the downconductor to be mounted directly on the mast or structure to be protected.
The Isolated Downconductor provides a traditional air terminal fitted to an isolated fiberglass-reinforced plastic (FRP) mast. The Isolated Downconductor internally connects to the air terminal inside the FRP. The FRP mast has natural isolation properties, high strength for windy sites and low weight to minimize mast loading.
The system features a lower-cost cable targeted at the typical shorter installation requirements of the telecommunication industry. The cable is designed, tested and applied to meet the requirements of IEC 62305 lightning protection standards, and appropriate products are tested in compliance with EN 50164-1 and EN 50164-2.
The Isolated Downconductor has also been successfully tested by an independent laboratory using the industry accepted “Zischank” method*. Here a length of cable is tested with voltage impulses in comparison to an air gap. If the parallel air gap breaks down repeatedly before the cable, then the equivalent safety distance of the cable is greater than the air gap distance.
W. Zischank “Insulators for isolated or partially isolated lightning protection system to verify safety distances” 23rd International Conference on Lightning Protection (ICLP), Firenze (1996), S 513-518.
- Can be mounted directly on the mast or structure to be protected
- Provides a traditional air terminal fitted to an isolated fiberglass-reinforced plastic (FRP) mast
- The FRP mast offers natural isolation properties, high strength for windy sites and low weight to minimize mast loading
- Features a lower-cost cable targeted at the typical shorter installation requirements of the telecommunication industry
- Meets the requirements of IEC 62305 lightning protection standards
- Complies with EN 50164-1 and EN 50164-2
|Implementation of the Isolated Downconductor system is based on two sections of the IEC 62305-3 standard
(Protection Against Lightning – Part 3: Physical damage to structures and life hazard). For correct installation,
the system must be designed and installed in accordance with these requirements:
Determine the required height of the air terminal to
provide protection according to the protection angle
method of IEC 62305 or the rolling-sphere method of
IEC 62305, NFPA780, AS1768, etc. The required
lightning protection level can be determined by IEC
62035-2 Risk Assessment, or simply using LPL I
for maximum protection. Using this information the
designer should determine the required minimum
height of the air terminal tip above the top of
mast/items to be protected. (Note: Isolated
Downconductor mast requires a minimum
clearance distance of 2 m).
Determine the length of downconductor required,
and for the selected lightning protection level, ensure
that it does not exceed the maximum length in the
following table. These lengths are derived from the
knowledge that the ISODC cable has a tested
separation distance of 1,000 mm (see IEC 62305-3
Section 6.3 or NFPA780 Section 4.21).
Meet ERICO’s mounting and installation requirements
and interconnect to a standard compliant grounding or
lightning protection system.
If the maximum cable limitations above cannot be adhered to, then it is possible to use two parallel downconductors. The ISODUAL adapter allows a second Isolated Downconductor to be connected to the air terminal. The second ISODC Downconductor is mounted externally to the Isolated Mast and fixed with UV-stable, non-conductive cable ties.