ILSE offers a family of air terminals and accessories. Our product design is based on the most recent advances in the field whilst maintaining proven principles associated with the successes of the past.

ILSE’s GuardianTM System 5 provides a purpose-designed package for direct lightning protection.

  1. A Family of ILSE CAT (Controlled Advanced Triggering) series air terminals.
  2. A Fibreglass Reinforced Plastic (FRP) mast which provides an insulated mast for mounting of ILSE CAT series air terminals.
  3. A purpose designed ILSE High Voltage Shielded Cable (HVSC) specifically designed for the conveying of lightning energy to ground. Alternatively, depending on the local codes and applications, other materials such as flat copper tape or stranded cable may be used.
  4. ILSE Lightning Strike Recorder (LSR) which confirms system efficiency and effectiveness.
  5. An earthing system consisting of earth rods, clamps, copper tapes and earth enhancing compounds such as ILSE Ground Resistance Improvement Powder (GRIP) or ILSE Reslo.

The ILSE GuardianTM System 5 provides a safe and efficient system for the protection of your facility from direct lightning strikes. The ILSE CAT terminal captures the lightning discharge at a preferred point and the energy is transferred to ground via the High Voltage Shielded Cable with minimal risk of electrifying the structure.Once the energy enters the dedicated lightning earth, it is safely dissipated without risk to personnel and equipment.


ILSE offers Guardian CAT Terminal in both Anodised Aluminium and Stainless Steel.
: CAT terminal model. Model I, II and III
YY: Blank for standard version,GI for 2 inch BSP GI Pipe adaptor
ZZ: G for Gold (anodized aluminium) Model,SS for Stainless Steel Model(only for I & II)

ILSE Guardian™ CAT series terminals consist of

  • A finial with a blunt tip
  • An electrically “floating” medium consisting of 4 electrically isolated panels
  • A triggering procedure which allows for an intercepting streamer to be released at the correct time, thus providing the greatest possible area of protection
  • A high voltage connection at the base of the finial

Principles of the ILSE Guardian™

guardian_terminalsThe ILSE GuardianTM CAT series are Controlled Advanced Triggering devices which intercept lightning discharges for the safe passage to a low impedance down-conductor system. The GuardianTM terminals have been designed to emit a "streamer" of ionised air at precisely the right time so that an approaching "down leader" is intercepted and brought under control.

The concept of controlled triggering is important because if a "streamer" is launched too early the median or ambient field will not be strong enough to sustain propagation and the "streamer" will stall or die. This will leave space charge behind which may inhibit future "streamer" development. An electric field of ~3MV/m is essential at the tip of the air terminal to initiate a corona streamer but an electric field of ~300KV/m is needed in the region between the air terminal and the down-leader to convert the streamer into an up-leader and to sustain propagation.

The dynamic response of the Guardian terminals to the approach of a lightning down leader is the key – detrimental space charge generation prior to leader approach is suppressed and the GuardianTM launches its streamer at the correct time to ensure both electric field criteria are met thus giving the greatest possible area of protection.

How does an ILSE Guardian™ Terminal operate?

Typical formation of lightningGuardian Terminal

A Guardian CAT terminal consists of a grounded blunt lightning rod surrounded by electrically floating metal panels. Rounded or blunt tips have now been proven to be more efficient than sharp points because of a reduced space charge effect. This has been clearly proven in tests conducted at South Baldy Peak in central New Mexico, USA.(Source: “The Measurement of Lightning Rod Responses to Nearby Strikes” by C.B.Moore, G.D. Aulich and W. Rison / 2001.)

During the static thunderstorm phase when the electric fields are steady at 5-15 KV/m the panels present as a relatively low field intensification surface aided by the blunt configuration of the finial tip. This restricts the production of “corona” or “point discharge” ions and is critical because excessive production of ions (corona) results in a “space charge cloud” above the air terminal which tends to mask the electrical field and inhibit the formation and progression of an up-leader. (See step 1).

The panels are isolated from each other as well as from the lightning rod to allow the panel facing the down-leader to rise in voltage due to capacitive coupling with the approaching down-leader. The electric field increases as the lightning downleader approaches closer causing increased voltage difference between the facing panel and the lightning rod. Eventually the voltage rises to the point where a triggering arc is generated between the facing panel and the lightning rod. (See step 2). By design and appropriate terminal placement this arc occurs at the right time to ensure the resulting streamer will form a stable progressive up-leader.(See step 3).

The triggering arc has two key effects, namely:
  1. It produces a large number of ions to aid the initiation of an up-leader.
  2. It causes a large increase in the electric field at a critical distance from the air terminal, aiding propagation through this critical area. This ensures a more efficient mode of protection with an enhanced area of protection.


ILSE’s Guardian CAT series terminals come in three sizes which permits the user to select a terminal which suits his particular application. See the accompanying chart for an indication of the model which best suits your requirements.

For a more accurate design for your project, ILSE uses a software based program which accurately takes into consideration important factors relating to your project such as thunderdays per year, height above sea level, level of protection desired / recommended (Standard – High – Very High), physical dimensions of your structures and materials used. Such additional care ensures that competing features (which themselves also have the ability to create streamer development) are taken into consideration.

Unlike other lightning terminal suppliers, ILSE consider the development of competing structural features as particularly critical on very tall buildings and on sites that comprise more than one major structure.

Such designs are certified by ILSE and therefore offer additional security with regard to the provision of satisfactory lightning protection levels particularly in relation to the lightning activity.

Advantages of Guardian Terminals

  • For most applications, a Guardian System consists of a single CAT lightning terminal which provides an enhanced area of protection, a single purpose designed shielded downconductor for sensitive structures, or a conventional type for standard structures and a single low impedance earthing system.
  • ILSE’s software based placement program can determine the number and location of terminals required for your project.
  • ILSE’s system can be installed to comply with most lightning protection standards.
  • ILSE’s Guardian system is simple to install and requires no special maintenance.
  • ILSE’s Guardian is a very economical solution for providing your lightning protection whilst providing superior security.
  • The design of ILSE’s CAT terminals are based on the most recent developments and improvements within the industry.