LPI Early Streamer Emission (ESE) Lightning Protection System

The Early Streamer Emission (ESE) lightning protection system uses a high-performance air terminal installed above the highest point of the building. The terminal is designed to begin generating an upward streamer earlier than a reference air terminal under test conditions. It defines the designed strike point, then carries the current through down conductors into the earthing system.

What the ESE system does well

• One air terminal covers a wide area, as calculated
• Reduces the number of air terminals and roof conductor runs compared with a mesh system on some projects
• Suits buildings or large open areas
• Easier to install on buildings with a simple roof shape
• Less impact on the appearance of the building
• Needs no external power supply
• Several models available to match the area and protection level
• Can be used with insulated down conductors
• The terminal and the conductor route are convenient to inspect
• Suits both new projects and refurbishment of existing buildings

LPI's ESE products are branded Stormaster ESE, made from 316 stainless steel, with models graded by advance time: ESE-15, ESE-30, ESE-50 and ESE-60. LPI states that the products are tested to NF C 17-102:2011.

How it works

As the electric field between cloud and ground rises, a downward leader moves from the cloud towards the ground. At the same time, objects on the ground can produce an upward leader, or streamer. The ESE air terminal is designed to produce an upward streamer earlier than a reference terminal under defined conditions. The sequence is:

1. The electric field around the building rises
2. The ESE terminal responds to the field without any external power supply
3. A streamer is released from the air terminal
4. The streamer connects with the charge descending from the cloud
5. The strike point is fixed at the ESE terminal
6. Lightning current flows through the terminal and the mast assembly
7. The down conductor carries the current to the earthing system
8. The current disperses into the mass of the ground
9. Bonding and surge protective devices reduce the effects of potential difference and surge

An ESE air terminal does not prevent lightning. It intercepts the strike within the designed area and provides a controlled path for discharging the current to earth.

Early streamer emission advance time

The performance of an ESE terminal is expressed as ΔT, or advance time, in microseconds. It comes from comparing the time an ESE terminal takes to produce an upward leader against a reference air terminal, under the standard's test procedure. The main LPI Stormaster models are:

The figures 15, 30, 50 and 60 are ΔT values, not a protection radius in metres. The actual protection radius has to be calculated to the standard, taking into account:

• The model and ΔT of the ESE terminal
• The protection level, LPL I–IV
• The height of the terminal above the reference area
• The shape and height of the building
• Equipment and obstructions on the roof
• The level of the area to be protected
• The surrounding environment

So it is wrong to state that a given ESE model has a fixed protection radius on every project.

Protection levels

Design to NF C 17-102 divides protection into four levels.

LPL I gives a stricter protected area than LPL IV, so with the same ESE model at the same height, the radius calculated for LPL I is smaller than for LPL IV.

Main components of an ESE system

1. Stormaster ESE air terminal

A high-performance air terminal installed on top of a mast, acting as the main strike point. LPI states the following properties:

• Made from 316 stainless steel
• Suitable for outdoor installation
• Requires no external power supply
• Available in several models by ΔT
• Tested to NF C 17-102:2011
• Tested at the ITE HV high voltage laboratory, according to the manufacturer
• Certified Australian Made

2. Mast

Raises the ESE terminal above the highest point and any obstructions in the area to be protected. The height of the terminal above the surface affects the protection radius. The mast must be designed to take:

• The weight of the terminal and its equipment
• Wind load
• Vibration
• The environment
• Corrosion
• The forces acting on the base fixing
• The building's structural requirements

Raising the mast can increase the protected area, but not beyond the conditions of the calculation and the limits of the standard.

3. Mast base and guy wire

The base fixes the mast to the roof or structure. Taller masts may need guy wires or bracing for stability. Load-bearing capacity and waterproofing at the base must be checked with the structural engineer and the architectural team.

4. Down conductor

Carries the lightning current from the ESE terminal to the earthing system. It may use a bare conductor to the standard, or a specific conductor as the system design requires. Key points are:

• Keep the route as short and direct as possible
• Avoid sharp bends
• Avoid loops
• Fix the conductor securely
• Protect against damage where people can reach it
• Keep clear of electrical cables and metal parts
• Install the number of conductors the standard requires
• Spread the conductor positions around the structure where more than one is required

NF C 17-102 generally requires at least two down conductor routes per ESE terminal where they can be installed, but the details must be confirmed against the building type, the project specification and the edition of the standard being referenced.

5. HVSCPLUS insulated down conductor

LPI offers HVSCPLUS, an insulated down conductor developed to carry lightning transient current. It is used where the separation distance has to be controlled, or where the risk of side flash near metal parts and internal systems has to be reduced. HVSCPLUS must be installed with the specified upper and lower termination kits, following the manufacturer's manual. It should not be jointed or modified like ordinary electrical cable.

6. Conductor fixing

Fixes the down conductor to a wall, mast or structure, controlling the run and preventing movement from wind and mechanical load.

7. Lightning event counter

Counts the number of times lightning current has passed through the down conductor, as information for inspection and maintenance. Once the counter has increased, check:

• The ESE terminal and its mast
• Joints and connectors
• The down conductor
• The test joint
• The earthing system
• The condition of the surge protective devices
• Signs of heat or arcing

A lightning counter does not protect against lightning and does not indicate the full severity of an event. It confirms that current passed through that path.

8. Test joint

A joint that lets the down conductor be separated from the earthing system, so that continuity can be checked and the earthing system measured.

9. Earth electrode system

Receives current from the down conductor and disperses it into the mass of the ground. It may consist of:

• Earth rods
• Radial conductors
• A ring earth
• An earth grid
• Earth plates
• A foundation earth
• An earth pit
• Soil resistance improvement compounds

The earthing system should be designed from measured soil resistivity, taking high-frequency current behaviour into account. It should not be judged on low-frequency earth resistance alone.

10. Equipotential bonding

Bonds metal parts and the earthing system together to reduce potential differences, for example:

• Steel structure
• Metal pipework
• Cable trays
• Electrical systems
• Communication systems
• Fire alarm systems
• CCTV systems
• Nurse call systems
• Air conditioning
• The building earthing system

Bonding must follow the drawings and the calculations, to prevent side flash without creating an inappropriate current path.

11. Surge protection device

The ESE terminal protects against the effects of a direct strike outside the building, but it cannot fully protect against surge voltage induced into, or entering through, the service lines. Surge protective devices must be installed as well, such as:

• Type 1 at the main incoming board
• Type 2 at distribution boards
• Type 3 close to highly sensitive end equipment
• Surge protective devices for telephone lines
• Surge protective devices for data and network cabling
• Surge protective devices for CCTV and control systems
• Surge protective devices for signal cabling from outside

Selecting a surge protective device means coordinating the protection level, voltage rating, earthing system and the building's electrical system.

Calculating the protection radius

The ESE protection radius is not a fixed cylinder. It changes with the height being considered, so the protected area is a volume around the air terminal. The calculation to NF C 17-102 uses these key variables:

• The radius of the protected area
• The height of the ESE terminal above the level to be protected
• The rolling sphere radius for the LPL
• The advance distance calculated from the advance time
• The ΔT of the ESE terminal

The radius has to be calculated separately at each level, such as the main roof, the plant room roof deck, the building edge and the ground. The radius at ground level should not be used to represent every level of the building.

Design steps

1. Survey the location and the size of the area
2. Assess the lightning risk
3. Set the standard the project accepts
4. Set the lightning protection level
5. Choose the Stormaster model by ΔT
6. Set the position and height of the ESE terminal
7. Calculate the protection radius at every level
8. Check obstructions and rooftop equipment
9. Set the number and routes of the down conductors
10. Calculate the separation distance
11. Design the earthing and bonding
12. Design the surge protective devices for power and signal
13. Check the mast base structure and wind load
14. Produce drawings, an equipment schedule and installation details

LPI offers ESE design to NF C 17-102, with 3D drawings, a bill of materials and general specifications for each project.

Where it is used

• Hospitals
• Office buildings
• Factories and warehouses
• Airports
• Hotels and resorts
• Shopping centres
• Schools and universities
• High-rise buildings
• Telecommunication masts
• Substations and utilities
• Solar farms
• Power generation systems
• Agricultural areas
• Material storage yards
• Buildings and open areas that want fewer air terminals

Inspection and maintenance

Inspect on the schedule set by the standard and the maintenance plan, and also after a lightning strike or building refurbishment. The checklist includes:

• The condition of the Stormaster ESE terminal
• The tightness of the terminal and mast
• Rust or corrosion
• The mast base and guy wires
• Down conductor continuity
• The condition of the HVSCPLUS insulation, where fitted
• The upper and lower termination points
• Joints and conductor fixings
• The lightning event counter
• The test joint
• The earth pit and earth electrodes
• System resistance and continuity readings
• The equipotential bonding system
• The status of the surge protective devices
• The protected area after any building extension

LPI supplies an air terminal tester for checking supported models, following the manufacturer's procedure, but testing the terminal alone does not replace inspecting the whole system.

Standards and cautions

The main standard LPI cites for Stormaster ESE products is NF C 17-102:2011, and all four Stormaster models appear in the product category referencing it. What matters is that the various standards do not all recognise the ESE method in the same way.

• NF C 17-102 – has a design and test method specifically for ESE
• IEC 62305 and BS EN 62305 – use conventional methods such as rolling sphere, mesh and protective angle, and do not grant additional radius from an ESE advance time
• NFPA 780 – does not define the ESE radius calculation of NF C 17-102
• AS 1768 – focuses on conventional systems and does not provide an ESE calculation based on ΔT

Before choosing ESE, therefore, check whether the building owner, the consultant, the insurer, the local authority and the legal requirements accept NF C 17-102. A radius derived from NF C 17-102 must not be presented as a radius under IEC 62305 or any other standard.

In short, the LPI Stormaster ESE system intercepts lightning on the early streamer emission principle, designed to NF C 17-102:2011. It fixes the strike point and covers an area to the calculated radius. A complete system needs the ESE terminal, the mast, down conductors, an earthing system, equipotential bonding and surge protective devices, together with design, testing and maintenance to the standard the project accepts.