Last quarter I sat in on a tender review where the MEP consultant had written one line that decided everything: “Air termination: ESE type, single mast, or conventional Franklin array — contractor to propose with calculations.” The contractors who proposed blind lost the room; the one who walked through the radius math, the standards map and the cost structure won the specification conversation before pricing was even discussed. That line in a specification is the question this article answers. An early streamer emission (ESE) arrester and a conventional Franklin rod both end at the same earth, but they reach it by different physics: the Franklin terminal waits passively for the stepped leader and protects a cone defined by its height — our 99% pure copper single-needle rods work to a 65° protection angle with a radius of 2.14×(h−h_x) — while the ESE head emits an upward streamer earlier than a passive point, effectively meeting the downward leader sooner and protecting a radius that grows with its triggering-time advantage. The choice between them decides how many masts you buy, which standard your design cites, and how your roof looks for the next thirty years. Here is the comparison exactly as I walk consultants through it.

Two Technologies, One Storm: How Each Terminal Actually Intercepts the Strike

A lightning strike to a structure is a race between leaders. The downward stepped leader approaches from the cloud; upward streamers rise from whatever sharp geometry the roof offers. A Franklin rod is the honest passive competitor in that race: a well-grounded point that presents the most attractive launch geometry on the structure and wins the attachment inside a protective cone. The physics is mature, the math is geometry, and the result is conservative by construction — our single-needle copper rods carry the classic specification set: air-rod heights to 200 m, a 65° protection angle, corresponding radius 2.14×(h−h_x), current gradient under 5 kA, average discharge current under 7 kA, and a grounding resistance target below 10 Ω.

An ESE arrester plays the same race with a head start. Its head contains a triggering device that launches the upward streamer tens of microseconds earlier than a passive point at the same height, because meeting the downward leader higher up means the protected zone on the ground widens. That triggering-time advantage — ΔT, measured in a high-voltage laboratory against a reference rod — is the single number the entire ESE value proposition hangs on, and it is why I tell consultants that an ESE unit without a credible ΔT test report is just an expensive Franklin rod with marketing attached. We cover the document side in depth in our companion guide on the certification documents customs and insurers ask for, and the standard itself is dissected in our NF C 17-102 explainer; this article stays on the engineering comparison.

Protection Radius in Numbers: How Far Does Each Rod Really Reach?

Radius math is where the two technologies stop being philosophies and become layouts. The Franklin calculation is transparent: with a 65° protection angle, a rod whose tip stands h metres above ground protects a radius of 2.14×(h−h_x) at the protected level h_x — geometry you can verify with a pencil. The ESE calculation, under the NF C 17-102 family of formulas, adds the ΔT term to the rolling-sphere geometry, so the same mast height protects a larger radius — how much larger depends on the ΔT class and the protection level the project requires per IEC 62305-1. I always run both sets of numbers for a client’s actual roof before recommending either, because the radius gap between the technologies is decisive on large flat footprints and nearly irrelevant on a tall, narrow structure where any terminal sits close to everything it protects.

ESE arrester heads from our range: the triggering device inside the head is what the ΔT test report certifies — the hardware difference behind the radius difference.

One honest caution belongs here: ESE radius claims are only as good as the ΔT behind them, and the market contains heads whose laboratory paperwork would not survive a consultant’s phone call to the lab. Because the radius formula amplifies ΔT into metres of claimed coverage, an exaggerated triggering time becomes an exaggerated protected area on your drawing — which is why the verification habit from our certification guide applies here with double force: ask for the lab, the report number, and the reference-rod comparison, and check all three.

The Compliance Map: Which Standard Governs Which Terminal?

Specification writers do not get to choose physics by preference; they choose the standard their jurisdiction, client and insurer recognize, and the standard chooses the physics. The map as I give it to consultants: conventional Franklin systems live squarely inside IEC 62305-1 and IEC 62305-3 territory — protection angle, rolling sphere and mesh methods — with NFPA 780 covering the same passive philosophy in North American practice. ESE systems are governed by their own national standards family, with NF C 17-102 the reference text most Gulf, African and francophone projects cite; component-level requirements for the air-termination hardware itself sit in IEC 62561-2 and its siblings. Because the two standards families measure different things, a specification that mixes their vocabularies — asking an ESE head to prove itself in rolling-sphere terms, or a Franklin array to submit a ΔT report — produces confused tenders and unenforceable contracts. Write the standard first; the product follows.

One practical note from the export desk: many projects in our order book name IEC 62305 for the overall LPS design and accept ESE terminals under the project country’s ESE standard for the air termination — a hybrid that works when the specification says so explicitly and fails as an assumption. And whichever route the design takes, the earth termination at the bottom of the down conductors answers to the same grounding discipline on both systems; our building lightning protection overview covers how the air terminal, down conductors and earth work as one chain.

Cost Compared Honestly: Where Does Each System Spend Your Project Budget?

I will not quote prices in this article — they move with copper markets, project scope and region, and any fixed number printed here would mislead within a season. What does not move is the cost structure, and the structure is what a consultant should compare. A Franklin system spreads its spend across multiplicity: many air terminals, multiple mast positions, roof conductor mesh, fixings and the labour to install and bond all of it — each element modest, the total driven by count and roof complexity. An ESE system concentrates its spend: one engineered head with certified electronics, one mast and its foundation and wind-loading design, and the documentation package — fewer elements, but each one heavier in engineering content. Because Franklin cost scales with roof area while ESE cost scales with mast engineering, large flat footprints tilt the structure toward ESE and small or complex roofs tilt it toward Franklin.

Conventional copper air terminal rods from our production: 99% pure copper single-needle construction, 65° protection angle, wind-resistant build for exposed roofs.

Reliability Over Decades: Who Maintains What on Each System?

Maintenance profiles differ in kind, not in existence. A Franklin array has no electronics and nothing to calibrate; its maintenance is inspection — corrosion at joints, conductor continuity, fixings after storms — plus periodic earth-resistance testing. An ESE head adds one question: is the triggering device still alive? Quality ESE heads are sealed and self-contained with no external power, and ours ship in export wooden cartons for exactly the journey they will make, but the professional habit is a periodic functional check per the manufacturer’s interval and the same inspection routine as any terminal. Because a dead ESE head silently degrades to a passive rod, the maintenance plan should include the functional check explicitly — written into the O&M manual, not left as an assumption. Either system also inherits the earth termination’s maintenance schedule, which is why we supply both technologies alongside the grounding materials they discharge into.

ESE and conventional terminals from our range side by side: different heads, same job — and the same earth system waiting underneath both.

Writing the Specification: How Do You Choose Without Regretting It?

The decision sequence I give consultants, in order:

1. Fix the governing standard first — IEC 62305/NFPA 780 for passive design, the project’s national ESE standard for active design, or an explicit hybrid.
2. Draw the protection geometry on the actual roof — run the Franklin radius (65°/2.14×(h−h_x)) and the ESE radius for the proposed ΔT class; the drawing, not the brochure, picks the winner.
3. Count what each design puts on the roof — terminals, masts, conductor runs, penetrations — and let the aesthetics and waterproofing consequences into the decision.
4. Write the verification documents into the tender — ΔT report per ESE unit, material certificates per rod, earth-resistance acceptance for both.
5. Close with the earth — name the grounding resistance target (our conventional rod specs work to below 10 Ω) and the electrode design, because both technologies are only as good as their earth.

Both routes are in our production range: the ESE lightning arrester line with its documentation package, the 99% pure copper single-needle lightning rod and copper air terminal rod for conventional arrays, all under the ESE lightning arrester and lightning rods category. Send us the roof drawing and the protection level your project requires, and we will return both radius calculations with the bill of materials for each — the same comparison this article describes, done on your actual building.