Marine Lightning Protection

The Basics

Tips (not an installation manual)

Tips (not an installation manual)



The basics of marine lightning protection haven't really changed much since the day of Benjamin Franklin. An air terminal (lightning rod), main lightning down conductor, grounding terminal (strip or plate) and side flash conductors are still the best protection for diverting the lightning energy away from people and critical equipment

The only significant difference in boating is that the lightning energy can also enter the boat through its shore power connection

(See NFPA 780 and ABYC TE-04) 

Tips (not an installation manual)

Tips (not an installation manual)

Tips (not an installation manual)


The air terminal should be installed at the highest point or points on the boat

The grounding terminal should be a corrosion resistant metal plate installed as close as practical to the waterline

The main lightning down conductor should run between the air terminal and grounding terminal in as straight a line as possible and away from other wiring

Side flash conductors must be installed to interconnect rigging, tanks and other large metal objects 

Marine lightning protection is primarily installed to protect personnel not property.

Common Fail Points

Tips (not an installation manual)

Myths and Misconceptions


FAIL-The air terminal is not the highest point on the mast with antennas being out of the zone of protection

FAIL-The lightning main conductor is secured to other wiring which induces high electrical currents in this wiring during a strike

FAIL-The bonding system is used as part of the lightning protection system which can energize bonded equipment during a strike 

FAIL-The propeller shaft is used as the grounding terminal which can energize the engine electronics during a strike.

FAIL-Side flash conductors not installed

Myths and Misconceptions

Myths and Misconceptions

Myths and Misconceptions


Aluminum masts can be used for a lightning main conductor but carbon fiber masts are not conductive enough 

Lightning rods and main conductors do not attract lightning to your boat but merely provide an attachment point for the lightning and will divert the lightning energy away from sensitive equipment. With no air terminal, lightning would attach a nearby antenna or grounded metal structure 

Fuzzy metal rods and uniquely shaped domes are marketed as lightning preventers. We have yet to see a peer reviewed study which supports this contention. Therefore, we continue to believe that a properly installed "old school" lightning protection system with strategically placed  SPDs offers the best protection

What is New!

Myths and Misconceptions

What is New!


Surge protection Devices (SPDs) are the newest and most exciting development in the marine industry.  These devices can be thought of as "voltage fuses" and work by sacrificing themselves to absorb the lightning energy, thereby keeping lightning surge voltage low

SPDs have long been available for 120 volt and 240 volt circuits but are now readily available for 12 VDC, 24 VDC, data systems, communication circuits and antennas

SPDs must be properly rated  (UL 1449) and installed correctly but can effectively protect expensive, lightning sensitive and mission critical equipment

Polyphaser, Transtector, ABB, Leviton and Eaton are only a few of the vendors who can provide SPDs

What's Next

Myths and Misconceptions

What is New!


The cost of marine lightning damage repairs lately seems to be rising exponentially

The repair cost increases are likely due to increasing use and complexity of marine electronic systems, rapid expansion of digital networks and the interconnection of onboard systems.

Costs can also be driven up by misunderstanding the nature of lightning damage, poor fiscal responsibility by repair vendors or the insured (open checkbook syndrome) and inadequate repair oversight

Expect to see significant changes in how carriers handle lightning damage in for boats in lightning prone areas

National Electrical Code & Surge Protection (per Eaton)

sa158003en (pdf)