Lightning Protection Interconnection with Equipment Earthing Grid

[SK07]

I have seen Lightning Protection Earthing grid (electrodes with interconnected conductor system) seperate from Equipment earthing grid without any interconnection.

I would like to know Recommended practice as relevant per IEC standard.

Are we supposed to interconnect Lighting protection grid with equipment grid or maintain as two seperate grids.

 

[SK07]

In addition to IEC Standard, we can refer to NFPA 780 as well.

 

[jghrist]

In the USA, NEC requires the two systems to be bonded. I think NFPA 780 also does. They should be bonded only in one place so that you don't get lightning surges flowing through the equipment earthing grid.

 

[Power0020]

Practically, the lightning current will induce voltages (and currents) in the grid even if not directly bonded but just nearby each other.

 

[DanEE]

In addition to Power0020's good point, the possibility of flashover from the lightning ground system to the other electrical equipment grounding system can happen if the two are not tied together.. My concern was a flashover happening in an area that may have combustible material in the vicinity.

NEC in the US was silent on this question years back; now has all grounding systems bonded together, which has been my practice all along..

 

[SK07]

Reference to my subject question, I would like to share the following,

IEC 62305-3: Protection against lightning – Part 3: Physical damage to structures and life hazard
Clause : 5.4.1 General
........From the viewpoint of lightning protection, a single integrated structure earth-termination system is preferable and is suitable for all purposes (i.e. lightning protection, power systems and telecommunication systems).


NFPA 780 – 2014 Edition : Standard for the Installation of Lightning Protection Systems
Clause: 4.14.3
This interconnection shall include all building grounding electrode systems, including lightning protection, electric service, communication, and antenna system grounding electrodes.

 

[dpc]

Seems as if you have answered your own question. Lightning protection ground should be bonded to other system grounds. The devil is in the details of how that it done.

 

[SK07]

dpc (Electrical)

Yes, i found the answer after a bit of search and thought to share with all interested.

 

[DanEE]

NFPA 780 – 2014 Edition : Standard for the Installation of Lightning Protection Systems
Clause: 4.14.3
This interconnection shall include all building grounding electrode systems, including lightning protection, electric service, communication, and antenna system grounding electrodes.

dpc (Electrical)
14 Dec 14 19:32
Seems as if you have answered your own question. Lightning protection ground should be bonded to other system grounds. The devil is in the details of how that it done.

My own home had a somewhat unique challenge... Due to high frequencies involved (and need to minimize transmission line loss, I have two separate antenna entry point locations, one at 70 feet, the other 38 feet in distance from the AC electrical service entrance.. also have lightning rods on the house.. The voltage ground shift from a nearby lightning strike would be guarantee damage to any electrical device making a connection to AC power and one of these antenna entry points, if these separate entry points were on isolated grounds not bonded together.

I installed a perimeter ground system all the way around the house to bond the above antenna entry points, electrical service entrance point and lightning protection system down lines together.. This follows lightning protection practice for wooden structures on mountain ridge lines (and typically poor earth conductivity).. i.e. perimeter ground and bird caging the building (down leads from the building ridge line aerial points) and of course multiple ground rods in the system.

In addition to surge suppressors at the appropriate entry points on the perimeter locations, equipment at interior locations some distance from the perimeter have additional surge suppressors on all wiring at the equipment to "island" the equipment, i.e. any surges from the different wiring (AC, antenna) will shunt on the surge protector ground plate. This is necessary to protect against nearby lightning strike induced currents into wiring interior to the building that follow separate paths to the equipment (and presenting a cross sectional area.. i.e. Maxwell's second equation).

It wasn't 2 months after this system was completed that we had a major lightning strike strong enough to blow out a neighbors 7200v to 240v AC utility transformer and burned the underground telephone trunk to my house open. We were on the same AC phase, so no power for a day while the transformer was being replaced.. When power came back up, no damage, even to the DSL modem or other telephone equipment.

Contrary to what many lay people believe, properly installed lightning protection systems do work... Nothing out of the ordinary above as these are USA practices typically found at TV transmitter, other tall tower sites, and PBX telephone plants in commercial buildings that I've done similar work.