| Structural Lightning Protection |

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| How to apply lightning protection |

Where ground conditions make deep driving of earth rods impossible, a matrix arrangement of rods coupled to one another by conductors can be used. If possible, the earth rods must be spaced at a distance at least equal to their driven depth.

If earth rods cannot be driven in a parallel line a "Crows Foot" configuration can be used, ensuring that the spacing/depth ratio is still maintained.

High resistivity soil conditions can be overcome by backfilling earth rods with a suitable medium such as Marconite conductive concrete which effectively increases the diameter of the earth rod and hence its surface area, thus lowering resistance to earth.

All metal work, including water pipes, gas pipes, handrails, air conditioning units, metal cladding, metal roofs etc, in the vicinity of the LPS must be bonded to it, to avoid the danger of side flashing.

For the same reason, the LPS earth should be bonded to the main electrical earth, as well as any other earthing system present in the structure.

Figure 7 - example of side flashing

The lightning conductors can, instantaneously, have a potential magnitude of megavolts (1,000,000V) with respect to true earth.

Typically, at instant of discharge:
Potential difference at A = 1,500,000V
Potential difference at B = 0V

Figure 8 - Bonding to prevent side flashing

1 Air termination
2 Down conductor
3 Bond to aerial
4 Bond to vent
5 Bond to re-bar
6 Bond to metal staircase
7 Bond to metal window frame
8 Bond to vent pipe
9 Bond to steel door/frame
10 Test clamp
11 Indicating plate
12 Main earthing terminal of electrical installation
13 Earth termination point