The Lightning Risk.

Radio Record, Volume II, Issue 11, 28 September 1928, Page 9

The Lightning Risk.

Earthed Aerial Safeguard. JN Wellington city and suburbs and, indeed, in many other parts of New Zealand, lightning is of exceedingly rare occurrence and listeners never worry over danger of their aerials being struck by lightning. The lightning hazard has been overemphasised by certain nervous listeners and is entirely a misconception. Protected properly, aerials are not the least bit dangerous but, to a certain degree, a protection to surrounding objects. Earthing Prevents Striking. The purpose of earthing an aerial system is not to lead lightning to the ground, if it were to strike, but to prevent it from Striking. : The theory involved is readily understood when it is known that lightning will seldom strike a grounded object which is at zero potential. An unearthed: outdoor aerial is dangerous, due to its ability to pick up a charge and inability to dispose of it through the ground. Yor example, suppose a cloud charged positively were to pass in the vicinity of the ungrounded aerial. Naturally, it being unearthed, it would tend to absorb a certain amount of positive charge. If a negatively charged cloud should pass in the vicinity of the positively charged aerial. there would be a potential

difference between the two and a natural attraction. Similar to Lightning Rod: The grounded aerial, however, would remain at zero potential regardless of the polarity of the cloud passing in the vicinity, and would offer a6 attraction to the lightning bolt.

From the foregoing it is readily seen that the properly earthed aerial system offers no attraction to the lightning discharges, but functions similarly to. the lightning rod. Being grounded, it tends to detract charges of static electricity from surrounding objects. This characteristic prevents the possibility of striking.