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From: dmturne@PacBell.COM (Dave Turner)
Newsgroups: sci.electronics
Subject: Re: lightning protection question
Message-ID: <6095@ptsfa.PacBell.COM>
Date: 5 Apr 91 19:01:00 GMT
References: <91093.214905XWUU@PURCCVM.BITNET>
Reply-To: dmturne@PacBell.COM (Dave Turner)
Organization: Pacific * Bell, San Ramon, CA
Lines: 30

In article <91093.214905XWUU@PURCCVM.BITNET> XWUU@PURCCVM.BITNET writes:
>I recently read in a reputable computer repair manual that one can gain
>some measure of lightning protection for an electronic device (computer, TV,
>etc.) if a simple overhand knot were tied loosely in the power cord.  The
>author says he got the idea from electronic specialists and that he uses this
>technique on all of his equipment since the last time lightning struck near his
> home.  It seems that his TV was the only electronic device damaged by the
>lightning and it was the only devive without the knot in the cord.  Even
>his sensitive computer and test equipment were not harmed.
>
>The theory is that the lightning somehow has to "work against itself" due to
>the overlapping coil of the knot.   Sounds like voo-doo to me.  What does any
>one else think.  Any validity to this theory?
>

It is well known that parallel wires carrying equal and opposite currents
produce magnetic fields which cancel.

This fact is used to explain this form of lightning protection.

The knotted wire produces tightly-coupled magnetic fields which induce
a reverse EMF into a part of the wire which effectively is in the reverse
direction. The current in the wire (especially in the knot) cancels and
protects the circuit.

This is only guaranteed to work on April 1.


-- 
Dave Turner	415/823-2001	{att,bellcore,sun,ames,decwrl}!pacbell!dmturne