jimlux wrote:
>Bruce Carpenter wrote:
>
>
>>Les
>>
>>I have read the message you posted on the lightning protection forum.
>>
>>First, we must recognize that no level of protection will totally protect
>>electronic equipment from lightning damage. We can however reduce the
>>probability of damage and the extent of the damage by taking selected steps.
>>Just think of what could have happened if you had not taken the steps you
>>did!
>>
>>It sounds like you have taken some excellent precautions but unfortunately
>>you failed to realize the necessity to bond the CATV cable to the ground
>>system. I am not sure what is meant by the term SPG.
>>
>>
>>
> This mainly applies to
>
>
>>AC and control line products. Use an SPD suited for the application.
>>Consider the operating voltage of the circuit to be protected and select an
>>SPD that has an operating voltage suitably above that point but not so high
>>that the clamping voltage of the SPD exceeds the breakdown voltage of the
>>device you are protecting.
>>
>>
>
>
>Clamping type transient protection (shunt suppressors) can actually
>aggravate the damage potential. Consider something like a long telephone
>line with a shunt protection device. The telephone line is a
>transmission line that has been "charged" by the transient (assuming
>we're talking a differential mode transient, not common mode, which the
>shunt suppressor wouldn't do anything for anyway). The suppressor
>fires, shorting the line. Now, all the stored energy in the line
>rapidly flows through the shunt, creating a magnetic field, which
>couples into the downstream line, inducing the very voltage you were
>trying to suppress.
>
>Series mode transient suppression is the way to go (and it suppresses
>common mode too!) or a combination of series and shunt.
>
>Cheap shunt mode suppressors using MOVs also gradually degrade and most
>designs do not "fail safe".
>
>
Hi Jim,
Shunt suppressors should terminate to ground (preferably at a SPG
bulkhead) not another parallel conductor.
BTW, I am not familiar with series suppressors (my own ignorance) other
than the series capacitor used in some of the polyphasers. FWIW, that
series capacitor shunt inductor thing works great for ESD protection of
sensitive microwave devices. The only caveat is that the operating
frequency needs to be higher than the dominate frequency components of
the transient. For lightning protection it would seem that this makes
the series cap/shunt L approach untenable for HF frequencies -
especially 80 and 160 meters.
73, Mike W4EF.......................
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