lightening arrestor from spark plugs---

[Catbrain]

I am stringing out my 180 ft of 4 inch ladder line. Thought I'd make some arrestors out of new spark plugs.
Im only using the radio- no amp so I would guess about 100 watts-- which if my math is right--- with 600 Ohm (4 inch) feed
line should result in a max voltage of about 250 Volts going out. I was wondering what gap I should use on the plugs........
i read that if a voltage is under 370 volts it will not jump a gap. And further--- if only a bit above that---- it wont jump if the gap is too small or too wide. it appears that I dont have to worry about the transmitted power jumping the gap to ground----- due to
the voltage being below the 370 V threshold. But-- I WOULD--- like any static charges or lightening to jump the gap as easily as possible. Does anyone know if there is an optimal gap to set the plugs at ? These are new conventional plugs- I think for lawn equipment----

Tim

 

[K4EET]

While back in the day, spark plugs were used for lightning protection, they are a bad idea in modern times for several reasons.

1. They are unreliable because of the “spark gap” question for the discharge voltage.
2. They do not dissipate the heat generated from a nearby lightning strike and will typically fail.
3. Modern day spark plugs are mostly resistor type which cannot be used. Back in the day, spark plugs did not have the internal series 5K ohms (+/-) resistor of modern day versions.

Of course a direct lightning strike will generally be catastrophic.

I would recommend PolyPhaser lightning arrestors (or equivalent) for your peace of mind. It is cheap insurance for their cost when you look at the big picture.

Finally, do a search for spark plug lightning arrestors that actually worked in a real and unfortunate scenario. You will not find a lot of success stories. Most articles that you find are theoretical “hope it works” designs.

<edit> Take a look at this posting of mine:

Antenna Coax Grounding by Whitham D. Reeve based on the National Electrical Code (NEC) Article 810

In many threads about running coax to antennas, some of us will usually mention "be sure to properly ground things" without going into a whole lot of details. We may even mention that the National Electrical Code (NEC) requires it for all homes and businesses within the United States. I found...

forums.radioreference.com

 

[K4EET]

I am stringing out my 180 ft of 4 inch ladder line. <snip>

Use something like this:

DX Engineering DXE-LLSP DX Engineering Ladder Line Surge Protector | DX Engineering

Free Shipping - DX Engineering Ladder Line Surge Protector with qualifying orders of $99. Shop Balanced Feedline Protectors and Components at DX Engineering.

www.dxengineering.com

 

[ArloG]

Yeah. A small price to pay using a proven and tested protection device. I'm a true believer in Tripp Lite surge arrestors and whole house arrestor cubes at the service panel that tie in to the main breaker. I hate scanners. But if the manual says use 50 ohm coax, I use 50 ohm coax.

Florida taught me one good thing. If you like your stuff and thunder rolls in. Divorce every means where a surge can find it's way in.
I used to listen to the surge arrestors *snap* during storms. I've seen lightning strike a 500kV transmission line in Tarpon springs and heard the surge go *zingg* sounding like a Star Wars sound effect as it went past towards Crystal River. Electricity is one of the sure-things in life. And not in it. Just go to Starke and ask Old Sparky.
A spark plug will spark. Is it designed for radio equipment that has no closed cycle internal combustion? Nah.
A couple of bucks and your impedance at least will stay matched.
Yeah....

 

[wtp]

i am a cheap guy.
the only guy i knew that used the sparkplug idea and disconnected all his equipment when done, that was in NJ.
i now live in Florida and have no outside antennas.
if two clouds bump heads, you can have lightning.
too much worry and work.
but, i would go with commercial stuff.
much less worry.
and you don't need one of these...

 

[EAFrizzle]

I always thought spark plugs were for building transmitters...

 

[prcguy]

Spark plugs were used a long time ago with tube type equipment that could survive a couple hundred volts on the antenna port with no problem. A spark plug would/should short out high voltage static from blowing wind on antenna wires and maybe from a nearby lightning strike and protect a tube type radio to some extent. A solid state radio, not so much.

 

[Catbrain]

I spent most of my life In Orlando. Very close to the highest lightening incidence for all of the US. So I know about it. all most hit several times. Seen it burn down a 200 foot tower in one hit. Microwave dish completely gone in one hit. Whole neighborhood of TV's and phones gone in one hit. Yards on fire. Nasty.

My plan was to use a commercial unit of some type at the house entry and the spark plug in the line maybe at base of tower and maybe half way down the ladder line run. Maybe a home made gap might work better than a spark plug. I figure if I can kill some of it before it gets to the house- and the store bought arrestor- all the better. Are the store bought ones all made using the gas discharge tubes ?

My understanding is that a slow build up of static on the exposed line is drained a different way that a lightening arrestor doesn't do. Is that a separate unit or is that an additional circuit inside the purpose made arrestors ?
would the DX engineering one have both of those inside the box ?

Tim

 

[prcguy]

You might read NEC article 810 to know what's legal to do then read Motorola R56 which might make you rethink things. Just putting spark plugs or an arrestor across your ladder line to a ground rod will probably not protect anything and could actually damage more stuff in the house from a direct hit. Spark plugs may help but there are a lot of other things that must be done besides the spark plugs or other ladder line arrestor.

 

[Catbrain]

ok - will do-----

 

[Catbrain]

I want to do what works--- so I dont mind researching things--- thank you-----

 

[Chronic]

The gap on a spark plug is what .30 - .50 of an inch , but yet Lightening arcs across Miles of sky/air yea , that should work out well

 

[merlin]

The voltage across a typical spark plug gap is like 25 to 35 Kv. While most solid state devices are protected to 15 KV, means a gap of like .oo1 to .003 inch. It will work, been used in the past.

 

[ArloG]

Me? I think being inventive and thrifty is taking a chance. The arrestors that I use in the image above depend on an important thing. The spark gap is enclosed and sealed and if and when a surge happens. The air in the plug is ionized. The ionized gas can't dissipate and stays conductive until voltage is reduced well below what an open air spark would sustain. I vote no for a spark plug.
A great option. And feel free to search and look. Are also inline coax gas tube spark arrestors.
For example the trusty NE-2 neon lamp has around a 70 volt trigger voltage. But after that is reached and the tube fires. It only takes like 50 volts to sustain it. Something that a spark plug won't. And with the enclosed conductors well over what merlin mentioned of 0.001 - 0.003 inch.
Think about capacitance and of course the impedance effect on the circuit.
I mean. Your coax cable impedance is established mainly on the inner conductor outer diameter to outer shield inner diameter. Screw with that by bending it in a tight radius, kinking it. Well....you surmise.
But hey man. It's your gear. And your bucks. Right!

I've seen the old school spark plug testers in auto parts stores where you could screw a plug in and attache the HV cap.
Then pump up air to different cylinder pressures. Crank up the kilovolts until the gap sparks. Crank the voltage down just a touch, the spark extinguishes. And I mean right now. There was no dial it up to 35 KV and down to 25 and she kept right on sparkin'.