lightning

The rats/mice in your neighbourhood must be wimps. The ones up here don't have any problem chewin' shielded wire. The only thing that will put a stop through that is using armoured cable or pulling your standard wire through EMT.

Appreciate first your problem. Lightning seeks earth ground. It will find earth via paths that you provide - even through powered off equipment. Your task is to provide a path to earth that is non- destructive.

Lightning took a more conductive path to earth via wooden church steeples. Yes, even wood is a conductor. What did Franklin do? Give lightning a more conductive path to earth. You don't stop surges. Earth them on low impedance (not just low resistance) paths.

Protection means every structure has a single point earth ground. Use this application note as an example of two structures:

wire that enters or leaves each structure must connect to single point earth. Connected directly (ie cable TV or satellite dish) or via a protector (telephone, AC electric, ethernet). Every wire in every cable must make that earthing connection.

That connection must be low impedance. That means short (ie 'less than 10 feet'). no sharp wire bends. No splices. Every grounding wire separate until all meet at the earthing electrode. A connection that must be separated from other non-grounding wires. Essential is a low impedance (not just low resistance) connection to single point ground.

Where does energy dissipate? Anything that might stop or block only forces the current to create a massive voltage. Current times increased voltage means increased energy - damage. Where do you want energy dissipated? It must dissipate someplace. Anything that would stop or absorb a surge will get blown through by that surge. So Franklin gave a direct lightning strike a high current, near zero voltage connection to earth. Near zero voltage means near zero energy. That is what your solution also must accomplish. You want energy, instead, dissipated in earth.

Energy dissipate in earth does not hunt for earth ground destructively via electronics. That energy not inside a building means protection inside all electronics is not overwhelmed.

Another example might be a building with cameras on remote poles, Therefore the pole must have its own single point earth ground. A protector connected short from each ethernet wire to that earth ground. That same wire enters a building at the service entrance to also connect short to that single point ground. Yes, all wires must enter at a common service entrance to be properly earthed to the same electrode. See that app note? Even underground wires must get the same treatment.

Where is energy harmlessly dissipated? How did you make that short connection to earth?

Perhaps if you used inverted boxes.... :^)

Thanks. The comments and application note are quite helpful.

Best, Christopher

Helpful? When did that start?

You must have been at lunch.

No. That won't work. The electrons would all fall out.

Thanks, that all makes sense. Thus far in summary:

- A direct lighting strike will destroy the equipment.

- A lightning rod could be used to transfer the energy to ground.

- Use surge protectors on all equipment.

- Use fully shielded cables.

- Use single point ground; avoid ground loops.

Here's a beter explanation of my question. Using Cat 6 shielded cable and connectors as an example, is continuity of the shield important? I reviewed a Cat 6 cable/connector installation guide, and it did not appear that there was any attempt to connect the cable shield to the connector shield. So, I'm assuming the shields float and are not tied to ground, is that correct?

Similar question regarding a low volage cable run. Assume an indoor Altronix power supply and an outdoor 24 VAC IR illuminator. Would you let the shielded power cable float, or would you ground the shield at the Altronix metal box?

Best, Christopher

Not if you tie a knot in your power cord

/sarcasm

For cat 6, if it is easy to connect a connector shield to the wire shield, then do so, but otherwise don't worry about it.

So far as being contiguous, for your application and floating, I would think non-contiguous would be better. If you were grounding it at one end and HAD to keep out ALL noise like for a medical application, then it would be important to have a contiguous ground shielding everything. Of course in that situation you would not have the medical equipment mounted up high outside!

As to the IR illuminator, it this was mounted high up outside, then I would think a non-grounded box and the box not connected to the wire shield and the wire shield not grounded would be best. The box would not be grounded and the conducting of electricity would stop right there - dead end! And the shielded wire would not be grounded, so another dead end! Not a path to ground. And the power to this would be via a transformer and the secondary winding would not be grounded, so another dead end, not a path to ground!

If I was a bolt of lightning, I would consider that IR illuminator a very poor choice of an object to strike as there would be no path to ground! I would strike elsewhere...

Thank Bill. Easy to understand and easy to implement. I appreciate your assisntance.

Best, Christopher