Lighting arrestors

[Wgibson]

I am installing the Meraki MV72 POE cameras and was wondering if lighting arrestors are needed between the POE switch and camera. If so, is there a distance that is recommended from the camera and lighting arrestors.

[NolanHerring]

I mean I guess it couldn't 'hurt' to use one but I don't really think camera's are highly sought after the way wireless access points with antenna dishes etc. are. If you want to 'fully' protect your switch from a lightning strike, the only way to do that is to use two fiber-to-ethernet converters, even if only for a few feet long fiber cable, because the lightning won't pass through the fiber glass.

[jdsilva]

Needed? Technically it probably would be by any "code" that would apply. You're running a conductor from an inside location to an outdoor where it would be susceptible to lightning so adding an arrestor is definitely a good protection measure. Most arrestors I've dealt with are passive devices and do not have any bearing on cable distances (i.e. you still have the 100 metre constraint from camera to switch, and the arrestor would go somewhere in that 100 metres).  

[PhilipDAth]

I'd love to know how effective lightening arrestors are at protecting kit like switches from nearby strikes (obviously a direct strike is going to kill any active kit).

The cost of actually using fibre for separation (really the only good option) is actually quite expensive.  A cold spare (aka backup insurance) is something that is highly likely to work after a strike (assuming you didn't keep the cold spare next to the active kit) and I suspect in many cases not that much difference in price.

I had a recent case in an area that gets semi-regular lightening strikes.  They use a lightening poll to draw the strike away from everything else.  It worked once and failed the second time.  When they pulled it out to find out why it failed they discovered the ground the pole was earth too was in soil with a high silica content (aka sandy).  The first strike melted the silica onto the grounding poll forming a glass insulator around it.  So it was no good after that.

Now they know they have to replace the grounding poll after every strike.  I've suggested they try getting a "counter" so they can tell there has been a strike.

They are considering to use fibre runs to increase insulation - but the problem is they then need to run active power out to power the media converters.  So now the lightening will be able to travel back along the power runs.  I think this will still result in kit death.

In the end, I think it might be easier to accept that the equipment will be killed, give up protecting it, and working on a sparing or redundancy plan.  I do like the idea of lightening polls though - and trying to encourage the strike to happen away from the kit ...

[jdsilva]

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@PhilipDAth wrote:

I'd love to know how effective lightening arrestors are at protecting kit like switches from nearby strikes (obviously a direct strike is going to kill any active kit).

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Absolutely effective, provided it's a relatively decent quality arrestor and it's been installed properly (read: grounded).

But, like you say, nothing will stop a direct strike. That is a guaranteed release of magic smoke.