Zapping Camera Problem

ferrites are what $0.50 each? at most $1 sometimes you can get a bunch of 'samples' to simply try .

Reply to
Robert Macy
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ferrites are what $0.50 each? at most $1 sometimes you can get a bunch of 'samples' to simply try .

Robert you missed my point of humor. "If only I had the budget........." of what it would take to build a Faraday Cage not for ferrites.

BTW if the grounding is not right, I could be wrong but I doubt that any number of ferrites would fix the problem. On the other hand if the grounding is almost correct then ferrites would soften the effects of a surge. Please correct me if I am wrong in that.

Reply to
ABLE1

Robert Macy's reply was spot on. Others misunderstood some of his points. For example, conduit or other grounds that are that long are (essentially) non-existent. For surge protection, even length of a wire is critical. Even a sharp wire bend compromises protection.

To resummarize his points. Your camera 200 feet away must be handled as if two completely different structures. Using the same protection method implemented between your home and the telco's CO. Each structure must have its own single point earth ground. Camera will never be earthed by the building's ground. Otherwise, a lightning strike to one building (ie the house) is a direct lightning strike to electronics in the other structure (video section of a camera).

Do not earth the camera. That makes a camera the better and destructive connection to earth. Earth every incoming conductor to that camera. And again, the earthing must be low impedance - as short as possible (ie 'less than 10 feet').

This professional's application note demonstrates the concept - The Need for Coordinated Protection:

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In your case, replace that antenna tower with a camera. The tower and building both have their own single point earth ground (all four words are electrically significant). Any wire that enter the building or camera must first connect to earth ground. Either directly (ie the shield of a coax) or via a protector (ie 12 VDC). If any one wire in any cable violates that rule, then damage can result either to electronics inside the building or camera.

Also important. Makes no difference if the wire is overhead or underground. Same rules apply as that application note says.

Do not earth a camera. Earth the surge. A major difference. Even joints in conduit compromise protection. If a ground wire is inside a metallic conduit, then it also does not earth a surge. It is not about wire thickness. Most critical is conductor 'length'. No splices. No sharp wire bends. Otherwise impedance is too high - the earth ground connection all but does not exist.

A surge is electrically different from electricity that powers appliances. Even wires must be routed with greatest care. Protectors are simple science. Most important is the art of protection - single point earth ground. =========================================================================

With this post it does clear up a few points.

Thanks, very helpful.

Les

Reply to
ABLE1

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"...grounding is not right." That's kind of 'by definition' it's wrong, because it didn't work.

One can think of feerites, and those 'lumps' like the "python swallowed the goat" appearances on computer cabling, a little like 'cutting' the cable right there, and turning the next section into a 'wireless' battery system. Well, at least at high frequency. You only have two things to work with here. One, a dead short, which is extremely difficult to make. Two, an open [high impedance] which actually is a bit easier to make. The ferrites are like a giant RF barrier. Theey let differential signals go through gang busters, but won't let common mode signals through - like ''lightning' trying to ride on your cables. The damage [if they're present] done by those commone mode signals is that they get converted into differential signals. And, differential signals that can be extrememly high voltage. result arc overs, breakdown, zapping so to speak.

Sadly, EMC and ESD protection has(ve) a bit of 'magic' in them. You can do everything 'right' [except for those necessary compromises] and actually be worse off than if you did everything 'wrong' Nothing like a successful ad hoc solution to befuddle one's mind. The key is in that phrase, necessary compromises.

If me, I'd follow either JIM's advice with a wireless system in the remote location [note that prevents a hard wire connection between the two buildings similar to ferrite clamps along a cable] and Rocky Squirrel's advice who has some actual operating data. plus his 'fix' did not sound costly, just a bit labour intensive.

Reply to
Robert Macy

"...grounding is not right." That's kind of 'by definition' it's wrong, because it didn't work.

One can think of feerites, and those 'lumps' like the "python swallowed the goat" appearances on computer cabling, a little like 'cutting' the cable right there, and turning the next section into a 'wireless' battery system. Well, at least at high frequency. You only have two things to work with here. One, a dead short, which is extremely difficult to make. Two, an open [high impedance] which actually is a bit easier to make. The ferrites are like a giant RF barrier. Theey let differential signals go through gang busters, but won't let common mode signals through - like ''lightning' trying to ride on your cables. The damage [if they're present] done by those commone mode signals is that they get converted into differential signals. And, differential signals that can be extrememly high voltage. result arc overs, breakdown, zapping so to speak.

Sadly, EMC and ESD protection has(ve) a bit of 'magic' in them. You can do everything 'right' [except for those necessary compromises] and actually be worse off than if you did everything 'wrong' Nothing like a successful ad hoc solution to befuddle one's mind. The key is in that phrase, necessary compromises.

If me, I'd follow either JIM's advice with a wireless system in the remote location [note that prevents a hard wire connection between the two buildings similar to ferrite clamps along a cable] and Rocky Squirrel's advice who has some actual operating data. plus his 'fix' did not sound costly, just a bit labour intensive.

======================================================== Robert,

Ok, I admit that I do not fully understand how they work or what "ferrite clamps" can do. As I said before I thought that they smoothed out or blended the voltage. However you seem to be saying that it will chop off the higher voltage spikes so that it will not pass on down the cable. It would seem that I need to do more research on the little buggers.

As for going wireless.................... not sure at this time. Need to investigate that as well. And going overhead just does not seem to be viable with out any support structure available.

Thanks for input.

Les

Reply to
ABLE1

Okay, I thought you grounded the camera chassis themselves.

How about a simple ground block where the coax enters the building? Just use "f" connectors, no need for BNC's. Do it just like the CATV setup. That way you get a ground right at the rod and building entry. I would still think you would need ground loop isolators since the reference is different at the out-building and the head-end.

Reply to
G. Morgan

Frank knows how to ground plastic!

Reply to
G. Morgan

Haven't installed any small dome cameras lately have you??

I agree that is part of what needs to be done.

Thanks,

Les

Reply to
ABLE1

No plastic ones outdoors, no.

That way you can catch both coax cables where they come in.

Reply to
G. Morgan

I don't think I've ever installed plastic housing cams outdoors come to think of it. The domes are usually Pelco, which have an all metal housing. I mount them to a deep 4 square box. If the building is sheet metal, the ground is right there on the box mounting tech-screws.

If it's a PTZ, the housing is always metal. I've always considered plastic for indoor use when vandal-resistance is unnecessary.

Are those ones you have rated for UV protection? I could only imagine a plastic housing standing up to years of direct sunlight unless it was designed that way with special polymers.

Reply to
G. Morgan

Graham,

Not sure how you got the idea that the cameras I am dealing with on this issue were outside?? They are interior cameras. Sorry for any confusion.

Les

Reply to
ABLE1

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