CCTV Ligtning Suppression Questions

[MAK]

I recently was sent to a site with a problem with some CCTV suppression units on a camera system. A former security technician (holds a Journeymen's license) from my company had installed this lightning suppression setup. http://www.ditekcorp.com/product-details.asp?ProdKey=43

There is a DVR in the main building and two pan, tilt, zoom cameras on light poles in the parking lot. All the associated camera cabling runs in the same pvc conduit that also feeds the parking lot pole lights, the cables are not seperated from the lighting circuit in any manner. There is a suppression device out at each pole camera for protection of the camera and there is a suppression device for each camera in an electrical room where the CCTV cabling enters the building. At the poles the there is a ground rod in the ground with a bare copper #8 conductor running from the ground rod into the base of the pole up about 15" inside the pole and exiting out the side of the pole to a metal box mounted on the pole where the suppression device iis terminated.

On the building side in the electrical room there are the same suppression units and the power supplies for the cameras mounted inside a metal enclosure about 10" from cable entering the building. The power supplies are 24vac 50va open frame transformers fed with a line cord plug into a outlet (just hot and neutral) the ground is not bonded to the enclosure but instead connected to the lightning suppression ground terminals. This is the only "ground" for the lightning suppression that protects the DVR in the building.

With that said here is what happened.
On a sunny day there were some electricians working on the lighting circuit to the pole cameras trying to troubleshoot a problem with a couple of the lights. There were a two security technicians working on another camera on the opposite side of the building. The cameras were working in the morning and by the afternoon the all four lightning suppression devices were melted, and the two ports on the DVR that the pole cameras were connected to were dead. Of course nobody knows what happened. The DVR has been repaired, lightning suppression replaced, and the bare copper ground wire was replaced out at the poles with a jacketed Thhwn #6 by my company but I am concerned that this will happen again.

Is it plausible that a fault on the lighting circuit and what I have tried to describe regarding the CCTV suppression setup could cause damage to this DVR?
I am sure the current CCTV suppression configuration is not sufficient or code compliant.
Is article 820 the one that covers this type of system? I am trying track down what article and sections would cover this. I was pretty certain that a ground rod would be needed in the building and that it needs to be bonded to the buildings ground. I have to prove that this install is incorrect to my supperiors. Any help would be appreciated.

 

[Rampage_Rick]

First off I'd like to point out that many surge protectors are designed for transient voltages (like lightning) not for sustained overvoltage.

The spec sheet at the link you gave states they use SAD technology.

Silicon Avalanche Diode (SAD) provides the perfect limiting action of protective component, but has a lower current capability. When voltage increases above the limit level, SAD will tolerate avalanche breakdown resulting voltage is conducted to ground.

So assuming that 120V got mixed into the CCTV wiring, the diode would faithfully dump it to ground until some part of the circuit failed. I'm guessing the diode on one surge protector failed first, then the other surge protector, then the DVR saw line voltage.

I had a scenario where someone else was pulling armored cable and it was rubbing against coax I had installed for a camera. The armor made contact with the shield of the coax, and even though everything should have been at the same potential (in theory) when the circuit was energized it fried 4 inputs on the DVR. Only 9 of the 16 channels were in use, so I ended up moving those 4 cameras to different inputs after taping up the coax.

This is one of the reasons I switched from coax to baluns over CAT5. The baluns act as isolation transformers so there isn't continuity from the camera to the DVR. Of course that still leaves the power and signal wires...

The only fault I find with those Ditek units is the 6.8V clamping voltage on the data lines. RS-422 specifies a ?6V signal, but RS-485 specifies -7V to +12V which would be seen as a surge... Likewise RS-232 specifies up to ?15V. There could be cases where that device interferes with specific protocols.

*edit*
As I was reading my own post, another possibility dawned on me. The surge protector at the pole was connected to it's own ground rod? Was it also bonded to an EGC for the lighting circuit? Assume for a moment that the surge protector at the pole has it's own ground, independant of the one at the building. Next assume there's a potential voltage between these two grounds. If it's greater than 13.6 V, the two surge protectors would create a path for current. Perhaps the lighting techs temporarily disconnected the pole's ground rod from the EGC?

 

[MAK]

*edit*
As I was reading my own post, another possibility dawned on me. The surge protector at the pole was connected to it's own ground rod? Was it also bonded to an EGC for the lighting circuit? Assume for a moment that the surge protector at the pole has it's own ground, independant of the one at the building. Next assume there's a potential voltage between these two grounds. If it's greater than 13.6 V, the two surge protectors would create a path for current. Perhaps the lighting techs temporarily disconnected the pole's ground rod from the EGC?

I don't believe that the pole camera ground rods were ever bonded to the lighting circuit EGC (at least not at the poles). I realize that there very well could be a voltage potential between the two grounds but the lightning suppression in the building end is kind of half assed tied into a receptacles ground via a plug in line cord. The voltage potential issue is what I was arguing about with a coworker. He says it has to be separate from the building and lighting circuit grounds.

The customer said the lighting circuit was 480. It's a pretty large parking lot or more like a series of parking lots.