This is an defintely an under-appreciated topic. Thanks Brian!
Even non-hazardous currents can greatly disrupt the quality and transmission of electrical impulses, typical to ethernet traffic. To a lesser extent than safety, ground provides an outlet for these potentially disruptive currents.
Can you describe where these currents originate and how the grounding avoids the disruption?
I have been under the impression that grounding actually creates these currents by providing a path between ground differentials, as you say later.
Good article Ethan... it harkens back to my days designing mainframe systems. One thing we used a lot of was flat copper strips within the racks due to the extra low impedance they provide. This helped a lot with signal integrity between the units as well as a good path to earth ground.
With IP video, this is not a common problem simply due to the twisted pair properties of UTP cabling. The cabling design makes it much more difficult for such a current to interfere and travel in a 'loop' of cable, and therefore is not a practical issue.
Does this become more common again for those who use various EoC devices to propagate their IP signal thru coax instead of twisted?
Also, when, if ever, is it appropriate to 'float ground'?
Thank you for the article because grounding is almost always overlooked. I am looking for articles on this topic which describes in details but easy to understand how to design proper grounding against lighting strikes for CCTV system. I have few questions on this topic, sorry if they might seem to naive but I am not an electrician:
Can cable shield grounding be enough against lighting strikes to protect camera or does it always have to be lightning arrester used ?
Can we connect earth point of lightning arrester to cable shield grounding ?
If we have a camera on a pole and lightning arrester next to it - can the grounding cable from lightning arrester be placed along camera data cable and go to earth point of the building or does lightning arrester have to be earthed to the pole earth point (if exists) ?
So one important point about Lightning Arresters: they do nothing to protect cameras, or whichever other devices they are connected inline outside a building. If lightning strikes your camera, it is toast. A lightning arrester primarily works to limit the harm of a lightning strike to only the camera.
It is kind of like a surge protector in reverse.
#1) "cable shield grounding be enough against lightning strikes to protect camera"
In general, no. Shielding is different than grounding, but there is really nothing that protects a camera from lightning. You can employ lightning rods (or some other more attractive conductor) that lightning may strike in lieu of cameras, but if lightning strikes your camera it almost certainly is a casualty.
#2) "Can we connect earth point of lightning arrester to cable shield grounding ?"
Again, shielding is different than grounding, but if we're discussing grounding like the article above mentions then yes, lightning arresters can be (and should be) connected to those points.
#3) "can the grounding cable from lightning arrester be placed along camera data cable and go to earth point of the building or does lightning arrester have to be earthed to the pole earth point (if exists) ?"
In general, the sooner you can ground a lightning arrestor, the better! I think either way you describe would work, but it sounds like physical distance to a ground point would be shorter at the pole.
Anytime a conductor carries hundreds of thousands to millions of volts (ie: a lightning strike) there is a high likelihood it will be obliterated in the process. Shorter ground paths = better because of less damage.
Great information, but I think it's also worth noting that most CCTV installers should not be dealing with grounding/bonding or lightning protection. That should be installed by qualified individuals who are trained for OSP cabling. Most people who attempt to do grounding or bonding end up doing more harm than good. (e.g. improperly grounding an IP camera connected to a network rack via shielded cable exposes defeats the grounding of the entire network.) It really is a specialty. When done improperly it is also a huge liability. The guy who does the grounding/bonding is typically responsible for the entire system and is often held responsible when disaster strikes.
Installing exterior cameras should really be done by OSP-trained individuals as well. In my state (Ohio) it's technically required, though rarely enforced--until something goes wrong.
I think you raise a good point that training is useful for 'doing it right', but I'll counter by saying subcontracting grounding out by security installers rarely, if ever, happens. And items like pole mounted camera grounds or lightning arrestors simply would not be installed at all.
So the pragmatic solution is for security installers is to understand the need and importance of proper grounding.
With that considered, however, are you familiar with/ can you share examples of whole-system liability by a video installer if not done correctly?
In many cases, camera installers are tying in to existing grounding infrastructure, not greenfielding it new, so that's an interesting dynamic.
This might need an update. 607C is pretty common but 607D is now out.
I just went through two BICSI bonding/grounding classes and can state that bonding/grounding is the #1 most misunderstood component of security... even the NEC code portion. I'm shocked at how little I knew.
I have seen many security integrator installation sites that use wireless point to point and point to multipoint radios for their IP camera networks where the RF points are not properly grounded, if any at all. Motorola R56 is a great source of fantastic information!