i'm not sure i understand this. so when lightning hits the cable before the SS, it travels down the cable and thru the SS and then starts to travel down a 3-foot patch cord; let's say it gets two feet down with a foot to go to the camera.
at that point the ss engages and provides a low-resistance path to ground at the SS. does this really pull back the high voltage EM wave about to hit the camera?
Ditek was explaining a situation where the surge suppressor is dealing with a surge coming from the PSE/PoE Switch traveling toward the camera, not traveling outside the building back towards the surge suppressor.
Yes, the general rule of thumb for best practice is a 3' minimum wire distance between a series-wired surge protector and the equipment being protected i.e. camera or a switch. That wire distance can be longer and coiled up near the equipment if you prefer.
To answer the first question, yes. The typical waveforms in surge testing are 8 x 20uS and 10 x 1000uS where "uS" = microseconds. The first number is rise time to peak voltage and the second number is the duration it takes to reach half peak voltage. The surge protection components react at the nS (nanosecond) scale, but you still need to build in a distance "buffer" before that surge has already entered your equipment and found a path to ground through your electronics. You can feel free to contact me to discuss further if you'd like!
Yes, that is specific to parallel-wired SPD's, like the type you'd have installed on your home electrical panel. And we always encourage our installers to use the shortest lead length possible when installing our parallel-wired SPD's. The 3 foot rule is applicable to series-wired surge protectors, and for specific reasons. If you'd like to contact me directly to discuss more in depth, my email is below. It may be more efficient than trying to communicate through this thread.
now the way i understand that is if a surge was induced on the field wiring, the surge could travel towards the SPD, where it would be (hopefully) stopped before exiting the SPD onto the > 3 ft cable segment to the device.
i also understand that if the surge was induced directly on the > 3 ft segment that the camera may be toast.
but would the surge be able to go the other way thru the SPD, and possibly to the head end, assuming there is no additional SPD at the head end?
If you'd like to contact me directly to discuss more in depth, my email is below. It may be more efficient than trying to communicate through this thread.
if you don't mind, i would prefer to discuss in-forum. there actually are several members that are more knowledgeable than i about such things, and even if so far are silent, may find your answers informative :)
That is a great question and far deeper than most are willing to travel! Yes, you are absolutely correct stating if the surge energy is induced on the short segment of cable between the surge protector and the camera, the camera would be toast. Typically, you would see that occur when lightning directly hits the camera pole, or the static discharge is so close that it gets induced onto that short span copper. However, the vast majority and higher incident rate occurs when the cloud to ground strike occurs in the vicinity and gets coupled onto the buried network cabling between the building and outdoor camera. Without giving away too many design secrets, even though the surge protector is wired in series, the protection components at the board level are in parallel with each of the 8 conductors of the network cable. So if the energy was coming in from either the "protected" or "unprotected" port, it would still cause a reaction and open a low resistance path to the ground conductor, or the shield if you're opting to use STP. With the head end being the "brain" and typically the most expensive equipment, it's the main reason why we absolutely recommend protecting both ends of the run when cables physically exit the building and are buried, or aerial, to a camera pole or separate building. In my experience, I would highly recommend not relying on the surge protector all the way out at the camera to prevent the "back feed" situation where you let energy into your network infrastructure. Very engaging conversation and I very much appreciate you asking these questions!
The "Protected" and "Unprotected" terms are just used to reference either the side leading to the equipment or the side connected to the field wiring. The NETS products actually use the terms "IN" and "OUT" on the device labeling in order to prevent thousands of calls from technicians and installers in the field asking "which side is the in and which side is the out" when they go to install the product :) You run your wiring from the field to the "IN" then "OUT" to the equipment you are intending to protect. Keeps things simple for install purposes!
The NETS products have been 3rd party tested at our request for bandwidth. These devices will easily support up to 100 Watt PoE (144 Watts is their max). We would also be more than happy to provide you with a single channel sample to run through your own field testing.