Security & Fire Protection Systems/Lightning etc.
QUESTION: What plan for a building should be requested to ascertain if proper grounding was installed to protect its' 485 communication loop connecting the control entry to garage access door system to protect the system from high voltage surges etc.?
ANSWER: According to Art. 250.94 of the NEC code book, the use of single point grounding must be used to insure against grounding differential for the use of RS485 data communication circuits.
However it is very difficult to achieve single point grounding on a gate access system. Since the motor is on the ground, the gate is metal and so-on you have entry ways for lightning to come in the back door case ground strikes that might not be attached to the same ground as the building ground.
What is single point grounding?
The utility must be the primary ground, and a #1, or #2, or upto a #10 stranded ground wire must be bonded to the Primary ground and the Gate Access motor ground, AC ground and any other physical grounds. The Key pad is usually forgotten....so remember the key pad and pedestal must be also grounded to the Electrical AC power Ground. If there is a phone line, that is also a problem because that is a ground loop you cannot get rid of...to eliminate that grounding differential, use a fiber optic device call Optelator...
The surge suppression for the RS495 is two kinds. One is a three stage and the other is a four stage protector with a transformer in it.
DDual2WDTB/G 16V 3 stage
DataISO2WDTB/G 16V 4 stage
Grounding as you know is critical.....
You need surge suppression and the Optelator find the products on www.gateaccessprotection.com
On this web page is the ability to down load a pdf file that covers all entry ways that lightning can come in on a gate access. This information is vital for your planning stages.
Knowing where lightning is coming in is one thing, but know how it might exit a system is another....so the idea is, how clever are you to create an alternative path way for lightning to by-pass the system...since you can not stop it?
I hope I have been helpful to you....this is not an easy thing you are doing. I can be of service to you in other ways as well....something to think about, but for now, look over the web page and get an idea what I am telling you.
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QUESTION: I ordered a strike next report as a followup to your reply.
Please find the data below.
Could strike within these distance effect the equipment we previously discussed...?
If you would like to see the whole report ..send me your email
Date Time Peak Current (kA) Distance From Center (mi) Distance From Center (km) Latitude Longitude
10/20/2012 2:51:15 -24.4 0.1 0.1 42.36470413 -71.14928436
10/20/2012 2:51:15 -23.6 0.2 0.3 42.36431885 -71.15090179
10/20/2012 2:51:15 -155.1 0.3 0.5 42.36513901 -71.15356445
10/20/2012 2:44:15 42.5 0.3 0.5 42.36713028 -71.15324402
10/20/2012 2:52:07 -21.9 0.5 0.8 42.3693161 -71.15507507
10/20/2012 2:52:07 -14 0.6 1 42.3728447 -71.15300751
10/20/2012 2:52:07 -90.7 0.8 1.3 42.37573624 -71.15288544
10/20/2012 3:20:09 63.2 0.8 1.4 42.37081909 -71.16236877
10/20/2012 2:43:04 42.9 0.9 1.4 42.37546921 -71.15752411
10/20/2012 2:53:03 -14.1 1.5 2.4 42.38622665 -71.14945984
10/20/2012 2:53:03 -24.8 1.6 2.6 42.34393311 -71.13376617
ANSWER: So long as there is a grounding differential, static electricity can take out PC boards for today technology. A strike of a mile, 10 miles, or next door can get you. If you have any kind of potential at all coming up the ground of the AC power, case ground of the panel, it must have a way out of that equipment....you noticed when you looked on the web page, not only was the DDual2WDTB/G available but also AC surge suppression was covered, the spike block to prevent bi-directional grounds and even isolation transformers used to eliminate multiple grounds that you cannot get rid of otherwise. A slice of the pie or a small part of the puzzle will not protect the panel fully. That is why you see all the other protectors too...they help you create an alternative pathway for lightning to bi-pass the panel. That is the clever way to trouble shoot a panel in trouble with lightning.
To answer your question....it is well and good to have a report on lightning strikes, but imagine that every thing in its wake, can be destroyed too. But they are not, why? Answer, they must likely a stand alone system that has a single point ground. They should have protection however to prevent chip corrosion.
The design of the building base on our conversion by phone is an issue too, this goes way back to the PE who did not bond the frame back to the electrical ground rod.
I would however like to see the report...email@example.com
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QUESTION: I understand the need for protection of the system...but could lightening strike in close proximity to the build enter into the circuit and cause damage as displayed on the graph or report...?
Yes, in Layman's terminology when lightning strikes, the EMP (Elector Mechanical Pulse) heavy current, heavy voltage goes into the ground....but what radiates from that is EMI (Electro Mechanical Interference)(like a bomb going off) which is high voltage low current, and any thing in its wave form path will increase in voltage, with no serious locomotive force. However, if there is a way out of the system, the path way is clear...and their maybe several components in it's path...it will go to ground leaving a wake of damages of surface mount technology which is extremely low capacitance to handle even the smallest current generated by EMI on the PC board. Normal size diodes and resisters, caps and transistors can deal with this issue, but not EMI or static electricity on SMT technology.
How does lightning travel....every foot is a nano second, so most protective devices respond in 15 nano seconds...so even the best laid plan for protection may not be fast enough for SMT technology...and that is why I promote tying three to four knots in the wire between the surge suppression and the termination on the PC board data loop. I also incorporate diodes in with my low voltage protection, now they respond in 1 nano second, but they are not as strong as MOV's, so the likelihood of blowing them out first is good....so what do I do? Answer...I incorporate MOVs for the incoming side (strong but slow to respond), and inductor to slow down the locomotive force between the MOV's and the Diodes....mathematically speaking causing the MOV's and the Diodes to respond exactly the same time by slowing down the EMI or EMP with the inductor or coils. It works great...and no one does it accept me....some others use carbon resistors but that will not work because they offer no impedance path way like an inductor does, only inductors work. Between this explanation and all the others explanations I hope I answer any and all our questions. I will look at the e-mail you now sent me.