Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KJ6EWX, Feb 12, 2018.
My rod is inside an exterior wall, starting from about a foot above the stem wall.
You are absolutely correct Mark, NEC does not require that. It is Best Practice and complies with NEC. NEC minimum spacing is 6 feet. Best Practice complies with 2 x Rod Length.
Again I agree with you 100% Mark. You know who I am and what I do from Mike Holt Code Forum. The point I am trying to make is we see a lot of non compliance issues with respect to NEC. Best practice complies with minimum NEC requirements, but many times that is not possible. When you cannot use Best Practice then you must meet minimum NEC requirement. May not be the best, but makes it safe and keeps you out of trouble.
I know what you are driving at, but not sure I completely agree with you 100%. Example how many hams do you see fail to bond Supplemental Electrodes like those used for the ADU, Coax entrance, Tower, and RF Radials? Most tend to leave them isolated which you and I know is extremely dangerous and can render the RX useless. If the minimum NEC requirement were met by bonding the Supplemental Electrodes now makes it acceptable safe and the RX usable.
Again absolutely true. But you and I know something most hams do not know. 547 and AFCI is a MONEY ISSUE and a financial burden. Flip it around to Chicago amendment that requires single story, single family dwelling units to use raceway (EMT) instead of using Romex. That requirement was put in by the UNIONS to keep homeowners from DIY electrical installations. Again follow the money.
Anyway you and I are on the same page and I got your back. Thanks for the assist.
No you are correct. However unless you can set up a Single Point Ground, you cannot prevent external faults from entering. Best you can do is apply proper bonding methods and layout to keep outside faults to acceptable limits. The killer is the loop created by the Coax and the AC power Green Wire ground used to power your radio equipment. For more detailed explanation read this thread I started. You may not be able to prevent the loop using Single Point Ground, but you can Shunt most of the fault around and keep most of it outside where it belongs. It should shine some light on the subject.
That must be painful.
Not to be persnickety, but I said 'safest'. What you mention has made the installation 'safe and usable', but (just as an example) adding an NFPA 780 lightning protection system would be the safest installation, which is not required by the NEC. In addition, using larger conductors may provide a safer installation, but not required by the NEC.
90.1 Purpose The purpose of this Code is the practical safeguarding of persons and property from the hazards arising from the use of electricity.
Note that it says practical, not best. Also, the purpose of the code is not meant for the safeguarding of hazards extraneous to the use of electricity, for instance lightning. Lightning hazard mitigation is covered in NFPA 780, a separate set of codes.
I do appreciate all the work you have put into your grounding articles and your contributions, especially when it comes to 'myth busting'. I am not trying to create an argument, more so it's that I am trying to help you 'fine tune' your work when it comes to the NEC, which I was burdened under for some time as a working electrician.
No worries, I never took it as being Persnickerty. As for NFPA 780 is not required, and if implemented is not enforceable by an AHJ to my knowledge. Typically the only inspection used for NFPA 780 is certification by a UL 96A Master Label certification which may or may not be used for radio systems. Just about every telephone office I built had UL Master Label. Some had microwave and most do not today with fiber being king of transport. .
Never took it as an argument and thank you for enforcement.My goal is not to get hams to use Best Practice as I know that can be a very expensive goal. I would be satisfied just meeting codes, and how to tweak code to their advantage and why things are done.
So you are not a Sparky anymore? Engineer now?
No, not an engineer. Still have my j-man's license, but kind of semi-retired.
780 isn't required by state law here in Michigan. When I was working for a Verizon sub, the grounding we did for the MESA enclosed gear was crazy. #2 solid bare tinned copper pulled through PVC conduit so it would not touch the cabinet or the gear, just the terminals. Ground rings, ufers and multiple ground rods all cad welded to the #2 SBTC. IIRC, they used 20' ground rods (those were in before we got there) at every corner of the ring and at 6' distances. They went way beyond any codes. I noticed they never used any type of strap, just big solid copper wire.
Which brings me to this question. As you read the NEC requirements for grounding electrode conductors, do you read that flat or braided strap is permitted in lieu of a 'wire or wire shaped' conductor?
Me too, I now do Consulting work. Me and a partner got laid off from MCI-Worldcom in 2003 and started our own Design/Build firm. We do the same thing for the same people, just make a lot more money doing it.
780 is not required by any state I know of, completely optional. Two types of customers use 780 and some DOD contractors. Telecom use it and have it UL Certified Master Label. Large companies use it and also have it certified UL Master Label to receive large Insurance premium discounts. Just recently we did the power and grounding at the McAlester OK Army Ammunition Plant on a new RDX Manufacturing building and we had to have it certified UL-96A. That plant basically uses the largest meanest UFER Ground I have ever used, seen or heard of. The concrete foundation has a 6 AWG copper grid matt on 32-inch centers and hundreds of Stub Ups fo rinterconnection to building steel and equipment frames. No static allowed for obvious reasons.
I was fortunate when I was in college. I got a 1-year internship while they were building Disney Epcot Center. I got to work on the electrical distribution and LPS. Disney parks in FL have the absolute best LPS in the country. Better than major airports. Only place I have seen that compare is DOD explosive manufactures.
They were using the standard I wrote for them while at MCI-Worldcom which because Verizon
Sure you can as long as it is LISTED and has the equivalent wire size. A lot of the UL and NFPA 780 stuff is the Braided conductor. Having said that it is a waste of money as there is nothing gained.
I am sure you have heard and seen the 5-Ohm requirement right? It is completely Bogus and if you were to ask Motorola, Ericson, and other manufactures why and where it comes from cannot answer. It is a hold over you hear a lot of. Because that is the way it is always done. It is foolish and lacks any credibility. That spec comes from Ma Bell way back when there were Party Lines. The Central Office needed low DC to 50 Hz Earth Resistance for the Ringer Circuits to operate. Back when party lines were used Ring Voltage used dirt as a conductor. Ring Voltage was applied to either T-G, R-G, or T-R. Couple that with selective frequency ringers of 20, 30, 40, and 50 Hz and you could put 12 customers with 12 different phone numbers on a single line. Those days are as dead as 8-Track tapes.
A 5 Ohm earth Impedance is a power impedance measurement of DC to 300 HZ. I think you know that because a Meggar uses 160 Hz on Dead Fall Potential right? Remember that? So lets say you use a 10-foot long 750 MCM GEC from the The Ground Bar to bond the GES to the Ground Bar. With me so far? Lightning has a characteristic frequency of 10 Mhz where most of the energy is contained. Do some simple math and add things up. If you consult IEEE Std 142 aka The Green Book a 10 foot section of 750 MCM has an impedance of roughly 2K Ohms at 10 Mhz. Now do the simple math. What is the Impedance of 5 Ohms in series with 2 K Ohms. Your answer had better be 2K Ohms or you failed math class.
Now lets back up to that 5 Ohm electrode for a minute. That 5 Ohms is at DC to 300 Hz. Care to guess what the impedance is at say 1 Mhz, 10 Mhz, 100 Mhz, and beyond. I cannot tell you what the answer is other than many magnitudes of 3 digits and thaty is at 1 Mhz. Go to 10 Mhz and its another magnitude of 10 and so on as you work up the scale. The 5-Ohm goal is complete BS. 5 ohms certainly will not protect a low voltage power application. Stop and think about it. A typical service to a cell tower is 200 amp 240/120. Apply 120 volts to 5 ohms and see what you come up with. Certainly will not operate the 200 Amp main breaker.
The goal of lightning protection is not the impedance. Lightning does not travel down a rod into earth, it flows outward along the surface. A good LPS will use radials going outward from the protected structure. To make it better use a Ground Ring with radial at each corner. Any radial larger than 4 AWG is a waste of money, and using 12 AWG Insulated stranded wire as RF ground radials is just plain silly and expensive.
Mark FWIW I was not necessarily talking to you. I think you know what I am talking about and what I have done for a living the last 40 years. I have known of you for at least 10-years at Mike's Forum. I know a few QRZ members from Mike's place. They are easy for me to spot.
I think they put all of the coax entry requirements in 820.