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Grounding System tips

Posted: Sun Jun 28, 2015 6:50 pm
by WA5TT
Just installed new grounding system at the house and came up with a few tips:


Grounding situations vary depending on location, but if you are running off of the mains power, you want to ground antennas and etc to mains. You also need to decide how to ground towers, feedlines from outside and protect against a lightning strike, etc... Your situation will vary, but this is one subject you should spend the time combing the web, QRZ forums, YouTube and talking to elmers about. If you have access to a local pro, consult them. I talked to some contesters and a broadcast engineer at the local clubs and did several hours of reading and video watching on the web.

First, make SURE you know where the other utilities and any other hazards are buried! :geek:

My situation is that the radio room where the antenna feedlines come in to the house and the mains ground are opposite each other. So I connected the ground rod outside the radio room to the mains ground rod with #4 wire buried about 6'' deep and tied to a 8' gound rod every 16'.

Ground rods were driven with a rented bit and a electrical impact hammer. This made the driving very easy and anticlimactic. Digging the trench for the wire is the harder job, since that was done by hand. (100', 6" deep in 90 degree, 90% humidity) The in-between ground rods were bonded to the #4 wire with Cadweld. The reaction is a fun lesson in exothermic chemistry. There is Polyphaser lightning arrestor on the outside radio room rod. The coax from the antenna is connected to the arrestor and a small coax goes into the bulkhead(wall) into the actual structure where the radios are. I did most of the work with a little help from family. (AD5VA and her brother.)

Ground rods, wire, and tools were from Home Depot.(Home Depot was much cheaper on the wire, ($152.00 for 200') than the electrical supply houses.) Cadweld was from a local electrical supply, but DX Engineering sells it. (Make sure you get the exact right type, there's dozens of variations.) Polyphaser and mounting plate were from the local HRO. Didn't have a diagonal cutter large enough for the #4 wire, but a large two hand pruning shears did the job. Cost was about 350, plus I have about 100' of #4 wire left.

Re: Grounding System tips

Posted: Tue Jun 30, 2015 2:12 pm
by KD7CAO
Excellent write up. I too have been contemplating how I will be installing my ground system. There is an interesting article that was put out by the Post Naval Graduate School on grounding titled: "THE MITIGATION OF
RADIO NOISE AND INTERFERENCE FROM ON-SITE SOURCES at RADIO RECEIVING SITES" Dated: November 2009. It is available for download here: http://www.arrl.org/files/file/Technolo ... ndbook.pdf

It states:
"Never use welded or CADWELD® joints in a ground system or at any other location in a receiving site. Numerous cases of poor welding have been noted in receiving sites which can be blown apart with a sudden surge of fault current. In addition, contamination in welded joints can result in inclusions with non linear electrical properties. These can produce intermodulation components and intermodulation noise when EMI current flows through them."

Motorola R56 Standards recommend the use of a CADWELD at this time, however it is rumored that in the R58 standards that are supposed to be released late next year that the use of compression connections will be recommended. CADWELDS or Exothermic Welding is considered hazardous for use inside of buildings and that according to studies has shown the connection itself to become an incidental radiator capable of increasing the noise level on receiving systems. The benefits of a CADWELD however are that they can be buried and often forgotten, whereas a mechanical fitting must be checked, cleaned, and torqued yearly.

Re: Grounding System tips

Posted: Tue Jun 30, 2015 8:38 pm
by WA5TT
Eric,

As for Cadweld, it was the best option for the buried rods at this time. There is supposed to be a way to put a compression fitting on the rods, but I couldn't locate such a tool for rental nor fittings for sell. Both the broadcast folks and the contesters said Cadweld was a good bet for my installation.

Chris
WA5TT

Re: Grounding System tips

Posted: Fri Jul 03, 2015 6:32 am
by WA5TT
I also reviewed NEC Article 810 with my FIL, (who is an electrician), looks like I've met or exceeded the code requirements. :D