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Author Topic: grounding question  (Read 773 times)

OK4FX

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Re: grounding question
« Reply #30 on: June 29, 2020, 09:34:23 AM »

Michael (N6MST):
He does have an obsession with spelling and capitalization though.  :)

Brian - K6BRN

It is caused by too much mhz here. :)

(I hope you noticed my smiley too.)
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Mira OK4FX

KD0REQ

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Re: grounding question
« Reply #31 on: June 29, 2020, 10:53:07 AM »

 HPQ, the chassis ground stud on equipment is there for connecting a common shack ground to all equipment to bring them to the same level. no circulating currents, RF hot here and not there, etc. if you check out the NEC electrical code, it commands that all transmitting equipment be enclosed in a metal case and grounded.

typically you'd like to run that common equipment ground to the RF system ground rods. theoretically, well-grounded antenna runs with coax to the rigs would serve. practically, you want the lowest impedance to static, lightning induction from near strikes, etc. because, circulating currents. so a nice stout wire,#8 copper being the code minimum, short and straight as possible, would be better.

if you have older equipment with 3-wire cords to internal power supplies, you have a circulating current through the electrical feed. code says it should all be bonded to the ground buss at the power entrance panel. if it isn't, you have circulating current. possible RF hot spots. likely no fun with a near-strike in a storm.

"ground" means different things in different circumstances. that's why the ARRL grounding book. "ground" is a shortcut for not saying "electrical safety ground and return," "RF ground for counterpoise," and "system common ground." which is too much shortcut.

Thanks for all the suggestions. To answer an early responder, I have an antenna ground. I'm looking for (I guess) an RF ground. Something to connect to the terminals on the back of all my equipment designated as "GND". Sorry if that is the incorrect name.
« Last Edit: June 29, 2020, 10:57:41 AM by KD0REQ »
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KD0REQ

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Re: grounding question
« Reply #32 on: June 29, 2020, 11:09:11 AM »

here's an extreme example of why circulating currents in grounds is bad.

back in the 80s, when I was wrangling minicomputers, we needed to use terminal servers. one vendor got me into an 8-building complex used by a customer relations outfit, and we discussed setups. they blew up a lot of top-line servers, and had the electricians chase down why. one electrician was checking things out, and touched two buildings, one per hand. he almost got electrocuted.

8 buildings. many power drops. several transformers and multiple points of ground. deadly circulating currents as a result. all build to code, but no common earth ground.  they ended up bonding all 8 buildings with strapping suitable for sinking all the current used in all 8 buildings, and the power company bonded all their transformer commons.

the varying resistances to "ground" referenced to the 3400 volt service lines to the area created different voltage references, and circulating currents sufficient to kill.

a decade before as a reporter, we had a big storm one night that took down the power feed to a building annex downtown. the neutral opened in the damaged feed, and a fire started in the main building from too much current chasing a ground (neutral) reference. the service was upgraded the next day to a common point.

some lessons you don't forget.
« Last Edit: June 29, 2020, 11:13:18 AM by KD0REQ »
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