Do I understand this correctly?

[tdenfuny]

I have read and hear from several places now that an HF transceiver running at most 100W doesn't need to be grounded because it is already grounded via the power supply. From what I understand then, the little ground log at the back of a transceiver doesn't do anything in terms of safety. The only concern is an RF ground and if one uses a dipole or a vertical with proper counterpoise wires on the ground, then that is also taken care of. As for an antenna reflecting power back to the transceiver and possibly to the chassis of the radio, an antenna tuner should take care of this.

Have I understood this correctly?

If so, as a follow up question: From what I understand a power supply might very well be grounded via the third plug (ground) in the outlet, but how is this ground connected to the transceiver if one just runs two wires from power supply to transceiver?

 

[jaspence]

Grounding

All of my power supplies have two wires, positive and negative. I don't now what you read, but even with a three prong plug on the PS, there is no guarantee of a true ground for the PS. True grounding consists of all equipment in the shack to be attached to a single point, usually a copper rod driven 8 feet into the ground. Only a single ground point is used to prevent ground loops. The following article goes into detail.

http://www.galvanelectrical.com/pdf/groundrodmarkingcompliance.pdf

 

[N2AL]

This is my personal method of operation, and other ham radio operators may have a better way of doing it.

I ground my antenna because it helps discharge static electricity from the antenna. I have less of a chance for a lightning strike.

SHOULD I take a lightning strike I do not want it to fry the power supply, or my radios. If I grounded the power supply only I would take that chance.

To take the best precaution against lightning killing my equipment I unhook the antenna when it is not in use, and when severe weather is imminent.

 

[lmrtek]

every 12 volt supply I have has a 3 prong plug

And the negative output reads continuity to the third prong

 

[nd5y]

And the negative output reads continuity to the third prong

Maybe yours does but not all of them are grounded.

 

[K7MH]

Good article about station grounding here;
Station Grounding

 

[tdenfuny]

Thanks for all the replies.

 

[SCPD]

Tdenfuny, a great question.
.
How you ground your equipment depends on what you want the ground to do, You are correct- if it is RF alone that you are looking for in a "ground," the countepoise of a dipole's element or the matrix beneath a vertical will provide that "ground'-- ie: the RF return. For an example; all you have to do is look at a 440 handheld- the 'ground' is capacitvely coupled from your body to the unit's chassis.
.
The "ground" you have in question, that terminal on the back of the radio and its power supply is there for another reason. I provides a direct ground return in the event the radio chassis goes high with respect to the AC power line. Any number of things can cause that, but it provides a direct ground thru that 'green wire'- instead of you- into the earth. Just like a hair dryer (sexist ,) that short'd circuit to the chassis will blow a Ground Fault Circuit Interrupter (GFCI)- hopefully (you have one, No? ) instead of electrocuting you-- should your body complete the ground circuit. Remember, your AC service has a ground return connect'd already (its the white wire, the 'common')- you do not want to be the substitute part of it !..... That chassis terminal also provides a dump for any static charges that accumulate on the equipment- but do not mistake it for anything lightning related-- if a lightning spike has made it that far into your equipment, everything is now toast.
.
This is my favorite guide to grounding:
.
http://lightningsafety.com/nlsi_lhm/IEEE_Guide.pdf
.
____________________________________________________
Historically, the concept of a 'hot' chassis goes back to the AC/DC AM radios of the 1950's(?)-- before my time. They actually had such things. These radios had two wire power plugs- the 'common' was directly connected to the chassis. Should anything open that return, the whole radio went "hot"-- this was in the days before the 'green wire' ground... and many were electrocuted.
.
While I am on a roll with Grounds, let me throw in a unique example.... the high power tube amplifier (transmitters too) with Pi-Net tuning outputs. Those familiar with these circuits know there is a high voltage capacitor between the amplifier tube(s) and the Pi-Net. It rare but sometimes that DC blocking capacitor fails- placing the full HV potential onto the antenna.... touch the antenna and..........Zap!
.
This happened to me once-- an apparent system failure- an HF antenna array failing to load.............. But nothing obvious show'd.
.
Hmmmmm--- First things first,
.
" Lets see what the SWR is on the antenna..."
so the amplifier was shut down and the antenna was being disconnected when ...."BAM !" ...........a Flash of Blue Light!
.
Even though the power was off, the residual voltage (++ thousand!) on the tube plates, had now shorted out directly to the antenna thru that failed capacitor-- it fortunately arc over to the chassis when the cable connector was being remove-- and not thru the Tech standing beside me.... leaving the two of us quite speechless.
How many of you out there have such amplifiers?... (we don't any longer!) Today I make sure that each new (tube) amp has an RF choke between the output coax and the chassis- providing a direct DC ground in case of such a short-out.... Pi-Net or no....
.
Just thought I mention that.
.
Tdenfuny, I'd highly advise you to look at that IEEE booklet.... it will answer your questions better than anything many of us can direct you towards.
.
.....................................CF

 

[bharvey2]

While I am on a roll with Grounds, let me throw in a unique example.... the high power tube amplifier (transmitters too) with Pi-Net tuning outputs. Those familiar with these circuits know there is a high voltage capacitor between the amplifier tube(s) and the Pi-Net. It rare but sometimes that DC blocking capacitor fails- placing the full HV potential onto the antenna.... touch the antenna and..........Zap!
.
This happened to me once-- an apparent system failure- an HF antenna array failing to load.............. But nothing obvious show'd.

A bit off topic but that DC blocking capacitor shows up in other tube (valve) devices as well. I've been a guitarist for many moons. I was using an old guitar amplifier of my dad's that developed a failed blocking capacitor that caused the guitar itself to become "electrified" I didn't recall knowing so many expletives!

Proper grounding is not something to be trifled with.

 

[SCPD]

Bharvey, personally I don't find that being Off Topic at all- it fits right in with equipment grounds, GFCI's etc...
.

.
I re-read what I posted last nite and found it very cryptic (I should know better than to write technically in an airport )
.
That terminal on the back of the radio serves the same function as the 'green wire' found in the 3 wire power cord. That green wire is Suppose to connect directly to the earth, and the power company's ground --so that in the event the chassis goes 'hot' for any reason, it will be shorted to earth thru that circuit, and back to the power company- and not thru you, earth connected standing a in a puddle of water. The "white wire" in the power cord is the common- it is connected to the power company's ground. Anything that breaks the path will seek its ground return to the power company thru what ever is in its way-- hopefully its the green wire or your direct ground rod connection- not you touching the chassis with one hand, and something earth-grounded with the other. This is the reason you really don't want to defeat the purpose of the 'green wire' with a 2-prong adapter to an unground'd AC receptacle- or if you do- prove a direct route thru that ground lug on the chassis.
.
I think I got it clear that time .... at least it sounds better to me now
.
Here's an experiment that can show just how well that ground circuit back to the power company's generator functions. Remember, that 'white wire'- the common, is connected to the earth- at the power generator, at the service pole outside your house-- everywhere.
Take a 3-wire power cable, strip back the the black (or red) 'hot' lead and connect it to one side of a 100 watt incandescent light bulb. Now run a wire from the other side of the bulb out to a ground rod, water pipe, wire fence-- and (carefully!) plug it in. See how that bulb glows! Now imagine yourself as that bulb.
.
This, btw, is a good, albeit crude method to test grounds and soil conductivity- although not so good for earth worms.
.
______________________________________
.
I wasn't clear on those 1950's radios either- With one side connected directly to the chassis- hopefully it was the 'white' grounded wire- Its rectifier didn't care about the polarity. With a non polarized plug, it would work just fine if the "black wire" was at chassis potential. Now imagine what would happen if you touched the bare metal of that radio and were standing in that puddle of water.... ............a neat Ground return to the power company thru................... "U" !
.
.
..........................CF

 

[cmdrwill]

I wasn't clear on those 1950's radios either- With one side connected directly to the chassis- hopefully it was the 'white' grounded wire- Its rectifier didn't care about the polarity. With a non polarized plug, it would work just fine if the "black wire" was at chassis potential. Now imagine what would happen if you touched the bare metal of that radio and were standing in that puddle of water.... ............a neat Ground return to the power company thru................... "U" !
...........................CF

That IS why those 'music' radios had a plastic or Bakelite case and knobs. No exposed metal so no one should get shocked. As C F mentions, many persons got shocked, or even killed, by the radios with poor or broken cases.

Back on topic, the 'ground' screw on the back of your HF radio should be connected to a real ground. So the radio or power supply does not depend totally on that 'third pin' on the AC plug. AC Safety 101.

 

[SCPD]

Another good point- there is no excuse not to ever use that ground lug on that radio.
.
How that ground is actually connected to the earth is a separate topic- one that got fairly well discussed in the Amateur Radio Antenna section of these forum just recently- but that had to do with lightning protection.
Personally, and professionally I follow pretty much the IEEE grounding guidelines I cited above (ie: I "float' all my equipment grounds, surge protectors, data filters, antenna arrestors- thru one and only one ground panel- one single connection-mounted right at my AC service box- all tied together to the single, common earth connection.)
.
Another little something while I'm on this--
.
While that ground lug will provide an RF return path, it should not be relied upon for that purpose. If there is RF appearing on the coax, because of common mode or the like, and someone is getting RF 'bites' back at the radio,- something is wrong. Connecting that lug to the ground may work to remove the bites, but its a Mickey Mouse fix- and that lug is not there for that purpose. Look to other causes.
.
This topic has gotten involved, No?.... smiles
.
.
............................CF

 

[paulears]

If your power supply is built into the radio, then the ground pin of the supply cord (trying to use US terms here - maybe incorrectly) Earth of the mains cable in English, provides the protective earth (Ground) The path of least resistance for fault currents to get to ground which should trip breakers/mcbs with overcorrect and cause leakage type circuit breakers to disconnect.

The big issue with connecting the wing nut to anything is to do with ground potential. An earth stake banged into to suitable material will be at the local ground potential - but if your radios are some distance from the electricity supply it's quite possible that the electrical ground potential is a few volts different. Considerable current can be available here so seeing a spark when you attach multiple grounds can be a surprise. Old music amps did indeed often have about half the supply voltage on the ground from faulty components - in the US at least this is 50-60V, think of us here with 110V on your guitar strings! In my view the random connecting of grounds is as dangerous as doing the old hum removal trick of removing an ground connection which only idiots now do!

 

[SCPD]

So very true... !
.

The potential between grounds can be shocking (pun intended.) Since, for all practical purposes, the only true zero voltage point for return ground currents is at the power generating station, anything along that path will encounter some resistance. That experiment with the light bulb I mention'd, shows the variable nature of the conductivity of soil. Connecting a piece of equipment directly to a ground rod thru a low resistance line will be a lower resistance path than thru your body-- thus standing in that puddle of water you will still be at a higher resistance for return than thru the direct rod connection to earth. There may be a few millivolts difference, tho you shouldn't get 'shocked.'
.
But now take a volt meter and measure the potential between that rod, and say, the ground common at the AC service box- that box represents the total system ground. That resistance seen in the soil may be significant- significant enough to bite you badly should you wish to test it by placing one hand on the ground rod, the other on that circuit box.
.
For this reason, I personally 'float' all my grounds thru a heavy guage copper braid, back to the power company's earth junction. I try very hard not to have any secondary grounds- both for this AC shock reason, as well as lightning protection.
.
.
......................CF