I have a cutomer building a new house, which he will have a ham radio. something about interference all outlets(not lighting) need to be on same circuit. he said he brought a 30 amp into his existing set up(at old house/future old house)and tapped 120 volt outlets off that, and drove ground rod down. I suggested putting a sub-panel and feeding ham radio 30 amp/240 volt outlet and 120 volt outlets from here.
he wants to drive a ground rod for radio, but i think that would be a violation since it wouldn't be tied with service ground rods. wouldn't the ground be well established with the four wire i feed sub with? that it would mitagate need for additional ground? and if additional ground rod neccessary then it would have to tie with the two at service which really would be redundant...of course the other suggestion could be to run 4 wire and a single gounding from service rods to sub panel. dont know much about ham radios and this interference he's worried about.
any help, comments appreciated.
thanks,
H2O
You can drive the ground rod your customer wants and connect it to the equipment grounding conductor at the proposed sub-panel or the transmitter. This rod does not need to be bonded to the other electrodes that may be present. See 250.54
Just remember that the earth cannot be used as the return path for ground faults, the sub-panel must have an equipment ground.
Big mistake not to bond the grounds together. All grounds need to be at the same potential. If lightning comes into the power line, and the radio ground system has a lower impedance than the power ground, the surge will seek the better ground THRU the radio. All grounds at the same potential, any voltage rise will be equal in the grounding system with no current flow, no damaged equipment. This is a code requirement. I install communications equipment, cell sites, radio towers,etc. We bond ALL grounds together. When bonding several ground rods together, do not use a complete loop, as this will create inductance, limiting current flow. (I teach a grounding course to Ham groups and others)Robert
If the electrical system is wired properly then additional ground rods are not needed. If the customer still wants additional ground rods and want to pay for them, put them in but they HAVE to be bonded together. As for the interference issue, I presuming (never assume) that what he is talking about is when dealing with ampliphiers, you want them on the same phase. you could get poor performance since the electical "push" through the equipment is 180 dergees out of since. I do not think this is an issue with todays electronics.
Fourth wire from service to sub panel will establish the bond for a supplementary ground rod. Recommend a #8 Cu even if the circuit is 30 amp wired with # 10 Cu.
See 250.54
After reading WESTUPLACE's post, I think you should explore this interference/grounding issue with your customer some more and perhaps post them again so WESTUPLACE can give us some additional guidance. I have the feeling that your customer may not be explaining his concerns properly. Though I am not a HAM operator, I'd like to find out what your customers problems might be and what the solution really is.
Supplementary grounding electrodes do not have to be bonded to other electrodes on the premises. The requirements of 250.50, 250.53(C) and 250.56 do not apply to supplementary electrodes.
Supplementary grounding electrodes do not have to be bonded to other electrodes on the premises. The requirements of 250.50, 250.53(C) and 250.56 do not apply to supplementary electrodes.
You have my undivided attention. Please reference where it is kosher NOT to bond all the grounding electrodes together inthe NEC that applies to the ham radio issue.
You have my undivided attention. Please reference where it is kosher NOT to bond all the grounding electrodes together inthe NEC that applies to the ham radio issue.
I don't see anything in Article 810 that would require a supplementary grounding electrode that is connected to a sub-panel or equipment ground of the radio equipment to be bonded to all other electrodes. If the ground rod was connected to the antenna mast or an antenna discharge unit, then there is definitely a requirement to do so.
Of course, I could be wildly mistaken, wouldn't be the first time.
When the supplementary ground rod is bonded to the ground in the sub panel it is also becoming bonded to the service, and all the grounding electrodes that the service is bonded to.
The hazard arises when the supplementary ground rod is not bonded to the system ground but, is isolated. That is when the Earth becomes the only link between the two rod systems, and it is prohibited.
The supplementary ground must be tied into the system ground. This ground is an RF ground; the conductors between the radio or tuner form part of the antenna's tuned circuit and must be short to be effective. The service ground is usually too far away to be useful at RF.
In reality, he probably wants to set up a ground window or ground plate to form a single-point ground where all of the cables enter the shack. This plate would have all of the lightning arrestors on it and should be bonded to the RF ground as well as the power ground. Ideally, all cables entering the shack should go thru arrestors on this plate.
They may want to look at the tech notes at
www.polyphaser.com for more info on grounding and lightning protection.
Placing a subpanel in the shack is a very good idea; I would use a main breaker to give a single point to shutdown everything in the room (except the lights) in an emergency.
Hopefully, the OP will post additional information about this installation. All the posts, including mine, seem to be based on a little bit of guessing what the owner wants to do.
Ham radio grounding is somewhat confusing, as there are three (3) types of "grounding" to consider; 1) Safety Ground, 2)Lightning Ground, and 3) RF Ground.
The 2002 NEC 810 Part III - Amateur Transmitting and Receiving Stations - Antenna Systems is the starting point to look at. 810.58 - Grounding Conductors -- Amateur Transmitting and Receiving Stations has you refer back to 810.21(A) through (J), which then refers you back to 250.50, 250.52, and 250.94. (are we confused yet?)
We need to find out just what type(s) of grounding this Ham operator is trying to install at the new location.
A good place to go for information about Ham radio grounding is "www.arrl.org". Doing a google search for "ham radio grounding" also brings up a great deal of useful (though at times contridiction) information.
If this were easy, it wouldn't be near as hard to do! (grin)
Even in big commercial transmit sites, they bond all the grounds together. The problem isn't that the grounds are bonded or connected electrically, it's that at radio frequencies, impedance through a traditional wire electrical ground is extremely high. Leads need to be kept shorter than normal to be effective. The best method is to install a large equipotential plane under the equipment- capacitive coupling between the plane and earth will reduce impedance and become a far more effective ground than the ground wire, even if there's no physical connection with the earth! Multipoint grounds like buried loops and multiple supplementary ground rods help, too.
I Inspected all the state radio shelters at the prisons and along the interstates (7 counties).
They had Ufers in every significant chunk of concrete, a ground ring around the shack and tower, 40' multipiece rods at the corners and radials going out from there.
Everything was CadWelded together at each intersection
The latest information revels that loops are not recommended. We have cut the loops on some sites. They use to install a loop around the structure and attach all the grounds and rods to it but it is now a practice not to make a complete circle. It was found that a closed loop can act as an inductor, causing resistance (or reactants ) to a lightning surge which is LF RF. Robert
That doesn't sound right; the loop would be perpendicular to the electric field of the lighting strike and in-plane with the magnetic field, so there shouldn't be much induced current or inductance. And breaking the loop in a ground wire doesn't open the circuit, it just increases resistance a bit because the earth is still highly conductive. I'm interested in hearing the theory behind that- do you know of any technical papers or references talking about the issue?
The closed loop does not act like an inductor in my understanding as it is perpendicular to the flow. To place them in to a grounding system at the base of the building helps to form an equal potential plane, but little to no current flows through them due to the equal potential plane they form, and, as such they do not provide additional "drain points" (for lack of being able to think of a better term) for the current of a lightning strike.
I close the loop everytime, but only have a ground loop installed at the base of the building. Loops further out away from the building are a waste of resources.
Been awhile since I've read tech papers on the subject. Try the military handbook "Grounding, Bonding, and Shielding for Electronic Facilities" mil-hnbk-419a, Motorola "Standard and Guidlines for Communication Sites" 68P81089E50-A, and if still available Polyphaser had some very well written manuals on the subject. Other references are to numerous and of the three mentioned I don't really care for the military handbook.
For deep stuff try the papers available at
www.jolr.org (the Journal of Lightning Research).
Shane
I have a copy of MIL-HDBK-419A on my desk
I haven't seen motorola or polyphaser's documents, but I speak fairly regularly to some of the nations top power experts, and none of them had mentioned this, even when we were specificlly discussing grounding at RF facilities. I was curious where the theory to break the grounding loop at come from, because it sounds wrong.
It is in Motorola R56 site grounding. It is in a addendum released 2005 I think. My copy has the Ver# and release date but to smeared to read. (a COPY) I will see if I can find a better copy or a source online. This is a recent change and is not in the original R56. Robert