Grounding Do's Don'ts & Why Part 1
The purpose of this thread is to clear up some of the confusion I see Ham operators go through with respect to proper equipment grounding techniques. It is also to get into some of the Doí Doníts and Why.
Grounding is a terrible word and one of the most misunderstood subjects there is in the electrical and electronic disciplines. The word GROUND itself is misinterpreted as most think it has something to do with earth or dirt when in fact it may or may not. So after 33 years as an EE with Telephone, electrical, and broadcast communications I wanted to take the opportunity to discuss the subject and maybe help some folks out
With respect to Amateur Radio operationsí ground falls into three major systems of; Safety, RF, and Lightning Protection. All three are different systems but common. DO NOT FALL into thinking they are 3 separate isolated systems, because they are NOT. If electrically isolated from each other is a guarantee of problems, some of which can cause fatalities and serious property/equipment damage. So this is where I will start.
As stated I see many folks who think they have to keep the Safety, Lightning, and RF Ground isolated and separated from each other. They have come to the impression that keeping them separate from each other will somehow make the system immune from noise, when in fact is creates electrical noise and some very serious safety problems.
From a safety and operating perspective the huge risk is what is called Gradient Step Potential differences. Step potential differences are caused by stray currents running through the earth. The earth is a very poor conductor of electricity with high resistance and current flowing through resistance produces voltage differences. The two major sources of this current are our public electric utility grid, and lightning. In addition wiring mistakes by man contribute to the currents.
Utilities use the earth as a conductor because it is much less expensive than wire. They use what is called a Multi-Grounded Neutral. At every forth pole or so (1/4 mile) they bond the small neutral conductor to a pole or tower ground. This causes normal load currents to flow in the earth. Utilities are the only ones allowed to use earth as a conductor. NEC forbids earth to be used as normal current carrying conductor. The reason why is the utilities operate run at very high voltages, and consumption is at very low voltages of 600 volts are less.
Lighting does cause very large amounts of current to flow in the earth with cloud to ground strikes. This is where the term Step Potential is derived from. You have certainly heard over the years about lightning striking a tree, and people in the vicinity that were not directly struck were either killed or injured. What is happening when a tree or object is struck, the current flows outward away from the point of where it enters the ground along the surface. The distance between your feet is enough resistance coupled with the very high current flowing to develop enough potential voltage difference to kill and injure. The voltages can reach the 10ís of thousands of volts.
The same Step Potential occurrence happens in electrical substations when the high voltage lines fault to ground. Extremely high current flow and workers in the yard are killed. In all electrical substations there is what is called a MESH GROUND Mat just underneath the crushed gravel. It is bonded to all the steel framework and ground rods spaced evenly around the yard to minimize the Step Potential differences. Yes Ground Loops are a very GOOD THING as it forms very low impedances between any two points
OK hopefully it is now apparent why you should not have your grounding systems isolated, and why the Electrical Code requires all the various grounding systems to be bonded together. It is to have a planned path to limit the voltage difference. Otherwise all the systems come together inside you shack. When the difference becomes high enough it will find a path to equalize. It will equalize either through you or the equipment. Even under normal operating conditions the potential differences are noise. Any unwanted signal or voltage is considered a noise, and can interfere with radio operation.
The trick is where to make the bonds. Well that is simple follow the Electrical Code as it is written. All ground electrodes must be bonded together to form a single ground electrode system. This is done outside by digging trenches, running the bonding jumper underground to bond the various systems together.
Later we can discuss techniques and topologies to use inside the shack.
Originally Posted by KF5LJW
I certainly hope you will QUICKLY follow up with Parts 2, 3, 4, and perhaps 5.
There's a telling but dangerous saying that "A little bit of knowledge can be a dangerous (or fatal) thing."
Unfortunately, in improperly installed ground system can be at least as dangerous as no ground system, so we need the complete follow-up.
To comprehensive of a subject to cover in 1 thread. The point of this one is all th esystems have to be bonded together to make a single Ground Electrode System. It is the foundation or first building block.
Originally Posted by WA9SVD
Originally Posted by KF5LJW
DEFINITELY understood; it's the ONLY way to even start effective grounding, with SAFETY involved as the building block to an effective system.
I'm currently trying to find the one, true utility ground at my location; there are conduits that go under the foundation of the house, and then there's the add-on addition that has it's own separate breaker box, but seems to be the entry point for the current electric co. wires.
Verizon FOIS just added a clamp to the Electric Co. Meter Panel on the addition; but that's not part of the original electric system, even though the old breaker panel (on the original part of the house) still carries some breakers. (Not sure if those are now "downstream" from breakers installed on the addition where the service enters the residence.)
Sometimes I wonder (READ: WORRY!) because about half of the house is still original (1940's) two wire outlets, and I have no way of knowing if ANY 3-wire outlet in the house was actually wired (or safely wired; some seems to have been a "DIY" project) as such, or if there's any true ground provided with even those 3-wire outlets!
Ok that is easy to find assuming your house wired correctly to code. It will be at the main disconnect from the utility service. Many times this will be the meter box itself, if not there inside the main breaker panel fed directly from the meter box.
Originally Posted by WA9SVD
As for Verizon Fios, CATV, Telco ect. they know the code and what they know is the Ground Electrode Conductor (GEC) for the service is bonded to the meter box as it is required.
As for the new addition, again assuming it was wired to code, the downstream panel is just a breaker panel with only a Equipment Ground Conductor, not a GEC. What they did is run 4 wires from the main breaker panel where neutral and the GEC were bonded together. You should have L1, L2, N, and G.
Real easy to tell with a DMM and something like blow dryer to test the ground in a 3-wire receptacle. First measure the AC voltage between the Ground Pin and Neutral. The voltage should be very close to 0 Volts. Now plug in a blow dryer set to the highest power level and read the voltage again. It should indicate a voltage of 3 volts or less. What you are measuring is the voltage drop induced on the neutral conductor from the main panel where N and G are bonded together.
If you see 0 volts with a load you have a Jack Leg ground meaning the electrician bonded the N-G together in the receptacle or somewhere close which is a huge No-No as the ground circuit is not intended to carry any load current and is dangerous. If you see phantom voltages you do not have a ground.
Originally Posted by KF5LJW
Here's where Murphy always raises his ugly head! My tower is in the back yard. The ham shack is at the very back of the house.
The electrical feed is at the front of the house! The main disconnect and ground point is at the front of the house, in the basement.
I guess I'm supposed to run battery cable sized copper wire the length of my basement, out and across a concrete patio to connect to the base of my tower.
Oh well, who said life is supposed to be easy?
Depends on what you call battery size cable and how your house is constructed.
Originally Posted by VE3EKJ
Supplemental electrodes are required to use a minimum 6 AWG copper or 4 AWG aluminum. I get the impression you are stuck inside the box thinking it is to physically go all the way to the AC service meter box which is not trueor nessecary. You just have to tap into the electrode system the house uses which are many and how your house is constructed. For example get to one of the water pipes or rebar in a concrete foundation as both are required to be used as electrodes in all new construction.
There are other methods of establishing a new ground point using a transformer.
Well, the house was built in the 1950's, near as I can determine. And although there is still some of the original copper piping installed much has been replaced with that new plastic PEZ tubing. I have no idea why but the previous owner had replaced the copper at the point where the water service entered the house with plastic, running about 12 feet before connecting to the original copper, and back to plastic about 12 feet further from that!
Originally Posted by KF5LJW
I've been in the house for a year now and I am still finding plumbing and particularly electrical things that are "loopy". It keeps me busy but it is an aggravation. I do like 3 wire outlets to actually have a ground wire running to them!
Obviously the plastic at the service entry breaks any ground path. He did have a real electrician install a new main disconnect and breaker panel and that electrician ran a number of solid conductors to strap the ground at both ends of that run of plastic, restoring the path. Unfortunately, further down the copper ends and its back to PEZ.
I've read in these threads that the service/breaker panel is supposed to be the common ground, which is why I was grumbling about a long run from the tower in the back yard. The simplest thing to do would be a ground rod at the tower, with a 10 ft run of large gauge wire into the shack and strapping the antenna tuner to it. The tower is a 40 ft self supporting Delhi, with a hinged base of welded angle iron and LARGE hinges to allow it to be tilted up or down!
The hinged base is mounted on a yard square piece of metal "checker plate", with some pieces of rebar welded on the bottom that have 90 deg bends. to allow more adhesion when dropped into a 3' x3' slab over 6" thick. Under the slab are 4 poured concrete "pillars" about 4-5 feet deep, each with a length of rebar extending up into the top slab "cap".
So it's a metal tower on a metal plate, onto a large slab with 4 deep legs each having a long piece of more metal in the form of rebar. Hopefully this will provide some ground protection. Adding a true ground rod beside the plate is no problem.
The specs called for a full cubic yard of concrete as a base, but of course Delhi spec's the same for a 40' tower as for their 80' version! having worked with engineers before I am quite familiar with their "overkill". My method was easier, since there was no way to get the concrete into my back yard except the hard way, mixing by hand in a wheel barrow. The soil is such a hard clay that in my younger days working in a concrete lab we actually made a test cylinder out of it, just for laughs. It actually withstood over 600 psi before it broke!
So my method used 16 bags of pre-mixed concrete, which still made slightly over 1000 lbs as a dead anchor weight to the base. Since I am using it simply as a support for wire antenna I don't expect any problems. The only wind resistance comes from a small UHF TV screen array for direct OTA television reception.
That's my situation and although it doesn't totally fit the various codes discussed in these threads I'm hoping I' reasonably safe! If someone has noticed something truly dangerous I would appreciate it if they pointed it out!
Well as I discussed if those ground electrodes are isolated and al lmeet inside your shack is dangerous IMO. Lightning does not have to strike your tower, house, or even your property to be dangerous. It can be your neighbors tree or a utility pole.
Originally Posted by VE3EKJ
I beg to disagree that the telco, cable television, etc., personnel know how to properly ground! Now they might "supposed to know" how to ground, but either many of them have forgotten or never learned correct techniques.
When I was with TXU, as one of the 4 RCDDs employed by the company, a significant part of my job was to inspect, and approve data, telephone, etc., installations before the contractors got paid for the job. During the last 2, or 3, years I was there, TXU was redoing the data installations in virtually all of their offices in the service area which encompassed almost half the State of Texas. The data contractors soon learned how to install ground connections but, unfortunately, most of the telephone installers never learned. Since the telephone employees reported directly to the telephone companies, and since the telephone companies demanded payment or else they would "cut off" the telephone service, there wasn't much that could be done except to redo the ground connections after the telephone company had finished.
In the larger offices, it became standard operating procedures to have the telephone lines brought into a "demarc" and then the switching equipment, individual telephone lines, and so forth, installed by TXU technicians. This was done so as to have as little problems as possible with the installations. The telephone company supplied the outside lines and TXU furnished the switching equipment, individual telephones, etc. Doing such produced a LOT less "headaches".
I have seen ground wires run in all sorts of geometric configurations, some with as many as 50 right angle bends on a 24 inch by 24 inch backboard! The geometric patterns might be "pretty", but they absolutely presented nothing that would protect the telephone system from lightning strikes, etc. I really believe that ground wires were provided in specific lengths and the telephone installers thought that every inch of the wire had to be used even if the actual length required was only a few inches!
There are numerous telephone and cable connections made in my neighborhood that consist of a piece of perforated metal strap holding the stripped end of a ground wire, no heavier than 14 gauge, often lighter, clamped directly to the conduit going to the AC mains meter. The metal is held in place by a machine screw run through a perforation at each end of the metal strap and the machine screw is tightened to hold the strap in place. It doesn't take very long for the copper wire to become corroded where in contact with the galvanized metal strap as well as the metal strap working loose.
The result is that I NEVER trust an employee of the telephone company or cable television company to properly install the grounds. I just let them "do their thing" and when they leave I just redo the grounding to meet BISCI standards!