Grounding By James Goss      Grounding is a term that we hear a lot about when we are dealing with electrical and electronic systems. It may be one of the most misunderstood terms associated with these fields.  It is referred to as grounding because in some electrical systems one of the conductors is actually connected to earth, thus the name grounding. Because of this term being used to a great extent, it is also used in systems that really are not referenced to ground. A lot of electrical and electronic systems are actually floating above ground, as far as potential goes, and has no reference to earth ground at all, but the term ground is still used to describe it. Because earth is a common reference point for all the electrical distribution systems, a common point for an electronic circuit board is also referred to as ground. Before I discuss grounding in our models, I would like to give you some background information that will help us to understand the term ground.      Most everyone is familiar with the automobile so I will use that as an example. The 12-volt battery in your car provides all the onboard systems with their voltages. The negative terminal of the battery is connected to the chassis of the car. The chassis being of metal acts as a conductor of electricity, it's not a good conductor, but being so large in size makes up for that deficiency. Any electrical load in your car, such as the radio, will also be connected to the chassis of the car. This provides a reference to the negative terminal of the battery and is the same as connecting a wire from the battery to the radio. The hot wire from the battery comes through the fuse block and has a fuse in series with this wire for over current protection. The chassis connection is referred to as ground, even though it is not really connected to earth ground. It is interesting to note that the positive battery terminal could be referenced to the chassis instead of the negative terminal. The system would work just as well; of course all loads that are polarity sensitive would need to have their polarity reversed for them to function normal. Some old autos did use positive ground and you may still run into an old tractor that is still going strong with a positive ground. With the positive lead connected to the chassis, it is still referred to as ground. Actually, ground can be any potential because it is only a reference point. In electronic systems we find both negative and positive grounds being used. So don't expect ground to always be the most negative point in a circuit.      In the electrical field, branch circuit wiring is used to distribute the 60 Hz power from one point to another. The requirements for branch circuit wiring are the same regardless of the type structure involved; residential, commercial, or industrial. Those requirements are to get the energy from the main distribution point, which is the main panel board, to the individual receptacle and lighting loads throughout the building. This distribution of power must be carried out in a manner that is safe.  My motto is “make it safe then make it work”. The National Electrical Code (NEC) has specific rules that all must use when installing electrical wiring in order to be safe. There have been more people killed by 120 volts than any other voltage known to man. I realize that our models are not going to electrocute us, but this information will give you a better understanding of grounding theory. The most important aspect of making a system safe is to use proper grounding techniques.      In building wiring we have three types of ground terminology used; systems ground, equipment ground, and neutral ground. The systems ground is referring to the earth ground at the service entrance to the building. This is where the building's electrical is connected to earth ground by a driven 5/8 inch ground rod being placed 8 feet in the earth, and also if metal water pipes are used in the building, they too must be connected at this point. Having an earth ground at this point assures us that if the neutral conductor from the transformer opens for any reason, the grounded equipment will not take on a potential in respect to a ground. Also it guards against lightning if it decides to strike your home or building. The water pipes in your home must be grounded because they are conductors of electricity. If they were not grounded and a hot-wire made contact to the pipes, the pipe system will be just as hot (electrically hot) as the hot wire. Can you imagine getting into your shower with this condition? It has happen many times and will continue to happen in the future. If the pipe system had been grounded, the circuit breaker would have tripped the instant the hot wire made contact with the pipes.  So you can see that grounding in buildings is required for people safety and not for equipment protection.     In building wiring, the equipment ground is also known as the grounding conductor and is bare or green in color. It is this conductor that connects to the chassis of your equipment being used. The electrical color-code is very simple, any color can be hot except white, gray, and green. White and gray is reserved for the neutral conductor and green is for ground. The hot conductor is referred to as “hot” because it measures 120 volts in respect to ground. The neutral is referred to as neutral because it has no voltage on it (neutral) in respect to ground. In electronics, black is the ground conductor. In the electrical field, black is a hot conductor. In years past the two fields, electrical and electronics, was far apart in applications. Today, they have become very close to each other, especially in industrial environments.        The equipment ground conductor will never pass current unless a fault occurs on the system. If a hot wire touches the chassis of a grounded appliance anywhere in the system, the circuit breaker will trip. If the chassis was not grounded and someone touches that piece of equipment, they could receive an electrical shock, just like in the shower above. So the idea of an equipment ground is to prevent people from receiving an electrical shock if an appliance becomes faulty. Lets take your refrigerator for an example and say that it is not grounded the way that it should be.  If the line cord on this appliance got pinched and the hot wire makes contact with the chassis, the circuit breaker will not trip and the chassis now has a 120 volt potential on it in respect to ground at all times. If you touch the refrigerator and are also touching a ground, you could get electrocuted. So the purpose of the equipment ground is to protect people from an accidental electrical shock.  Take note that the equipment ground is independent of earth ground. The earth ground can be lost and the equipment ground will still trip the breaker during a fault.      The neutral conductor is the third type of ground that we find in building wiring. It is also known as the grounded conductor because it originates on the neutral bar in the main panel, and the neutral bar is connected to earth ground. The neutral conductor does just as much work as the hot wire and is just as important. It is white or gray in color, normally white, and passes the same current as the hot wire.  If you want to get 120 volts, you must have a neutral conductor because it is connected to the center tap of the transformer that supplies your building, and this point is connected directly to earth ground. Every branch circuit must have a neutral conductor if it is to be 120 volts.      The whole idea of grounding theory is to prevent two pieces of equipment from having a voltage difference between them. If you tie both of them together electrically, then it would be impossible for a voltage difference to exist. Two objects that have the same potential will not have current flow between them. They may both be electrically hot, but if they are at the same potential, the voltage difference between them will still be zero. Just like a bird setting on a 13,000-volt power line. His body, and the wire that he is sitting on, both have the same potential, so no current will flow through his body, there is no circuit. There must be current flow between two points in order to have a circuit.  But take the squirrel that is walking down the power line and comes to a transformer. He decides to step across to the lightning arrester, which is grounded, and gets blown to smithereens. The instant he touches the top of the grounded lightning arrester, 7600 volts is across his body.  This is the phase to neutral voltage on a three-phase distribution system.         It is obvious that when we speak of ground in our airplanes that we are not in reference to the earth, but instead we are in reference to the negative 4.8 volt battery lead, the black lead. This lead would be like the systems ground mentioned above. It is the common reference point for all of the voltages used by the receiver. Actually any auxiliary equipment on board should be tied into this common ground. Remember that the common earth ground on our power line distribution system assures that all 120-volt loads will receive 120-volts, this is what makes it a balanced system. Having a common ground on the receiver will do the same thing for us. It will maintain the correct voltages needed by the receiver. If it was not for common grounds, the voltage drops that should be fixed throughout the circuit would depend on current flow at any given time, and the resistance of the load. As the load changed, so would the voltage drops. Now you might think that all the loads are fixed in our receiver, but as the amplifiers handle more and less signal, they change amplification levels constantly. This means that the transistors are passing more or less current through them, so the load is always changing. The common ground in the receiver is fixed and we can do nothing about that, it is taken care of. When we plug the battery into the receiver, it connects to a common voltage bus that distributes voltage to all the servos as they are plugged into the receiver. When you plug a servo into its receiver, both the ground and positive supply voltages automatically connects to the servo.       If all the metal parts that we use on our models were grounded to a common point (equipment grounding), then there could be no voltage difference between them. I am talking about grounding everything to the negative terminal of the battery. This would include the receiver, all-auxiliary batteries, electrical pumps for smoke, metal push rods, main landing gear, extension lead shields, tail wheel bracket, nose gear, the wood fuselage and above all the engine. Any thing that is a conductor of electricity will be bounded together. Again, being tied together will prevent any voltage buildup between these components. Now you may wonder how the main gear or the engine could develop a voltage if it is not connected to any voltage system. The answer is static electricity.      We are all familiar with static voltages from experiences such as walking across carpet and then receiving a shock when you reach for the doorknob. Also getting out of your car and sliding across the car seat, when you touch ground and then the car door, you again receive a pretty good shock.  Not to mention the king of all static voltages, lightning. You may not realize it but your body can charge up to about 50,000 volts and you will not even be aware of it, that is until you discharge to another object and it scares the heck out of you. It takes about 10,000 volts to arc just 1/8 of an inch. When you touch the doorknob and have an electrical discharge of ¼ inch or more, you have just had a 20,000 to 30,000 volt discharge. It is the friction between your body and an insulator, such as the carpet that creates the charge. Any object that is in motion and is an insulator is capable of developing a high voltage static charge.      Our model airplanes will also develop an electrostatic charge, especially when they are in flight. The friction between the airplane and the molecules of the gasses that make up the atmosphere is what creates the static charge. Insulators will charge up better than a conductor, but even a conductor that has no path to discharge will also charge. The landing gear is a good example of a conductor that has no place to discharge, other than to the wood fuselage. If the gear is charged when you touch down for that perfect landing, there will be an electrical discharge between the wheels and earth when the plane gets close enough to the earth.      I have checked the electrostatic charge on some of my models while they were sitting on the ground. Before the engine is run there is little or no charger present. I was using a device called an electroscope to make the measurements. This is a piece of equipment that you don't see being used very often. It is mainly a laboratory type tester, but very simple in use and works fine for experiments like this. After the engine was running, a definite charge was seen on the engine area. Now this was on a very humid day that makes it hard for a static charge to build up, plus the plane was in contact with the ground by way of the wheels. This was a constant discharge on the plane electrostatic field. The electroscope being only inches from the ground makes it very hard to get a reading from the scope. I need to try the same experiment with the plane about three or four feet above the ground and have the plane sitting on styrofoam.      The prop turning at such high speed is sure to develop a lot of static buildup. Let's say that you are using a metal push rod with a nylon clevis to control your throttle. The push rod runs very close to the engine, but is insulated by the nylon clevis. If the engine develops a large enough static charge it will arc over to the push rod. This little arc over could interfere with your radio in the form of a glitch. It may give you that beautiful knife-edge snap roll you have wanted to see, and then you would wonder where it came from. You may announce to everyone that you just got hit from another signal in the area. You would be right about getting a hit, but it came from your own plane. I am sure this is common with our models, especially on a cool dry day. This is when static is at its best, the dryer the air the higher the voltage. Moisture is the number one enemy to static build up. You do not have to worry about static on a hot humid day.      You have all heard that you should not allow two pieces of metal to rub against each other or it may generate interference in your radio equipment. When two metals such as a metal push rod and the metal control horn on the engines throttle rub together, there is an electron transfer between the two metals, thus setting up a potential difference between them. This transfer of electrons is in the form of a current flow, and any time you have current flow there is a magnetic field associated with it. This magnetic field is radiated and picked up by the antenna. The faster the two metals vibrate and rub each other, the more current flow there is. This is very easy to prove by using this simple experiment. With your engine not running hold two pieces of music wire, one in each hand close to the antenna. The music wire should be about the same length as your antenna, about 41 inches long. Diameter is not a factor, other than they should be rigid enough to support themselves. Hold the wire as closet to your plane as you can and softly rub the wire together. You will hear your servos chatter in response to you rubbing the wires. This proves that it takes very little radiation to affect our planes and any static discharge can very easily duplicate the above experiment.         By connecting everything together, including the high resistance devices such as the fuselage, no arc over is allowed to occur. But the plane as a unit will still take on a high static charge while in flight, and if it comes near to any other object, such as earth during a landing, a discharge will occur. To prevent this we could install static wicks on the trailing edges of our control surfaces. Static wicks are used on full-scale planes to prevent exactly what I am talking about here. You can build a static wick by taking a piece of number 12 awg copper stranded wire (or smaller gauge) and cut it about 2 inches long. Unweave the strands on one end and make a brush out of it. The other end can be connected to the airframe. The brush points to the rear of the plane.     Voltage has a tendency to discharge from a sharp pointed object more readily than from a blunt object. This is due to the concentration of the electrostatic lines of force at sharp points. Take the lightning rod for example, it always has a sharp point on it to allow the electrons to enter or escape with less resistance. When a charged cloud comes in the area of the rod, a small stream of electrons will travel from the rod to the cloud or from the cloud to the rod, depending on the polarity of the cloud. This small trickle of electrons will neutralize the cloud before it has time to build up to a violent discharge.      Another example of preventing static discharge is found on your car radio antenna. I am sure you have noticed the little ball on top of the antenna. This ball is known as a corona ball, and is there to prevent an electrical discharge from occurring at the top of the antenna. Driving down the highway with the antenna directly in the wind will create an electrical charge on the body of the antenna. The top of the antenna having the sharpest point would allow electrons to arc into the air around the tip of the antenna. This arcing into the surrounding air is known as corona. Corona will show up in the radio system as static noise or popping in the sound system. If it happens on an automobile you know it can happen on our fast flying planes.        I had a question the other day from a gentleman in Canada concerning grounding his model. He wanted to know if he could use shielded audio cable from radio shack to build some extension servo wires in his plane, and how to ground the shield. Shielded audio cable normally has two conductors enclosed in the braided shield and he would have to use the shield as the ground wire to the servo. Three conductor shielded cable would be better because all current caring conductors would be totally enclosed in a grounded environment. To ground the shield solder a pigtail (a small jumper wire) to the shield and attach it to the common negative battery lead. Be sure to ground the shield at the battery end only. If you ground the shield at both ends you may have a loop current flowing between the negative battery lead and the shield, this would create noise instead of preventing it. I guess the shielded leads would be the best way to prevent noise pickup, but the noise buffer is really easy to install. It uses common mode rejection to cancel unwanted signals. Of course the buffer uses electronics and that is more parts to go bad. The fewer parts used, while maintaining a good safe system, the better. Now I know it sounds like a lot of trouble to get everything on your plane connected to a common ground point, and it is, but you just may have the ultimate radio system if you did.