Grounding can be a very complex source of problems and life threatening hazards. Figuring out whether this is something you can resolve yourself without injury or if you need a professional can be difficult. The key to most problems is multiple ground points and this may require the use of an adapter to prevent the third pin, ground, from being connected or a device which isolates an antenna cable input ground from your system.
Commercial, Industrial Equipment
Grounding in these cases is typically about safety and it is imperative that it be done correctly or somebody could be injured resulting in legal damages that your insurance may not cover. Bypassing the grounding pin is not recommended. I am talking about refrigerators, mixers, temp controls, microwave ovens, sump pumps, AC and DC drives, etc. If a piece of equipment supports the third pin you better use it. If this is causing a problem get an electrician, you need professional help.
Professional Equipment
Grounding in these cases is typically about noise. Defeating the ground pin on these products should not cause safety problems but this could affect signal to noise ratio within the system. It is not common to have grounding problems with this type of equipment since most of it is designed to properly use the AC ground circuit.
Consumer Equipment
Most consumer products do not support the third grounding pin. For those that do there are varying ways manufacturers apply this circuit to their products. Unless you have a satellite or cable receiver this is typically not a safety issue but defeating the ground pin could increase noise in the system as well as improve it. This will depend on how the ground was designed into the equipment and what your application is. Many products with a ground pin also use an AC input PIE filter to prevent contamination of noise from either the product or the AC source. Just because a product has such an AC cord and input jack on the back means nothing without opening the product and inspecting the AC input to see what is really in there and how it is being applied. Often times the ground pin is tied to the case of the product which unfortunately is also tied to the actual circuits within the case. Professionally this is wrong unless there is a switch to disconnect the ground pin from the case or the circuits from the case.
Surge Suppressors, Lightning Arresters, Line Conditioners, AC Synthesizers
Defeating the ground pin on these devices will defeat the very purpose they were intended for. DO NOT defeat the ground pin on these products. One more time, DO NOT defeat the ground pin on these products.
Computer Equipment
Do not defeat the AC ground pin on computers. Computers are great at generating RF noise that can interfere with other products in your home. That is what that sheet is all about with the FCC codes and warnings that you get when you buy one from a turn key retailer.
Trouble Shooting Safety
When you work with grounds you must follow the old rule of one hand in your pocket and rubber sole shoes such as tennis/sports shoes. Electricity kills you by running across your chest area based upon what two objects the two parts of your body are touching with the most common being hand to hand or hand to leg. So when you remove a cable DO NOT touch something else with your other hand while unscrewing it; One hand in your pocket. I have been shocked numerous times throughout my career doing nothing more than making me know I am alive and grumpy. Only one time have I been severely electrocuted and I ‘ll give you three guesses as to why that happened.
Hazardous Ground Loops
This is what most folks are trying to get rid of due to noise or hum in an audio or video system. There is another much rarer group that were shocked by a ground loop and another very teeny tiny group that did not live to talk about it. A ground loop is caused by a voltage being referenced to two or more different potentials or grounding points when it should be referenced to one and only one grounding point that is common to the earth, your AC power and any antenna system. A proper ground means that you can touch it with your bare feet on concrete and you will not be shocked in the slightest because there is no potential difference in voltage.
The following is for those who have electronic products associated to one room or electrical circuit. If you have multiroom distribution for sound and video then you should consult a professional if you are having a problem.
The most common ground loop is caused by an outside RF antenna, cable service or satellite service and will be called the antenna cable for the rest of this article. It is not uncommon for these antenna systems to be referenced to a different grounding rod than your AC power. In most cases this is not a safety hazard and just an annoyance. This can be checked by simply disconnecting the antenna and see if the symptom goes away. If it does then touch the barrel of the connector to the input jack you removed it from and if you see the slightest spark then you have a potential grounding hazard. Sometimes though they are so far apart in electrical relationship that a potential voltage difference is high enough to shock you. Keep your other hand in your pocket! That is a safety hazard that must be addressed by a professional. If this is not the case then you can proceed with trying to resolve this yourself. If you are using an outside antenna or cable you can use a product called a “Magic Box” that will isolate the antenna cable from your antenna input using a transformer and is the preferred method. If using a surge protector this product is installed on the output antenna connection going to your TV or set top box. If you are on satellite you cannot use this product because satellite feeds a voltage on the antenna cable that requires devices that use a direct connection. In this case you need to find out where in your system is a product using a 3 prong AC cord besides the satellite receiver. Install an AC ground adapter and the problem should be solved.
FOR YOUR SAFETY you must have at least one ground reference for your equipment if you have an antenna cable. A ground reference is a properly grounded antenna cable or an AC strip, surge suppressor, lightning arrester, conditioner, synthesizer that everything plugs into and uses the third ground pin from the AC wall plate/plug. These conditions will vary depending on the complexity of your system.
Annoying Ground Loops
Most consumer equipment does not have the ground pin but some do and depending on your application may be the source of a ground loop. First step is to understand that every electronic product must be referenced to a common point we call ground. This can be floating, very common, or referenced to the AC power or an antenna cable. For this example it is floating and an antenna cable is not being used in the system. So lets say you have a component audio system and your CD player is one of those hi-end jobs and has a three pin AC cord and this is plugged into your wall outlet. It runs to a preamp and from there across the room to power amplifiers which also have the 3 pin AC plug and they are plugged into a different wall outlet. More than likely this system will have a hum problem due to a ground loop. The ground of the interconnect cables creates the correct reference point between the components. Like most consumer products the CD player and amps have tied the circuit and case to the ground pin of the AC plug. This creates another ground connection using the house wiring between them. This creates a ground loop between the interconnect cables and the house wiring and ground current is divided unequally between them. This is what causes the hum because the circuits no longer have a clear ground reference for the signals connected to them. This is easily resolved by defeating one of the ground pin of one of the plugs. Another method, quite rare, is that one of the units has a ground switch that will disconnect the circuit ground from the case. This will eliminate the ground loop while retaining RF shielding for the circuits because the case is grounded via the AC cord. Even if you disconnect the ground pin on a unit the case is still performing RF shielding provided you have at least one unit in the system connected to AC ground. With that information you can also see why you would not want to float a system where you want the best performance. You would not have any RF shielding.
Finally
For most consumers this is plenty for what they are trying to achieve which is the removal of hum in the audio or rolling bars in the video without compromising safety. If performance is important then I cannot recommend enough you get with a home theater specialist such as an ISF or HAA calibrator or hi-end home theater store. Grounding is complex and there are other concerns that can only be handled individually by a professional sometimes requiring modification of equipment, electrical repair or reinstallation of the antenna cable.
Richard F. Fisher
Have you been calibrated? ISF and HAA Trained
Mastertech Repair Corporation, Lawrenceville, GA
770-513-3987 E-Mail - help@mastertechtv.com
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