Grounding: that strange, annoying noise

We have often discussed how aspects that have nothing to do with the equipment itself affect the final result of our installation. For example, Luis Llana treated us to a series of basic articles on acoustics, in which we looked at some of these aspects, and we also know that different loudspeaker placements improve or worsen the listening experience. But there is another important issue that often goes unnoticed: the mains power. All electronic equipment needs power to operate, and the vast majority relies on the "wall socket". Unless portability is needed (as with remote controls) and exhaustible sources can be used (such as disposable or rechargeable batteries, although their cost per volt is much higher), the best and most common approach is to connect them to the mains. Nowadays we can find a socket in almost every corner of our homes, a luxury we have grown accustomed to all too easily. We know that power is "transmitted" through two wires, forming an endless loop that is necessary for it (volts and amps) to be useful to us. But there is a third wire, also essential, that ensures we are not literally left "stuck" when an accidental electric shock occurs: the ground. Even so, some people only become aware of its existence when their system produces strange sounds or their projector shows annoying continuous bars on screen. Is the ground to blame? If it causes these problems, why don't we just do without it? Let no one even think of it. There are other methods.

Energy is indispensable today. Everything has a plug or a compartment for batteries. The cheapest form of energy is electricity, cheap to produce, transform and distribute, although the installation costs, at the time, are quite high. But it also offers higher efficiency than the thermal energy used at the beginning of the last century, in the midst of the industrial revolution. Producing electricity costs us very little: hydroelectric, thermoelectric, nuclear, solar, wind, tidal and geothermal power plants, and so on. From its source to our home, into a simple plastic socket that we have grown used to living with. We could even say that we need it. From the moment we get up, we are surrounded by electrical appliances: alarm clocks, coffee makers, water heaters, elevators, electric doors, cell phones, computers, lights, stoves, refrigerators... and our home theater system, the stereo and the video projector. I'm sure many of you have had an electric shock at some point and, no less importantly, are still alive to tell the tale. How can that be? And, more significantly, what does this have to do with our hobby?

Every modern electrical installation needs three wires. We have all seen the four cables that run through our cities, hanging along building facades (although, for aesthetic reasons, many city councils have finally decided to bury them). In the past, and it is still quite common, a 220 V three-phase configuration was used for power distribution. Three-phase means "three phases", although there are four wires: the neutral still has to be defined. Each of these phases has a potential of 120 V, while the neutral has a potential of 0 V. In fact, the neutral is like the "ground" of the power station in question. To obtain current, we need a loop that allows electrons to flow. By choosing one of these phases and the neutral, we obtain a potential difference of 120 V: we now have current. Many will remember the days when you still had to know whether a socket was 120 or 220 V. Today, on our continent, all equipment runs on 220 V, for the sake of a standardization that made it possible to save costs in the manufacture of electrical components. To obtain 220 V in our homes with the old three-phase system, the connection was "tapped" between two phases, obtaining the desired voltage. Little by little, the 220 V three-phase system has been replaced by the 380 V one, needed on the one hand by industry, which increasingly demanded more powerful machinery, while at the same time making it possible to obtain the desired 220 V in homes. We are now once again connected to the neutral, since each phase has a voltage, roughly speaking, of 220/240 V (if we connected between two phases we would get the 380 V used by industry or by the elevator in our building).



GROUNDING: AN ALLY AT HOME



Do you remember that dry, sunny day when you touched the refrigerator door and got a shock? Our body conducts electricity, but if it is dry it can even act like a rechargeable battery. We are constantly building up static charge and, like any form of energy and like everything in nature, it seeks a normal state: rest. An electric charge literally wants to discharge, and it is always looking for zero potential difference: the Earth. That is why lightning strikes during storms: the clouds become electrically charged and our world, at a potential of 0 V, attracts that current in the form of lightning.

When electric current leaves its normal path (for example, because a piece of equipment malfunctions due to an accidental short), it seeks a way out toward the point of lowest voltage. If at that moment we accidentally put our hand there and, remembering that we are conductive, the current may pass through us in search of the point of lowest voltage: the floor. The result can be disastrous and could even kill us. In addition to designing equipment circuits and power supplies properly, the safest system of protection against electric shocks in our homes is grounding. In this way, we provide all equipment with a "mandatory" escape point that will generally attract all stray currents.

The ground connection is as simple as its name suggests. Every building has a 0 V point in its installation, usually in the ground beneath it, consisting of a series of copper rods surrounded by conductive material. The intention is for this to be the lowest possible voltage point. Fortunately, all of this has been explicitly regulated for years, so our safety has generally been assured for a long time. There is another element we cannot ignore either: the residual current device.

Next to the various circuit breakers in our homes (roughly speaking, switches that are somewhat more sophisticated than usual) we find the residual current device. This is one of the most important safety switches in the home. Its circuit constantly analyzes the current in the loop (incoming and outgoing). Incidentally, you should know that it is not voltage that "bites" us, but amperage (or current). When the incoming current is greater than the outgoing current, part of the current is "leaking" from our installation, so the residual current device immediately cuts off the power supply. For domestic use, it is set to "trip" when the difference is equal to or greater than 30 mA and to cut the power in less than 50 ms. This will not spare us a huge fright, but it will spare our lives. The system cannot detect the dangerous leak if there is no ground connection, since in that case the current finds no way out and lies in wait to discharge all its potential through our body. But what does this have to do with our hobby?

Sometimes we have heard an annoying noise from our system, a low, continuous hum, or a sporadic one when, for example, someone switches on a light on the other side of the house. What is going on? If we have no ground installation, the first and most important thing is to have one installed, and this can only be done by a professional, something we strongly recommend. But even if there is a ground connection, we may not escape the problem. There are two possibilities: the equipment has been badly installed or, most likely, the ground does not have the necessary neutral potential. We have already seen that current seeks the lowest potential to complete its path, and if there is any point in our installation whose potential is lower than that of the ground, the current will inevitably head toward it. It may be the amplifier or, worse still, our body (which is "connected" to the floor, another ground) when we touch the amplifier's volume control, for example. When this happens, it may well be because we have inadvertently created a loop between all the equipment in our home, including not only the audiovisual equipment but also the other appliances such as the refrigerator, the lights or the hair dryer. Every time we connect one piece of equipment to another (audio cables, video cables, etc.), we also do so from an electrical point of view. This affects the path taken by wasted current (including leakage to chassis ground, which is nothing more than low-voltage current lost by many circuits and dissipated in the chassis as heat) and can cause annoying playback defects: random or constant noise in the audio, or artifacts in the video image.



HOW TO FIX IT



First of all, as we said earlier, by checking that the ground connection is correct, something we will do with our electrician or a qualified professional at our side. But we can also take the precaution of checking that all the connected equipment is properly grounded and does not form loops. The losses or leakage from a DVD-Video player, for example, will be much lower than those from a power amplifier. The latter works with higher voltages and currents in order to literally move the cones of a loudspeaker. The amplifier therefore needs a safe and reliable ground connection. One way to avoid noise and artifacts is to "lift" the ground. This breaks the loop that causes the stray current to affect the equipment, but it is a totally inadvisable measure, since it opens up the possibility that any harmful electrical leakage could end up passing through our body. We should certainly never, ever, think of lifting grounds unless we are certain that one piece of equipment is connected to another including its chassis ground. In that case it is appropriate, and even advisable, leaving "floating" the piece of equipment with the lowest risk of electrocution (a source or a processor, but not an amplifier or a display). In this way we force the leakage currents to pass through a single point only: from the source they will pass to the amplifier through their interconnection, and from the amplifier to the corresponding ground. This avoids the loop, eliminates the noise, and lets us enjoy our system 100%.