Grounding Electrode (Ground Rod) Info and Install Suggestions
One thing that I always ask my clients about is the entire electrical chain feeding their audio system. How your audio system obtains AC power is a pretty big and important topic to talk about, but for this paper, I will only examine how your house is grounded to the Earth. It's not a fancy topic, and this will not be an in-depth information document. Still, it goes over the basics in obtaining a low impedance path to Earth for the electrical service in your home. Ensuring a low impedance path to Earth here can yield a surprising jump in the performance of your audio system, provided the AC and ground path don't get compromised between the main service entrance and the audio system.
The primary importance of your electrical system's connection to Earth is to dissipate hazardous and destructive electrical energy during a lightning storm. A low impedance path to Earth also helps make the safety ground network in your home more efficient, and in the case of high-end audio components, helps to create a quieter and more stable electronic environment. The better the Earth ground system is, the more effective the electrical service will be in all these areas.
The Earth ground relationship for a residential electrical system is traditionally achieved using a grounding electrode, commonly called the ground rod. Geeky technical detail here: A ground rod only becomes a grounding electrode when installed into the Earth. Until then, it's just a metal rod. The NEC (National Electrical Code) requires the grounding electrode to Earth impedance of 25 ohms or lower for residential electrical installations. Ideally, for a home with a high-end audio system, achieving 5 ohms or lower is highly desirable, and lower still is ideal. If the Earth to grounding electrode impedance is above 25 ohms, the grounding rod may have deteriorated or may not be long enough in the current soil conditions. The grounding electrode at your home was probably initially installed correctly, or it would not have passed the electrical inspection when the home was built. That said, soil conditions may have changed since the initial installation, and it may need to be re-evaluated to achieve the required low impedance result.
Suppose you do have an electrician re-evaluating the grounding electrode setup. In that case, it might be a good time to install a new ground rod with optimal performance in mind, rather than just getting by to meet code requirements. And if you live in a home older than 20 years, a new rod would be a good idea anyway as corrosion will have probably compromised a low impedance relationship the Earth. NEC requires a minimum 8' length rod, but multiple rods connected to go deeper will probably yield better results depending on your area's soil and water table. There are various diameter rods available. Keep in mind that the larger the diameter of the rod, the greater the contact area with the soil there will be, which may lead to a lower impedance value between it and the soil. Since a ground rod is generally thought to last quite a while, a homeowner rarely thinks about it. With the electronic complexity found throughout modern homes, the grounding electrode should probably be a regular part of home maintenance. High salt or mineral levels in the soil can speed up the corrosion process quite a bit, depending on the material from which it is made. One can purchase a highly conductive pure copper ground rod, but copper is a pretty soft material and can easily get misshapen when attempting to drive it into the hard or rocky soil. A copper-bonded rod has negligibly less conductivity than copper, is much tougher, and is considerably less expensive than pure copper. For folks living in areas with high salt in the soil, there are also stainless steel grounding rods, which are very resistant to corrosion but have slightly higher resistance to Earth. As an alternative to going deeper with the existing ground rod, a second electrode located some distance from the first can also help achieve a lower impedance value. It will get bonded to the primary electrode and provide a greater surface area in contact with Earth. If it is determined that a second ground electrode is a good choice, NEC requires at least a 6' distance between the electrodes, but there are some technical advantages to the electrode distance being equal or greater than the rod lengths. 8' ground rod means the second electrode would be 8' or greater away, and doubled up 8' rods that are 16' deep means the second electrode is 16' away from the initial electrode. Anyway, get that Earth to grounding electrode impedance as low as you can!
For those of you who are wildly ambitious, there is another option to establish a very stable grounding electrode called an enhanced ground rod. An enhanced ground rod involves a copper tube filled with electrolytic salts and can be highly effective at establishing a long-term, very low impedance Earth to grounding electrode relationship. Enhanced ground rods require a significantly more sophisticated and costly installation process, not to mention the higher cost of the unit itself. But, if you live in an area where it is difficult to establish a low impedance result, or if you want to really take grounding to the highest level of effectiveness, an enhanced ground rod may be just the height of grounding improvements. Bear in mind that, unlike the common ground rod approach, an enhanced ground rod type system does require regular maintenance to keep it maximally effective.
Next, you must deliver that optimized low impedance path for Earth ground to your home electrical system. When bonding the grounding electrode to the grounding electrode conductor (The wire going inside your house to the breaker box), there are, of course, options on how that is accomplished. Since we probably don't want to be thinking about the house grounding all the time, I would suggest having the conductor exothermically welded (using thermite) to the electrode rather than clamping it. The conductor is clamped onto the electrode with a bolt-on type connector with most homes, resulting in a potentially poor connection. In many instances, I'll bet this connection is loose or is at least somewhat compromised due to corrosion or oxidation. In that instance, there is a significantly higher impedance to Earth ground, regardless of the impedance between the electrode and Earth. Once it's welded, it's there to stay, and the impedance of the bond is extremely low. It's an old and common practice and should not be expensive to have done.
There are kits on Amazon for you to DIY the thing if you're cool with igniting thermite…but I'd let the electrician do it if I were you. Besides, if an open neutral leg is somewhere in the electrical system, the grounding electrode could carry hazardous current levels (read lethal). Yet another reason to let your electrician do this work for you. There are also very high compression bonding products and techniques that seem just as solid, long-lasting, and low resistance as thermite welding, but special tools and products are required to do this properly. This technique is well beyond getting the connection "really, really tight." There are pluses and minuses to both methods that you should ask your electrician about, but please consider one of these methods rather than clamping.
NEC dictates that the size of the grounding electrode conductor is no smaller than 6 gauge for copper wire. You can use aluminum wire here, but you introduce a dissimilar metal relationship to the grounding electrode, which causes galvanic corrosion between the two metals. I believe a very low impedance copper braid is probably the lowest impedance path you can provide, but check with your electrician for his recommendations and code requirements before plowing ahead by yourself.
Once in the house, the electrode grounding conductor is connected to the ground bus at the electrical service entrance for the house electrical system. Once the electrical system enters the house, many things can be done to foul up all the excellent work put into establishing everything discussed above. That is for another discussion.
There is a grounding topic I get questions about, and man, is it a scary one, not to mention disastrous for the system's performance! You do not want to connect the audio system safety ground to a dedicated second grounding electrode close to your audio system while disconnecting the house ground from the system. Somehow there is info out there that provides the cleanest ground because nothing else in the house is connected to the system ground.
By doing this, the system's electrical system will not be grounded, nor will your house meet code. The safety ground of the electrical system MUST be connected to the neutral leg of the AC, which is the whole point of safety grounding. You can add a second grounding electrode near the audio system, but it absolutely MUST be connected back to the house grounding electrode to complete the circuit. But, this practice will probably do nothing but create ground potential issues (a ground loop) and add more noise. In other words, the audio system ground will have two paths back to the breaker box where it connects to the neutral leg, one directly through the house and the other to the secondary grounding electrode and then from there to the breaker box. Each ground path will have a different and UNEQUAL impedance value. The unequal resistance value between those two ground paths that connect to the same point means that current WILL flow to the safety ground. That's unwanted noise.
So don't do it.