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| Subject - Grounding, basic but tough topic | |
| unsaint34 |
There are many questions I have about grounding. But I am willig to solve them one at a time. I am intentionally avoiding the term "ground" since it has such many usages. Question 1) Among many reasons, connecting an electrical system to earth provides a reference point for input voltage, therefore achieving steady voltage to loads. But, since we connect all neutral conductors together at the main service panel, why can't the neutral conductor be used as the reference point, instead of connecting the circuit to earth? If I have a neutral conductor bonded at the service panel and no part of my system (not even the service transfromers) is connected to the earth, wouldn't I still get stable voltages to the loads in the circuit? Question 2) Along the same question ... I also read that connecting circuit to earth stabilizes the "voltage to earth" or "voltage to ground" under normal operation. But, why do I care about the voltage to earth as long as I have voltage to loads? I'll appreciate your answer. |
| lctrc789 | Well you do have some good questions here for sure, Ground what does that mean in an electrical service. Whether accidental or intentional a ground between an electrical circuit or piece of equipment and the earth or to some other conductor that ends up in the earth. Code and safety standards are the reason we ground all grounded conductors to the earth. If you had a system not grounded you could use it but could have some serious problems for sure. The bulls eye or where you state that the nuetrals and grounds go merely are grounded as to the effect that you could have spikes, surges, etc and take the shortest path to earth. Why? Well grounding eliminates Voltage pressure to ground, nothing to push current through the body. Grounding builds"Low oposition path for current flow and gives path for current flow other than your body. I guess in laymens terms grounding causes a potential difference to prevent shocks and for safety. All neutrals are grounded conductors ( except corner grounded delta systems) there is no difference of potential or voltage between them or lets say there shouldn't be. Grounding systems and circuits are for safety of PEOPLE, PROTECTION OF EQUIPMENT,to limit voltages due to LIGHTNING, LINE SURGES, and Unintentional contact with higher voltage lines. As well as Stabilize voltage to ground in normal usage and and to help in case of an overcurrent problem in a ground fault system. Agian he earth is a great place to put your potential of difference it can handle this and is the best way to hanlde all the surges and spikes and lightning stikes. Actually we are not putting voltage to earth unless it is unintentional as described above. I hope this has helped you some what there are many reasons for grounding, bonding and using different types of grounds. |
| Randy L | quote: Just how old is the service transformer? Article 250 of the NEC requires both the supply source (service transformer in most cases) and the main service disconnecting means (main service panel) be bonded to ground. This is accomplished by a grounding means (rod, connection to a water pipe, etc.) at both the transformer and the main panel. I'm sure that some very "ancient" systems won't have this ground. But, if you are doing work/renovation in that panel, the code requires you to upgrade to current standards, right? |
| Energreen | Food for thought: 1) There's one key use for the word ground. And that's the reference to Earth provided by ground electrodes. 2) The ground wires between panels and junction boxes, etc., are bonds. 3) Electrical current takes any and all paths to ground that it can find. Not just the path of least resistance. However, the path with the least resistance will carry more of the current than the paths with more resistance. Conveniently enough, Copper has much less resistance than you do! 4) Ground rods are there so that each part of an electrical system has the same potential with respect to Earth. Differences in potential are dangerous, because that's what makes current flow when it finds a path. And we walk on Earth and sometimes touch things that are energized. If there isn't a low impedance ground in place when that happens, current is happy to use us as the primary path to ground. 5) Current does flow through the Earth. A grounding system helps to eliminate "step potential". If there's stray voltage in the Earth due to an electrical system fault, there can be enough potential difference between your feet when you're walking to zap you. This is a much greater risk for horses and cattle because there's a greater potential difference in their stride. Stray voltage is notorious for killing cattle who graze beneath high tension power lines. 6) Never trust an Earth ground to act as an equipment bond. For example, if you drive a ground rod at an out building, you still have to run an equipment ground conductor between the panels. An Earth Ground isn't solid enough to predictably clear a circuit breaker if there's a ground fault. 7) If you increase circuit conductor size to compensate for voltage drop in long runs, code requires that you must increase the equipment ground conductor the proportional amount. i.e.- If your current carrying conductors are increased two sizes larger, your ground conductor must be increased two sizes as well. That's because equipment ground conductors suffer from voltage drop as well! If there's too much voltage drop, a breaker might not clear a fault to ground as fast as it should. 8) Two very important things you want to accomplish in a ground system are: a) A circuit breaker probably won't trip if there's a short to an electrical cabinet or metal junction box, but no equipment ground conductor bonding that box back to the panel. An equipment ground conductor completes the circuit when there's a ground fault, thereby carrying enough current to clear the breaker. Suppose you touch an energized metal box that hasn't been cleared by the breaker? ouch! b) If there's a ground fault in a metal box, conduit or cabinet, and the breaker doesn't clear it (some have been known to stick, like FPE), the metal stays energized. If there's a low impedance Earth reference (a good ground electrode system), when you touch that energized metal box, there's not enough potential difference between the energized metal and Earth ground to cause current to flow through your body. It's ALL about safety. I don't see how it has anything to do with stablizing voltages. But maybe someone else can tell us? The information in Soare's Book on Grounding has "recently" been investigated and subjected to a battery of engineering tests, which have shown that Soare got it right. It's a good resource. Cheers, EG |
| lctrc789 | It is really all about safety and is has nothing to do with the voltage aspects in how it works etc. Just like my post stated is is about equipment protection and People protection 1st. |
| Ryan_J | Earth does NOT stabalize voltage. If it did, that would mean that I couldn't use a grounded system, say, in Antarctica, where you would never hit earth. |