Heres something I typed up a month ago, but I think its well worth it in this thread:
Here is the irony: In the EU and other parts of the world the term earth simply means the exact same thing as ground to us: an all encompassing term for everything in article 250. Earth not only means soil, but EGC, bond, and a list of other things which most of them have nothing to do with soil.
The truth is both our term ''ground'' and the European Unions term ''Earth'' is incorrect. In fact IMO the only ones who have the term right is Canada which refers to EGCs as bond wires. Fault clearing and equal potential the heart of electrical safety and the ultimate intention of article 250 have everything to do with bonding with little to do in the way of earthing.
Basically it boils down to two parts:
A. Equal potential based on a faraday cage design: which is connecting (bonding) all metallic parts that could become energized together with a large enough conductor.
B. Bonding jumper. If the first part is successful this part is theoretically optional, but still needed most of the time: Connecting (bonding) the equal potential (faraday cage) to the source with a sufficiently sized conductor. The primary purpose is to intentionally allow a place for current on the equal potential system to go during a fault thus immediately tripping a breaker.
Both parts relay entirely on bonding.
The ground rod is really only for lightning discharge, which helps to lessen the damage.
Yes grounds rod dissipate a lightening strike, and they do in a few occurrences, but they do nothing for human safety. Even when a high voltage primary crosses over into a secondary, yes a ground rod provides another path for that current, and they may help in such a case, but what really protects people and property is bonding.
Consider these 2 examples; both identical buildings with a concrete rebar enforced slab foundation and wood framing. In many buildings there is a huge flaw from the start, that being no ufer bonding takes place. Building 1 has no UFER and thus ground rods are driven, while building 2 has a UFER bond but no ground rods. Both water lines are plastic going into the structure but transition to metal in the building. No gas exists but an AHU inadvertently bonds the duct work to the metal frame with an EGC.
Here is what happens during an open neutral. Both example hold true with a 120, 230 and 277 ect volt service. When the neutral opens the ground system will become energized by what ever the difference is between the 120 or 277 volt loads relative to remote earth. Under the voltage imbalance something may overheat and short circuit hot to neutral putting 120 or 277 volts on the bonding system. In a 230 volt single phase feed the potential will be 230 volts since the neutral is not shared. For the sake of the argument lets say the bonding system is 120 volts to remote earth. The key here is human safety:
1. In building #1 all appliances relative to each other will read zero volts. Contacting a fridge and an oven will give no dangerous potential. Washer to dryer no potential. Even metal plumbing, such as a sink to a light switch no potential. Plumbing to duct work, no potential. Nothing will be dangerous relative to one another. An exception is an outdoor water spigot that will read 120 volts to earth. If that reading was taken within inches of the ground rods potential will be perhaps less than 120 volts (say 60 volts), but go beyond a few inches it will be close to 120 volts. Soil resistance dictates how low the voltage will be around the ground, but regardless of soil conditions, go past a foot or two at best and the ground rod will no longer give equal potential. I could drive more ground rods, but it would change nothing. Id be safest literally standing on a ground rod (zero volts) while contacting the water spigot, but beyond that I have no protection. Nor do I get a second neutral for my loads.
One would think the person inside is safe, since they are not in contact with soil. FALSE. Like most buildings the UFER was left out of the picture. The potential between a sink and the bathroom floor will be 120 volts. Between duct work and the floor 120. Bonded Drill and floor 120. This voltage potential only exists from the lack of bonding, even though the UFER is the ultimate ground rod. If a person took off their shoes and touched the electrical panel cover or anything else metal, the probability of electrocution is there.
2. Now in building #2 the Ufer is bonded. When the neutral opens, being barefoot will not expose the person to dangerous step touch potential. I could be wet, barefoot and touching the furnace, stove, electrical panel... because the UFER is bonded I will not be in any danger. Even if the UFER's resistance to soil is to high to be a good neutral bath back to the source, or even if its close to zero ohms, it does not matter since bonding will maintain that equal potential regardless what happens. I can go further in that equal potential not only protects people it eliminates fire hazards. A difference in potential can cause immense current to flow unrestrained on something that might not be able to carry it.
That same concept also hold true for incidental contact with higher voltages. Its not so much the grounding, but the bonding that protects people and property. With that said places with out a UFER are no different that places with unbounded plumbing, yet AHJ make the wrong assumption one is dangerous the other is not.
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