Courtesy of Mike Holt Enterprises…
after reading the document you sent me, my mind exploded with assumptions, and specifically the grounding/neutral systems of Puerto Rico. I hope you offer these thoughts to your newsletter readers and experts so they can provide us all with their thoughts. I call this THE GROUNDING "TRUTH."
The Earthing Systems’ Worldwide document is most illuminating and, as you say, you don’t think there is a technical reason to ground the distribution system within a building and that there are more ways of using the earth connection. In fact, there are places in the world, like Norway, where distribution systems don’t have any grounding; some don’t even have a neutral at the high voltage. You should carefully read this document yourself as it helps to better understand the issue of grounding and why the U.S., and Puerto Rico for that matter, is one of a couple of countries that grounds every neutral and metal part they can.
Mike Holt’s Comment: And probably Iraq and Afghanistan in the next few years when we get done with them.
The principle of grounding comes with the mysterious capacitance that is created between electrical wires and the earth itself. This develops a potential just waiting to complete a circuit. The completion comes when ground fault occurs. At that moment, the fault current is very small due to the nature of the circuit (line-air-earth-line, imagine the impedance). It seems that generally this current is harmless, but if for some reason it increases or becomes a true short by means of another path, it certainly may become dangerous. Obviously, at the time the distribution system began, no sensitive devices were available to protect against this kind of fault, so earthing the system provided a more manageable current (ironically higher) and protective devices could be manufactured. This is all besides the obvious protection against lightning.
That action alone created the “common knowledge” that grounding was necessary for the electrical systems.
The method used by Norway is known as the IT System and the only things grounded are the metal casings and parts at the load, which share a common ground line NOT bonded to the neutral. Norway uses it particularly because the earth has very low conductivity and other countries use it around hospitals or where human safety is emphasized. There are basically two other systems; the one used by the U.S. is the TN System in which all neutrals, casings, and metal parts are bonded to the earth. Essentially, this system forces the earth to share the common point of the distribution system.
The pros of the TN System are that it’s very easy for protection devices to detect faults and the earth can be used as a (supposedly) temporary conductor to maintain the continuity of distribution. The cons you know better than me - the earth is now “energized” directly at the distribution’s potential and its wide use as a conductor is becoming a hazard for people and animals. As no devices are created for separating the service neutral from the load neutral at a high-voltage fault, all the loads are affected by it. Also, the quality of the signal is diminishing as more demanding and sensitive equipment is used in the continent and my island. A measure of improvement is the use of the fourth wire at the loads, where this wire goes directly to the neutral of the service and provides a better, less dangerous path for the fault currents.
The last system is the TT System where the supplies’ neutrals are grounded and only the casings and metal parts of the load are grounded. This provides for better detection of low-power ground faults and, although the earth is still used as a conductor for these faults, their paths are less and accidents are fewer. This is the most widely used grounding system in the world, a product of its versatility and reasonable cost of protection devices.
- The grounding of the distribution system is NOT NECESSARY for the system itself; it’s only useful when providing protection against lightning. The line voltage protections should be referred to the neutral or common point, a line that should be provided even if not needed for the distribution itself.
- The IT System is the safer system, but it needs more sophisticated equipment to detect, trace, and eliminate ground faults. Because of the economical implications of this system, only a few countries use it and some others use it where human safety is maximized.
- A few countries use the TN System, including the U.S. and Great Britain. It’s the most economical as protective devices are easily manufactured and operated, but the wide use of the earth as a conductor is transforming it into a health hazard. Also, additional equipment is necessary where a cleaner signal and extra protection are needed.
- The TT System is the most widely used, although less safe than the IT System and the earth is used as a conductor, its selective use of grounding is certainly less hazardous for humans and the electrical signal is cleaner. The use of ground-fault devices is necessary but can be less sophisticated than with the IT System. Nowadays, ground- fault devices are more economical so it’s feasible for everyone. They are already included in the U.S.'s National Electrical Code for specific situations.
- Personally, I would promote the use of the IT System, since most industrialized countries have more than enough money to deal with sophisticated devices and better insulation equipment. From an economical point of view, the TT is the most versatile and then should be a good transition point from the TN System. The TN System should be eliminated.
Recommendations for Puerto Rico (U.S. too?):
- The integrity of the neutral/common point should be addressed with serious intent. The size of the neutral wire is usually half that of the principal lines, which is a mistake because at any given point, the neutral may carry as much current as the principal lines. The neutral line should be, at least, the same size as the principal lines. Also, it’s not as well maintained as the other lines. All this diminishes its current-carrying capacity. The excess current will naturally try to use other paths; the most probable are the earth connections.
- Ground connections should be analyzed and selectively removed from where the system doesn’t need them. Excessive use of neutral bonded grounds (at every pole and at every load) is an important factor of low-power quality and also increases the potential for accidents. Sometimes a ground is used to complete the circuit of a broken neutral.
- Devices should be created that normally maintain the neutral of the load connected to the neutral of the service, only at the event of a high-voltage surge the device will switch to a ground rod. Although this will leave the load temporarily without service, it’s preferable to submitting equipment, and possibly people, to the high-voltage surge.
- The use of the 4th line, the protective wire that goes all the way to the service neutral connection, should be mandatory. It’s the safest way to activate the protective devices in line-neutral and metal-case faults. Line-neutral and ground faults should be referred to the neutral connection, not to ground.
- The use of ground-fault devices should be promoted and possibly regulated; it’s the best defense against low-voltage ground faults.
These recommendations should help protect humans against electrocution when devices work as expected, and will provide for better power quality of the distribution system. I invite Mike’s industry friends to read the Worldwide Earthing document, analyze it, and compare it with my discussion here. If my recommendations need a revision, or if I’m wrong in any of my assumptions, please feel free to correct me or offer your opinion. But please - one that helps continue the constructive discussion and solution searching for our grounding issues.