Several reasons; among them are:WHY do we use a grounded system for power?
Exactly the same thing as you would do with a grounded system. Unless the system is very small, there is a shock hazard between the circuit conductors of an ungrounded system and the earth.In a ungrounded system like a delta 3 phase what must I do to get shocked ?
WHY do we use a grounded system for power?
Even in case of ungrounded system, insulation failures would occur in it in case of accidental contact with higher voltage lines (primary falls on service drop).
Sure, capacitive coupling is not strong enough to trip ocpd if there is a ground fault. But still the metal parts of the ungrounded system is grounded with a ground wire not an EGC.Well the main reason a we would want a grounded residential system in this case is so that a utility ocpd will clear quickly. If the utility system is ungrounded, I am not sure if capacitive coupling gets strong enough to trip their ocpd if there is a ground fault?
There was another thread going recently that had a post about the power system in Europe. In Norway they run ungrounded and based on what I read running ungrounded has it's problems as well.In case of accidental contact with higher voltage lines (primary falls on service drop). IMO, there is a fair amount of voodoo with system grounding; the purported benefits are not commensurate with the actual benefits, and the benefits of ungrounded system are typically ignored.
Sure, capacitive coupling is not strong enough to trip ocpd if there is a ground fault. But still the metal parts of the ungrounded system is grounded with a ground wire not an EGC.
There was another thread going recently that had a post about the power system in Europe. In Norway they run ungrounded and based on what I read running ungrounded has it's problems as well.
When we call an EGC an EGC? When it is connected with neutral at the service equipment. But in an ungrounded system the ground wire is not connected to the neutral. Still it serves its safety purpose: if a MV line, say 4160V, itself ungrounded falls on the exposed metal parts of an equipment so grounded, the resulting voltage on the equipment may not be dangerous to life.In the above statement are you referring to the utility side of things? Here in the states for premise wiring we would still call it an EGC even if its in an ungrounded system. In a grounded system, an equipment grounding conductor is serving two purposes: it is providing the low impedence fault path back to the source and it is connecting equipment to the earth which is also required by the NEC. Regarding what I said about the high voltage line falling on a service drop, well its actually a long shot - dont blame me, the NEC says it. The thinking is that if the messenger/neutral is not grounded then the 4160V or whatever would energize parts of the premise wiring system and not necessarily clear the fault. In reality, I have never seen an ungrounded system that used a bare messenger as one of the ungrounded conductors - the messenger terminates at the attachment point and all the phase conductors are insulated. Sure the insulation on the service drop isnt rated for 4160 so who knows what would actually happen. I guess the thinking is the 4160 will pierce the insulation and wreak havoc with the premise electrical system where if it was grounded, the bare messenger would conduct the fault to ground thru the premise grounding electrode system. But for this to work they seem to assume the primary system is grounded which is often not the case.
Under the rules of the NEC, it is an EGC no matter what type of system it is associated with.When we call an EGC an EGC? When it is connected with neutral at the service equipment. But in an ungrounded system the ground wire is not connected to the neutral. ...
Found the thread I mentioned - dude needed to hit "Enter" a few times, but if you click on reply with quote you can break it up and make it readable.I would like to know what those problems are and why grounded systems seem to be preferred. I really have never heard any concise explanation. Maybe there is a utility EE on here that can give some specific documented reasons and examples.