AC voltage IN THE BEGINNING
- Thread starter domnic
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I am going with no.
If it would stay ungrounded that would be another matter but between faults and capacitance coupling it would not protect humans from shocks.
The ungrounded systems in hospitals are kept small and with constant monitoring to endpsure they stay isolated
If it would stay ungrounded that would be another matter but between faults and capacitance coupling it would not protect humans from shocks.
The ungrounded systems in hospitals are kept small and with constant monitoring to endpsure they stay isolated
jaggedben
Senior Member
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- Solar and Energy Storage Installer
France and Japan don't use grounded systems. My understanding is that they rebuilt with new standards after WWII, once RCDs were available.
As to whether they are safer.... I guess there are advantages and disadvantages.
See: https://en.m.wikipedia.org/wiki/Earthing_system
As to whether they are safer.... I guess there are advantages and disadvantages.
See: https://en.m.wikipedia.org/wiki/Earthing_system
Ac voltage
Ac voltage
We all deal with capacitance coupling but I never heard of it being capable of a fatal sock. can you give me a example of this in a home and a biasness and industrial please ?
Ac voltage
We all deal with capacitance coupling but I never heard of it being capable of a fatal sock. can you give me a example of this in a home and a biasness and industrial please ?
iceworm
Curmudgeon still using printed IEEE Color Books
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Ungrounded where?
Are you saying:
The utility distribution is ungrounded?
The customer side of the service transformer is ungrounded?
Or maybe both?
ice
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
That is a really difficult question. As mentioned by others, there are many countries that have been using ungrounded systems for a long time and both systems have a proven track record of being safe. I have never heard of any studies saying one is safer than the other. Perhaps the more important questions is, if we had gone the ungrounded route, would we call our panelboards "consumer units"?
big john
Senior Member
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- Portland, ME
Speaking as someone who has received a very strong shock on an ungrounded system, I can absolutely attest to this hazard. I might even argue that the potential for shock is more severe as phase voltage floats compared to earth. In my case it was about 400 volts.
The larger the system and the more surface areaof the conductors and insulstion, the higher the cumulative leakage and capacitive current. On larger industrial systems this can be enough watts of power to dimmly illuminate incandescent GF indicator lamps; more than enough to electrocute a person.
In a small, low voltage system like a house it might offer limited protection, but we would need to install sensing circuits at every main or the ungrounded status would never be maintained.
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- Retired PV System Designer
So, not just one ground fault detector per secondary, but a "super duper directional GF detector" that could detect the low capacitive current from an accidental ground, or else a lower resistance deliberate ground current generator/detector such as the indicator lamps used for commercial ground detection, but somehow isolated from everyone else on the same secondary.
Sounds like a piece of cake.
electrofelon
Senior Member
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- Cherry Valley NY, Seattle, WA
I have heard that in countries that use ungrounded systems, a first fault is fairly common and may go un-noticed and un-addressed for a long time. This sounds bad, but as long as each service has its own transformer and people servicing the system are treating it as a grounded system, there isnt really any problem - you just used your "get out of fault free" card and now its a grounded system.
iceworm
Curmudgeon still using printed IEEE Color Books
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Alright - both.
First - suggest you separate out the distribution from the consumer. These have way different issues. Suggest the demark is the customer transformer.
second - Suggest you discount any post that contains "I think" or "I heard". Personal opinion: You are looking for physics or statistical data. Nothing else matters.
Jump subject to distribution
Outdoor, overhead, ungrounded distribution is very failure prone. Lightning strikes on ungrounded distribution lines have a much higher potential (pun intended) for destroying equipment than strikes on grounded distribution lines.
Jump to consummer side
Ungrounded systems are subject to arcing re-striking ground faults. This can raise the voltage up over 2x system voltage - destroys a lot of equipment.
Jump to Both
As already noted, ungrounded is hard to maintain (read CUBIC MONEY)
Jump to personal opinion
I can build you an electrical system that is 10x - 100x safer than the existing. But you are going to pay plenty for it. Yep - all y'all consumers personally. And, it won't really matter if the system is grounded or ungrounded.
iceworm
kwired
Electron manager
- Location
- NE Nebraska
With typical 120/240 or even 208/120 systems what we currently have is already referenced to ground at the neutral point - so the upper limit of the capacitively coupled voltages will be limited to 120 volts. You can increase this to 277 for systems that operate at that voltage to neutral.
If we do not ground the neutral to keep voltage to ground to at least the "mid point" voltage level you can easily have capacitively coupled voltages up to full system voltage (208/240/480 volts) to ground.
How much current can flow in such a coupled source depends on how big of a capacitor is present to store that energy regardless of voltage. In most small homes or businesses there usually is not enough naturally occuring capacitor to store enough energy to present a harmful amount of current, as circuit lengths, or segments of such circuits that can make up a capacitor are usually fairly short and are not optimally designed to be a storage capacitor either.
Curious nerd
Member
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- Washington State, USA
"Lightning strikes on ungrounded distribution lines have a much higher potential (pun intended) for destroying equipment than strikes on grounded distribution lines."
Why doesn't anyone combine the advantages of an ungrounded system with the improved lightning safety of a grounded one by doing the grounding through a gas discharge tube or other lightning arrestor, something normally open but which will snub an overvoltage to ground?
Why doesn't anyone combine the advantages of an ungrounded system with the improved lightning safety of a grounded one by doing the grounding through a gas discharge tube or other lightning arrestor, something normally open but which will snub an overvoltage to ground?
iceworm
Curmudgeon still using printed IEEE Color Books
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- EE (Field - as little design as possible)
Really suggest to limit the discussion to either Distribution MV/HV, or comsumer side MV, or industrial LV (480V), or consumer 240/208V. Otherwise the topic is way too broad. The issues are not the same.
Your post appears to be about distribution. The short answer is, I don't know. Distribution is not as area of my expertise. I can tell you that three distribution systems I have been around (138kv, two 69kv) do have surge arresters. My current understanding (easily changed by someone who is in their area of expertise) is the systems do take lightning strikes, the surge arresters do operate, devestating surges/transients are snubbed. I've never seen an un-grounded HV or MV outside, above ground, distribution system. They likely exist. I just haven't seen one - or didn't know it if I did.
If your question is about applying snubbers to un-grounded, consumer side LV, that's different. I can tell you that there is historical evidence (back to the 1900s) of arguments about if grounded or un-grounded is safer.
ice
iceworm
Curmudgeon still using printed IEEE Color Books
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The OP said both distribution and Consumer side of transformer, but most all of the posts appear to be about consumer. So, addressing consumer side, I don't know - probably money.
However, if we are addressing ripping out the entire US non-utility electrical systems and replacing with a systems that stress personnel safety, structural safety (fire), and continuity of service - Maybe investigate:
All distribution from the substation to the consumer transformers are underground - all pad mound transformers. I'll leave the distribution grounded/un-grounded issues alone.
Do not connect the consumer side neutral to the distribution side neutral.
Consumer side (480, 208)is all 3phase, HRG, underground to Consumer first disconnect. All loads are line to line - no line to neutral loads available.
Set the ground detectors to shut off the power if gf is detected
Wire buildings in MI cable. Or if the money bleed gets to where the customers are dying out, go with MC-HL - that will just leave them somewhat anemic.
So, my answer is: Neither grounded nor un-grounded - rather HRG
Mind you , these are just random thoughts, indiscriminately leaking out. I'm certainly not telling anyone this is the answer.
ice
- Occupation
- Licensed Electrician
I like your idea. I would say that the same system with conventional wiring methods would be a functional and safer, using MI cable is just gilding the Lilly.
kwired
Electron manager
- Location
- NE Nebraska
I understand how HRG works, never been around such a system though.
I have also heard from people that have been around them that there never seems to be any concern when a ground fault is indicated, which leaves you wonder why they have the HRG in the first place if they are going to ignore faults that are indicated, a second fault is going to present problems, maybe nothing severe if you are lucky for it to be on same phase as the first fault, but there is still potential for objectionable current in unpredictable paths when that happens.
iceworm
Curmudgeon still using printed IEEE Color Books
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Yeah, that is pretty poor if the maintenance is not pulled. Although there are some (ground faults) that can be left alone fairly safely. For example, say the fault is out at a light in the process area - small wire, long ways. And one can verify that. Then add -40F ambient and 40 knots. It is really hard, miserable, and higher risk to fix now as opposed to wait and fix in the Spring. If a second fault occurs, the worst is a tripped 20A CB. I'm not saying this is right - but it is a common practice. And yes, one has to pay attention and not just ignore.
As for generally ignoring faults and not pulling maintenance - that's a bad idea no matter what the system is. HRG is not excepted.
So why HRG? Two reasons:
Note: Following is narrowly limited to industrial 480V
For grounded systems, faults generally start line to ground. The impedance is high and currents are easily in a range where the trip time is long - lots of damage until the fault goes L-L. Then the currents jump and the OCP trips quickly.
HRG gets rid of this issue. An L-G fault is limited to 5A or 10A - No damage. For L-L faults. the current builds quickly and the OCP trips quickly - Definitely limits damage.
Second is Continuity of Service. Sort of important if one wants to keep making money while finding and fixing the issue - and one must do that safely. And yes, it can be done safely.
ice
iceworm
Curmudgeon still using printed IEEE Color Books
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Note to OP on un-grounded systems:
There is one class of installations I know of that are designed un-grounded 480D - Naval Ships.
I heard one argument it is done for safety - everything one stands on or touches is a good solid ground and likely damp and salt coated. I have first hand evidence that incidential contact is not necessarily lethal.
Second argument was continuity of service when the ship is shot to pieces in the middle of a battle. They will keep fighting if possible. If they can't and still have way, they will get out of Dodge. Either of those takes power.
For industrial consumers, other than a few special equipment installations, there is little need. In fact, again except for a few special cases, the only un-grounded systems I saw appeared to be screw-ups (personal opinion)
ice
There is one class of installations I know of that are designed un-grounded 480D - Naval Ships.
I heard one argument it is done for safety - everything one stands on or touches is a good solid ground and likely damp and salt coated. I have first hand evidence that incidential contact is not necessarily lethal.
Second argument was continuity of service when the ship is shot to pieces in the middle of a battle. They will keep fighting if possible. If they can't and still have way, they will get out of Dodge. Either of those takes power.
For industrial consumers, other than a few special equipment installations, there is little need. In fact, again except for a few special cases, the only un-grounded systems I saw appeared to be screw-ups (personal opinion)
ice
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
I rather like the idea of HRG systems combined with ground fault circuit interruption (not necessarily at GFCI levels).
GFCI devices are well developed and reliable.
HRG systems provide good voltage reference and provide a path to ground for extraneous high voltage (eg. leakage across transformers or static discharge). At the same time fault current levels are reduced to amps rather than kiloamps.
Today HRG systems are used for continuity of service, where you detect but don't interrupt ground faults. If you actually interrupt current in the event of a ground fault, then IMHO you could (not per current code, but in principal) serve line-neutral loads safely.
You would reduce (but not eliminate) shock hazard. You would greatly reduce stress on components during ground faults. You would eliminate the problem of 'effective ground fault path'. If most faults are ground faults detected electronically then you can probably more tightly control trip curves and improve coordination.
On the down side, you would probably see problems where the electronics in the breakers dies....although if the goal is to detect ground faults in the ampere range you might be able to use an electromechanical ground fault detector (more reliable??? but less accurate).
Also just thinking out loud.
With respect to the OP: I highly recommend Soares Grounding. The book includes historical references that help to understand why we use what we use today...IMHO if we could somehow transport today's technology back in time the decisions would likely have been different.
-Jon
GFCI devices are well developed and reliable.
HRG systems provide good voltage reference and provide a path to ground for extraneous high voltage (eg. leakage across transformers or static discharge). At the same time fault current levels are reduced to amps rather than kiloamps.
Today HRG systems are used for continuity of service, where you detect but don't interrupt ground faults. If you actually interrupt current in the event of a ground fault, then IMHO you could (not per current code, but in principal) serve line-neutral loads safely.
You would reduce (but not eliminate) shock hazard. You would greatly reduce stress on components during ground faults. You would eliminate the problem of 'effective ground fault path'. If most faults are ground faults detected electronically then you can probably more tightly control trip curves and improve coordination.
On the down side, you would probably see problems where the electronics in the breakers dies....although if the goal is to detect ground faults in the ampere range you might be able to use an electromechanical ground fault detector (more reliable??? but less accurate).
Also just thinking out loud.
With respect to the OP: I highly recommend Soares Grounding. The book includes historical references that help to understand why we use what we use today...IMHO if we could somehow transport today's technology back in time the decisions would likely have been different.
-Jon
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