Just how would you have a hot white wire? What bazaar failure mode do you anticipate for this to occur? If both of the ungrounded current carrying conductors are open were will the voltage for this condition come from?
-- Tom H
I mentioned the same think and just *knew* someone would question that, so I spent some time looking for it. Search for 'GFCI "grounded neutral"' (with the extra quotes around the phrase 'grounded neutral' to get an exact phrase match).
Here are a couple of links....
daestrom
It does and here is how....
By tripping as soon as the neutral touches ground (even before a load is started), portable tools with such a fault will trip the unit *before* the operator can turn them on. Saves from having to pass even small current through operator (if only the IR imbalance were used, then a current through the operator would be needed).
Notice that not all units open both the 'hot' and neutral, some only open 'hot' while others open both.
daestrom P.S. This also shows the test button in a typical unit.
And what problem would that be? The GFCI's internal circuitry (except for the neutral-ground excitation coil) is deenergized when the hot is opened. Now you have only the voltage drop thru the neutral from the main panel to the sub panel. At most this is ~3.5VAC. With a 'bolted fault' between neutral and EGC, the full load of the sub panel would split 50-50 between the two conductors and the resulting voltage above the main panel's ground bus would be ~1.75VAC. Hardly any sort of problem at all.
Exactly. That is what I was saying. And this voltage is at most about 3.5 VAC in a fully loaded, but properly sized sub panel fed from 100ft of wire from the main panel. Are you suggesting that 3.5 VAC is lethal to some folks?? Why??
daestrom
The potential lies in almost any junction box that has a switch loop and a GFCI protected circuit. Once folks get used to connecting white wires with black wires they can easily go on to connect the WRONG white and black wires together.
If the white wire run through a GFCI that detects faults the SERIOUS wiring error will merely trip the GFCI but leave the WHITE wire quite hot, thank you.
The house I now live was extensive re-wired by a DIY type. The "improvements" included two "Three way" light circuits and one "Three way, four way" light circuit. NONE of these worked properly when we took over the place. Also, many ground wires were cut short rather than connected to metal boxes or to the grounding screw on switches.
In one ceiling junction box (which had cables to two different junction boxes with wall switches) a "wire nut" connection just opened up one afternoon.
(Yes, we got the place for a good price.)
Anyway, mistakes happen.
We always 'mark' such white wires when needed (mostly three-way switch installations). Of course, it isn't absolutely required by code, but it does mention it. It sure makes me feel better when I open up a switch box and find a black wire on one side, and a white wire with black marking on the other.
daestrom
Actually, in deliberate wiring of two three-way switches to a light between them is one example where the 'white' wire actually ends up carrying 'switched hot'. Code allows this. It should be 'marked' with black marker or tape, but you never know what the guy before you did.
daestrom
How do you arrive at 6 volts on a neutral? Even a fully loaded 30A service to a sub-panel 100 ft from the main panel does not result in 4 volts.
The imbalanced load, in combination with the length of the neutral wire, must develop enough voltage to be hazardous. How long a wire at what loading would be needed for 6 VAC???
how would this happen???
daestrom
Well, the "extra" core has a winding that attempts to inject a common mode current into the pair. If there is no common leakage path there no common mode current will be injected. If there is (regardless of which conductor) there will be a common mode current and the "main" coil will detect this and cause the device to trip. I believe the common mode injection frequency is double the line frequency.
Don't have a reference at hand. A year ago or so someone posted a URL to a schematic diagram of a GFCI and it showed the extra core and winding. If you are clever you might get Google to tell you where it is.
Fairly brute force, actually. Just an additional core and winding with an excitation source. "Clever" would eliminate the extra core and attempt to accomplish it with a single core.
The resister is connected between the load side of the ungrounded current carrying conductor (hot) to the line side of the grounded current carrying conductor (neutral). It is done this way so that the test button will work when the GFCI is installed to replace an ungrounded outlet as permitted by
406.3 General Installation Requirements. Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210. General installation requirements shall be in accordance with 406.3(A) through (F). (D) Replacements. Replacement of receptacles shall comply with 406.3(D)(1), (2), and (3) as applicable. (b) A nongrounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter-type of receptacle(s). These receptacles shall be marked ?No Equipment Ground.? An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.-- Tom H
in article 72MUd.2379$ snipped-for-privacy@newsread3.news.atl.earthlink.net, HorneTD at snipped-for-privacy@mindspring.com wrote on 2/28/05 1:28 PM:
It is possible, because I ran across it. Supose two fixtures are wired in parallel with separated switches. I was replacing one by removing the wire nuts. That broke the neutral conducting path. With the switch of the other fixture on, the neutral was at 120V hot albeit in series with an incandescant lamp.
Bill
In contact with the water is not the same as inside the human being. An adult in good health would be safe from anything the neutral would expose them to and a modern GFCI receptacle opens the neutral anyway. Getting back to your hot tub breaker there may not be a neutral to the hot tub but if there is it will only serve 120 volt pumps that have no exposure to contact. In addition the controls on a listed hot tub are mechanically operated not by direct electrical switching.
For six volts to be present on the neutral there has to be a high resistance connection or other resistive fault on the neutral. For the human being to make contact with that potential there has to be an additional failure in the neutral, a code violation in the placement of a receptacle, or an extension cord in use by a Darwin Award candidate.
How?
Describe it.
Under what circumstances?
In that statement you are plain wrong. There are combinations of contactor and ground fault detectors that are listed as type A GFCIs. That is in fact the standard method for protecting the larger commercial therapeutic hot tubs that are used in rehab centers and hospitals.
-- Tom H
That doesn't explain how I then get a hot neutral in the panel.
-- Tom H
in article woMUd.40718$ snipped-for-privacy@twister.nyroc.rr.com, daestrom at daestrom@NO_SPAM_HEREtwcny.rr.com wrote on 2/28/05 1:52 PM:
The second reference was the most useful. I did not realize how complicated GFIC devices can be.
Bill
Dry-ish feet on a dry floor?
jYou are kidding, right? ~>
You know I'm not..... The OP is emphasizing on The Neutral wire here, Not everyone that comes here is (or thinks he is) as versed and knowledgable as You & Bill "seem" to be.
If it's about the Finger Testing that you ask, My cousin, a seasoned electrician, uses that system to test live circuits anywhere, of course the calluses on his hands & fingers from firing M16 in Nam and other weapons while training rookies help him alot. Maybe Bill knows him., wanna ?
Keep it up & it's later..4.. you guys, you seem to try to slam me every chance you get., let me know when you get tired of doing it all yourselves. it's what a tech's supposed to do ~>
If 25 Ohms to Earth/Ground tested true at the Service Entrance the service panel would require an additional Grounding Electrode or Grounding Means....(?????)
some of you say I'm wrong them you go and state the exact same thing i said n your own words, then you talk about incorrect sentence structure like your Hemingway ... i could go on, n on.,
you think "You " Make Sense..... " cast the beam out of thine own eye before " ~> you say I've got it bad.
[who wons the group ?]
complicated
AND the extra complication is solely to keep the consumer safe even if the device is wired incorrectly!
Just to clarify for some readers... The code is making a reference to the "actual" resistance of the ground, which is often difficult to measure. (Must be 25 ohms or less) You need a device called a "Megger", reference ground rods etc.
Merely measuring the resistance between the grounding wires or the ground buss and the neutral at an outlet or a service entrance is not going to give you any indication of the actual qualitiy (= low resistance) of the ground installation at the site.
I'm told it's fairly common practice to install a second ground rod just to avoid making this measurement where the code permits.
Beachcomber
Beachcomber thanks for clearing that up.
Reported Stray Voltage on the streets comes to mind, but that has enough Fat in itself for a whole new Topic.
Yes, one of the benefits of having a good grounding system is that it will eliminate or minimize the effects of stray voltage. If you've got a farm and the livestock are getting shocked just by walking around, you've definitely got a problem.
For just a house though, a poor ground can be a safety hazard for the people living there. A poor ground can be caused by broken or loose connections, corroded grounding electrodes, or extremely dry soil conditions. The double danger is you may think your grounding system is perfectly fine, but your water pipes might be actually carrying dangerous voltages, you get shocked touching the dryer and the sink, the metal case holding your electric meter might be energized with respect to the surface ground, and your whole electrical system is subject to increased lightning damage, etc.
Beachcomber
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