just how dangerous is the neutral wire?

| Don't look BUT most "stuff" today is double insulated. The "ground" pin | just isn't used by a lot of things. The computer plugs still have "ground" | but anything that uses a "wall wart" or and AC/DC converter isn't | "grounded." In the kitchen, most food processors and toasters and mixers | don't use the third pin.

Nor would they need to with GFCI around. But a hazard exists if the neutral wire is not interrupted when there is some fault path to ground. As I understand it, 120 volt GFCI receptacles do disconnect the neutral when they trip. I will eventually test this.

| So? Back in 1947 (or whenever) women would use a clothes washing machine | that was connected to an overhead combination suspended lamp holder and | outlet. They often would plug in the washer with soap/water covered | hands. The third pin was an improvement that allowed "backward | compatibility." The third pin also provides a greater margin for wiring | errors. | | "Starting from scratch" we would be as well served by oversized neutrals and | plugs than ensured the neutral/ground was made BEFORE the hots.

If "starting from scratch", my design would not use a 3-wire Edison system. I'd go with the European system or some approximation of it.

| If you want to worry about the neutral getting lethal voltages then you | might was well worry about the "ground" getting lethal voltages. In the | real world, it's much easier for the ground connection to be broken and then | crossed with HOT than it is for the neutral.

The neutral doesn't have to be broken and crossed over for it to get voltages that can be lethal to some people.

|> What is the reason for GFCI protecting a hot tub if people are not |> touching the wires? Well, I think the reason is because something can |> go wrong. | | Duh!

But if not all the current carrying wires are disconnected, it's only a job 2/3's done.

| Well, sport, IF somehow the neutral is broken then GROUNDED objects are more | dangerous than "floating" objects. Were "ground" and "neutral" permitted to | be crossed wheneven convenient it would almost be impossible for all paths | to the panel neutral to be broken.

The neutral doesn't have to be broken and crossed over for it to get voltages that can be lethal to some people.

| The basic principal of electrical safety is that it must take at least | two failures to introduce a hazard. The neutral is a current carrying | conductor that is insulated. It is no longer permissible to use the | neutral to ground the exposed metallic frames of appliances or other non | current carrying metal parts of the electrical system. So there is no | exposure to neutral contact. The voltage on the neutral is far less than

But that same logic, neither of the hot wires poses a risk, either. Then in that case, we don't need GFCI in the kitchen or bathroom because the grounded frame will protect us. But in reality, any of these wires can get in contact with water if an appliance is dropped in the sink.

| the thirty volts it takes to break through a healthy humans skin

Human skin does not exhibit a fixed voltage drop. A mere 6 volts can get the current up to the painful level, depending on various conditions such as skin moisture. For some people, like elderly, it can even kill at these current levels (5 ma). This is why the GFCI settings are in this range. And 6 volts can be present on the neutral.

| resistance. In order for the shock hazard to exist a failure must occur | in the continuity of the neutral so that it's voltage would rise to the

It only needs to be an imbalanced load with some significant length of neutral wire run.

| service voltage AND the insulation would have to fail in a way that

Don't need an insulation failure for this to happen. It can happen with normal wiring.

| exposed you to contact. With the motor frames and all metallic | enclosures grounded via the Equipment Grounding Conductor (EGC) there | are three failures between you and a shock. Given the purpose of the US | NEC that is considered sufficient.

Only 1 failure to reach a level hazardous to some people.

| The reason that GFCIs are used to protect spa users is that the voltage | drop on the EGC might well be over thirty volts under a fault condition | that involves an ungrounded conductor. The likelihood of that being | true for a neutral fault condition is far lower.

No guarantee that a fault is going back to the EGC first. The person might be in series with that path.

| There is nothing stopping you from installing a three pole breaker with | a shunt trip coil and a ground fault detector to raise the level of | safety even higher. Alternatively you could use a contactor to energize | the circuit with the contactors coil current supplied via a ground fault | detection circuit. A three pole contactor would open all of the current | carrying conductors including the neutral.

It would not be UL listed.

|> |> Where can one find a GFCI protection device that disconnects |> |> both hot phase wires and the neutral at the same time? |> | |> | That is done by installing a separate detection circuit to control a |> | three pole contactor or shunt trip circuit breaker and it is not cheap. |>

|> So, the average home hot tub is a hazard waiting for a tragedy. | | | According to an electrical inspector that I had coffee with on Sunday, | | The typical residential GFCI outlet and breaker DOES open the neutral upon a | trip.

The receptacle GFCI very well might open the neutral. But the breaker GFCI definitely does not. Switch one off and test the continuity between the pigtail and neutral terminal.

| Neither of us have actually tested this so I would get a meter out before I | played you bet your life. | | Personally I will not use any water based appliance with the light on. I | figure that my life is worth more than 10 bucks. In the early days of | GFCI's I saw that they would not trip, they failed more than they worked. I | know technology has gotten better but I still feel that my life is worth | more.

It might be wise to keep water and electricity far apart. OK, no outlets in the bathroom at all, and none within 6 feet of the sink in the kitchen. Now that should be safer :-)

| GFCIs do open both sides. Some times you can see this demonstrated | when the neutral contact fails. You get a polarity revesed indication | on a 3 light tester.

Tell me a Square-D or Cutler-Hammer breaker model number that does open the neutral (besides the SWN breakers for gas pumps which are not GFCI).

| The 120 volt GFCIs do open both sides (I took one apart just for fun to | determine this.) The reason is to protect folks from improper installation | (revering hot and neutral.)

You are speaking of receptacles, not breakers, right?

| The 240 volt models for spas, etc.? I don't think so, but I don't have a | failed one to "sacrifice" for the cause.

I've never seen a 240 volt receptacle GFCI. If they make them up to

60 amp levels, that would work (as long as it opens all contacts).

Otherwise, hot tubs designed for 2-wire connection are safer that hot tubs designed for 3-wire connection.

|> So why does the NEC now require the groundING wire on these in new or |> upgrade construction? | | 1) they like to worry.

Better safe than sorry.

| 2) it uses more copper

I figured that might be playing a part :-)

| 3) the three wire plugs aren't good at connecting the neutral first and | disconnecting it last.

They could have required that.

| Had they addressed the "real problem" we would have lower costs and more | safety.

Which is?

I think the _real_ problem is they still allow 3-wire loads and still allow any switch/breaker to any circuit near water to leave one wire connected.

| |> Test your GFCI receptacle and see if it trips when a short is placed |> between the neutral and the ground. |>

| | Modern GFCI receptacles *do* trip when neutral and ground are connected | downstream. *BUT* they will do this even if the neutral on a single circuit | going straight back to the main service entrance with absolutely *no other | load*. | | GFCI trip on neutral to ground faults, *not* because there is some | mysterious voltage on the neutral line that makes it more hazardous. They | trip on neutral to ground faults because that is *exactly* how they are | designed. The GFCI deliberately induces a very small signal into the | neutral line. If the ground is connected to the neutral at the service | panel (as it should be) *and* somewhere downstream of the GFCI because of a | wiring error or fault, the signal will circulate a tiny current through the | completed loop and this trips the GFCI. This is a deliberate part of the | design to ensure the grounding conductor is never connected to the | electrical circuit downstream of the GFCI.

However, w/o this design, they would also trip if there is any current on the neutral bassing through the current sensor that is not balanced by an equal current passing back through the hot wire. That can happen if the neutral is connected to ground downstream if there is any out of balance condition on circuits near this circuit which would use that neutral to ground connection as an additional path back to the source.

Then if the GFCI circuitry is powered from the line side, it will see the fault condition until the neutral is opened. If it never opens the neutral, you have a new problem.

| Considering the proper voltage drop that would be available even on the | 'sub-panel feeding a hot tub scenario', just how much voltage do you think a | neutral will have to ground? The hot tub properly bonded and grounded, and | its occupant somehow contacting a neutral that goes to a sub panel, while | the sub panel supplies some other 'heavy' 120V load?? 100 ft of #10AWG | carrying 30A would have a voltage 'rise' of about 3.5 volts. Mind you, | that's 100ft between the main service panel and the sub panel and a full 30A | load on. Of course, if the sub-panel is supplying a 30A load *and* a hot | tub, then the conductors are larger than #10AWG, resulting in even less | voltage 'rise' when the GFCI to the hot-tub is open. With the GFCI open, | there can *not* be any voltage drop on the neutral from the hot tub to the | GFCI. Is this 3.5V the stray voltage you're worrying about?

The voltage is coming in on the neutral from the subpanel due to the voltage drop between the subpanel and the point where the neutral is bonded to ground.

| The makers of the GFCIs go to a lot of trouble to add this feature. There | is a second "core" used solely for the purpose os injecting a common mode | signal onto the pair. If you have an old GFCI laying about you can take it | apart and see for yourself.

These can be tripped by an open neutral. Since the EGC pin disconnects last, and the other 2 prongs are about the same, if you pull the plug of the extension cord out such that neutral disconnects first, it can trip. I presume this injected common mode signals does this. But it must be connected to the ground for power, too, to get power to do it.

| (I am only speaking about the 120 volt models, not the 240 volt stuff.)

If 2-wire 240 volt, no neutral involved. IMHO this is better than the

3-wire 120/240 system.

|> | if things have gone so badly that there is dangerous voltage on the | neutral |> | wire that same voltage will probably be on the ground wire too... | referenced |> | to earth. |>

|> You can add extra local grounding and attach it to the grounding wire, |> creating a solid local reference. You can't do that with the neutral |> wire. | | 1) Actually, you can. Think about how power is distributed about in an | automobile. Because of the large amounts of plastic, they can't count on | metal objects being grounded so there are a lot of 'negative' wiresss | running about but every time a negative wire is connected to something in | conect with the frame, another 'neutral' path is created. | | 2) "local" grounds from water pipes or short rods into the ground just | aren't very good.

Attaching the neutral to other ground sources at other places creates the parallel return path scenario. The code prohibits this. Neutral is to be bonded to ground at one place only.

Run power from house to garage. Now connect the neutral to a ground rod. See if the inspector approves (if he finds it).

| why assume a sub-panel? most residences don't have them.

Many do. Alternatively, we can ban subpanels. Not sure how you'd wire up multiple circuits in additional buildings w/o a subpanel.

|> |> Then when something does go wrong, it only takes one such thing to put |> |> the full voltage on the neutral. |> |>

|> | |> | and then if all goes well the breaker trips or the fuse blows |>

|> If the ground fault is on the neutral circuit, it can still leak over |> 2ma to 6ma of current over that path. That would trip the breaker. |> But the neutral path would still be connected, and the fault current |> still flowing. Depending on the breaker mechanism design, you could |> even end up with continuous trip solenoid energization, heating up, and |> (because it is probably not designed for 100% continuous duty) |> overheating and burning up, melting the breaker case, and causing an |> even greater fault. |>

| | once the breaker trips is not the solenoid and the rest of the GFI circuit | reenergized? if you open a knife switch in a series circuit no current flows | regardless which side of the load its on.

A miniscule charging current flows. There is voltage potential.

|> | They always recommend you Shut Off All Power to any Targeted Circuits |> | before working on them, the theory is: under those conditions Neither |> | Conductor shouldn't present any Real Danger ...... |>

|> But in typical wiring, that does not shut off the neutral. So even if |> you put all the breakers in the OFF position, you can still have some |> voltage between the neutral and ground that's coming in over the |> service drop, especially if the ground at the pole transformer is |> corroded or broken, or there's an open neutral between that bonding at |> the transformer and the junction point where you neighbors get power |> (their neutral now seeking any and all paths back to the transformer |> for the imbalanced load they have). | | Your service should have its own ground, and its own neutral to earth bond. | No need to worry about a potential difference on the service since you tie | the neutral to local earth ground at your main.

The further away from that point of bonding you get, the further above ground the neutral can float.

| I've found: GFCI's do not perform their function without a proper | ground, they just won't trip so the third wire or equipment bond is | essential.... crossing the Neutral & The Ground in a fully bonded system | will cause the crossed circuit to trip, it won't let the Breaker get | energized.

I disagree.

Put a GFCI receptacle in an old house with no EGC grounding wire and

2 prong outlets. Now connect a 10 kohm resistor between the hot wire on the load side, and a good grounding source like a cold water pipe. It should have about 12ma of current. That won't trip any overcurrent devices. It should trip the GFCI due to current in the sensor (a CT) that isn't canceled by equal return current on the neutral.

| Neutral Conductors as I know them are Isolated from the equipment in | devices they supply, when I was younger I'd come across a radio or other | apparatus with the neutral tied onto the chassis {Hot Chassis} ., as | mentioned, I am happy this practice was banned in consumer goods and the | Ground or Bonding Conductor was applied instead.

My first electrical shock was with a capacitor meter that has such a chassis connection. I had plugged it in hot. I was barefoot on the concrete basement floor. I got a fair portion of that 120 volts.

| BTW: Proper NEC Bonding, as perscribed, is hardly practiced in my neck | of the woods since tightly connected armored cable & emt provides a fair | ground. I've seldom come across it in NYC 1, 2 nor 3Phase Panels., Long | Island on the other hand uses UF or Romex 3+ Conductors The Bonding Wire | Code is practiced of need I guess. | | Earth/Ground must be 25 ohms or less ?

That's the minimum I see required. 25 ohms to where?

in article snipped-for-privacy@individual.net, Charles Perry at snipped-for-privacy@hotmail.com wrote on 2/28/05 6:28 AM:

Probably not. He does not understand things well and writes things up poorly.

Bill

in article snipped-for-privacy@adelphia.com, TimPerry at snipped-for-privacy@noaspamadelphia.net wrote on 2/28/05 9:55 AM:

Than you. You answered my question. GFCI works the way I thought it would.

Someone, I do not remember who, thought that somehow the circuitry detected a connection between ground and neutral even in the absence of IR drops. That did not make much sense.

I did not consider the test button in my post. There indeed is a resistor connected to the test button. I have also found that a capacitor of 0.25µF from hot to ground will trip GFIC. That has an impedance of about 10K with a consequent flow of about 12mA. I think that filtering capacitors in surge protectors and other devices often cause "unexplained" GFCI trips.

Bill

Nope!

The neutral wire just isn't dangerous.

That they do (at least the one I took apart did.) But in that case they are protecting folks from improper installation whereby neutral and hot are reversed. Disconnecting the "neutral" when it really is "hot" is a GOOD IDEA.

You can test it yourself with a cheap (or expensive) VOM. "Test" the GFCI and then measure the voltages to GROUND. THEN (if zero voltage is found) measure the resistance between neutral and ground.

The UK system (0-240) is inferior to the US 120-0-120 system from a safety view. It "looks good" because the UK uses mostly 240 volt appliances whereas in the US just about no "portable" device uses 240. The UK outlets and plugs are in a different league than the US version.

Gad! Then those "some people" must live in terror of 9 volt "transistor" batteries, door bell circuits, and telephones.

The job is DONE when the hots are disconnected.

>

Right!

I would be quite surprised is the breaker type GFCI disconnected the white wire. It's bad enough that switch loops end up with "hot" white wires. But a GFCI breaking the white wire in the panel could result in a HOT white wire where one would least expect it.

Yep! But "they" didn't.

A nice, solid, near "idiot proof" combination neutral and ground.

Unless you "make" the neutral first and "break" it last then disconnecting neutral can cause unexpected voltages in unexpected places.

Well, we were not talking about "code" or the law htee. We were talking about basic safety regardless of the law or the code.

One hopes that would legislatures will pass laws that increase safety but there is no guarantee that is so.

>

in article 42236f9b$0$ snipped-for-privacy@dingus.crosslink.net, John Gilmer at snipped-for-privacy@crosslink.net wrote on 2/28/05 11:28 AM:

This explanation is in conflict with Tim Perry's. When I posted, I was leaning toward Perry's explanation. It certainly is not obvious to me how the second core can be used to detect leakage between neutral and ground. Can you give a reference as to how that works? I would expect something clever.

Bill