just how dangerous is the neutral wire?

| 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).

On Sun, 27 Feb 2005 05:07:18 GMT Repeating Rifle wrote: | in article snipped-for-privacy@news4.newsguy.com, snipped-for-privacy@ipal.net at | snipped-for-privacy@ipal.net wrote on 2/26/05 5:48 AM: | |> In the 3-wire 120/240 volt Edison style single phase wiring |> system as found in North American, a neutral can be shared |> between opposite phases, carrying only the current for the |> imbalance between the phases. In times long ago, there was |> no separate grounding wire; the neutral served as the ground. |> But the grounding wire was added, initially required only on |> some circuits (the laundry room was first). |> | | | | Considering all the crappy wiring I have seen, I would not tempt fate by | assuming th wiring was done competently even if it were done by a competent | electrician. | | In my son's case, a home he bought recently was "upgraded" by installing | grounded recepticles near a bathtub. The problem was that there was no | ground wire available to connect to the ground.

Were these GFCI receptacles? Replacing existing ungrounded receptacles with GFCI receptacles, and marking them appropriately, increases safety, even without the ground wire.

OTOH, if they were ordinary grounded receptacles, my next question would be if the electrician who did this still has his license.

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.

What the "third pin" does right is that USUALLY, it is connected first and disconnected last. In a two wire plug or a three wire 120/0/120 plug the neutral CAN be disconnected first.

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 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.

Duh!

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.

2) it uses more copper

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

you can upsize the wire thereby reducing the IR drop under load.

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

its not up to code until it is done. you have to touch it to make it done. when its done there should be little or no voltage on the neutral. if you have say 50 Vac on the neutral that's 50 volts you don't have across the load (or 50 volts too much) your load is either browned out or burnt out.

according to legend a nurse with nylon panties can kill a pacemaker patient with a static touch.

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.

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.

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?

EGC (the equipment grounding conductor) was first added to portable tools and receptacles because a lot of portable tools had metal frames. These frames were *not* connected to the neutral they just 'floated'. And a lot of portable tools developed faults to the frame. Dirt, water, wet sawdust, workman's sweat, metal chips/debris all were common causes. So then the tool had the metal frame connected to *some* part of the circuit, sometimes neutral, sometimes hot, sometimes a voltage in between. A worker holding the tool had this voltage applied across their body, resulting in a lot of shock injuries. The EGC was added to provide a low resistance path for the frame back to the service panel and to keep the frame near ground potential. This minimized the voltage applied across the worker's body and thus minimized their risk of injury.

EGC was first mandated on portable tools and receptacles while 'neutral grounding' (use of just two hots and neutral)of major appliances such as electric stoves and dryers was still allowed. Separate EGC for appliances came about later.

daestrom

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| Phil Howard KA9WGN |

| (first name) at ipal.net |

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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 the thirty volts it takes to break through a healthy humans skin 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 service voltage AND the insulation would have to fail in a way that 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.

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.

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.

-- Tom H

in article 5voUd.39694$ snipped-for-privacy@twister.nyroc.rr.com, daestrom at daestrom@NO_SPAM_HEREtwcny.rr.com wrote on 2/27/05 10:41 AM:

I found out about neutral to ground protection when testing a portable GFIC cord. I shorted the neutral to ground to get a trip. I still do not quite understand how that works. I presumed that because a neutral to ground short had little series impedance, even small resistive drops would draw enough current to trip. I do not quite understand why or how a signal would be induced onto the neutral for testing. Wouldn't any winding in series with the neutral conductor just increase the resistive drop?

Bill

A "dangerous neutral" can be caused by a floating, (open), neutral on a

Another good reason for the EGC!

i got my head handed to me a while back (on another group) because i misunderstood how the GFI works so i had to research it. you take 2 conductors (hot and neutral) and run then through a toroid coil. if the currents in each direction are equal the EM field cancels out and no voltage is produced by the coil. under a fault condition some of the current goes somewhere other then back where it came from. this voltage is then electronically massaged and used to trip the GFI.

it was pretty a elegant solution i thought :)

the debate arose over whether it was better (safer) to use isolation transformers or GFI to service electronic equipment.

I presumed that because a neutral to ground short

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.

Charles Perry P.E.

in article nJCdnc06MpF5pL snipped-for-privacy@adelphia.com, TimPerry at snipped-for-privacy@noaspamadelphia.net wrote on 2/27/05 1:21 PM:

I guess that I did not ask my question clearly enough.

1. When the neutral and ground connect to each other through some kind of a leak, is the leakage current driven just by IR drop in the neutral?

1. If there were no loads to generate a voltage drop along the neutral or ground conductors, and assuming neutral and ground conductors were connected together at the system ground, would shorting neutral to ground trip the GFIC? How is the unbalanced tripping current generated under such circumstances?

Bill

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.

They way i see it, or rather the way The Neutral should be seen is: Any wire [conductor] proceeding from the Electrical System should be considered Dangerous and dealt with cautiously.

Experience tends to make one take this for granted. Example" Touching the 120vac Hot Bus to the Panel Edge with a one hand finger to finger shunt, to see if the service is present rather than take a tester to it..... don't try it unless you have thick skin & Calluses.

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.

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 ?

You are kidding, right?

Charles Perry P.E.

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. 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.

yes

no

How is the unbalanced tripping current generated under such

You mean the test button? I dont know for sure. I havent busted an old one apart yet. I'd assume its a resister to ground.

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.)

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.