GFCI on 2 wire systems

I simply stated the facts.

[quote="cevans, post:3, topic:43774"]

I wouldn't say they prevent, but rather that they reduce the potential for someone to get shocked. People can always find ways to electrocute themselves.

Many older homes' electrical systems are not grounded, however, short of fully rewiring the house, GFCI can be an effective way of providing improved protection against shocks and maintain "code" compliance with three prong outlets (use the "no equipment ground" stickers).
[/quote]

Since you picked up on Michaels comment but not mine, I will repeat:
They DO NOT reduce the potential for electrical shocks.

Also, the only "improved protection" they provide is to reduce the risk of death by electrocution.

You can also maintain "code compliance" by using 2-prong receptacles.

Personally I only recommend GFCI's in an ungrounded system at the same places I would recommend them with a grounded system. I do add a comment that "addition of a grounding conductor will reduce the risk of less dangerous electrical shocks".

[quote="rbrady, post:22, topic:43774"]

Personally I only recommend GFCI's in an ungrounded system at the same places I would recommend them with a grounded system. I do add a comment that "addition of a grounding conductor will reduce the risk of less dangerous electrical shocks".
[/quote]
Agreed

It is not the volts: It is the amps! One amp can kill!

[quote="rbrady, post:13, topic:43774"]

From what I have heard, at least 220 will knock you off, unlike 110 which just makes your muscles hold tighter.
[/quote]

That is false.

[quote="thowell, post:1, topic:43774"]

Looking for some help on clarification. My understanding is a GFCI will prevent elec shock in a 2 wire system. I have seen them in bathrooms and kitchens. The part that trips me up is, a 2 wire system is still not grounded. That should be a safety concern, but not unsafe with a GFCI installed. (correct?)
Second part of question, in a home with 2 wire outlets why couldn't a person put GFCIs in all the locations? Like the living room for example. I was ask this question the other day. The occupants would be protected, correct?
Thanks folks.
[/quote]

Tim, without getting into a long detailed explanation (which most would probably find boring anyway), let me dispel one common misunderstanding. Two-wire systems are grounded. It is because they are grounded that GFCIs work on them.

Damage caused by electrical shock is a function of time and current. Humans are particularly vulnerable to electric current. The challenge to manufacturers of GFCI devices is to limit current to a where it cannot seriously injure a person but do not deenergize circuits that should not be deenergized. Some loads (specifically, reactive loads) are more difficult than others.

GFCI receptacles have come a long way since the early GFCI devices still, they should not be used on circuits that have heavy motor loads because they could trip when we don't want them to trip. It would be a good idea, for example, not to put a refrigerator on a GFCI receptacle.

It is worth noting that false tripping problems only arise with reactive loads (motors, capacitors, etc). Resistive loads (heating elements, etc) do not cause false tripping (unless, of course, the appliance has malfunctioned).

[quote="rbrady, post:13, topic:43774"]

Have you ever tripped a GFCI with your body (across two fingers doesn't count)? I don't recommend trying it, but would be interested in hearing if anyone has.

From what I have heard, at least 220 will knock you off, unlike 110 which just makes your muscles hold tighter.
[/quote]

While in electricians school(many moons ago) one instructor took an entire class to prove that a AAA battery could potentially kill a person. The technique involved two pieces of wire, two needles and a soldering iron. {you figure it out} He showed where if a needle was stuck in each arm(into a vein) and the battery applied, enough current would flow to stop the heart. As I remember, and it has been many years, .1 milliamp will stop the heart.

Both 220 and 110 will "tend" to throw you off since they are AC voltages. It is DC voltages that will lock you on. Granted 220vac will do a much better job of throwing you off than 110vac will. The rule of thumb is Low voltage AC and Hi voltage DC are the most dangerous.
My largest shock was aboard a submarine where I took a "shot" from the back of my upper arm to my sweaty hand through a pinhole leak in a pair of heavy rubber gloves. It was 440 vac, 400 cycle. Came to about 10 feet away and couldn't use my arm for awhile. The burns hurt like hell. The only long term affect was a very strong desire to never do it again!

[quote="gwells, post:26, topic:43774"]

let me dispel one common misunderstanding. Two-wire systems are grounded.
[/quote]

I think most everyone understands that the neutral wire is the 'grounded conductor', and as such is grounded, even in a 2-wire system. It's kind of a given, that when we discuss un-grounded systems, we are refering to the lack of a 'grounding conductor'.

One thing that I think most people don't realize is that grounding the system acutally increases the risk of shock. If both conductors were isolated from ground, you would have to make contact with both sides (positive & negative) to get a shock - earth ground would not be the negative side. Grounding is used to stabilize the voltage.

[quote="gwells, post:26, topic:43774"]

GFCI receptacles have come a long way since the early GFCI devices still, they should not be used on circuits that have heavy motor loads because they could trip when we don't want them to trip. It would be a good idea, for example, not to put a refrigerator on a GFCI receptacle.

It is worth noting that false tripping problems only arise with reactive loads (motors, capacitors, etc). Resistive loads (heating elements, etc) do not cause false tripping (unless, of course, the appliance has malfunctioned).
[/quote]

If motor loads are causing a GFI to trip the appliance is leaking current in excess of the allowable UL amount. For example a sump pump motor under the UL standard is only allowed to leak a small fraction of the 4-6mA that a Class A GFI would trip at. I cannot find the exact leakage allowed.

As a side note refrigerators in a commercial kitchen are REQUIRED to be GFI protected.

I would ask which is better, a refrigerator with a tripped GFIand spoiled food or a faulty refrigerator with a fault and a dead person?

:shock:
Those of you that try to predict when an electric current will, hurt, make you hold on, make you let go kill or seriously injure you are doing a disservice to those that are looking for answers.

It takes VERY little current to kill a person under the right circumstances A/C or D/C. If you must have a specific answer it is less than a milli amp. It can not be predicted with any degree of accuracy, to try is reckless.

I will step off the soap box now.:mrgreen:

[quote="jshishilla, post:30, topic:43774"]

:shock:
Those of you that try to predict when an electric current will, hurt, make you hold on, make you let go kill or seriously injure you are doing a disservice to those that are looking for answers.

It takes VERY little current to kill a person under the right circumstances A/C or D/C. If you must have a specific answer it is less than a milli amp. It can not be predicted with any degree of accuracy, to try is reckless.

I will step off the soap box now.:mrgreen:
[/quote]
As I said earlier 5 mA is non lethal in a normal person.

Hospital requirements are much lower for patient care areas. The limits are on the order of 100 microAmps allowable leakage current and 10 microAmps in certain areas without gong into more detail than is needed here.

[quote="mlarson, post:31, topic:43774"]

As I said earlier 5 mA is non lethal in a normal person.

Hospital requirements are much lower for patient care areas. The limits are on the order of 100 microAmps allowable leakage current and 10 microAmps in certain areas without gong into more detail than is needed here.
[/quote]

Michael,

my comment was not directed towards you. I just felt it necessary to explain to those without any electrical background because of the nature of the thread.

[quote="jshishilla, post:32, topic:43774"]

Michael,

my comment was not directed towards you. I just felt it necessary to explain to those without any electrical background because of the nature of the thread.
[/quote]
I was trying to keep it simple too.;-)

Electricity is not well understood by many including home inspectors.

I worked in hospitals for years were it was my primary concern.

[quote="mlarson, post:17, topic:43774"]

I used to work with a maintence electrician that would wet two fingers and swipe at wire exposed wires to make sure they were dead. :roll:
[/quote]

That's the electrician's version of Russian Roulette.

[quote="mlarson, post:4, topic:43774"]

They prevent a fault current in excess of 5 mA from going through a person.

That is sufficient to prevent electrocution in most of the population.

Those at risk are ones that have a pathway via inter-venous lines or a compromise layer of skin.

GFCI outlets in non three wire systems need to be labeled appropriately.
[/quote]

your like the guy that knows everything. LOL:shock:

[quote="mnorthrup, post:35, topic:43774"]

your like the guy that knows everything. LOL:shock:
[/quote]
Nah, I just know a lot.;-)

[quote="mlarson, post:6, topic:43774"]

Conduit in Iowa?

Come on Bob get real.
[/quote]

Good one guys LOL, Iowa does have conduit. I've seen it at Menards.
Anyway, thanks everyone for all the info.
Why wouldn't a TV be protected on a 2 wire system that has a GFCI. Or maybe a better question. How would a surge protector work on a 2 wire system with a GFCI outlet.

The GFCI does not provide protection for appliances.

It basically monitors the current in the ""hot and "neutral" legs and if they are more than 5 mA apart it removes power from the outlet.

[quote="thowell, post:37, topic:43774"]

Or maybe a better question. How would a surge protector work on a 2 wire system with a GFCI outlet.
[/quote]

Not very well.

Most (if not all) surge protectors with a warranty require that the circuit be grounded. While there is some in line protection, most of the surge is routed through a sacraficial MOV to ground. Also things like memory and CPU's are very sensitive to static, which is controlled best with grounding the outer case/frame. Here is an article I use on my website:

[FONT=Times New Roman][size=5]Surges, spikes, zaps, grounding and your electronics
**[/size][/FONT][FONT=Times New Roman][size=2]Theoretically, the power coming into your house is a perfect AC sine wave. It is usually quite close. But occasionally, it won't be. Lightning strikes and other events will affect the power. These usually fall into two general categories: very high voltage spikes (often into 1000s of volts, but usually only a few microseconds in length) or surges (longer duration, but usually much lower voltage). Most of your electrical equipment, motors, transformeroperated
electronics, lights, etc., won't even notice these one-shot events. However, certain types of solid-state electronics, particularly computers with switching power supplies and MOS semiconductors, can be damaged by these occurances. For example, a spike can "punch a hole" through an insulating layer in a MOS device (such as that several hundred dollar CPU), thereby destroying it. The traditional approach to protecting your electronics is to use "surge suppressors" or "line filters". These are usually devices that you plug in between the outlet and your electronics.
Roughly speaking, surge suppressors work by detecting overvoltages, and shorting them out. Think of them as voltage limiters. Line filters usually use frequencydependent circuits (inductors, capacitors etc.) to "tune out" undesirable spikes - preventing them from reaching your electronics. So, you should consider using suppressors or filters on your sensitive equipment. These devices come in a very wide price range. From a couple of dollars to several hundred. We believe that you can protect your equipment from the vast majority of power problems by selecting devices in the $20- 50 range.
[/size][/FONT]
[FONT=Times New Roman][size=2]A word about grounding: **[/size][/FONT][FONT=Times New Roman][size=2]most suppressors and EFI filters require real grounds. Any that don't are next to useless.
For example, most surge suppressors use MOVs (metal oxide varistors) to "clamp" overvoltages. Yes, you can have a suppressor that only has a MOV between neutral and hot to combat differential-mode voltage excursions, but that isn't enough. You need common-mode protection too. Good suppressors should have 3 MOVs, one between each pair of
wires. Which means you should have a good solid ground. Eg: a solidly connected 14ga wire back to the panel, not rusty BX armour or galvanized pipe with condensation turning the copper connection green. Without a ground, a surge or spike is free to "lift" your entire electronics system well away from ground. Which is ideal for blowing out
interface electronics for printer ports etc. Secondly, static electricity is one of the major enemies of electronics.
Having good frame grounds is one way of protecting against static zaps. If you're in the situation of wanting to install computer equipment on two wire groundless circuits take note: Adding a GFCI outlet to the circuit makes the circuit safe for you, but it doesn't make it safe for your equipment - you need a ground to make surge suppressors or line filters effective.

[FONT=Times New Roman][size=1][FONT=Times New Roman][size=1]Copyright 1991-2004 Steven Bellovin (smb(at)research.att.com) Chris Lewis (clewis(at)ferret.ocunix.on.ca)
Redistribution for profit, or in altered content/format prohibited without permission of the authors. Redistribution via printed book or
CDROM expressly prohibited without consent of the author. Any other redistribution must include this copyright notice and attribution.
[/size][/size][/FONT][/FONT][/size][/FONT]

[quote="Jim_Port, post:29, topic:43774"]

If motor loads are causing a GFI to trip the appliance is leaking current in excess of the allowable UL amount.
[/quote]

Nuisance tripping is caused by phase shift in a reactive circuit.