GFCI on 2 wire systems

[John Shishilla]

Originally Posted by mlarson

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.

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.

[Michael Larson]

Originally Posted by jshishilla

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.

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.

[George P. Wells, CMI]

Originally Posted by mlarson

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.

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

[Mark E. Northrup]

Originally Posted by mlarson

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.

your like the guy that knows everything. LOL

[Michael Larson]

Originally Posted by mnorthrup

your like the guy that knows everything. LOL

Nah, I just know a lot.

[Tim C. Howell]

Originally Posted by mlarson

Conduit in Iowa?

Come on Bob get real.

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.

[Michael Larson]

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.

[Ralph Brady]

Originally Posted by thowell

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

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:

Surges, spikes, zaps, grounding and your electronics

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.

A word about grounding:

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.

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.

[George P. Wells, CMI]

Originally Posted by Jim Port

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

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

[George P. Wells, CMI]

Originally Posted by rbrady

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'.

There is a difference between a device that is ungrounded and an ungrounded system. It is true that the term "ungrounded" is often misused but using correct terminology helps those who are trying to learn about electrical systems.