View Single Post
Old 11/11/09, 10:20 AM
rbrady's Avatar
rbrady rbrady is offline
Active Poster
Join Date: Feb 2007
Location: Eureka, CA
Posts: 619
Please Note: rbrady is a non-member guest and is in no way affiliated with InterNACHI or its members.
Default Re: GFCI on 2 wire systems

Originally Posted by thowell View Post
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) Chris Lewis (clewis(at)
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.