How to easily prove a local false ground on a receptacle

Originally Posted By: bking
This post was automatically imported from our archived forum.



First make sure the outlet checks normal.


If you put a quality, correctly operating digital voltmeter on the 200mv AC scale and measure between the Neut and Gnd. you should see some small AC voltages present or fluctuating on a properly wired receptacle. Even the ones close to the panel. This is due to induced signals from adjacent wires and noise and also if current is flowing on the neutral you will see some small voltages. If you get zero millivolts then you have a false ground wired at that receptacle.


It is still possible that a false ground is wired upstream and might look normal but could show up as a lower millivolt reading too. I measured from 3mv to 25mv on mine, some are long runs and I know they are wired correctly ![icon_cool.gif](upload://oPnLkqdJc33Dyf2uA3TQwRkfhwd.gif)

Practice this at home since some meters might not be correct or adequate. Don't touch the meter leads or wires with your fingers because it will cause the meter to respond. I have a BeckMan Tech 310, its over 20 years old and the best meter I have ever used. I have 28 years experience as electronics technician in several different fields.

Make sure 120v is not present between N and G before using meter on lower scale. Also make a plug and cord to get good connections, don't poke the meter leads in the socket. And Don't do this if you are not experienced with electrical testing.

other indications of common problems: 30 to 40 volts AC indicate miswiring. Basically a problem exists if you read less than one millivolt or more than three volts across the N and G. Three volt reading would only exist with a large 120v load present such as a spa pump.


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www.BAKingHomeInspections.com

Originally Posted By: jpope
This post was automatically imported from our archived forum.



Is this not how the SureTest operates? Or does it simply measure resistance?



Jeff Pope


JPI Home Inspection Service


“At JPI, we’ll help you look better”


(661) 212-0738

Originally Posted By: bking
This post was automatically imported from our archived forum.



I don’t know which method the sure test uses but it has a predetermined threshold level in the firmware that triggers the “false ground” display. The measurement I described allows you to observe the millivolts or lack of it and make your own determination. I have found that anything less than one millivolt (.001 v) across N and G is a false ground


You can make a test cable for your meter to plug in easily and safely.
Just remember to always select the higher voltage range first in case 120v is across the N and G or your meter may smoke depending on the protection it has.


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www.BAKingHomeInspections.com