Can the Distance of a Subpanel affect Outlet Tester Results

Question

I got help with wiring my cabin here: Requesting Evaluation of Power Plan at Rural Cabin

and here: Cabin Wiring Plan Revisited

I also put a follow up comment there, but now I'm not sure that was the right place to ask this, since others may have the same question.

So, the sub panel is about 300ft away from the main panel and is wired with 2 hots and a neutral plus ground, and the neutral is not bonded to ground at the subpanel, and is bonded at the main panel. This is brand new, the PoCo just turned on the power and installed their meter yesterday.

I have a little commercial electric tester, this one: https://www.homedepot.com/p/Stop-Shock-GFCI-Outlet-Circuit-Tester-CE-HGT6120/204501748

When I plug it into the outlet the middle indicator goes green & the outer lights off ... then after about a half-second goes to where only the right red light is on.

Could the distance be affecting the tester?

I am tempted to disconnect my subpanel ground and bond the neutral and test it again.

Thanks in advance!

Answer 1

The distance from the panel should not affect tester results for any reasonable value of distance and wire size. Yours are reasonable.

Even if the distances were outrageous, it should still ring out properly if the tester is the only load. E=IR, and if I is very small, E is small for almost any purchasable value of R.

That tester is a mystery

Standard 3-lamp testers simply put a neon light between each pin on the plug. The legends are useless (I call them "magic 8-ball"), but they are an easy way to make 3 lamp tests at once. You can identify this type because 2 lights on is "good" and a third red light coming on is "bad".

This particular one has an onboard microcomputer. Most unfortunately, the computer is intervening between the wires and the lights, which means you are only looking at the simple computer's interpretation of what it sees. Even worse, they have chosen to bring its indicators out to three lights, which fools people into thinking it's a 3-light tester.

Obviously the marketers of this device want to fool you, and think they are doing you some great favor of giving you a better circuit analyzer. They are not. They have only succeeded in making the legend problem even worse. Now we must spend extra time reverse-engineering why the computer thinks the ground is bad. This is a waste of time.

I myself would exploit Home Depot's ample returns policy and then acquire a quality voltmeter, 2-prong neon tester, or simple 3-light tester. One that is made in my home country.

Answer 2

I've never used that specific model but the OEM specifications indicate that it does more than a standard 3-wire tester which simply puts LEDs between each wire and a resistor in series with a test push button to short H and G. It looks like red implies a high resistance between N and G (> 7 ohm or > 10 ohm depending on the source I find online). This might in fact be what you have if the bonding point is so far from the house sub-panel.

Check your math on size of the N and G conductors. If you don't find an error check your connections.

Also, measure N-G resistance directly with a DVM or ohmmeter. I would measure between N and G at the subpanel then repeat at the outlet.

http://www.sperryinstruments.com/en/hgt6120

Answer 3

Read the ratings/reviews on homedepot.com. There are a lot of reviews stating that the unit mis-reports bad grounds! I generally take these reviews with a big grain of salt but there are too many of them to ignore.

It may well be that you have a problem but it is also possible that there is none except for the tester. As suggested in the other answer, I’d use a multimeter to test the resistance between neutral and ground (with the power off to be safe).