Electrical conundrum quiz

[Bobbo]

I have solved this problem, but thought the electrical experts might try their hand at diagnosing this problem.

My father in law made a homemade extension cord. He took a 12/2 wG cable and put a plug on one end. He wired a box with a SPST ON/OFF switch to the hot wire. He then wired the other end with a duplex 15 amp outlet.

When he plugged ANYTHING into the outlet, it would not work. It was like it had no power, so he called me. (I have a reputation of being able to fix anything.)

I plugged in one of the 3 light testers.

With the power switch turned ON, all 3 lights were lit.

With the power switch turned OFF, the red and middle lights were lit up which normally indicates a hot/neutral reversal, but the right light was not on. Note that this is with the power switch turned OFF.

Anyone care to guess?

[Bobbo]

Everything else is house wiring from when the house was built. Now, it IS an old house, but this is the only thing left that he wired. (After I re-wired the water heater.)

But, I agree it does not explain the symptoms.

I am not trying to get defensive. I am trying to understand what I am being told.

[wnjj]

Bobbo wrote:

wnjj wrote:
There's no good explanation for a red light on the 3-light tester in ANY receptacle that has the neutral and ground connected (which are ultimately directly shorted together in the main panel of the house).

The neutral and ground were not connected. The hot wire strands were touching the neutral screw. That is the whole problem I found in the system. The ground was not connected to either the hot or the neutral in any way.

Or am I misunderstanding?

I meant that if the neutral and ground wires are well connected to the neutral and ground screws on the receptacle. That means they should have a nice, low resistance connection to each other via the house wiring all the way back to the main panel.

Ditto what Hking Hunter said. Thanks for posting this. I enjoy a good puzzle but the reason nobody came up with your answer is it simply doesn't explain it. I'm concerned there is still an issue, particularly in light of your comments about the skill level of your father-in-law when it comes to wiring.

[Hiking_Hunter]

Bobbo, I know it seems like we're beating up on you, but we're not. I appreciate you presenting the case in the first place as a troubleshooting problem. Good stuff to challenge the mind.

But, I agree with wnjj,

wnjj wrote:
Either you did without knowing it or something is still wrong.... I'd make really sure something still isn't wired wrong, intermittent or reversed.... Unexplained symptoms always indicate a misunderstood problem.

I also have many years (>40) troubleshooting electronics. What wnjj is saying is don't give up, don't assume anything, and don't fool yourself.

Who knows - It very well could have been something out of left field like a overtightened cable clamp that shorted wires together or to the box, and that connection is mechanically intermittent - clearing itself at the most inopportune time. Ask me how I know - I had that happen energizing a whole metal sunroom frame. It wasn't discovered until a year later when the weather was cooler and things contracted, and someone grabbed the frame in bare feet. All the outlets in the sunroom tested and worked fine.

Something just didn't add up for the symptoms you originally reported.

But, thanks for the challenge...

[Bobbo]

wnjj wrote:
There's no good explanation for a red light on the 3-light tester in ANY receptacle that has the neutral and ground connected (which are ultimately directly shorted together in the main panel of the house).

The neutral and ground were not connected. The hot wire strands were touching the neutral screw. That is the whole problem I found in the system. The ground was not connected to either the hot or the neutral in any way.

Or am I misunderstanding?

[wnjj]

Bobbo wrote:

wnjj wrote:

Bobbo wrote:
I agree that the symptoms are not explained. That is why I have posted this here, hoping someone with more knowledge can enlighten me.

The red light in the tester is a light bulb connected between neutral and ground. The only way I can see the red light coming on is if neutral is not connected to ground (and the strands power up the neutral). This could be an open in the plug, the receptacle it's plugged into or anywhere in the wiring all the way back to the main panel.

If the neutral and ground both have good connections from the receptacle you are testing all the way back to the main panel where ground and neutral are connected, it's not possible to have a voltage potential across that red light.

I think I'd plug s decent sized load into it and measure the voltage on everything.

Again:

Bobbo wrote:
He wired everything correctly. BUT! He used stranded wire and did not get all of the strands under the screws in the plug. One or two of the strands from the hot wire were touching the neutral screw inside the plug.

And:

Bobbo wrote:
I have already fixed the problem. Further testing of the old problem is not possible.

I understood a long time ago that you already fixed it. I'm not referring to the stuff he built but rather the existing receptacle he plugged into and the wiring upstream of it. I'm also suggesting you perform more tests on what is there now.

There's no good explanation for a red light on the 3-light tester in ANY receptacle that has the neutral and ground connected (which are ultimately directly shorted together in the main panel of the house). It makes no difference if there were any additional shorts like strands of wire. You said you did nothing to correct any poor neutral or ground connections themselves (other than the shorted strands). Either you did without knowing it or something is still wrong.

If it were me, I'd make really sure something still isn't wired wrong, intermittent or reversed. I'm a EE of 25 years and do this kind of debugging (but on electronics) every day. Unexplained symptoms always indicate a misunderstood problem.

Also some interesting reading here as to why you cannot always trust those testers or (even a voltmeter for that matter).

[Bobbo]

wnjj wrote:

Bobbo wrote:
I agree that the symptoms are not explained. That is why I have posted this here, hoping someone with more knowledge can enlighten me.

The red light in the tester is a light bulb connected between neutral and ground. The only way I can see the red light coming on is if neutral is not connected to ground (and the strands power up the neutral). This could be an open in the plug, the receptacle it's plugged into or anywhere in the wiring all the way back to the main panel.

If the neutral and ground both have good connections from the receptacle you are testing all the way back to the main panel where ground and neutral are connected, it's not possible to have a voltage potential across that red light.

I think I'd plug s decent sized load into it and measure the voltage on everything.

Again:

Bobbo wrote:
He wired everything correctly. BUT! He used stranded wire and did not get all of the strands under the screws in the plug. One or two of the strands from the hot wire were touching the neutral screw inside the plug.

And:

Bobbo wrote:
I have already fixed the problem. Further testing of the old problem is not possible.

[Bobbo]

Yes, it is a SPST switch.

[enblethen]

Are you sure he has a single pole switch and not a three way?
One a three way the dark (black)screw is a traveler to the other switch. One a single pole the dark (green) screw is ground. with the switch in what is to believed off position power would be connected to the ground.

[wnjj]

Bobbo wrote:
I agree that the symptoms are not explained. That is why I have posted this here, hoping someone with more knowledge can enlighten me.

The red light in the tester is a light bulb connected between neutral and ground. The only way I can see the red light coming on is if neutral is not connected to ground (and the strands power up the neutral). This could be an open in the plug, the receptacle it's plugged into or anywhere in the wiring all the way back to the main panel.

If the neutral and ground both have good connections from the receptacle you are testing all the way back to the main panel where ground and neutral are connected, it's not possible to have a voltage potential across that red light.

I think I'd plug s decent sized load into it and measure the voltage on everything.

[wnjj]

Nevermind. I re-read better. The shorted strands were at the plug, not the receptacle.

[Bobbo]

enblethen wrote:
Try putting a three way plug tape or power strip into receptacle and then plug in tester to see if makes any difference.

I have already fixed the problem. Further testing of the old problem is not possible.

Hiking Hunter wrote:
Bobbo -
When you originally tested the circuit you had a three light tester. Was the load you tested with (that didn't work) just a two wire ungrounded load?

No, it was a pair of 4 foot 2 bulb fluorescent shop lights with 3 prong plugs. Now, I haven't opened up the lights to see if the ground wire is hooked up in them.

As soon as I re-wired the plug, the lights worked.

The actual, physical, setup is this. He hung 2 of the shop light fixtures from the ceiling but had nowhere to plug them in. He put a box on the wall beside them with a duplex outlet and plugged them in. He ran about 3 feet of wire down to a box he attached to the wall at chest height and put a SPST switch in. From the switch he was about 1 foot from a normal wall outlet, so he wired up a 1 foot long piece and plugged it in.

I tested it with the 3 light tester by unplugging the light fixtures.

[Hiking_Hunter]

Bobbo -
When you originally tested the circuit you had a three light tester. Was the load you tested with (that didn't work) just a two wire ungrounded load?

[enblethen]

Four feet is not long enough for induced current.
Try putting a three way plug tape or power strip into receptacle and then plug in tester to see if makes any difference.

[Bobbo]

enblethen wrote:
How long is the run and what type of wire? It is possible that it could be induced current.

About 4 feet of stranded 12/2 wG NM-B cable.