MAC702
Senior Member
- Location
- Clark County, NV
Except for certified home inspectors.
HOT/NEU Reversal?
- Thread starter drcampbell
- Start date
- Status
Except for certified home inspectors.
You mean 'Graduates of the Class of Tuesday, 10:30 AM"?
Yep. They are notoriously bad at detecting bootleg grounds.
MAC702
Senior Member
- Location
- Clark County, NV
I'm going to steal that one! :lol:
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
So ... finally made it back to the site.
I'm revising my estimate of the age of this house -- now 1946-1959 -- after noticing 2-wire cloth-jacketed NM cable and black-enameled junction/device boxes.
The circuit in question is in the breakfast nook, which is a later addition. There are four ordinary 5-15R receptacles and a ceiling light on a 15-amp breaker. The Sperry plug-in tester shows the same HOT/NEU REV fault indication in all four receptacles.
I pulled the two receptacles nearest to and farthest from the breaker panel. They're wired with yellow plastic-jacketed NM cable. The bare wires are wire-nutted together, with stubs to the receptacles' ground terminals. The black & white wires are screwed to the receptacles -- no backstabbing -- are on the correct terminals, use the receptacles themselves to provide continuity, and are clean & tight. No surprises; good-quality work.
Using the low-impedance meter function yielded different measurements but no additional insight. Likewise putting the circuit under load.
Unloaded, the circuit voltage was a trifle below nominal. With a ten-ohm (?) load, there was an unsurprising and totally-acceptable amount of voltage drop.
But the goofy thing: 13 volts between green & black. In Lo-Z mode, so it's apparently not a phantom voltage, and unchanged by loading the circuit.
The other goofy thing: When the Fluke 117 was in the circuit in Lo-Z mode, the Sperry tester began flashing between "HOT/NEU REV" and "BAD GROUND". Seemingly at random, at about 3 Hz, and nowhere near a 50% duty cycle.
- - -
This circuit's breaker feeds a 2-wire cloth-covered NM cable, which disappears into a first-floor wall cavity immediately above the breaker box. Thirty feet east, the receptacles are connected with 3-wire plastic-jacketed NM cable. I was unable to locate a junction box -- if there is one -- where the two meet.
So as far as the house wiring goes, mystery solved.
The only remaining mystery: Why the goofy instrument indications?
I'm revising my estimate of the age of this house -- now 1946-1959 -- after noticing 2-wire cloth-jacketed NM cable and black-enameled junction/device boxes.
The circuit in question is in the breakfast nook, which is a later addition. There are four ordinary 5-15R receptacles and a ceiling light on a 15-amp breaker. The Sperry plug-in tester shows the same HOT/NEU REV fault indication in all four receptacles.
I pulled the two receptacles nearest to and farthest from the breaker panel. They're wired with yellow plastic-jacketed NM cable. The bare wires are wire-nutted together, with stubs to the receptacles' ground terminals. The black & white wires are screwed to the receptacles -- no backstabbing -- are on the correct terminals, use the receptacles themselves to provide continuity, and are clean & tight. No surprises; good-quality work.
Using the low-impedance meter function yielded different measurements but no additional insight. Likewise putting the circuit under load.
Unloaded, the circuit voltage was a trifle below nominal. With a ten-ohm (?) load, there was an unsurprising and totally-acceptable amount of voltage drop.
But the goofy thing: 13 volts between green & black. In Lo-Z mode, so it's apparently not a phantom voltage, and unchanged by loading the circuit.
The other goofy thing: When the Fluke 117 was in the circuit in Lo-Z mode, the Sperry tester began flashing between "HOT/NEU REV" and "BAD GROUND". Seemingly at random, at about 3 Hz, and nowhere near a 50% duty cycle.
- - -
This circuit's breaker feeds a 2-wire cloth-covered NM cable, which disappears into a first-floor wall cavity immediately above the breaker box. Thirty feet east, the receptacles are connected with 3-wire plastic-jacketed NM cable. I was unable to locate a junction box -- if there is one -- where the two meet.
So as far as the house wiring goes, mystery solved.
The only remaining mystery: Why the goofy instrument indications?
growler
Senior Member
- Location
- Atlanta,GA
If I have read this correctly you have 2 wire cloth over NM leaving the panel on this circuit.
Where is the circuit supposed to pick up a ground?
Somewhere there is a transition to 3 were cable. You have opened the receptacle so that's not it and this was an addition.
You say that there is also a light on this circuit ( which probably means also a switch).
Next place to look is the light fixture junction box. Lots of old house wired to light fixtures first.
growler
Senior Member
- Location
- Atlanta,GA
You don't have a ground. At least not a good ground, if you did you would get the same reading from black to green as from white to green.
Pull the light fixture and look for burned wires in what probably a metal box. The ground wires and neutral may be touching in that box.
How do you figure that the mystery is solved regarding the house wiring?
The instrument readings are goofy because the wiring is goofy. I bet if you were to measure the resistance between the ground terminal of that outlet and the ground bus in the distribution panel, you'll find get a reading of about ~24,000Ω.
You need to find where the 2-wire cloth jacketed NM joins the 3-wire Romex. I bet you'll find a bad ground there.
mtfallsmikey
Senior Member
I'd be looking for my>>>>
~RJ~
Wanna borrow mine?
mtfallsmikey
Senior Member
QRZ? de W4KAV
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
[MENTION=150197]drcampbell[/MENTION]
Take a pigtail light socket w/bulb with alligator clips, at the receptacle, put the black lead on the hot/black wire and put the white lead on the ground wire. If the bulb lights full brightness the ground is good, if it lights somewhat less than full brightness, you have a weak ground, if it doesn't light at all, you have no/bad ground.
Also agree with taking the light apart and checking there, and probably the switch box as well.
Take a pigtail light socket w/bulb with alligator clips, at the receptacle, put the black lead on the hot/black wire and put the white lead on the ground wire. If the bulb lights full brightness the ground is good, if it lights somewhat less than full brightness, you have a weak ground, if it doesn't light at all, you have no/bad ground.
Also agree with taking the light apart and checking there, and probably the switch box as well.
K8MHZ
Senior Member
- Occupation
- Electrician
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Amateurs! :roll: 
D)
D)
K8MHZ
Senior Member
- Occupation
- Electrician
Amateurs! :roll:
25 years continuous licensing for me come the 16th of this month.
K8MHZ
Senior Member
- Occupation
- Electrician
I am not sure what the problem we are trying to solve actually is. I may have missed that somewhere.
Is there a light not working or a receptacle that won't power up a device somewhere? I saw all the voltage measurements. What exactly would an electrician be troubleshooting? What is not working?
The branch circuit in question almost assuredly has a high-resistance ground. In my book, that's something in the electrical system that's "not working" and requires troubleshooting and correction.
If Fluke makes their LoZ setting in their 117 multimeter the same as they make their SV225, then that bad ground has a total resistance of almost exactly 24,000Ω. I didn't just pull that number out of the air.
growler
Senior Member
- Location
- Atlanta,GA
If you have a three pronged receptacle that's showing any sort of incorrect wiring with a plug in tester that's a problem ( if your are going to sell a house, home inspection).
It's kind of obvious they don't have a ground so you have to wonder why it's not showing an open ground.
One possible answer is that they boot-legged the ground and there is a loose connection.
Another possible answer is they just left the bare copper in the junction box and now the neutral is making contact with the box or with the bare copper ( accidental bootleg ).
growler
Senior Member
- Location
- Atlanta,GA
I once found one like this that turned out to be an open ground except the two ground wires were touching a metal junction box that had for some reason been painted on the inside.
In areas where I normally work it is required that bare grounds be twisted and crimped.
If you just use wire nuts then grounds come loose as often as other conductors.
In this case we have no idea where they are even connecting to any sort of ground.
I agree. Which is why I stated (as did you) that he needs to find where the old 2-wire NM meets up with the new 2+G NM. I'm guessing that whoever did the wiring for the addition made some kind of ground connection at that junction and it has either become a bad connection, or the source of the ground was poor to begin with.
- Status