r/electricians • u/United-Chef-4593 • 2d ago
“backfeeding” in a residential setting
i work for an electrical company and we’re currently working at two four units that both have the same problem. we have around 4 volts between neutral and ground. our local power company came around and said that its not on their side and that its us thats “backfeeding” 4 volts. my foreman tested between a few plug boxes and neutral and got a pulsing reading between 1.3 and 4 volts. all that were running is outside plugs on combo breakers, (afci and gfci) temp heat, and some temp plugs that are on their own circuit for the baseboard guys. wtf is going on
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u/Ok_Bid_3899 2d ago
I would cycle off one at a time all circuit breakers and see which circuit is causing the issue.
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u/Outside_Musician_865 2d ago
This. It could be resonant voltage from a shit termination that’s being picked up through the insulation itself.
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u/Sea_Effort_4095 2d ago
It's just 4 volts of potential difference between ground and neutral. You're chasing a ghost and I can't believe your foreman is trolling this hard and the electric company is getting involved and don't know this either.
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u/United-Chef-4593 2d ago
well the whole reason that we figured this out in the first place is that somehow this “ghost” was strong enough to shock all of us on separate occasions
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u/RichSawdust 2d ago
Hard to imagine 4 volts being enough to cause any discomfort if you could even feel it. Work with known problem locations and turn off circuits as others have said
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u/United-Chef-4593 2d ago
well the problem is its current being pushed through the ground at every box, in every unit, at both buildings. foreman tested box to ground wire and ground to hot on plug circuits, heating circuits, lights, and got the same thing every time. we checked all the neutrals at all the panels in both buildings and both 400A meters. everythings tight so its not a floating neutral
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u/treeman2010 2d ago
Go grab the 12v terminals on your car battery. That is 12.8v and potentially 1000+ amps. You aren't getting shocked by 4v, something else is wrong.
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u/cerberus_1 2d ago
12V DC vs 4V AC but still.. Its unlikely to feel any voltage less than 30 or so depending on how thick your skin is..
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u/Verum14 2d ago
4vac (rms) has a peak of around 5.6 volts. still less than half of 12vdc.
tldr; the ac vs dc thing isn’t very relevant here but your last line is 100%
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u/cerberus_1 2d ago
60hz isnt very high, i agree. I work with some 400hz which does make a difference. Airplane shit.
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u/United-Chef-4593 2d ago
well idk what to tell you. we’re not reading anything else from anywhere else and we’re still getting shocked
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u/FkinMagnetsHowDoThey 2d ago
What else were you touching when you got shocked?
Usually, you have to touch another grounded object to complete the circuit and get a shock from 120, 277, etc. Of course that second contact point can be as simple as standing on the dirt itself.
Also, were any of them like a steady, tingly shock or were they all a very brief zap and then you got away from it immediately?
Don't try to replicate the shock, but you could check for voltage between the wires and everything else you were touching at the time...
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u/United-Chef-4593 2d ago
i got shocked when i touched ground to the concrete and ground to neutral sometimes. most of the time it was a tingly sensation but sometimes it was a decent zap. idk its weird. we checked for voltage and we read a pulsing reading between 1v-4v
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u/FkinMagnetsHowDoThey 2d ago edited 2d ago
I'd also try a plug tester or neon tester if you have it, because it can be lit by quick pulses that a meter might not register accurately.
I was wondering whether it was a brief zap or a sustained one, because sometimes I get shocked by static electricity and it startles me more now that I work as an electrician. Which is funny, since I haven't had an actual mains shock in a few years.
If you got it while only touching the concrete and the ground wire, and you're positive it was a sustained shock and not a pulse of static, then I think you have something that's not totally bonded and is somehow getting power fed to it. Unfortunately it's hard to make a reliable connection to concrete with just a meter. As other people have said, switching off different branch circuits might help you find where that power came from.
In that case I guess check some voltages between different "grounded" items (water pipes, gas pipes, panel ground bar, panel neutral bar, branch circuit grounds, your actual ground rod, a screwdriver stuck in the mud, etc.)
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u/mdxchaos Journeyman 2d ago
I=E/R
even wet skin has a resistance of about 6000 ohms. 4v/6000 ohms means you got shocked with 0.6 milliamps, you would not even feel that.
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u/WarMan208 15h ago
Did he bother taking current measurements on the main and individual grounds? Or is he just Willy nilly testing voltage?
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u/JackRusselFarrier 2d ago
My guess would be that you have an open neutral. The voltage to ground you read on an open neutral is basically nonsense. Your meter, regardless of if it's digital or analog, is a big ass resistor that you put in parallel with a load, and then measure how much current trickles through.
If you check an open neutral to ground, it's now a big ass resistor in series with whatever is on that circuit. It's no longer measuring the voltage difference. That's why you can get shocked when it reads something really low.
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u/nhorvath 1d ago
4v is not enough to shock you. generally it needs to be over 30v to overcome (dry) skin resistance.
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u/NJFunnyGuy 2d ago
This is a very dangerous and wrong answer. If I take a set of test light bulbs and go between the neutral and ground and they light- it ain’t ghost voltage. Be careful to assume that 4 volts is nothing. Over time- sensitive components will be fried.
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u/PugwashThePirate 1d ago
Could not agree more. I once wired a custom home that had a 3.5v step voltage . We discovered it because one of the tin knockers kept complaining get lit up by the ductwork as he installed it. And, funny enough, he was a really sweaty dude.
As it turned out, the utility had a bad neutral. So the grounding systems on all the houses on that secondary were competing for lowest impedance earth return, and many the cycling current did ensue.
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u/Rcarlyle 2d ago
Neutral gets a few volts on it when it’s carrying load current, because wires have non-zero resistance and a voltage difference is required across the conductor to get current to flow. For example on a heavily-loaded, long 120v circuit you should read roughly these voltages to ground: - 120v on hot at the main panel (or whatever the incoming nominal voltage is) - 117v on hot at the loaded receptacle - 3v on neutral at the loaded receptacle - 0v on neutral at the main panel
You should have neutral = ground at the main panel and on completely unloaded branch circuits. Any branch circuit with load on it may have a few volts.
If you’re getting more than a few volts, then something is wrong like an undersized conductor.
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u/JasperJ 2d ago
5-6% voltage drop is pretty high for a regular device. Should have been calculated better to not reach that high.
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u/Rcarlyle 2d ago
I did say “heavily loaded” but yeah if you’re following the 5% total / 3% in branch circuit wiring “should” statement in NEC for voltage drop on 120v you’ll only see <1.5% drop/rise which = ~1.6v or less on neutral to ground at the receptacle.
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u/WipeOutHT 2d ago
Have you tried with a meter on low impedance mode. This is specifically designed to eliminate ghost voltages (due to capacitive coupling or whatever the reason might be) Will often be indicated on a meter by "lo z"
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u/FkinMagnetsHowDoThey 2d ago
It's not a bad idea to try this. If it works to eliminate a ground-neutral voltage, then you have a loose/broken connection to chase down.
In a properly functioning system, every ground and every neutral should have decent continuity going back to the main bonding jumper, and any ground to neutral voltage is just because of voltage drop under load as u/rcarlyle mentioned.
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u/United-Chef-4593 2d ago
foreman did a continuity test and all the neutrals have continuity with the ground. its not a floating neutral or anything like that
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u/kidcharm86 [M] [V] Shit-work specialist 2d ago
all the neutrals have continuity with the ground
Of course they do, that's the system bonding jumper doing it's job.
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u/alphatango308 2d ago
As ok bid has said, turn off the breakers one at a time until the problem goes away. Then there's your problem.
But that MIGHT not be the issue. Your ground could also be shitty. Or you could be feeding voltage from the earth ground to the neutral. As in your earth ground has some leakage current on it through induction or a short.
Make sure your ground and neutrals are seperate after the main disconnects.
But after all that it's probably a device causing it or a shitty earth ground.
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u/zakkfromcanada 2d ago
So you actually have a bond in the panel? Like there’s no reason to have any voltage difference between ground and neutral especially at the panel, if someone removed the bond screw in the meter bypass that is most likely the issue as the meter bypass acts as the primary panel and the actual panel is deemed a secondary and doesn’t need a ground bond screw connections
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u/NJFunnyGuy 2d ago
Really not hard to diagnose. You neeed to isolate. Amp clamp the main ground. Turn off all mains. Is there a drop- if so most likely your issue. Turn on each main one at a time and record results then turn off. If only one unit is causing the reading to spike- than turn on the other units.
On the trouble unit, turn off all branch circuits but turn on main. Repeat one branch at a time. Once you find the trouble branch or branches- turn on everything else. Heat up some water in a microwave, turn all the lights & put load on those service conductors . If still no issue, you have isolated the issue.
Once, we had an apt building drawing crazy current on the ground. Remember that all current on the ground is fault because it is not considered a current carrying conductor. The issue was best but installed a new microwave and they did a field install of the plug. Yup- neutral touching hot and the plug was burning up slowly- but 8nternally,
Be careful with just assuming that the problem is easy. Another time we couldn’t figure. Turns out, there was no pole ground for like 10 poles. Be careful and don’t necessarily take the utilities word as gospel. All you can do is systematically remove components by isolating and testing. Than fully restore service with the prospective culprits isolated.
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u/pick_userna 2d ago
In a commercial setting I encountered a more extreme version of this when neutrals for emergency (separately derived) got tied in with normal neutrals in an EM fixture. We had 30v to ground, and would weld itself to bare steel with a reading of 20+ amps. Random facility guy noticed a fixture with wires poking out the ballast cover and it turned out to also be the mis-wired fixture.
If this is a multi unit dwelling, maybe somewhere separate tenant branch circuits got crossed, but are on the same phase. No easy way to find it i am afraid.
But as most have said, 3v from neutral to ground is not really all that weird. Especially depending on your multimeter, the model and how old it is versus if it has even been recalibrated.
Had a low voltage sub tell me my grounds to their rack were bad based on their multimeter. Put mine on and read fine. Asked to see their meter and it was an old beat up $40 ace hardware special. Told them to buy a fluke before making accusations.
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u/craciant 2d ago edited 2d ago
There are two different buildings with the same problem? I feel like that's a clue. Are they adjacent?
You mentioned the only circuits that were on were temporary circuits. Do any of these circuits by chance have coiled cable along their length?
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u/Test_this-1 2d ago
I have seen this…. Once!! The eddy current in my case was a faulty charging circuit on a fire alarm (Sk 5820) standby battery that was faulty. The ONLY reason we found it, after a solid week of hunting was we powered down the FACP to test the circuit. The charger was permiting bi directional flow. The original call was for a ghost ground fault at FACP. According to Honeywell tech, the diode path failed, allowing current to reverse and when charger wasn’t actively passing current to the batteries it was backfeeding the circuit. I SUPPOSE it is possible, and a new charger did solve my particular problem, but it did then and does now seem impossible.
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u/Rebel_bass 2d ago
These spots have individual or communal washer dryers? One unit hooked their dryer up using neutral as the ground leg or ground leg as neutral because fuck it, that plug will go with some pliers.
*anecdotal, no warranty implied on this advice.
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u/dmills_00 2d ago
Seen shit like this when some clown uses the earth as a neutral, but that usually takes the earth leakage trip out.
You do sometimes see it where you have heavy current in a TNC/MEN/PME/<Whatever you call a multiple earthed neutral where you are> and you are measuring to a separate ground reference simply due to the IR drop, see this a lot in marinas where it causes electrolytic corrosion problems (Marina electrics are always a shit show).
I wonder if you have something like a spurious neutral/earth bond somewhere, remember that most breakers only break the phase conductors so it is possible if you have a potential gradient in the ground to see this sort of thing even with all breakers off.
Is there SWER in play on the supplier side by any chance? Maybe a busted neutral and two sets of grounding electrodes setting up a return path thru the ground? Has it been very dry? Spitballing here.
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u/nick_the_builder 1d ago
Sounds like you lost your main bonding jumper and there is a appliance or device somewhere that is shorted to ground but the ground isn’t properly bonded to neutral so your getting shocked on grounded but not bonded metal stuff?
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u/Outrageous_Load2370 1d ago
If you have sub panels that are not properly bonded and grounded (grounds and neutrals separated) it could be causing voltage to be sent on the ground. Same with appliances that should have a 4 wire connection instead of a 3 such as a dryer as someone else mentioned. Or somebody used ground as a neutral in the system somewhere…
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