I have a new house under construction, almost finished, but with no outside power source attached to it. My plumber noticed a tingle when he touched a ground wire and the concrete in the garage. Sure enough, I measure 6/10 of a volt between the single ground wire from the house and the ground rod. I guess it's DC since the polarity changes if I reverse the meter leads. What's causing this?
He wouldn't feel a thing with 0.6VDC -- any more than you feel while holding both ends of a 1.5VDC flashlight battery. Have you checked with your meter set to measure AC? The lower threshold that causes a 'tingle' varies with many conditions but will typically be at least 12VAC.
You will probably get more learned opinions here later but I wanted to get some reply to you right away.
0.6V DC is almost impossible to feel, take for example a 1.5V flashlight battery. Have you ever felt current flow touching the terminals of one? How about a 12V car battery? DC is hard to feel at even higher voltages... (don't hold onto the car battery terminals while the starter is being engaged/disengaged, or you'll get hit with a higher Voltage 'spike')
I bet it's AC 'leaking' in from from some unknown source. It for sure needs to be found and positively corrected.
A local indoor public swimming pool had an issue like this. Someone discovered the water to be electrically 'hot'. I didn't follow the story all that close, but recall hearing the mystery current source didn't seem come from within the pool facility, and the pool was closed many month while they searched...
The reason I thought it was DC instead of AC is because the +/- reading would change on my meter if I switched leads. I'll try sticking a test light on it this evening. And also see what the reading is with the meter in the AC position.
I couldn't understand how anything could be "leaking" since there is nothing hooked to the house. The temp service is sitting in the yard, no power to the house at all.
If this is something I putting back in the grid, maybe the power company will pay me for it ;-)
Well, for starters if you are feeling it, it isn't DC. Even at AC you need 2 to 4 volts to be noticeable unless your skin is salt-sweaty wet and very conductive. But it could be a big problem.
Check your temporary power pole feed to the construction site - if the Neutral connection coming in from the Edison transformer is open or not bonded properly and all the 120V loads are running on the ground rod connection for their return, it will energize the dirt in the vicinity of the ground rod. The voltage differential will lessen in "rings" going out from the rod, just like ripples in a pond when you toss in a rock...
Look at the voltages at the temp panel with a good Digital Voltmeter from each side to what you /think/ is ground, and then hit a large load on one leg - if the voltage to neutral (bonded to ground) sags on the loaded leg and spikes on the unloaded one, but the voltage from phase-to-phase stays at a rock solid 240V, it's an open neutral.
If this effect lessens if you trickle a garden hose on the ground rod and make a big ball of damp earth there to make a really good ground, you just confirmed it. Lowering the ground resistance with a big dose of water makes the alternative power return path work better, as the power makes it back to the transformer ground via the butt plate ground on the power pole, or the local ground rod at the underground transformer vault/pad.
Call the power utility and the company who leased you the temporary power pole, get them both out there pronto, and let them figure out who goofed and where. Either way, it needs to be fixed, and soon.
Until then, leave that garden hose trickling on the temp power pole's ground rod. And don't do any unnecessary work with older grounded-case power tools until it's sorted out. Lights and newer double-insulated tools okay if you are careful.
And no computers, televisions or sensitive electronics on that service until it's fixed - they tend to go blooey and turn into expensive paperweights when you hit them with big voltage spikes and sags.
The 0.6 V jumps out as the drop across a typical silicon diode, and pretty high to be coming from just a galvanic junction.
Your first investigation should be where else is your house grounded - telephone service entrance? Satellite antenna entrance? Metal plumbing with earth or concrete contact? A heating control box bolted to a grounded pipe and bonded to the electrical ground? Two earth grounds at different locations can be at different potentials, but 0.6 V seems like a lot for that...
Are there any battery powered items installed? Like maybe a fancy thermostat connected to the heating control box? A TV cable box connected to the cable and to the house wiring? AC powered smoke alarms with battery backup? A security system with a battery and a telephone connection? Anything connected to a telephone line and any other wiring or plumbing?
If the potential really is from galvanic action, you probably want to find it before you bond the electrical system to the ground rod and let whatever it is start corroding away!
You measured voltage between a "ground wire" (in a receptacle?) in the garage and the ground rod (driven into a corner of the garage concrete pad ?), so they're close together ?
This is puzzleing. I don't think we've enough info., but when you do get it worked out how about telling us.
Thanks Bruce. I'll check this out tomorrow. I did test again this afternoon and you could not fill the tingle, but the volt meter was reading 0.9 volts (9/10). As far as I know, this one ground (rod) is the only one the house has. There is one, of course, at the temp pole. We will get the final next week and the power company will turn the power on. I'll ask them what's going on when they get there.
It has a setting for AC and one for DC. What I meant by my polarity statement was to say that the voltage I was reading was a DC voltage. I figured it to be DC because the sign would change if I switched leads.
I should have made this clearer. Here's the long version. The plumber was finishing his installation of a tankless, gas hot water heater. The (three conductor) electrical wire, that operates the igniter, was roughed in. Since all the pipes are plastic, he would have felt no voltage between the HW heater itself and the electrical wire. But for some reason, he touched the ground wire and the concrete floor (in the garage) and felt this tingle. Now this is not a "stand your hair up" thing. He even mentioned wetting his finger when touching the concrete to feel it better. He knew there was on power hooked to the house, so he was asking me what was causing it. This is when I decided to put a meter on it. Between the ground wire (eventually going to the igniter) and the concrete showed 6/10 volts. Between the ground wire and the other two wires, nothing. The next day, the electrician finished hooking everything up. He drove his ground rod beside the (future) meter base and connected the one copper wire (from the main panel) to it. If I disconnect this wire from the rod, I can read a voltage of 0.6 - 0.9 between the wire and the rod.
So that's my story. My house is a battery, I guess.
I would not get too excited. The two components that matter are voltage and current flow. I'm thinking that there is an issue with either your service ground or the utility pole ground.
The typical service is 240 volt with the center of transformer tapped and grounded. This makes a single conductor to ground 120v. Safety issue. I'd rather get bit by 120v than 240v since as you double the voltage you quadruple the power.
Years ago, I read about ELF communications and for chits and grins, I drove two rods about 6 feet apart and connected my record player to it. 20 feet away and 6 feet separation I hooked up the speakers. I could hear the music from the record I was playing. Not very loud but it was audiable. I my speakers saw .6 volt or better.
a low voltage (0.6V) could be caused by electrochemical reaction between soil moisture & earth stake perhaps. Like copper / iron nails in a potato or lemon etc.
Working in electronics you some times see 100+ volts of AC where you shouldn't - often its leakage from mains filter capacitors and due to its high impedance it dissappears if you use you fingers to short across the probes (not recommended if you are not sure what is going on). I wouldn't expect to see too much in a unconnected system - perhaps the wiring is picking up radiated power.
Not only is your house a battery, but so is nearly everything else. A penny and a nickel on each side of a damp paper towel will generate easily measured voltage. Likewise, copper, iron, moist dirt, and sweat. Nothing you have mentioned, other than the tingle, is uncommon. I suspect the tingle may have been due to a static charge developed on the disconnected wire, which is also not uncommon. Since so many people now have high impedance digital voltmeters there are an awful lot of "ghost" voltages being reported. They have always been present, just not noticed and of no concern.
If you live near any am commercial transmitter site your wiring will be loaded with rf voltage. I knew a telephone repair man that worked in teh area of Lodi NJ where the WABC 50 kw tower is located. He said that close to the tower on the phone lines they could draw an arc over a half inch. It would burn you but not shock you since it would not penetrate beneath the surface of your skin, but the smell of burning flesh stinks.
It was 0.6 when I first tested it. This afternoon it was
0.9.
Understand that there is nothing hooked to the house. To operate a saw or something, an extension cord is run to the temp service, 75 feet away.
I'll try this but don't think it will have any effect.
A while ago someone asked "why so many OT subjects". It's simple. It doesn't matter what the question is, someone on r.c.m. will have an answer. I've lurked this group for a long time and have learned a lot about lots of subjects. I appreciate everybody's input to this question and to the group in general.
Try letting your multimeter leads dangle in free space - observe voltage. Wave them around, spread them apart, connect one to ground, measure a metal fence - see if you still get millivolt readings - I would expect that it would. Picking up stray rf, whatever....if your worried about this, get a qualified sparky in to do a test - which, imcidentally, SHOULD be done before the job is signed off anyway.....
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