Stray 110 voltage

[lanceh5]

I have installed a 110 volt circuit in a new house that goes through a GFI receptacle then to a duplex switch box which then feeds to a some lights down stream. So the switch box as four circuits, power in from the GFI, power out to the downstream lights, switched outside light and switched fountain pump. These are 12 gauge wires with ground and metal boxes, no plastic. The four wires to the switch box go through a snug fit 1" hole in a 6" x 8". <p>Inside the duplex switch box, the white, neutrals, are connected by a wire nut. The black power in is wire nutted to the power out and pig tails to both switches. <p>When the fountain switch is off, the circuit to the fountain pump junction box has a 5 volt reading on a digital multimeter. I replaced the switch and have the same reading. I disconected the switch and have the same 5 volt reading. I replaced the wire to the junction box through the same hole in the 6 x 8 and have the same 5 volt reading. The second switch in the box does not have any stray voltage. When I trip the GFI which feeds the switch box there is no voltage. <p>How can stray voltage get to this circuit??

[Chris Smith]

Place a resistor of say 1000 ohms or so across the stray to a good ground, when it is de energized, and measure the voltage again and it should clamp it to around zero voltage, or about zero, showing that you have capacitance induced voltage of no Appreciable current from the wires being parallel to a hot wire. <p>This is not uncommon. <p>BUT, if the resistor arcs, sparks, or gets hot, you have a real or actual problem. <p>If you stand under high tension lines, 50 feet away, you would be suprized how much of a reading you will get!<p>[ August 07, 2004: Message edited by: Chris Smith ]</p>

[perfectbite]

As Chris says:<p>"This is not uncommon."<p>Even the voltage frequency off a phone line will, if it starts ringing when you are holding the bare wire(s) and the conditions are right, stop your heart (it interferes with your heart's sinus rythm). Low amperage, 50 Hz (European Hz) can be lethal. Like the phone line(s), the 50Hz interferes with the heart but at 60Hz, a much more benign frequency, given the lack of any appreciable amperage, (it is less than 10 mA because the 'I assume good' GFCI isn't tripping) you should be all right. (110VAC GFCIs trip at 10mA or less within one 60 Hz cycle.)<p>I think you are right in trying to chase that stray (tramp) voltage down. With that end run switch off I would try an Amp reading from that line wire to ground or neutral. It could be in the uA range and, along with Chris' 1K resistor test you'll know what you are dealing with (do Chris' test first) AND, because it is 60Hz, there really isn't any danger if there is just very low voltage and very, very low micro amperage.<p>[ August 08, 2004: Message edited by: perfectbite ]</p>

[upsmaster]

my guess is their is no voltage. Digital meters give false readings when the circuit is open that they measure across. try a analog meter. and adding a resistor at that point will make the circuit complete and the 5 volt reading will go away.<p> joe

[JS]

I agree with the group, sounds like an induced voltage. If your going to be in the the electrical trade may I suggust buying a "Wiggins",or Wiggy. These are a solenoid driven voltage meter and will load down a stray, the meter won't pull in and the indicator lamp will not light. I use a Knopp brand, old company with a bullet proof product. I also use a Fluke T5-1000 digital amp/volt/resistance meter for a detailed look. Again a very good product. I have been in the trade for some years now and have learned respect for the 120V, 240v, 480v systems. You can read a 480 V panel with digital meter but when the old time wiggy goes on there by drawing a small arc and pulling in hard, one gains quick respect for the available power. Always check your leads and good luck. JS

[dyarker]

What is the voltage from neutral to ground (white wire to green wire)? If it is 5V, then you're measuring that voltage thru the pump motor. No problem HERE.<p>Do not put a resistor from hot to ground after a GFI unit. GFIs measure the hot and neutral currents. If the difference is like 2.5mA the GFI assumes a fault (like someone getting shocked) and pops open. 5mA is seriously uncomfortable, but probably won't kill you; so less than that for a trip point. The trip point can't be microAmps because normal capacitive leakage would being tripping it when there's no fault.<p>A 1K Ohm resistor would have a current of 120mA! And needs to be more than 15W to leave in circuit when pump is on.<p>What is the neutral to ground voltage at an outlet NOT thru a GFI? If its 5V with air conditioners and electric oven going that's on the high side of okay. You may, MAY, have a loose or dirty neutral connection somewhere. If you've got 5V with only a couple of lights on, either you're a LONG way from the transformer, sharing a transformer with power hungry neighbors, or slight maybe that power company needs to fix the neutral/ground bond at the transformer.<p>The neutral voltage after the GFI can be a LITTLE higher than the neutral voltage before it.<p>[ August 08, 2004: Message edited by: Dale Y ]</p>

[perfectbite]

Per JS I also have a Knopp K-60 'wiggy' and a digital Fluke T5-600. What I have found is that the Fluke won't trip a GFI (GFCI) on a voltage reading, Line to Ground (black wire to green wire) because it 'sips' so little current to register the voltage. The Knopp however will trip a GFI on a line to ground reading because it needs amperage to pull the solenoid's disc into the window's mark. In essence, depending on what you want to test, you may need the Knopp 'wiggy' AND that Fluke T-5 600 or T-5 1000. Old tech and new tech. <p>If I remember rightly the T-5 600 will give voltages to the nearest .5 (not much good for testing batteries) but the T-5 1000 will give voltages to .1 or .2. It is a much more expensive tester. Of course. Both of them worth every penny though. I use but don't really trust those little voltage indicator beeper thingies. If I hear it it means there is voltage, if I don't hear it it could mean anything. <p>ALWAYS test the tester on a known live circuit immediately before testing on the circuit you are working on and ALWAYS keep one hand fixed in your pocket or firmly behind your back around open mains connections so that you don't accidentally ground yourself. It is good practice. (It saved my life with 480VAC once in a tight space. I deliberately and knowingly wasn't grounded. It blew the ends of my fingers up and hurt my pride when I fell off the fibreglass stepladder but I survived and got to ride in an ambulance. Not an experience I'd recommend. ANY contact with 480VAC is considered lethal. I guess it wasn't my time to go. 110VAC can do a number on you too if the conditions are right.)<p>Apparently AC voltage will jump 1/8" for every 100 Volts. So 240 could reach out and grab you. So be careful.<p>Also that 6x8 metal box is a big box and if you have a few turns of in and out wire in there either laying together or laying next to the box's walls that may be enough to induce your 'tramp' 5 Volts.

[Dean Huster]

Fluke does make a few digital multimeters aimed at the industrial maintanance sector of the market that, like the venerable Simpson 260, do load down the circuit somewhat so that open lines that would otherwise have a phantom voltage that reads on a "normal" DMM will be loaded down and read correctly.<p>Dean

[dyarker]

That's a good one! Ever been chased by fire ball that came out of a 1/2inch thin wall EMT because some idiot installer bridged the 5A breakers at the equipment rack even though each was separately feed by 15A breakers in the wall panel?<p>I'm hoping "lh" comes back and tells us what he found. I don't believe there is that much stray pickup on a terminated wire (low Z to neutral thru the motor). On wires open on both ends, yeah.<p>see ya,

[lanceh5]

The wire to the fountain is about 25 feet away from the junction and switch. Today I checked the voltage at the fountain pump using two digital multi-meters and a 30 yr old Radio Shack analog volt-ohm meter that is the size of a pack of cigarets. <p>With the switch off, both digital meters read 1.3 volts, hot to neutral and also hot to ground. The analog meter did not read any voltage. So I think the circuit is OK.<p>What is strange to me, is the stray digital voltage at the junction box was 5 volts and now at the fountain 25 feet away it is 1.3. Strange. <p>Thanks everyone for your input.

[dyarker]

"What is strange to me, is the stray digital voltage at the junction box was 5 volts and now at the fountain 25 feet away it is 1.3. Strange."<p>With black open (power off), the black wire at the pump its a 25ft. antenna. At the junction box its a 50ft. antenna. At the pump is less than half because the pump motor winding has capacitance to ground (motor casing) as well as series inductance. So the others were right about stray pickup. (neutral to ground voltage could have been a problem till your last post. (thanx))<p>DMMs have an impedance like 10M or 11M Ohms. A cheap analog VOM may have an impedance of 10K Ohms per Volt (where Volt refers to the range switch). DMMs don't load the wire enough. I agree that the circuit is OK.<p>C U L -

[Bob Scott]

You cannot twist together regular neutrals With GFI neutrals.

[perfectbite]

Bob Scott. Are you saying that neutral wires from GFIs should be dedicated to the breaker box's neutral strip?<p>[ September 01, 2004: Message edited by: perfectbite ]</p>

[dyarker]

DEFINITELY DO NOT connect the neutral that comes out of the GFI to any other neutrals (neither from a non-GFI circuit, nor from a different GFI). The possible imbalance in return current will cause false GFI tripping.<p>In any case the wiring should look like a tree. Branches are okay, but branches NEVER reconnect to each other. So any circuit off a breaker, GFI or not, should not interconnected with the circuit of another breaker.<p>Cheers,

[Bob Scott]

[QUOTE]Originally posted by perfectbite:
[QB]Bob Scott. Are you saying that neutral wires from GFIs should be dedicated to the breaker box's neutral strip?<p>perfectbite,<p>No, but it depends on the type of GFI. If it's one of those GFI bathroom receptacles, the code here says that you can connect the power that goes into the GFI from the power that supplies your bathroom light, including the neutral line.<p>If you have a GFI circuit breaker in the breaker box, the neutral line definitely DOES NOT connect to the neutral bus. The outgoing protected neutral line must connect to the GFI breaker's neutral terminal. The breaker has its own white neutral wire that connects to the neutral bus. Why:<p>The GFI does not detect ground current as I originally used to think. It detects slight differences between the outgoing current in the hot line and returning current in the neutral line. If there is a difference, the GFI trips. That's why both GFI protected hot and neutral connect to the GFI, so that it can detect the sum of the currents in both lines.<p>But I don't think that's his problem any more. He does not report any GFI tripping.<p>I have noticed some strange AC stuff. 20 years ago I worked as a tech at a TV broadcast station. We got emergency notice that one of the satellite dish rotators was not working. (At a TV station anything that can effect on-air broadcast is an "emergency".) I went up on the roof and checked voltage going to the motor...160VAC to a 120V motor and it refused to turn. Puzzled I checked the voltage to ground from the neutral line. I forget what it was, but it was more than 50V, so I went down to the AC breaker panel to find the big thick main incoming neutral wire had never been tightened down. So I tightened it, the dish rotator worked and I still don't understand why it did not rotate with 160V across it. It's not possible to be "out of phase" which I thought for years. There would still be a power vector at 90 degrees phase shift. It was a 2 phase motor. <p>Of course there is another possibility: My 20 year old memories are not guaranteed 100% accurate. eg: memories of old girfriends get more attractive with age.<p>Bob