[jamiedolan]

Hello;

Hope everyone here is well, I've not been around in a while. Many DIY projects got put on hold for a few years due to some circumstances in my life. I'm back at a few projects again.

I had a bit of a confusing reading with my Ideal RMS digital meter.

I took an outlet out with 2 pieces of 14-2 with ground in the box. Had the 4 wires sticking out of the box.

I knew 1 set (one romex cable) went to source and 1 went to an box 6 feet away with nothing connected to the wires.

I identified which CCC and neutral where together and read 120v. But then I tested the Hot to the neutral in the wire that was not connected to anything and got around 90 volts.

Tried this with a $5 harbor freight meter and it read nothing.

I've seen some much lower voltage numbers at times in the past and thought that was phantom / induced voltage, but have never seen it read so high.

Could there be a circumstance where this is normal or a problem with the meter?

It was confusing to see such a high number, but I was able to physically confirm the wire I was reading 90 volts on was not connected to or spliced to anything.

I had one other weird reading with this meter, but that will take longer to explain, so lets see if any of this makes sense so far.

Thank You.

 

[dmxtothemax]

is this normal or a problem with the meter?

Thank You.

Normal !
Yes, voltages that high can easily be induced into a high impedance
multi meter.

no fault in meter except cheap design.

http://support.fluke.com/find-sales/Download/Asset/2105317_A_w.pdf

 

[ddawg16]

What you read depends a lot on the input impedance of the meter you are using. I suspect the HF has a lower input impedance which would reduce any induced (phantom) voltage readings.

Even a 6' length feed can have induced voltage....if it's parallel to an active ckt.

If I'm measuring 90 volts....I'm pretty confident it's induced voltage. My fluke can handle AC voltage in the ohms pos....so I'll go to ohms and make a measurement. If it's a true AC voltage, it makes noise.

 

[gregzoll]

There is really no such thing as Phantom Induced voltage. What you read is the meter reading its own induced voltage. Happens when there is not a diode that is supposed to be in it to keep it from happening. We usually just put a load like a small lightbulb on one lead to keep it from happening.

I use a $30 Sperry Digital Multi-Meter with no issues.

 

[Big_John]

There is really no such thing as Phantom Induced voltage.

Incorrect. t's called capacitive coupling.

What you read is the meter reading its own induced voltage. Happens when there is not a diode that is supposed to be in it to keep it from happening.

Incorrect. It's caused because the impedance of the meter is too high to shunt that capacitance. Severe enough coupling can light up a neon bulb, which obviously isn't "inducing its own voktage".

 

[emtnut]

There are quality high impedance, and low impedance meters ... and low quality of both.


Right tool for the right job.

 

[jamiedolan]

Thanks for the answers. The meter is over at my neighbors at the moment, but I'm almost positive this is the model:

http://www.amazon.com/Ideal-Digital-Multimeter-Test-pro%C2%AE-Contractor/dp/B00011Q6XS

Could I have the lead in the wrong hole? Or is this just going to be a problem with this meter unless I put a bulb on the end of the circuit?

 

[ddawg16]

Don't sweat it. Unless you are getting a solid reading 110 volts are more, chances are it's induced voltage.

In my regular line of work, I deal with it all the time. AC wiring is is straight un-twisted wires.

If you recall electricity 101....current flow through a wire produces a magnetic field. Any wires near or adjacent to that wire and running parallel will have voltage induced on it.

This is why you see signal wires (like Ethernet) where the wires are twisted at or close to 90 deg to each other. This cancels out the induced voltage and current.

 

[Know A Little]

Thanks for the answers. The meter is over at my neighbors at the moment, but I'm almost positive this is the model:

http://www.amazon.com/Ideal-Digital-Multimeter-Test-pro®-Contractor/dp/B00011Q6XS

Could I have the lead in the wrong hole? Or is this just going to be a problem with this meter unless I put a bulb on the end of the circuit?

The average electrician much less DIY'er is better off using a go no go tester such as the Knopp. There are times you may need a DMM but how often do you need to know if the voltage is 118.74 or 114.56 so 99.9% of the time you need to know live/energized/on or Off/dead/de-energized and for that a go no go Wiggy type tester should be your tool of choice.

Just my opinion based on the number of this type of questions I have run across in all my years of being involved with electrical testing.


http://www.knoppinc.com/tools.htm#K-60

 

[gregzoll]

Com for Black, Red hoes into V (Ohm). You should not need to load the circuit with a bulb or hairdryer for that meter.

There really is no need to be measring voltage on the wires, unless you have a dead hot and trying to figure out where it lost power.

Playing with live electricity will give you a Permanent Perm. That is why we wear proper clothing a safety gear. Even if it is only 120.

 

[Wirenuting]

There is really no such thing as Phantom Induced voltage. What you read is the meter reading its own induced voltage. Happens when there is not a diode that is supposed to be in it to keep it from happening. We usually just put a load like a small lightbulb on one lead to keep it from happening.

I use a $30 Sperry Digital Multi-Meter with no issues.

Sorry guy, but this is a left field wrong answer.
You must never have worked on any 3 phase systems.

Induced voltage = ghost and carries no current.
Leaked voltage = real and can carry current.

You need to know what you have.

 

[jamiedolan]

Here is the other weird thing that I saw happen. I tested the hot on one circuit to the ground on another and got a reading of 180 volts.

I thought there had to be voltage on that ground somehow from that circuit. I added in an additional wire and it absolutely is bonded to the panel now, I haven't tested it again. If it was a hot wire leaking onto the ground, it should have opened the breaker once it was bonded to the panel, but it didn't. Perhaps the neutral is crossed with the ground on that circuit?

So this is the same phenomenon? It seems weird that I didn't notice readings to this extent in my own house or my parents.

 

[jamiedolan]

One other question along these lines, what do you to do check if a ground and neutral are tied together somewhere on a circuit? Besides physically inspecting every box?

Put a load on the line and check that the hot and neutral box have the same return at the panel with a clamp meter? If the neutral was connected to the ground at some point, then you would expect at least some of the current to return on the ground wire.

Or is there an easier way to test?

 

[ddawg16]

One other question along these lines, what do you to do check if a ground and neutral are tied together somewhere on a circuit? Besides physically inspecting every box?

Put a load on the line and check that the hot and neutral box have the same return at the panel with a clamp meter? If the neutral was connected to the ground at some point, then you would expect at least some of the current to return on the ground wire.

Or is there an easier way to test?

Ground and Neutral MUST be tied together....but at only one spot....the load center.

If you are concerned about it, turn off your main breaker and then lift the ground from your neutral buss. There should now be an open between neutral and ground. Depending on what is hooked up and plugged in, you might measure some resistance between earth ground and neutral....but if you have a hard connection, it's going to be 1-2 ohms.

As for the 180v you measured above....confirm it was from hot to earth ground? If so, I'd be measuring from neutral to ground as well.

 

[Know A Little]

Here is the other weird thing that I saw happen. I tested the hot on one circuit to the ground on another and got a reading of 180 volts.

I thought there had to be voltage on that ground somehow from that circuit. I added in an additional wire and it absolutely is bonded to the panel now, I haven't tested it again. If it was a hot wire leaking onto the ground, it should have opened the breaker once it was bonded to the panel, but it didn't. Perhaps the neutral is crossed with the ground on that circuit?

So this is the same phenomenon? It seems weird that I didn't notice readings to this extent in my own house or my parents.

Here is what I find, WHICH IS WHY I RECOMMEND a Wiggy style tester. Many times electricians see 180(or something similar) and freak out on a supposedly de-energized line and they do not see the mv after the number MILLI-VOLTS. 180mv not 180V

 

[gregzoll]

If you got 180 with that more expensive and better meter, something is not right for how the meter is reading and may have to be sent off to be recalibrated. If it was that cheap Harbor Freight unit. That would be expected.

 

[Know A Little]

Com for Black, Red hoes into V (Ohm). You should not need to load the circuit with a bulb or hairdryer for that meter.

There really is no need to be measring voltage on the wires, unless you have a dead hot and trying to figure out where it lost power.

Playing with live electricity will give you a Permanent Perm. That is why we wear proper clothing a safety gear. Even if it is only 120.

A serious question and not trying to get on your case, but are you an electrician? engineer? or just an experienced DIY'er.

 

[jamiedolan]

Ground and Neutral MUST be tied together....but at only one spot....the load center.

Thanks. I fully understand this, but am trying to figure out if someone screwed things up and connected a ground to a neutral somewhere.

If you are concerned about it, turn off your main breaker and then lift the ground from your neutral buss. There should now be an open between neutral and ground. Depending on what is hooked up and plugged in, you might measure some resistance between earth ground and neutral....but if you have a hard connection, it's going to be 1-2 ohms.

Thanks, this makes sense to see if the ground in connected to a neutral in a box.

As for the 180v you measured above....confirm it was from hot to earth ground? If so, I'd be measuring from neutral to ground as well.

Circuit A Hot wire to Ground on Circuit B (earth ground / bonding wire) 180.

Circuit A Neutral to Ground on Circuit B I don't remember if this was just a couple volts or was closer to 20, either way, it was low.

Circuit B ground to copper water pipe on heating system read around 20 volts.

The copper water pipes do appear to be bonded as testing live to pipe in other parts of the house to the pipes gets 120v. I'm going to add a bonding wire from the panel to those pipes to be sure they are properly bonded.

 

[gregzoll]

You would not be able to read curent leakage without the proper tools. The only place that ground and Neutral are tied together is either at the Main Panel or at the outside if there is a main disconnect that acts as a Main Circuit Breaker box and the inside panel is treated like a Sub-panel.

If you find a "Boot Leg" ground or a "Boot Leg Ground with a Reverse Neutral". Then someone before you was not paying attention.

 

[jamiedolan]

Here is what I find, WHICH IS WHY I RECOMMEND a Wiggy style tester. Many times electricians see 180(or something similar) and freak out on a supposedly de-energized line and they do not see the mv after the number MILLI-VOLTS. 180mv not 180V

I'll look at my meter again, but am pretty sure it was volts. I have to switch modes to read down into the mv range.