Voltage indicators???

| Everyone has seen or maybe used those inexpensive AC voltage indicators that | beep or light a neon lamp when help close to an ungrounded "hot" conductor. I'm | wondering - do they just sense the varying electric field around the conductor? | Since they don't require any current flow in the conductor they're can't be | using any magnetic field component.

Are you touching the metal part of that indicator when you operate it? I think that is part of the key. It could be sensing static voltages being drawn off through it to your body.

Yes, most of them detect the electric field. I say "most" because it would not surprise me if there is a product that does it differently, but I only know of products that use the electric field.

Charles Perry P.E.

The ones I have seen are all plastic. No metal to touch (good thing too since you are using it near energized conductors).

Charles Perry P.E.

|> | Everyone has seen or maybe used those inexpensive AC voltage indicators |> that |> | beep or light a neon lamp when help close to an ungrounded "hot" |> conductor. I'm |> | wondering - do they just sense the varying electric field around the |> conductor? |> | Since they don't require any current flow in the conductor they're can't |> be |> | using any magnetic field component. |>

|> Are you touching the metal part of that indicator when you operate it? |> I think that is part of the key. It could be sensing static voltages |> being drawn off through it to your body. | | The ones I have seen are all plastic. No metal to touch (good thing too | since you are using it near energized conductors).

Mine is the "pocket pen" type. The clip actually carries one end of the battery voltage to a small tab of metal to close the DC circuit to make it work. I just imagined that it could also be using that to get more "air ground" to make the detection more effective, since you have to hold that clip down onto the tab to keep it working. At least it does beep once when you close the contact. But I haven't yet decided to sacrifice of these to see what kind of circuit it has inside. But it definitely has to detect on more than just current.

BTW, it gets more use entertaining the cat and the 2 year old than it does checking for voltage.

| Yes, most of them detect the electric field. I say "most" because it would | not surprise me if there is a product that does it differently, but I only | know of products that use the electric field.

Got any schematics so I don't have to destroy one? My big curiosity is if it sees the AC as 60 Hz or 120 Hz. If I built two detectors like it and fed the rectified signal via an LED, with each on oppose sides of a

120/240 circuit, would the LEDs alternate "railroad crossing style" at 60 Hz or would they just blink in unison at 120 Hz?

No. I don't have any schematics. I would imagine finding one wouldn't be impossible. I don't think they care about frequency. The ones I have used have a battery and thus the LED lights via DC current, not induced AC from the field.

Charles Perry P.E.

|> | Yes, most of them detect the electric field. I say "most" because it |> would |> | not surprise me if there is a product that does it differently, but I |> only |> | know of products that use the electric field. |>

|> Got any schematics so I don't have to destroy one? My big curiosity is |> if it sees the AC as 60 Hz or 120 Hz. If I built two detectors like it |> and fed the rectified signal via an LED, with each on oppose sides of a |> 120/240 circuit, would the LEDs alternate "railroad crossing style" at |> 60 Hz or would they just blink in unison at 120 Hz? |>

| No. I don't have any schematics. I would imagine finding one wouldn't be | impossible. I don't think they care about frequency. The ones I have used | have a battery and thus the LED lights via DC current, not induced AC from | the field.

It's not the frequency I care about. What I want to do is set up 2 of them on 2 hot wires, one fed by a red LED and one fed by a green LED, and have a

3rd device receiving those LED blinks determining if the wires represent opposite or same phase. Or maybe even phase angle.

I understand what you want, but there are no "blinks" with the normal devices. The LED goes full on via a DC voltage when an electric field of the correct parameters is detected.

You need to keep in mind that what you would be "detecting" would be an e-field that was the sum of the sources. I doubt you could distinguish one line from the other if both were energized.

Charles Perry P.E.

| I understand what you want, but there are no "blinks" with the normal | devices. The LED goes full on via a DC voltage when an electric field of | the correct parameters is detected.

But if the electric field goes back off, it should cease detecting. It certainly quits flashing and beeping when I pull it away from the hot wire, so I know it doesn't latch into the on state. There is obviously some modulation at about 4 pulses per second on the light and beeper. Whether the 60 or 120 Hz is coming through as well I can't see. But at the actual point of detection (as opposed to the circuit driving the LED and beeper) it should be in a non-detect state during zero crossing. The question is whether this detection can distinguish a positive vs. negative field. A new circuit would be required to select the desired polarity and pass the 60 Hz literally to the LED (I wouldn't have any beeper on this one).

| You need to keep in mind that what you would be "detecting" would be an | e-field that was the sum of the sources. I doubt you could distinguish one | line from the other if both were energized.

With sufficient line separation and sufficient desensitizing of the detector, why can't this be accomplished? Surely at some point in proximity, the closer field overwhelms the more distant field and its polarity prevails in detection.