Fixing Capacitive Coupling (Phantom Voltage) issues with pull down resistor

winnie said:
3000 ft is in line with my estimate for how long the wires would need to be for the capacitance to cause that much leakage. (There were very wide error bars on my estimate, but at 3000 ft it is totally plausible that 120V could cause a couple of mA of capacitive coupling.)


Are the 120V secondary coils grounded? The neutral should not be floating at 40V to ground unless you _intend_ to have an ungrounded system.

With 3000 ft of wire, that is totally to be expected. The capacitive coupling would be more than enough to light LEDs.



Remember that 'Phantom voltage' is a _real_ voltage. 'Phantom' in this case doesn't mean that it is some ghost version of voltage, simply that this voltage is derived through a high impedance pathway, and goes away if you have a low impedance load or meter. Don't think of 43V of phantom voltage, think instead of 120V in series with a 46K capacitive leakage path. That leakage path forms a divider with your load impedance. This is why the old electromechanical actuators didn't have a problem; they were very low impedance and that swamped the leakage impedance. The new actuator has a high impedance input, which is why you are considering adding a parallel resistor to lower the total load impedance.


Agreed.


Spitballing here:

1) If some of your 120V control circuits are ungrounded, then you need to think of the conduit as a possible source of phantom voltage. Every bit of metal in the conduit, including the conduit itself, forms a capacitor with every other bit of metal. If your neutral (which is also your signal reference voltage) is floating at 40V, then the conduit is 'pulling' your signal lines away from the neutral potential.

2) Will your new actuators function with _DC_ control signals? How about your LED indicators? DC would eliminate the capacitive coupling form of phantom voltage.
Click to expand...
Totally agree. I will open up the #39 actuator and check the 120V transformer if it's Gnd. #38 has been torn down so I can't tell. But like I said, #40 & #41 are same set up with #38 and all control wires run in same conduit but #40/#41 only have 2.2V phantom on the seven control wires to Gnd/N. I quit scratching my head on this as I can't afford to lose any more hairs off the top, lol. I am focusing on getting my new electronic actuator controls(Remote) to work properly.
DC external control is out of the question as it require engineering and industrial codes regulations. I have some follow through mentioned above when I can get to them. I'll post update. Appreciate the precious time you're investing in my adventure. Thx
PS: A similar situation happened about 3 months past with one of our AC units controls. AC stopped working(10yrs) called AC company and their technician said we have faulty wiring cause he was getting 460/230V on the control control transformer but only 40V to Gnd. I showed the technician that he was getting the 230V at the trx but since the secondary was not Gnd it's a floating neutral but the control relay is somehow dumping the 230V so it's not getting the required voltage. Same wiring we have had for 10yrs. He found burnt relay contacts. Replace and Voilla!
 
I was told to separate the 230V 3-phase wires from the control wires for the #38 Actuator and run them in a separate
conduit. However I am not sure that's going to resolve my 44V phantom. If I turn off all power(230V 3-phase/120V) to
#38(completely dead) I still measure the 44V phantom on the control wires... it did not go away. By experiment, it seems
like each of the 4 actuators(#38,#39,#40,& #41 contribute approximately 11V Phantom = 44V total. So turning off all power
to #38 dropped it down to 33V.
At this point, I am thinking of a pull down resistors(550 - 1K ohms, 20-30W) set up(isolation relay) so the resistors are
isolated when the 120V is dropped on the particular control wire due to high heat dissipation. 120v/1000-ohms = 120mA x 120V = 14.4W
 
40 V, 10megohm meter, current = 4 uA so stray cap = 30megohm reactive, about 90 pF

10K resistor drops phantom voltage to 40 mV, 500 ohms to below 2 meter decimal places
but across 120ac gives about 30watts! 10k only 1,5 or so watts.

No idea what the inside circuitry of low Z setting of a fluke meter is, but suspect they may look at phase angle and adjust screen readout to be zero for a large PF reading.
 
Thank you all that suggested using a LoZ meter. However the LoZ reading is not the issue. It is a phantom 44V and it affects the Electronic
controls/circuitry of the Actuator. If I can eliminate this 44V phantom voltage it will be perfect. The actuator says 19V will interfere with the electronics controls but did not specify if it's a actual or a phantom voltage specification. I can experiment dropping it to say 10V phantom see if it still affects the controls. If not then a higher value pull down resistor and less heat dissipation to deal with then I may not need a pull down resistor isolation set up when the 120V is on the wire. Say 5K-ohms(9.8V phantom) then 120/5000 = 0.024A(24mA) x 120V = 2.4W.
So a 5K-ohms, 5W might work. Cont'd
 
What kind of separation is there between power circuits and this low voltage signal pair? Is the signal pair at least twisted pair cable? shielded cable likely to help even more. Assuming not in same raceway as power conductors, but sounds like possibly in same raceway as some other 120 volt control/signal conductors or possibly in non metallic wiring methods and in close proximity for a significant distance as the power conductors?

Someone did mention 4-20 mA signal would probably be less susceptible to this and I agree if it is possible to convert to that type of signal.
 
To @CoolWill : The issue with pulldown resistors is not the heating when removing the 'phantom', it is the heating when the circuit is supposed to be on. The 'phantom' coupling here has an impedance of about 46K. Place this in series with a 500 ohm resistor and the heating on the resistor is negligible. The problem comes when the control switch is toggled and now you have 120V across that 500 ohm resistor.

To @Shuntme : You say "The actuator says 19V will interfere with the electronics controls but did not specify if it's a actual or a phantom voltage specification." This suggests a conceptual error on your part. "Phantom voltage" is actual voltage, not some different beast. The reason it is called 'phantom' is because the source of the voltage is very high impedance, so a low impedance load will make this voltage go away. But this voltage is every bit as real as the output of any voltage divider. Instead of thinking of 'phantom voltage', think 'real voltage in series with a high impedance' and you will have a better understanding of what you need to deal with.

IMHO there are several open questions:
1) Is the source of this 'phantom voltage' capacitive coupling between energized wires and the control wire, or is it coupling from the grounded conduit to an _ungrounded_ control wire. I think that the grounding of this system hasn't been nailed down.

2) Is the source of this 'phantom voltage' capacitive coupling between wires or something else. The current (2.6 mA) is high enough that I suspected something like an LED indicator built into the switch (sort of like the residential lighted switches that function by passing a tiny amount of current through the load when off), but the 3000 foot long run is enough to make 2.6mA of capacitive coupled current quite plausible.

As to solutions:

You describe this system as "seven wires per actuator controls(3-open/off/close + power(L/N) + 2 indicators(position)" I read this that you have 3 switches that can energize (connect to L power) one of 3 wires to make your system do something.

Can you change the control switches to be double pole, so that they either connect to power or connect to neutral? In this way the wire will either be actively powered at 120V, or actively attached to your 0V reference. I think right now the control wire is left floating, which is the key problem.

A shielded pair as @herding_cats describes is an elegant approach but expensive at 3000 feet.

A pull down resistor is simple but as you've noted will have problems with heat dissipation. Some sort of active circuit that has a fixed current draw would be better; some circuit that draws say 2.6mA over the range of 5V to 120V AC would pull down the phantom voltage nicely, but dissipate 0.3W when energized.

-Jonathan
 
kwired said:
What kind of separation is there between power circuits and this low voltage signal pair? Is the signal pair at least twisted pair cable? shielded cable likely to help even more. Assuming not in same raceway as power conductors, but sounds like possibly in same raceway as some other 120 volt control/signal conductors or possibly in non metallic wiring methods and in close proximity for a significant distance as the power conductors?

Someone did mention 4-20 mA signal would probably be less susceptible to this and I agree if it is possible to convert to that type of signal.
Click to expand...
The 230V 3-ph separate conduit(one pvc) from the control wires conduit(pvc) to a JB for 4 actuators(electro-mechanical) then Control wires bundled together with the 230V 3-ph wires to each actuator from the JB with a plastic flex.
winnie said:
To @CoolWill : The issue with pulldown resistors is not the heating when removing the 'phantom', it is the heating when the circuit is supposed to be on. The 'phantom' coupling here has an impedance of about 46K. Place this in series with a 500 ohm resistor and the heating on the resistor is negligible. The problem comes when the control switch is toggled and now you have 120V across that 500 ohm resistor.

To @Shuntme : You say "The actuator says 19V will interfere with the electronics controls but did not specify if it's a actual or a phantom voltage specification." This suggests a conceptual error on your part. "Phantom voltage" is actual voltage, not some different beast. The reason it is called 'phantom' is because the source of the voltage is very high impedance, so a low impedance load will make this voltage go away. But this voltage is every bit as real as the output of any voltage divider. Instead of thinking of 'phantom voltage', think 'real voltage in series with a high impedance' and you will have a better understanding of what you need to deal with.

IMHO there are several open questions:
1) Is the source of this 'phantom voltage' capacitive coupling between energized wires and the control wire, or is it coupling from the grounded conduit to an _ungrounded_ control wire. I think that the grounding of this system hasn't been nailed down.

2) Is the source of this 'phantom voltage' capacitive coupling between wires or something else. The current (2.6 mA) is high enough that I suspected something like an LED indicator built into the switch (sort of like the residential lighted switches that function by passing a tiny amount of current through the load when off), but the 3000 foot long run is enough to make 2.6mA of capacitive coupled current quite plausible.

As to solutions:

You describe this system as "seven wires per actuator controls(3-open/off/close + power(L/N) + 2 indicators(position)" I read this that you have 3 switches that can energize (connect to L power) one of 3 wires to make your system do something.

Can you change the control switches to be double pole, so that they either connect to power or connect to neutral? In this way the wire will either be actively powered at 120V, or actively attached to your 0V reference. I think right now the control wire is left floating, which is the key problem.

A shielded pair as @herding_cats describes is an elegant approach but expensive at 3000 feet.

A pull down resistor is simple but as you've noted will have problems with heat dissipation. Some sort of active circuit that has a fixed current draw would be better; some circuit that draws say 2.6mA over the range of 5V to 120V AC would pull down the phantom voltage nicely, but dissipate 0.3W when energized.

-Jonathan
Click to expand...
Thank you for the insight and valuable considerations. You are absolutely correct on the phantom voltage. I just call it the because it does not do work or power any significant load other than being a nuisance interference for electronics imho. It's induced due to the cap of the wires like you and others pointed out.
1.yes on the 1st point of solutions accept the control switches are momentary, not maintained.
 
Thank you for the insight and valuable considerations. You are absolutely correct on the phantom voltage. I just call it the because it does not do work or power any significant load other than being a nuisance interference for electronics imho. It's induced due to the cap of the wires like you and others pointed out.
1. Yes on the 1st point of solutions.
2. The control switches are momentary, not maintained.
3. Last resort as the conduit with all those wires are imbedded into the Dam(reservoir) structure
4. I can get rid of the 44V phantom at the Remote control panel using the pull down resistor option(solves the LEDs Open/Closed positions being both on regardless) but it does not remove it from the Actuator controls terminals. This 44V is confusing the Actuator(imho) not knowing if its Open or Closed so it does nothing.
This has been a fun scenario and all the comments have been absolutely positive and educational. I know we will figure this thing out eventually.
Going back to the actuator supplier suggestion to separate the 230V 3-ph from the control wires; I commented that i don't see how it will help since I already tested by turning off the 230V 3-ph and the 44V phantom is still there(dropped to 33V). but a light bulb just went on in my head due to previous comments. Even though I turned off 230V 3-ph to the actuator #38 bundled with the control wires from the JB, the 230V 3-ph is still bundled with the other 230V 3-ph for the other 3 actuator(on) from the Electrical panel to the JB. So I will separate the 230V 3-ph for actuator #38 at the JB and keeping fingers crossed it will make that 44V disappear
 
If the control switches are the kind with replaceable contact blocks, perhaps you could add a NC contact block that would be maintained, and a NO contact block that is momentary. The NC block would connect the control wire to neutral (or connect the control wire to a low value resistor to neutral to avoid any issue of shorting during the transition) and the NO block would connect the control wire to 120V.
 
winnie said:
If the control switches are the kind with replaceable contact blocks, perhaps you could add a NC contact block that would be maintained, and a NO contact block that is momentary. The NC block would connect the control wire to neutral (or connect the control wire to a low value resistor to neutral to avoid any issue of shorting during the transition) and the NO block would connect the control wire to 120V.
Click to expand...
Great idea. That will take care of the remote control panel issues(3000ft away) but I still have the 44V sitting on the Actuator terminals on the other end of the control wires. I'll try the 230V 3-ph separation method 1st see what results I get then maybe get rid of the plastic/pvc flex for the control wires and run them in a liquid tight metal flex instead to help ground out the 44V. I'll post results asap.
Thank you all.
 
CoolWill said:
If a phantom voltage can drive enough current to heat a power resistor, I would say that it is not a phantom. Somewhere real power is entering the circuit.
Click to expand...
The 44V phantom does not heat up the pull down resistor as it only has 5mA. However the 120V will be on this same wire when the actuator function is called for and it's the 120V heat dissipation that's posing another issue. Like I mentioned earlier, 550ohms will make the phantom volts 0V but the 120V will draw 30W power and it gets pretty hot on that resistor. A 1K will drop it down to 3V but again it heats up pretty good with the 120V. Cont'd
Thank you
 
Shuntme said:
Great idea. That will take care of the remote control panel issues(3000ft away) but I still have the 44V sitting on the Actuator terminals on the other end of the control wires. I'll try the 230V 3-ph separation method 1st see what results I get then maybe get rid of the plastic/pvc flex for the control wires and run them in a liquid tight metal flex instead to help ground out the 44V. I'll post results asap.
Thank you all.
Click to expand...

I _bet_ that if the control wire is tied to neutral at the control panel, it would bleed the 'phantom voltage' at the actuator terminals down to 0.

But the world is weird and wonderful, so I won't guarantee it :)
 
winnie said:
I _bet_ that if the control wire is tied to neutral at the control panel, it would bleed the 'phantom voltage' at the actuator terminals down to 0.

But the world is weird and wonderful, so I won't guarantee it :)
Click to expand...
You are absolutely correct. I have already done that using a 1k-ohm pull down resistor at the control panel for each control wire
and no more phantom voltage at the control panel but the 44V still present on the actuator terminals(3000ft away), lol.
It's progress though.:)
 
Shuntme said:
You are absolutely correct. I have already done that using a 1k-ohm pull down resistor at the control panel for each control wire
and no more phantom voltage at the control panel but the 44V still present on the actuator terminals(3000ft away), lol.
It's progress though.:)
Click to expand...

That is really interesting. 0V wire to neutral at one end, 44V wire to neutral at the other end.

That suggests some sort of magnetic coupling or transformer action rather than capacitive coupling.

IMHO possible, but I'd double check that measurement.

Jonathan
 
winnie said:
That is really interesting. 0V wire to neutral at one end, 44V wire to neutral at the other end.

That suggests some sort of magnetic coupling or transformer action rather than capacitive coupling.

IMHO possible, but I'd double check that measurement.

Jonathan
Click to expand...
Checked and checked and checked. #38(previous), #39, #40 & #41 have 230/120V internal control transformers. However this new actuator has external 120V supply and the neutral is connected at the panel.
Out of curiosity, the 230/120V electrical panel has 4-wires with Gnd. I get 230V 3-phase and 120V -N on one of the legs. My electrician told me he had to install the 120V breaker on a certain leg of the 230V to get 120V ............... ummmmmmmmmmmmmm. I'll have to look at it myself to verify cause 230- N should be 230/1.732 = 133V and it shouldn't matter which leg of the 230V you connect to at the panel. How am I getting a 120V to N and why only on one particular leg of the 230V(per electrician)
What am I missing???
 
Shuntme said:
What am I missing???
Click to expand...
Your formula only applies to a wye system, which is not common except as 208Y/120 and 480Y/277.
You likely have a nominal 240V Delta 3-phase 4-Wire system. This system has one of the delta windings center tapped at 120V. These are often called wild or high leg systems because the B phase to Neutral is at 208V not the 120V which is on the A and C phases.
 
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