Grounding required for foam insulation near cables?

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bio mass

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Building Industry
Hello,
I have some new 14/2 cables + speaker wire installed near foam insulation. I have noticed that the installed foam insulation carries static electricity, which i do not want for the low voltage, and have some concerns about the line voltage. I wanted to know if this could be neutralized by grounding the foam once, or if the foam can be bonded to a piece of metal inside the walls, maybe to a sacrifical piece of metal.

I am not entirely sure how safe this is, but XPS foam insulation in walls all the time.

I have noticed that i can install metal mesh on the foam to neutralize the electric field (similar to a faraday cage), but would rather try to control or reduce the XPS insulaton charge if i can.
Thanks
 
bio mass said:
I have noticed that the installed foam insulation carries static electricity, which i do not want for the low voltage,
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Umm, how did you determine that it "carries static electricity" and why do you think that it would be a concern with the low voltage and line voltage wiring?

-Hal
 
Where does the static charge build up.
The surface isn’t attached all the way through the house.

Aren’t your LV wires shielded?
 
I noticed the static electricity when i was using a non-contact voltage detector (Gardner Bender) to locate any possible hidden cables in the stud frame wall when attaching it (the wood frame wall goes on after the foam is installef). when the tester moves close to the insulation, it begins to trigger, and the indicator increases in frequiency the closer it gets to the insulation. There is currently one extisting live cable that is in front of the insulation (touching) which runsin to an existing electrical box. The instulation was installed behind it. I am wondering if the XPS foam insulation is conducting a small current somehow?

For the moment, asuming there is a charge, If a static charge builds up, can it just be discharged once, provided it is done safely? There must be a way to test for that.

I thought low voltage wires are not shielded. It is just speaker wire. The conern about low voltage is interferance on the line to a speaker. On line voltage conern, i am not sure if that was a concern for any reason such as arcing.
 
Foam insulation is non-conductive. Further, non-contact voltage detectors are not 100% reliable. A positive indication should be used as a warning to investigate further, not that absolutely there is a voltage present.

What you theorize just can't happen. If you are that worried about it contact an EC and ask him or her to look at it.

-Hal
 
At static control workstations, typical resistances for wrist bands and work surfaces are around 1 megohm. You don't need a low resistance path to dissipate static electricity. But how you get it out of the foam I don't know. And if you put a screen, nail and wire, or foil tape over it in places, would it drain the static from the entire sheet???

But as others have said, I would not worry about it.
 
hbiss said:
I'm not convinced that there is static or that a NCVD would detect it.
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While there is no current to speak of, EPS does tend to generate a lot of static, which is voltage.

B5LyO_CIYAATcvI.jpg
 
Its interesting. i can only speak to what i saw on more than one and the LCVD did detect it. Although it is good to know it wont interfere with high or low voltage.
 
LarryFine said:
While there is no current to speak of, EPS does tend to generate a lot of static, which is voltage.

B5LyO_CIYAATcvI.jpg
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Well, it is plastic. And like carpet or anything else like it, when the humidity is low I suppose it can generate a static charge when rubbed. However, I don't believe that a non-contact voltage detector is capable of detecting such a charge. It's designed to pick up an AC field, using it on a DC circuit wouldn't cause it to do anything. A static charge is DC after all. Like I said above, NCVDs are not reliable and should never be relied upon for determining weather a circuit or object is energized or not. I have no idea what yours is picking up, I know I can wave one around a room and get indications from many different places.

So again, to answer your original question, your whole idea is preposterous. Foam insulation is used commonly today and if there was a situation like you believe, don't you think there would be all kinds of news and warnings about it? Throw that voltage detector away and get on with your work. There is no problem with the wiring nor is there going to be.

-Hal
 
'Static' electricity can attain extremely high voltages, and in some cases can present a real hazard, however I doubt that _stationary_ XPS panels in a normal residential situation will be an issue.

Static control is a safety issue if you have rapidly moving materials (eg. dust collection systems with plastic piping), or if small sparks present an extreme hazard (explosive atmospheres, etc). Static can also be a nuisance or can cause issues such as surfaces collecting dust.

If you rub a balloon in your hair and then let it stick to the ceiling, that is static electricity at work. The dust rings that collect around such balloons are also caused by static electricity.....

-Jon
 
winnie said:
Static control is a safety issue if you have rapidly moving materials (eg. dust collection systems with plastic piping), or if small sparks present an extreme hazard (explosive atmospheres, etc). Static can also be a nuisance or can cause issues such as surfaces collecting dust.
Click to expand...

Only thing that comes to mind in a residential setting is central vac systems. You often see the plastic piping collecting dust on the outside surfaces. Still, it doesn't present a problem.

-Hal
 
hbiss said:
Well, it is plastic. And like carpet or anything else like it, when the humidity is low I suppose it can generate a static charge when rubbed. However, I don't believe that a non-contact voltage detector is capable of detecting such a charge. It's designed to pick up an AC field, using it on a DC circuit wouldn't cause it to do anything. A static charge is DC after all. Like I said above, NCVDs are not reliable and should never be relied upon for determining weather a circuit or object is energized or not. I have no idea what yours is picking up, I know I can wave one around a room and get indications from many different places.

So again, to answer your original question, your whole idea is preposterous. Foam insulation is used commonly today and if there was a situation like you believe, don't you think there would be all kinds of news and warnings about it? Throw that voltage detector away and get on with your work. There is no problem with the wiring nor is there going to be.

-Hal
Click to expand...
I don't remember what brand it was, I think a Greenlee NCVT I once had. It not only lit up but also made audible sound when sensing voltage. With AC the sound was a sort of buzzing - probably at 60 Hz when checking 60 Hz supplies. This thing would at times make a random beep while in tool puch or even rub it past your pant leg and would make a single beep, and flash the indicator light one time. About had to be a reaction to static.

I also had held it (doesn't need to be nearly as close as it does to a 120 VAC conductor) near electric fence line and it would beep/flash as the line was pulsed. could hold it like 3 feet away and it would indicate this. Most those are capacitive discharge DC voltage.

I also once held it up to a conductor I had connected to my underground locator. It beeps/flashes in sync with the pulsing signal the locator puts out on the line to be located, also a pulsing DC signal.
 
It triggers on the rise and fall of the DC pulse. Same with a random static discharge. I think all it has is a pickup coil and the voltage has to be "moving" for it to output anything. If something has a steady DC charge on it a coil held near it isn't going to output anything- unless maybe you wave it around in and out of the field.

Another cheap and dirty method some may use is to just connect a probe to the input of an audio amplifier, preferably one tuned to 60Hz. When the amplifier output reaches a certain level have it trigger an LED, tone, etc. Again, that's not going to do anything when near DC either.

-Hal
 
A third cheap method is to have a probe that is connected to the gate of a FET. This FET operates the rest of the circuit. This will detect pretty much any voltage relative to the rest of the circuit, usually capacitively coupled to the hand of the person holding the unit. It can't detect DC, but the impedance is very high and leakage low, so it will detect high enough voltages at very low frequency (say the 'frequency' of moving the device toward the static charged object).

-Jon
 
Ive installed thousands of feet of cat 1 thru 6 cable for voice and data communications as well as PA and other low voltage apps over last 20 + years and never had a problem with static. I used to fool female apprientices by rubbing my arm with one of those non contact lights and it would ligh due to static generated by rubbing my hairy arm, then I'd hand it to them and have them try it, having less hair it never ligthed up. while a nice trick to play on apprentices the point is static needs movement to generate it. so yea you might get some light rubbing a wire or something on the foam but it's not going to stay on the foam long.
 
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