Questions - Help - 3DOF AC Platform IT Begins -

BlazinH · Jun 14, 2014

I did a little reading to test myself and I did find that...

“Shielding cannot always block static or slowly varying magnetic fields, such as the earths magnetic field (a compass will still work inside). To a large degree, though, they shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation.”
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And I found a more technical answer than saying magnetism repels the electricity...

A shield works by three mechanisms: (1) the conductive layer reflects incoming fields, (2) the conductor absorbs incoming energy, and (3) the cage acts to create opposing fields. All of these work to safeguard the contents from excessive field levels. Field cancellation occurs when the free carriers in the conductive material rapidly realign to oppose the incident electric field. If the cage is made from something non-conductive, the free carriers are not mobile enough to realign and cancel the incident field.
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And a better explanation on the effects of grounding it...

There is a great deal of confusion regarding grounding of a Faraday shield. Grounding of the shield (i.e., connecting it to some Earth-referenced source of charge) has little effect on the field levels seen inside the box. Grounding primarily helps to keep the cage from becoming charged and perhaps re-radiating. The bottom line is that an ungrounded cage protects the contents from harmful electromagnetic fields as well as a grounded one.
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cthiggin · Jun 14, 2014

BlazinH,
GOOD stuff...
Will put 14-3 w/g and foiling INSIDE flex conduit. Will put shielded pot cable on outside of flex conduit, zip tie........
To me, maybe overkill, but should not have to explore that component of the build as a problem area.......
Of course, the 14-3 will be earth grounded - will NOT ground the pot cable.

Thanks to you and all,

Tom

telfel · Jun 14, 2014

Hi
you can use CY flexible cable, comes in various size's and number of cores, you still need an earth core as well as the screen. Then you can zip tie your CAT6 cable to the CY.

I do not think home made screening earthing / methods are suitable for HV wiring,
If your are not familiar with HV wiring methods and practice I would recommend you get an electrician to check it out.
Mains voltage especially at high frequencies is a killer.

regards Terry

SeatTime · Jun 14, 2014

BlazinH said: ↑

Hi Tom, There’s always a possibility of interference when wires are close to each other as you apparently know or you wouldn’t be asking. But if all the AC wires are shielded, this should greatly reduce if not totally eliminate the chances of it. This is even more so if your pots wires are shielded also of course. I don’t think you will have problems but the way to know for sure is to try it! Sorry I’m not stating a definitive answer that you are probably looking for.

However, it’s said a car (with a metal body and when your not touching the metal itself) is one of the safest places to be in a lightning storm because when the lightning strikes the car (metal), the electricity produces a magnetic field (Faraday shield or cage) around it shielding the passengers within from the electricity itself. Shielded wire just has the opposite effect, keeping everything on the inside instead of on the outside.
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Also don't mix up a signal ground and a electrical ground/earth. Be aware also of signal earth loops.

BlazinH · Jun 14, 2014

How thick should the conducting layer be for shielding?
The conductive layer can be very thin because of something known as the skin effect. That term describes the tendency of current to flow primarily on the skin of a conductor. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large. The skin depth is a function of the frequency of the wave and the conductor material. As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns. EMP pulses can have frequency content that ranges up to 1,000 MHz. Therefore, wrapping a wire in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields.
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I like the idea of zipping your pots cable to the outside of your flex cable. For home security systems, experts recommend keeping its cable a distance of at least 2 inches from household wiring to avoid problems. But they said short runs are less likely to cause interference. So, the bottom line is you will just have to try it! If your pots do give erroneous results, it will be easy to cut the zip ties and reroute them with them being on the outside.

Also, heed SeatTime's warning!

cthiggin · Jun 14, 2014

Hello Gentlemen,
THANKS so much for your advice and wealth of information.
I now have a workable "game plan" and will proceed forward.....
With your information, hopefully I can do this ONE TIME and not have to be worried with interference.
I have, will, do understand and heed your warnings.

Have a blessed one,

Tom

Tags..(VR) · Aug 12, 2018

inside my motors , i have no wire brush touching the inside side of the motor. i haven't cut and soldered because i haven't been able to figure out which is the earth ground wire. but what if i were to run a ground wire from the casing on the motor to the ground of the terminal thats on the power supply unit and ground it that way? anyone try that?

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Questions - Help - 3DOF AC Platform IT Begins -

BlazinH Well-Known Member

cthiggin Active Member

telfel Active Member

SeatTime Well-Known Member

BlazinH Well-Known Member

cthiggin Active Member

Tags..(VR) Member