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Garage wiring - EMF Concern

Discussion in 'Model S: Battery & Charging' started by gavine, May 1, 2014.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

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    I will be wiring my garage for my 14-50 outlet and the wire will be run through the ceiling in my garage which is directly below my bedroom. I plan on charging overnight. With 40A of current flowing through the wires, I wonder if I need to be concerned about EMF.

    Do I not worry about it? Do I run the wire a different way? Do I shield the wire with metal conduit?

    Any feedback would be greatly appreciated.
     
  2. Johan

    Johan Took a TSLA bear test. Came back negative.

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    There is absolutely no need for concern. The distance is far to great. Also, EMF is not a threat to your health.
     
  3. Klaus

    Klaus Member

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    @gavine, there is your absolute and final answer above :) Certainly helps to have absolute knowledge ...

    In my 40 years as EE and MD I've learned that there is no such thing as absolute certainty when it comes to health effects and technology.
    I would recommend you do your own research, and don't stop at the first "final" answer.
     
  4. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    There is very, very little to be concerned about. If this were a concern, people would worry about the power to an electric hot water heater or electric heat running near their bedroom. In reality, the two conductors run nearly adjacent to each other; therefore the magnetic fields of the two conductors almost completely cancel each other at at distances large compared to the spacing between the two conductors.

    See Ampere's Circuital law - Wikipedia for reference. Think about that green wire in the picture being replaced with red and black wires next to each other carrying equal and opposite currents (if the currents are not equal and opposite, the difference will trigger the GFCI and turn everything off!). Those equal and opposite currents produce canceling magnetic fields.
     
  5. Johan

    Johan Took a TSLA bear test. Came back negative.

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    He asked and I answered. He came to this site to do research. You didn't answer his question. Also I mistyped, I mean distance (a full story between garage and bedroom I presume) is too great for any possible effect, if if there were/are such health effects of EMF radiation.

    Also, I am also an MD and I do believe that EMF may be dangerous but not in the levels that can be brought about in daily life with our regular appliances including EVs.
     
  6. gavine

    gavine Petrol Head turned EV Enthusiast

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    Just to be clear, the wire will basically be directly under my bed. My bedroom is above the garage and the floor of the bedroom is the ceiling of the garage. So , the distance I will be from the wires would be about 4ft. Does that change the answer where you said the distance was too great now that I know you assumed there was a Storey in-between?
     
  7. tga

    tga Active Member

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    And if the OP is really concerned, he could also run THHN through conduit, pre-twist the two hot wires, and wrap electrical tape around the pair every few feet to keep them together. I'm not sure how you'd maintain the twist pulling the pair through the conduit, but twisting them would create a high current Unshielded Twisted Pair cable, further reducing the EMF.
     
  8. Klaus

    Klaus Member

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    I don't really want to argue about this. You answered in absolute terms, partly with factually incorrect statements. Maybe it was the brevity, and you corrected some of that above.

    With regards to EMF, there is an "E" (electric) and an "M" (magnetic) component. I agree with you and with Cottonwood that the magnetic field is likely to be insignificant provided that the conductors are closely paired throughout the cabling run. That is not necessarily guaranteed in conduits running individual wires, but still very likely of little concern. The electric component would be easily shielded by a well grounded metallic conduit. Good grounding is not guaranteed unless the installer knows how to do his/her job properly and doesn't take any shortcuts or uses poor technique.

    So - if I had that situation in my house, I would pay attention to the installer's work for those particular features, and not just rely on the final inspection.

    @gavine, if you have a choice, have the installer run the conduit on one side farthest away from and not right under your bed. Distance helps, anywhere between inverse linear and inverse square depending on the conductor configuration. It won't hurt the quality of your sleep :wink:

    - - - Updated - - -

    That is a great idea to address the wire separation issue I mentioned above.
     
  9. mknox

    mknox Well-Known Member

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    I think I'm going to regret jumping into the mix here, but this statement has me curious. I work in the electric utility industry and this issue comes up from time to time. As an MD, what causes you to believe EMFs can be dangerous? We manage voltages and currents a lot higher than residential wiring and have linemen "exposed" to these conditions day in and day out for years. Everything I hear (and I'll just say I'm no expert) seems to suggest non-ionizing radiation is not a problem.

    Personally, if I were the OP I'd be more concerned about fire, and with ensuring the wiring and installation is done safely and properly to ensure there are no heating concerns. (I'm talking about fire caused by faulty wiring, not the car :wink:)
     
  10. tom66

    tom66 Member

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    At 4ft, the magnetic field of Earth is stronger by about 10x than 40A flowing through conductors (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html). If it were DC you could demonstrate this with a magnetic compass; it will not budge until you closely approach the wire. With AC you would need a field meter or pickup coil and oscilloscope/voltmeter. Next time you are at a supercharger, try it.

    Since life has had ~3.7bn years on this planet to adapt to its magnetic field, I'd say you are fairly safe.
     
  11. Klaus

    Klaus Member

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    Thank you for that reference. I must admit that I keep forgetting the orders of magnitude.

    I can't think of a source for similar long term exposure to electric fields, especially not AC, other than lightning. Maybe electric shielding is not a bad idea? Anyone have a model handy for the E-field arising from closely spaced wires with opposite polarity distant from a ground plane, vs. a hot and neutral pair?
     
  12. tom66

    tom66 Member

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    Well, keeping the two conductors together in a pair should minimise the magnetic field by as much as possible.

    But I would like to add there is so far no evidence to suggest reasonable magnetic fields (up to 100 Gauss) have any effect on the human body, regardless of frequency.

    At extreme limits (1000 Gauss+) perhaps there may be harmful effects such as from an AC magnetic field leading to heating of the body (due to metal trace elements)? I'm not a medical professional, though, so not sure if this is actually possible.

    For a comparison the average MRI is 5,000 to 30,000 gauss at the peak field line. If you do have free ferrous metal in your body it won't shoot out violently, but it will get hot very quickly, leading to internal burns... not good.
     
  13. Johan

    Johan Took a TSLA bear test. Came back negative.

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    tom said it well below. When we approach extreme levels of magnetic fields there will be heating issues that may well be harmful, but I know of no real-life situations where this applies. There were some small studies that suggested than train drivers (electric train) had more brain tumors than the general population, but these studies were later contradicted by larger studies with better methodology.
     
  14. wycolo

    wycolo Active Member

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    Just run the cables at or below 4 ft in the walls or dug into the concrete floor if you intend a centrally located EVSE.
    --
     
  15. mknox

    mknox Well-Known Member

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    Yes, as they say correlation doesn't imply causation. In my neck of the woods, rail companies used to go heavy on arsenic based vegetation controls along corridors, so sometimes there are other unconsidered factors at play.
     
  16. RAM_Eh

    RAM_Eh Member

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    I have to chime in here.

    when two or more current carrying conductors are running in parallel each one is giving off a EFM(parallel runs single conductors). When they are pulled in conduit they basically zero out each others EMF. The ideal setup for reducing EMF is for multiple conductors in a "cable" instead of individual conductors in conduit. A manufactured cable such as a 6/3 has been twisted together from the manufacturer so if you are worried don't be.

    This will minimize EMF. As for the 40A you are charging at EFM is minimal at this amperage and voltage.

    By the way taping a cable and running it in a conduit is against electrical code!
     
  17. dsm363

    dsm363 Roadster + Sig Model S

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    If this really is a concern then why not pay extra to have the wire routed a different path?
     
  18. tga

    tga Active Member

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    I did sort of wonder about code after I posted that. Well, free advice is worth what you pay for it (and internet forum advice may be worth even less!)
     
  19. miimura

    miimura Active Member

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    I just received an Owner's Manual Supplement from Toyota for my RAV4 EV and it made me think of this thread.
    This is the relevant part.

    Owner's Manual Supplement_Charging.jpg

    They also mentioned that the same people should stay away from the "SmartKey" antennas.
     
  20. William13

    William13 Member

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    Toyota's message is due to lawyers, not science. Cell phones and high power lines have been studied without significant findings. Thus at worst it must be a small effect if any. If like mercury in vaccines you have a worry, move the cable slightly.
     

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