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Thread: Bonding ... grounding in a high-rise

  1. #1

    Default Bonding ... grounding in a high-rise

    Hope this is the right forum to place this post.

    As I'm trying to get a better understanding of grounding and bonding, this is the first step I've been working on. I have several components to my radio and at times I've noticed that when I touch the box, I would get a slight shock. I always thought it was just me walking across the carpet but now I'm starting to get a better understanding of things, but still a long ways to go.

    I have started with bonding my system. I have a copper bar mounted to the wall behind my gear and I am going to run flat braid copper from the chassis of each box directly to this bar. Then my understanding is that I should run a wire from the bar to ground ... and here's the problem.

    I live on the 10th floor of a high-rise and have nothing to attach it to. No incoming water pipe (all pvc), no A/C copper lines, and if I understand this correctly, I can't use the ground in a 120v electrical socket either (green wire?).

    So how do I go about grounding this properly? Any thoughts much appreciated.

  2. #2

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    You have HVAC of some sort? Ground to a radiator? If you have an forced air you could ground to the ductwork. If it's a rental unit you could use metal tape to tape a ground wire to the ductwork inside a vent cover.


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  3. #3

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    So, your saying it just needs to be a large piece of metal? Basically everything in my unit is it's own little island. All incoming and outgoing are pvc of some sort.

    If that's the case, I do have a 40 ft. steel balcony railing that is bolted into the concrete floor. Would that be ok? This is also the railing I hang my antennas off of.
    Last edited by rrlangly; Tue 28th May 2019 at 00:26.

  4. #4
    Ots's Avatar
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    "I live on the 10th floor of a high-rise and have nothing to attach it to. No incoming water pipe (all pvc), no A/C copper lines, and if I understand this correctly, I can't use the ground in a 120v electrical socket either (green wire?)."

    Why not? That is for case grounding to earth. If the outlets have the third ground wire any appliance with a three prong plug will have its chassis ground going there.

    My power supply has the three wires and it's the kind with extra output terminals for L and N, and I use the ground wire terminal as my ground for all my equipment.

    Cheers,

    Bill

  5. #5

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    Let me try to find this in my grounding and bonding book from ARRL, but I've also had other people tell me it's not the same thing, though I could be wrong.

    If I could use it and it were safe, I'd like that to be the case as it sounds like it's my best option.

    Also, if this is ok, it sounds like what I need is an earth bonding plug from the bus bar to a socket? Does it go by another name? Haven't really found the exact one yet.
    Last edited by rrlangly; Tue 28th May 2019 at 00:44.

  6. #6
    Ots's Avatar
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    There are other types of grounding situations where it wouldn't be the right way to go, you're right. But the ground wire on a three prong plug is for case grounding which is what you're looking for.

    See section 28.1.5 of the ARRL Handbook.

    Or section 3.3 of ARRL Grounding and Bonding.
    Last edited by Ots; Tue 28th May 2019 at 01:29.

  7. #7

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    Quote Originally Posted by rrlangly View Post
    So, your saying it just needs to be a large piece of metal? Basically everything in my unit is it's own little island. All incoming and outgoing are pvc of some sort.

    If that's the case, I do have a 40 ft. steel balcony railing that is bolted into the concrete floor. Would that be ok? This is also the railing I hang my antennas off of.
    The radiator or duct work will eventually lead back to an AHU or to a boiler. Both will be metal and grounded.

    I wouldn't use the grounds or neutral of a 110v plug. When a gfci trips it is because of a short from the hot wire to ground. You have 10 floors of people that could cause a short or monkey around with their ground and energize your radio.




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  8. #8
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    Quote Originally Posted by Redbicycle View Post
    The radiator or duct work will eventually lead back to an AHU or to a boiler. Both will be metal and grounded.

    I wouldn't use the grounds or neutral of a 110v plug. When a gfci trips it is because of a short from the hot wire to ground. You have 10 floors of people that could cause a short or monkey around with their ground and energize your radio.




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    Neutral would never be used for case grounding - that's what the third wire is for. GFCI's would be localized to the individual apartment's outlets. It's the apartment complex circuit breakers that would trip that would cause an outage in multiple units, but the GFCI's should prevent that from happening. Only the circuit in the GFCI in the individual outlet would be tripped in case of a fault.

    Again, the best advice is from the ARRL publications and they are perfectly clear on this.

  9. #9

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    Define "slight shock". Like a DC discharge or an AC buzz?

    Just use the outlet ground as Ots says, I definitely second that. Just hope you can trust the guy who wired the apartment! The balcony and concrete don't conduct enough to be useful for any more than static buildup.

    Do not ground to the ventilation system. Many times those have rubber joints for vibration dampening or wire-reinforced mylar ducting that can't conduct more than static. If its not grounded all the way, you could put your voltage problem in some kids room down the hall.

    Unfortunately, there are many unprofessional "professionals" with a license to practice their misunderstood shortcuts around the NEC on places like your apartment. Case in point, those darn outlets where you just cram the wire in the back as opposed to wrapping it around the screw. Those push-in connections are made with a thin metal catch tab to hold the wire in and press it against a metal surface. This allows for movement on a contact with already-limited surface area. After a few years of that outlet being used, the mounting screws loosen up (if the outlet was tight to begin with) and now the socket wiggles a little bit every time you plug in the vacuum cleaner. That's a problem because now that little tab is moving on the wire and copper is soft. When the contact gets loose, the resistance goes up and so does your house (in flames).

    My story:
    My Paco G-30 signal generator used to shock me every time my elbow touched the corner of my painted metal desk where the metal was exposed. Turns out, the people who made the paco kit did something very dumb in their schematic:
    https://www.hamradioforum.net/attach...8&d=1553402807
    Notice on the input of the power transformer the capacitors that provide RF shunting... Well, when I got the paco, the previous owner had a non-grounded cord on it so the capacitors acted like a low-current voltage divider putting ~60 volts on the case. The reason I point the blame at the paco design and not the "cord swapper" is because that 60 volts still needs to go all the way to the breaker panel to be shunted. They could have used just one cap between the transformer leads and one from neutral to ground instead of making a voltage divider out of it.

    EDIT: as for redbycicles concern of GFCI's or someone in another unit messing around... unfounded. Each unit is (or should be) on separate breakers, each having their own independent ground wires. GFCI outlets are only required in places near water like kitchens and bathrooms, also on separate circuits.
    Last edited by brandon lind; Tue 28th May 2019 at 02:44.

  10. #10
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    Thanks Brandon, and yes, sometimes things haven't been done right!

  11. #11

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    Quote Originally Posted by Redbycle lind View Post
    The radiator or duct work will eventually lead back to an AHU or to a boiler. Both will be metal and grounded.
    The duct work is all within the unit, each unit has it's own AC so nothing leads back to a centralized AHU or boiler.

    Quote Originally Posted by brandon lind View Post
    Define "slight shock". Like a DC discharge or an AC buzz?
    It's like a walking around the house w/ socks across carpet and touching something metal, just a quick shock, no buzz. Like static out of the dryer.

  12. #12

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    Is it a minor zap that you can sometimes hear but is too small to make your muscles contract, or does it make your arm twitch?

    Static electricity IS one possibility, especially during dry weather. Shocks from static electricity work because the body acts like a capacitor plate building up and holding like charges until you come in contact with something of a different static potential (like something metal, whether its grounded or not). It is important (in this respect) to ground the equipment so that static buildup or discharge through the case doesn't have to go through those precious mosfets or cmos cjips in the equipment to find some way out. Something as low as 20 volts, which you would never hear or feel discharging, is enough to punch through the microscopic layer of silicon dioxide between the gate and substrate destroying the mosfet device. For the discharge of static electricity, grounding the equipment will not stop you from getting zapped, but it will save your equipment if that zap has nowhere to go but inside the radio.

    If it makes your muscles contract: Whats the "box"? Is it a tube device running on high voltage? You could have a loose HV wire occasionally touching the case or, if the case isn't properly grounded with respect to the high voltage inside, the case itself may be acting like a capacitor plate building up a charge.

    Sometimes, both manufacturers and home brewers, forget to add a star washer between the case and chassis ground wire or between the case and the ground side of the HV DC circuit. That silly little star washer is super important because the dissimilar metals form a galvanic cell and air can oxidize the surfaces between them eventually breaking the contact. The star washer forms an air-tight pressure contact at the tips which prevents oxidation on those parts of the surface ensuring it stays connected. Just because it looks connected doesn't mean it is! But that's unlikely in your situation because that's a small gap that's easily jumped, just wanted to mention it because at 120v, its a real issue..
    Last edited by brandon lind; Tue 28th May 2019 at 13:55.

  13. #13

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    It's that, a minor zap that I can sometimes hear. Nothing as strong as making my muscles contract.

    I've always thought it was static electricity (and still think so during winter), but it's very humid where I live (Tx.) and when it happens in summer, it makes me wonder.

    By, "the box", I meant the chassis of my radio.

    Thanks for the info about the star washer, I didn't know that.

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