Results 1 to 5 of 5

Thread: Dealing with electrical surges

  1. #1
    Junior Member
    Join Date
    Mar 2015
    Location
    Queensland
    Posts
    140
    Thanks
    0
    Thanked 13 Times in 11 Posts
    Rep Power
    120
    Reputation
    270

    Default Dealing with electrical surges

    Hi all, I’m curious about the following - with the equipment that we deal with(RS485 based data equipment) the manufacturer makes a point of correct earthing and bonding between equipment. It appears that with electrical surges caused by lightening, a low impedance path to ground is best to eliminate unwanted energy from the delicate circuitry. Is it a case that the faster you can eliminate the energy to ground, the less possible damage it can cause to the circuit? Also, I notice that in the case of providing an electrical earth to appliances like a hot water system, they commonly use a coil in the earth wire, is this to resist a change in current flow? If so, what is the difference in application and the way shunting current to earth is desirable?

    Thanks very much in advance



Look Here ->
  • #2
    Banned

    Join Date
    Jan 2017
    Location
    still above ground level
    Posts
    1,779
    Thanks
    5,562
    Thanked 1,964 Times in 714 Posts
    Rep Power
    0
    Reputation
    35657

    Default

    TO start with electrical surges are not caused by lightening they are mains bound rises and falls in your supply voltage caused by numerous reasons . It has always been desirable to provide the lowest resistance / impedance to ground .I suspect that the coil you mention is a useless habit that allows the electrician to have some spare cable to remake the earthing without the wiring looking ugly . You will never be able to beat a lightening " strike " and as far as the least possible damage is concerned the odds are better on a slow horse than betting on a static discharge cos they dont follow any rules it all a guess good luck Don

  • The Following User Says Thank You to hinekadon For This Useful Post:

    loopyloo (04-11-19)

  • #3
    Senior Member

    Join Date
    May 2018
    Posts
    2,251
    Thanks
    527
    Thanked 1,857 Times in 894 Posts
    Rep Power
    881
    Reputation
    36714

    Default

    Surge arrestors are useless for preventing lightening induced surges. I have seen them with all sorts of stupid voltage ratings but the fact is by the time the things can act the damage is done.
    Unless a strike is on the pole outside your premises, it's probably been grounded 50 Times or more but that does not help because that's where is wants to go anyway.
    Whatever gets in the way is just bad luck... and often Vaporised.

  • The Following User Says Thank You to george65 For This Useful Post:

    loopyloo (04-11-19)

  • #4
    LSemmens
    lsemmens's Avatar
    Join Date
    Dec 2011
    Location
    Rural South OZ
    Posts
    10,585
    Thanks
    11,868
    Thanked 7,061 Times in 3,338 Posts
    Rep Power
    3153
    Reputation
    132592

    Default

    I worked for Telstra in Darwin in the 80s. Good surge suppression DOES WORK! We had techs working full time and on overtime working to to repair lightning damaged equipment. When we finally could convince the "southerners" that Darwin had special needs in relation to lightning protection (Darwin has the highest number of thunderdays of any capital city in the world) we eventually found some surge arrestors that actually worked. I still have one.

    Now - for a case in point. I had this arrestor plugged into my computer, that was the only suppression in my premises. The kids were playing a playstation plugged into the TV in the living room. My computer was plugged in (to the arrestor) and turned on. We had a TV in another room, plugged in but not turned on. Along with the usual, fridge, washing machine, microwave, etc. All plugged in. The building next door took a direct strike. It took out most stuff in that building - It was a school classroom and was several days before they were up and running again. On the other side was a Church, again, lost a lot of light globes and few other bits and pieces. All that happened in our place -
    Kids got a mild shock (not bad) via their game controllers, the computer re-started, blew a few light globes and a fuse in the TV in the bedroom. That was it!!!

    Cheap surge arrestors are next to useless and are only there for "feel good", the ONLY certain protection is to unplug anything that you do not want to lose in a strike. Good Arrestors do work, but, like anyone with a false sense of security, they can fail. The only certain way of preventing surge damage - unplug the gear!
    Last edited by lsemmens; 03-11-19 at 07:42 PM.
    I'm out of my mind, but feel free to leave a message...

  • The Following User Says Thank You to lsemmens For This Useful Post:

    loopyloo (04-11-19)

  • #5
    Senior Member
    trash's Avatar
    Join Date
    Jan 2008
    Location
    Tamworth
    Posts
    4,088
    Thanks
    148
    Thanked 3,229 Times in 1,451 Posts
    Rep Power
    1287
    Reputation
    47674

    Default

    It appears that with electrical surges caused by lightening, a low impedance path to ground is best to eliminate unwanted energy from the delicate circuitry. Is it a case that the faster you can eliminate the energy to ground, the less possible damage it can cause to the circuit?
    It's not the correct way to think about it. Each situation is different.
    With lightning, your not trying to make anything go faster because.. the speed of light doesn't change. What you're trying to do is eliminate step potential.

    On sites where we can expect a lightning strike there is nothing we can do to divert the energy of the strike. Instead we try to keep everything at the same potential and ride out the storm so to speak. Everything comes up to 1 million volts together and everything falls back to 0V together. Any difference in potential is a flow of current so the other way this is considered is as a low resistance between any points of potential.

    A piece of equipment I recently serviced was having serious issues with static electricity. Poor design and the manufacture didn't know how to fix the problem.
    They didn't understand the problem of how static was damaging their equipment. It was no different to a lightning strike so I built a tiny little lightning mitigation system for it.
    It didn't try to eliminate the static as the manufacturer had been trying to do. Rather it encouraged the static discharge (OSI layer 8 problem -- because you can't eliminate the stupid human from the equation). The MCU board fails as the static caused a step potential between the human, the keypad, the sensors, the MCU, power supply and chassis.
    Bringing the chassis up to the potential of the human is the way everybody thinks of solving the problem, but it makes the problem worse, because there is still a step potential, but now it's just from both ends which are not equipotential with respect to the other components.

    The point of contact was fairly predictable, since the humans almost always touched the same place first. The earth system acts like the chassis normally would (if it wasn't mostly plastic). The earth wiring system is such that the MCU, sensors and keyboard are all kept at the same potential as much as possible even though they are each a metre apart.
    The chassis and the power supply are next in the food chain to make sure that other boards in the unit are also brought up to potential together.
    The PSU is the only actual route to actual earth via the power protective earth wire. It's bonded to the static earthing system, which really does nothing for it other than provide an Earth potential reference. The static is mitigated just as well without it. If for some reason there was a nearby real lightning strike (basically impossible) this unit would survive a step potential as all the boards and sensors would come up with the Earth potential at the same time, even if the wet meat bag human had his finger on the button at the time.

    Actually... the human could be struck by lightning while pressing the button. The rig would probably survive while the human probably would not
    Yes I am an agent of Satan, but my duties are largely ceremonial.

  • The Following 4 Users Say Thank You to trash For This Useful Post:

    hinekadon (04-11-19),loopyloo (04-11-19),lsemmens (04-11-19),Skepticist (06-11-19)

  • Bookmarks

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •