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  1. #21
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    Quote Originally Posted by digger doug View Post
    Many of the machine tool foundations I made drawings for had extensive grounding from the manuf.
    a grid of ground rods all around the machine, bonded with thermite junctions in place.
    Thanks Doug for your input,

    Should grounding rods be used for non cnc applications as well?

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    Quote Originally Posted by otrlt View Post
    Hello Naeg;le,
    This is a very important subject that I have been interested in for quite some time. My shop is located in Northern California and in 30 years I can count 7 to 10 outages that include flickers of power disruption. I do all the wiring here and I do not use a grounding rod at any machinetool at my location. I would like to hear more from you and others of this practice.
    thanks
    I had one at a Bridgeport CNC, that machine had gremlins Big time. It was always doing something unexpected. Service guy said to take it out, it creates a ground loop when you are grounded back to the panel and it's ground rod. I disconnected it and all the issues disappeared. Some kind of black magic I guess.

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    Quote Originally Posted by otrlt View Post
    Hello Naeg;le,
    This is a very important subject that I have been interested in for quite some time. My shop is located in Northern California and in 30 years I can count 7 to 10 outages that include flickers of power disruption. I do all the wiring here and I do not use a grounding rod at any machinetool at my location. I would like to hear more from you and others of this practice.
    thanks
    The debate has come up in the past on here. From my understanding it boils down to simple redundancy, giving a surge an easy path to the ground rather than needing to travel to the buildings main ground or go through (comparatively) less conductive electrical components to get there. I don't have any scientific proof if grounding rods for each machine matter or not, but it's cheap to do and we've had good results. This is over the course of three machines at our old shop (14,000 sq ft.) and four at our current shop (15,000 sq ft.) over 20 years. Our shops were also located in the city, so the grid already has lots of ground compared to a country property where your buildings grounding rod might be the only one for a few miles, which IMO makes a difference in how hard a surge hits you.

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    Quote Originally Posted by moonlight machine View Post
    I had one at a Bridgeport CNC, that machine had gremlins Big time. It was always doing something unexpected. Service guy said to take it out, it creates a ground loop when you are grounded back to the panel and it's ground rod. I disconnected it and all the issues disappeared. Some kind of black magic I guess.
    I've run into some cases like that servicing other non-cnc machinery, but it was usually because the machine was making use of a neutral leg and ground and neutral were not isolated from each other.

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    For whatever it's worth, and without any cost considerations (admittedly):

    In a past life dealing with "critical function" facilities, this issue was dealt with through installation of of a backup generator that would auto-engage on a power drop + UPS installations where appropriate to bridge that small gap between outage and generator kicking in to protect computers and other critical functions (e.g. Radio, door & alarm actuators, etc.) Offhand I don't know how that kind of UPS config for the building would be with heavy equipment and power requirements in your environment, but I'd guess someone out there has backup power solutions that would fit the requirements.

    This is a significant investment I'd guess, but as an idea seemed relevant if you guys are "in the sticks" and it's "not uncommon".

    So, with all that cash laying around on your shop floor you have to sweep up every morning . . .

  6. Likes M.B. Naegle, henrya liked this post
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    Running CNC machines of any size on a UPS system? Hardly feasible unless someone else is paying for it...UPS gets quite expensive as the HP goes up.

    Run a refinery or chem plant....maybe consuming 75,000HP continuously....and you're making $1M per day in profit. What do you do when the power goes out? Do you have it all on a UPS system? Nope. You shut down and lose $1M/day. That's because it's cheaper to lose $1M/day than it is to have a UPS system.

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    Lots of good stuff here and food for thought. The post about "gremlins" is pretty familiar. Where we are is a way out on a major trunk line which runs up a state highway. We're kind of in between sub stations so if anything happens locally the line gets affected. Results are often a brown out lasting a couple of seconds, and it's not uncommon for three of our more complicated CNC's to start getting quirky, requiring a full shut down and cold reboot.

    I've instituted a procedure for when we lose power entirely, as we have lost control components due to surges when power was restored. Meaning that once power is lost they still have to turn the disconnects off before power comes back on. We lost an $8K power supply in our robot bending cell last year because the disconnect was left on and when the power came back on *poof*.

    I've considered Industrial UPS installs on our three most sensitive machines, but I'm going for low hanging fruit first as it's hard to get upper management to spend large sums on things that are not direct production (even though we're talking about lost production on existing machines).

    Localized Grounding is an interesting idea although I think the problem with brown outs is more related to voltage drops affecting either control components or the computer running the controls. I had not considered this but all three machines have embedded windows running Fanuc or Fanuc style controls.

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    Quote Originally Posted by digger doug View Post
    Many of the machine tool foundations I made drawings for had extensive grounding from the manuf.
    a grid of ground rods all around the machine, bonded with thermite junctions in place.
    Thermite junctions

    THat would be fun to watch during a lightning strike!

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    Quote Originally Posted by moonlight machine View Post
    I had one at a Bridgeport CNC, that machine had gremlins Big time. It was always doing something unexpected. Service guy said to take it out, it creates a ground loop when you are grounded back to the panel and it's ground rod. I disconnected it and all the issues disappeared. Some kind of black magic I guess.
    Yeah, ground isn't ground
    Even a couple of volt difference from a far off panel puts current in low voltage circuits and makes enough noise to screw things up.

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    Ground rods are not effective in dry ground.

    A effective ground can be achieved by connecting machine ground cables to the reinforcing bar grid embedded in the concrete floor. This design practice was developed in the 1940's by the military for bunkers containing explosives. It also became the standard for the building code.

    The ground connection should be a low inductance copper strap rather than a stranded wire.

    Ufer ground - Wikipedia

    https://electrical-engineering-porta...on-grounding-2

    Isolation transformers and transient voltage suppressors at each machine will provide additional high voltage arc protection at a reasonable cost.

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    Quote Originally Posted by swarfmeister View Post
    So we have several CNC profit centers that tend to be sensitive to partial and intermittent power outages. Historically, it's been the call of the department leads and the shift supervisor to run during times of significant risk of loss of power. We're kinda in the boonies, so this is not a particularly uncommon occurrence.

    When the remnants of Ida came through we had what was likely a crash due to power fluctuation on one of our main production machines being run on second shift. Since the operator wasn't quite up to speed on how to recover, several downstream problems happened resulting in the machine being down for the next four days.

    In hindsight, getting those few extra hours of production time at the cost of four days of downtime wasn't such a good bargain. So I'm wondering if anyone has a formal set of hard limits in place saying that if one or more of the following conditions exist, or are likely to exist, shut this machine down. I'm looking to establish a formally documented baseline so that we're all more or less all working out of the same playbook.
    Everywhere I have worked the call was made on the fly. Many times we did not even know bad weather was coming through as we were so busy. It is best for someone to try to keep up with the weather as a descision can be implemented quicker and save at least some parts which might be scrapped in a power outage situation.

    Like you describe is good to do. These machines are expensive and during these storms they can be adversely affected plus repair can be very expensive. It my boss says run it through I will unless I am sure it is dangerous safety wise.

    Costly material and the chance that a interruption will occur is a red flag for me this a possible scrapped piece is evaluated and considered by me.

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    Look up "motor-generator" set - used in large computing installations at one time.

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    Never worked at a place that shut down for storms...if the power went out, it went out lol.

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    The batteries only need to bridge the gap between sensing of coming failure of the line power and the start of back up generator power. The solution already exists, there is nothing to invent.

    But if you lose $1M per year to power failures and the cure costs $2 to implement then maybe you just live with failure.
    Last edited by henrya; 09-11-2021 at 07:11 AM.

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    Quote Originally Posted by TeachMePlease View Post
    I'm in Florida... Summer thunderstorms can shut down the whole plant/city for a few minutes.

    We just run until they stop.
    Same here. If we shut down for every storm we wouldn't get much done~

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    Quote Originally Posted by digger doug View Post
    How to account for the energy usage to clean the SNOW off the panels 5 months out of the year ?
    Back feed them from the powerco, and heat them up ?
    Having lived in the miserable state of Connecticut for far too long before escaping to the free world, I can tell you that snow collecting on solar panels is not a significant problem if they are set at any reasonable angle. The frozen northeast gets miserable weather, but long sticking snow is pretty rare in recent decades.

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    Quote Originally Posted by M.B. Naegle View Post
    ... Our shops were also located in the city, so the grid already has lots of ground compared to a country property where your buildings grounding rod might be the only one for a few miles, which IMO makes a difference in how hard a surge hits you.
    Most every power pole has a ground connection, they aren't large gauge or to a rod, it's typically a coil of the wire stapled to the bottom of the pole sunk in the ground. It may not sound like much, but at typical 150' pole spacing that's a lot of distributed grounding.

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    Quote Originally Posted by wp6529 View Post
    It's time for a "green" investment along with any tax credits. Install a sizeable solar PV system grid tie with significant battery capacity and put your CNC machines on that. Effectively it gives you a UPS for them at taxpayer subsidized expense and "green" feel-good credits. It will also reduce your electric bill so you'll recoup some of the cost eventually.

    Won't help at all. Grid tied solar systems go down with the grid to prevent backfeeding and killing the people working to restore service.

    Download "Weatherbug" on your phone. It will show lightning strikes in real time and tell you how close. The rest of the app sucks tho.

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    Some inexpensive small UPSs (even for the home) have usb or serial ports which provide detailed power quality info. You can log that to a computer to get an idea how much your power fluctuates, or use their app. That would not give detailed info for all legs of 3 phase but I think monitoring the 120v would show a lot.

    If your office ups shows power getting wonky during a storm, that would be a hint to shutdown.

    APC makes nice units. Here are some examples of data and their apps.

    powerchute reports - Google Search

    Beyond storms, power quality issues can be very serious but hidden. I was having problems with the microwave, TV, etc at my home. Microwave cutting out during use and then needing to be unplugged to reset, TV turning on and going crazy in the middle of the night at full volume, etc. I thought they were failing. A power crew showed up and replaced the underground line along the street. They said it was about 25 years old (I think more like 36) and had been failing for a couple years. They could see it on their diag gear. That resolved all of the appliance problems. This was the type of problem that could quietly disrupt your business/life.


    Quote Originally Posted by digger doug View Post
    How to account for the energy usage to clean the SNOW off the panels 5 months out of the year ?
    The solar array they are installing in my area has single axis tracking panels that pivot east to west. They position vertically to remove snow and clean in the rain.

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    Quote Originally Posted by aliva View Post
    You could buy a lightning detector, We used to use them when doing any critical hoisting with cranes
    There are apps for your phone for this very thing.

    We went to FL earlier in the year and the dolphin watch dude had one.......Pretty cool.


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