On 12/20/2015 8:37 AM, Gene Heskett wrote: > Start with a roll of flat braid equ to a 8 or 10 gauge wire. Establish a > bolt to the case of the controller as a master ground, and make sure > everything that references ground in the controller box is grounded at > this bolt. > > Tie this bolt to the buildings static ground using that pin of the > controllers power cable, BUT not to the building supply neutral as thats > usually noisy as can be. Or to a real ground rod but that may have a > considerable damaging joltage on it when there is lightning nearby so is > both against the NEC and would be poor practice. I'll start here, I see 4 places where things are grounded, the encoders all have a ground connection to the electrical cabinet and one on the other cabinet where the VFD lives. I know without looking that every panel has the neutral bonded to ground and I have two ground rods one for the house and one for the garage/shop (one panel for each one back to back). I do think this is local to the machine as I have other machines in the shop that do not have this problem. Let me study the grounds a bit... > Then extend that ground, using this braid, to the bridgeports main > casting, and perhaps also to the table and knee as the lube oil in the > ways might preclude a really good ground on the table without it. > > Extend that ground from that bolt to the computers case if it is > separated from the controller box. > > This is called a star ground system, where everything is common at this > bolt. If you can disconnect each wire from that bolt, and still measure > continuity of 200 ohms or less from the bolt to the disconnected wire, > then that wire has an unwanted ground somewhere, run it down and remove > it, you want that to be "grounded" only at that bolt. > > The idea is that even if it does bounce a bit from a nearby lightning > strike, it all bounces in unison with no big voltage drops between > anything that can damage it, or induce noise that would be miss-detected > as a signal. > > Years ago when I was screwing with vz & their bad copper, I figured on > losing a modem everytime I heard thunder. Getting PO'd, I first opened > up the wall a bit, pulled out the duplex that was going to power what I > had in mind, and soldered all the connections in that box. Then I bought > the biggest surge arrestor I could find, one that had phone line & cable > tv arrestors in it. And I bought the biggest home UPS I could find. > Everything in this room but the lights is plugged in either to that UPS > or that surge arrestor, and both are plugged into this all soldered > duplex. Now lightning can hit the pole my transformer is on, possibly > bouncing everything in this room by 100 kilovolts, but it all bounces in > unison and I haven't lost a modem or anything else that I could > associate the loss with local lightning strikes. But since I did get, > from a wired keyboard I was typing on at the time, a really good jolt > thru my fingers like shuffling ones feet on the rug and then grabbing > the doorknob, but it didn't hurt the computer or the keyboard, but I now > use wireless keyboard and mice. > > If the frame of the bridgeport is grounded thru other means, such as a > 3rd pin on a power cable, this should be defeated in order to remove the > potential ground loop which can be a source of quite a bit of induced > noise. > > Motor drive, and feedback cables from the motors should be shielded, with > the shields cut off at the motor ends of the cable but tied to this bolt > at the controller end, thereby interrupting that potential ground loop. > > The general idea is to have one common "ground" point, even if its is not > an earthen ground. That s/b, by the NEC, at the service entrance, a > minimum of two full rods driven 6 feet apart, with an 8 gauge wire > bonding them to the buildings static ground for the 3rd pin of all the > duplexes and neutral from the pole drop, the only place it is legal to > interconnect them. Hanging an amprobe on any of the bare static wires > in the service box should get you a zero reading regardless of what is > powered up. If you do see a reading, something out on that circuit is > miss-wired. Fix it. Its just good practice. > > It and I, may sound arbitrary John, but it works. And its NEC legal. > If you have a decent scope, just waving a probe around with the gain > turned up near suspected noise sources can be very educational. > > I've had to follow too many electricians around, fixing their mix-n-match > attitude about static and neutral being the same thing, way too many > times. > > Let us know what you did find when you've cleaned up the problem, please. > > Cheers, Gene Heskett
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