Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: trparker on October 20, 2012, 08:38:24 PM
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I found out this weekend that the receptacle I was using for the cnc
was not grounded....trying to account for erratic behavior I first began
to check for proper grounds when I found this...I have now run a new
line to for the cnc a dedicated breaker which is grounded...
In addition to this normal circuit ground I have read where a cnc's metal frame (chassis) is also
grounded to a separate earth ground.. a hole is drilled through the floor a ground rod is driven
into the ground and the machine is grounded to this via # 8 copper ground wire....
will this help with noise and interference issue....
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What type of cnc machine are you using....mill, router?
RICH
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I using Heiz 1000 from germany, I have it about 3 weeks...
I using router...
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A hole drilled beside the machine is typically a useless ground, think about it you are driving a rod into dry earth, that has been dry for years as there is a building over it and will thus remain dry and a lousy ground. Some machines, such as a plasma cutter, can make use of a local ground rod usually driven outside the building as close to the machine as possible. The local ground rod must be bonded to the electrical ground or will will create more problems for yourself. Two rods driven in the ground just 100' apart can have enough potential difference (voltage) across them to create a deadly shock hazard.
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so then the ground provided by the normal electrical circuit is enough?
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Yes, unless you are using a plasma table etc. On your machine all the items that need an earth ground should be tied to a single point (bonding bar) and you would connect your earth ground there.
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There is a difference between grounds from an electrical and noise point of view.
Electrical grounding should be done to satisfy your countries authority and local electrical code.
They deal with and provide for life safety.
Noise is a rather loosely used term, and for simplicity for this reply, i will just say that noise is an
unwanted signal which is part of or added to the original signal traveling on the same conductor or
recieved and travels on a conductor. Noise is created by the router and the intensity gets smaller as the distance
from the source increases.
Interference is the result of noise due to the intensity of the noise which can affect connected circuitry.
Grounding is done differently for noise as compared to electrical and again i use grounding rather loosely.
RICH
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A copper ground rod is for safety - it will do nothing at all for noise.
Regards,
Ray L.
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There is a difference between grounds from an electrical and noise point of view.
Earth Ground is Earth Ground is Earth Ground, Earth Ground does not change into something else when being used for noise abatement. While the primary purpose of the ground wire being added to electrical system was safety having a low impedance path to earth (a path which had no current flow from any circuit) was also a perfect place to bleed off electrical noise.
A copper ground rod is for safety - it will do nothing at all for noise.
That is incorrect. Crack open the power supply on your PC, where do all the filter parts get bonded to? The Earth Ground! Why? It is a low impedance path to ground. In the case of a machine like a Plasma Cutting table, Automated TIG welding machine etc, the local ground rod provides a low impedance path to the earth rather than rely on the small gauge ground wire that runs all the way back through the plant to the electrical service entrance. Any local ground rod should be bonded to the buildings electrical ground to prevent a potential shock hazard between the two.
I'm not meaning to sound like a 'know-it-all' here, I just want to dispel myths about grounding. I used to design, install and service automated welding and cutting systems and have had first hand experience with about every type of noise issue there is. I just want to share that experience with others.
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Jeff,
The difference I was meaning is relative to the cause and the affect and how a low impedance path may need to be different to a ground in the case of noise. Myth's come about from not understanding what is happening and become truths because for some situation something done worked.
Interesting you should mention about the conductivity of a ground rod. In industrial facilites the ground system is tested before installation and must meet certain standards ad certified on a continuing basis.The ground can be prepared to improve conductivity.
I'm not a "Sparky" just a dumb process / mechanical guy that has to deal with the Sparkies at work..........
we do like each other though and value the thinking differences. :D
RICH
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http://www.powerlogic.com/literature/AR_ECM_Bonding-Grounding_1-09_Waterer-Ray.pdf
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Terry - That is a good article! Thanks for sharing. The one use for the term 'ground' they kind of skipped of was 'DC Common'. A lot of guys try to use the machine frame as a current return path for sensor, probes, etc. Since the frame is generally connected to the earth ground you wind up with small control currents running through earth ground which causes all sort of problems.
Rich - Yeah there are fancy meters for testing how good a ground is. When installing plasma cutters, welding robots, etc we would do a quick 'red neck' test on the local ground rod for the machine. Hook a 100W light bulb between the neutral of the power source and the local ground rod. If the bulb was anything other than very dim the local ground rod was not good. After testing the local ground and building ground were tied together.
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There is a difference between grounds from an electrical and noise point of view.
Earth Ground is Earth Ground is Earth Ground, Earth Ground does not change into something else when being used for noise abatement. While the primary purpose of the ground wire being added to electrical system was safety having a low impedance path to earth (a path which had no current flow from any circuit) was also a perfect place to bleed off electrical noise.
A copper ground rod is for safety - it will do nothing at all for noise.
That is incorrect. Crack open the power supply on your PC, where do all the filter parts get bonded to? The Earth Ground! Why? It is a low impedance path to ground. In the case of a machine like a Plasma Cutting table, Automated TIG welding machine etc, the local ground rod provides a low impedance path to the earth rather than rely on the small gauge ground wire that runs all the way back through the plant to the electrical service entrance. Any local ground rod should be bonded to the buildings electrical ground to prevent a potential shock hazard between the two.
I'm not meaning to sound like a 'know-it-all' here, I just want to dispel myths about grounding. I used to design, install and service automated welding and cutting systems and have had first hand experience with about every type of noise issue there is. I just want to share that experience with others.
Jeff,
Sorry, but I have to disagree. For small signal stuff, like we're dealing with here, the earth ground is not going to do much of anything to reduce noise - the impedance through that path is orders of magnitude higher than the direct path through the ground conductor, even all the way back to the main panel. It is quite common to have significant potential difference between the "local" earth ground, and the power panel earth ground, if the two are separated by any significant distance. This creates a local shock hazard if the machine is connected only to the panel ground through the ground terminal of the circuit. This IS a safety hazard if, for example, the user is foolish enough to be standing in a puddle of coolant on the floor, and there is a short somewhere in the machine making some part of the machine "live". With the machine grounded to a local ground rod, this hazard is eliminated.
The situation, and hazards, with high-current welding equipment are quite different from what folks are dealing with here, and if someone is having problems with, for example, spurious E-stop or limit triggers, tying the machine ground to a local ground rod is exceedingly unlikely to make any difference at all with those problems.
Regards,
Ray L.
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The situation, and hazards, with high-current welding equipment are quite different from what folks are dealing with here, and if someone is having problems with, for example, spurious E-stop or limit triggers, tying the machine ground to a local ground rod is exceedingly unlikely to make any difference at all with those problems.
If you'll read my first few responses I also said that unless there is some need, i.e. plasma table etc, then a local ground rod is not required.
It is quite common to have significant potential difference between the "local" earth ground, and the power panel earth ground,
Also please note I said the two ground rods should be tied together. The article Terry posted the link to says the same thing.
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One common error is the improper connection of neutral wires to ground buses or ground wires to neutral buses. This error allows neutral currents to flow on the bonded system, thereby creating voltage transients. Neutral wires are only allowed to be connected to the bonded system at a service entrance or at a step-down transformer