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Grounding machines?

dabigguy

Aluminum
Joined
Dec 9, 2005
Location
Wisconsin east coast
As the title says. Do you ground your CNC machines or other machines for that matter? Boss man says they do not need to be grounded I disagree. What is your practice? Thanks.
 

SIM

Titanium
Joined
Feb 19, 2004
Location
Staten Island NewYork USA
Well yeah all my machines are grounded.
However I think you mean are they grounded individually to a grounding rod. To that answer I can say only one of mine is done that way. it was done as we seemed to have a stray current, tech said to sink a grounding rod and we did.
Did it make a difference..yup!. We now have a grounding rod sticking out of our floor. Otherwise nope, nada.
 

EJD3

Plastic
Joined
Jan 25, 2016
they must be properly bonded to the building ground system, according to code requirements.
NFPA also states that you should follow manufacturer's recommendations regarding this.
 

EJD3

Plastic
Joined
Jan 25, 2016
Either way, gotta be bonded to ground.
If the manufacturer says a ground rod, go that way, but the rod should be bonded to building ground as well. If the manufacturer doesn't state anything, bond to building ground system.
 
O

otrlt

Guest
Hello dabigguy
I will closely monitor the replies on this post, this is a very good question to ask. Personally, I do not use a grounding rod, but in some parts of the country where thunderstorms are more prevalent I probably would be taking more precautions that would perhaps include secondary grounding.
otrlt
 

ifixcnc

Hot Rolled
Joined
Feb 6, 2015
Location
Cleveland Ohio
The National Electrical Code book has said no to individual ground circuits for a longtime. The theory being that if two machines are at different ground potential, and the one with the lesser ground has an short to ground, a person could offer the current a better path to ground by touching both. POOF one electrocution to go. The old way (rod at each machine) worked for years but, I can see the merit in the new code.
 

SAF

Stainless
Joined
Jul 20, 2014
Location
MI USA
Properly Grounding CNC Machinery And Sensative Equipment.

All machines need to be grounded, to prevent electrocution and to provide a path for short circuits to go back to the service source, in order to trip the breaker or fuse as quick as possible to remove the leakage hazard.

How to go about that is to run a ground wire with the circuit that supplies the machine. A dedicated insulated ground wire run direct to the ground buss in the service is the best method to reduce noise on the circuit to the machine.

Using the conduit system for a ground is acceptable according to the code, but is not a good practice for CNC machines or sensitive equipment. The conduit system can have electrical noise on it from other equipment, and can be coupled into your CNC controls. It will protect you from short circuit faults and electrocution, but can be noisy and cause logic errors on sensitive equipment.

Using a isolated ground rod without an additional connection to the building service ground bus is very hazardous to the operator as well as the equipment, even though some machine specifications may call for this. It's also non code compliant for this reason.

The reason that some Asian manufacturers specify this method is because their power distribution is different than what is used in the US. It is applicable to their power system, but not here in the US. And their install instructions usually don't differentiate the differences.

Adding a supplemental ground rod (additional local rod) is acceptable by code, but is usually not a good idea. It can cause more problems than it solves. It can pick up local electrical disturbances in the earth from downed power lines and nearby lighting strikes and run these surges through your equipment, in order for the pulses to reach the service grounding system.

When you install a dedicated insulated ground wire back to the service it mitigates most normal problems. If you still encounter issues, it's usually caused by the service equipment not being properly bonded to the building steel, water pipe, service ground rods, or other earth electrodes.

Here's a link to a sparky code forum asking the same questions. At the bottom there is a link to a Video from a class instruction on grounding issues. The video is half an hour, and is well worth your time if you really want to get a better education on the issues involved. The CNC grounding specific portion begins at about the 10 minute mark.

Grounding of CNC machines???

6 of 7 Grounding Myths (26min:55sec) - YouTube

SAF Ω
 

SeymourDumore

Diamond
Joined
Aug 2, 2005
Location
CT
Using a isolated ground rod without an additional connection to the building service ground bus is very hazardous to the operator as well as the equipment, even though some machine specifications may call for this. It's also non code compliant for this reason.

That right there, highlighted in case someone missed it.

There are cases where some specific equipment must "float" due usually to the nature of said equipment, but there is no case
where individual ISOLATED ground rods can be substituted as a proper ground connection.
 

FredC

Titanium
Joined
Oct 29, 2010
Location
Dewees Texas
I worked for a place that only had the 3 hot wires to the machines. I walked between the lathe I was running and a near by machine and got zapped. I asked the electrician why my machine was not grounded his reply was that none of them were. He put a new thread whirler on the lathe to replace the one that shorted to the machine casting but I do not think he grounded either machine. After a couple of other near death experiences I found another place to work.
You know something is wrong at work when the supervisor gives a lecture about not running to the accidents that were happening regularly. We were asked to notice how he walked to said accidents!
 

tteitgen

Aluminum
Joined
Jun 16, 2013
Location
Muskegon
We added an additional 10 foot earth grounding rod to all of our machines. Got rid of some of those ghost problems.
 

garyhlucas

Stainless
Joined
Oct 17, 2013
Location
New Jersey
Back when there was the Alt.cnc newsgroup I was considered to be the machine grounding guru as I have many years of experience with this. If a ground rod improves the operation of your CNC machine then it is wired wrong, period no exceptions. It goes right along with the mythical 'clean ground' that simply does not exist.
Electronics engineers don't seem to comprehend that signal grounding and safety grounding are completely different. Signal grounding demands that there never be more than one ground path to each device. Safety grounding demands that every device be grounded to everything else as often as possible. Safety grounds are never 'clean'. Every electrical device leaks a little current through insulation to ground. When a device fails it often sends tens of thousands of amps into the safety ground system, and it goes everywhere.
So a ground rod is never a fix for a machine with glitches. You are simply covering up a wiring problem, and may even be exposing the machine to serious damage.
 

Vancbiker

Diamond
Joined
Jan 5, 2014
Location
Vancouver, WA. USA
......Using the conduit system for a ground is acceptable according to the code, but is not a good practice for CNC machines or sensitive equipment. The conduit system can have electrical noise on it from other equipment, and can be coupled into your CNC controls. It will protect you from short circuit faults and electrocution, but can be noisy and cause logic errors on sensitive equipment.

IMO it is also a dangerous practice. I have seen several instances where conduit runs have had joints pulled apart. Now there is no ground path and a fault in the machine wiring can leave the machine floating at line voltage to ground. If anyone touches that machine and something that is grounded, a shock or worse will occur.

I found one of these once when trying to connect a RS232 cable.....
 

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
yes, I run copper ground on all circuits including "household" type. (5-15R, 5-20R).

I have a bunch of pictures of discontinuous raceways. EMT, armored (BX), conduit, IMT. seen WAY too many to trust that as a vital link in a safety system.

if I am not mistaken, it is very important to bond (both ends?) of a metal raceway the copper ground lives in. if this is not done, it acts like a very low impedance choke, and blocks some high frequency or transient leakage or fault currents. this could be why you find the ground rod helps, but it is not the correct way to solve that problem.

how close did I get that, from memory, ground gurus?
 

cyanidekid

Titanium
Joined
Jun 4, 2016
Location
Brooklyn NYC
oh, and insisting your machines not be grounded AT ALL is the very definition of criminal negligence.

no wait, actually, depending on local law, if someone dies, it could easily be manslaughter or (man 2?)
 
O

otrlt

Guest
Hello Fredc,
You just reminded me of an incident 37 years ago in Gardena, Ca does anyone remember Chalco Engineering?
otrlt
 
O

otrlt

Guest
Good Evening dabigigguy,
Your post has addressed one of the most relevant issues of the safety of our machinist, I personally, thank you.
otrlt
 

SAF

Stainless
Joined
Jul 20, 2014
Location
MI USA
Additional CNC Circuit Considerations

Most CNC's require or have built in a transformer on the supply circuit to the machine. This accomplishes two functions. First is voltage adjustment. Second is isolation from the building service.

In my experience older equipment needs the transformer provided by the user. Newer machines can come with the transformer built in the machine.

This additional requirement can also cause confusion on the proper method of connection and transformer type selection, as well as grounding.

The first requirement is the transformer type. Almost all (Asian & European) 3Φ drives require a Y input, for proper operation and voltage symmetry with respect to ground.

This means that your transformer must have a Y output for reliable operation and long component life.

Some machines come with a Y 3Φ autotransformer built in for adjusting input voltage. Others require that the transformer be installed externally.

If your service supply is a Y (120/208 or 277/480V) to begin with. That makes using a Y autotransfomer simpler. Symmetrical Y input and output.

If your service is a delta (120/240V High Leg) This would include RPC's. You need an isolation transformer to convert to a Y output from a delta input. Even if the machine has a built in 3Φ Y autotransformer.

This is where the grounding uncertainty comes in. What system you start with and what type transformer or two you have, determines how the grounding connections should be made.

There's many possibilities and combinations of equipment and systems.

An isolation transformer grounding and bonding requirements will be different from an autotransformer type.

An isolation type needs additional bonding requirements on the output side. Because the output is magnetically isolated, it needs to be bonded to the building ground electrode system (structural steel, metal water pipe, service ground bus)

If this is not done properly you will have problems. Some worse than others, but none of them good. There are too many possibilities to try and go into detail here, but the details really do matter.

It's best to think of the isolation transformer grounding required as a low impedance return path back to the transformer secondary coil Y center. Then secondarily to the building grounding electrode system (earth). Both of the bonding functions need to be connected properly in order for the system to be safe and reliable, as well as suited for the purpose.

SAF Ω
 

garyhlucas

Stainless
Joined
Oct 17, 2013
Location
New Jersey
In the US you will find that virtually all 3 phase transformers are Delta on the input side and Y on the output. The reason is to prevent direct one to one coupling of noise from primary to secondary.
 

CNCKrazed

Plastic
Joined
Oct 7, 2016
As the title says. Do you ground your CNC machines or other machines for that matter? Boss man says they do not need to be grounded I disagree. What is your practice? Thanks.

Every machine I've seen installed and I've seen alot (3-5 a year, every year for the last 9 years)has been grounded both with a separate ground rod and to building service ground.
 








 
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