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Old December 2nd, 2002, 07:41 PM   #1
Grover
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Effective Equipment Grounding

Greetings.

We have a floor full of packaging machines that were installed in a building that did not have a grounding scheme designed into it, such as a grid in the concrete. The machines typically receive their safety ground connections through the 12AWG wire found within the 480VAC input power cable. A grounding block is then used to distribute the ground potential to various electrical components and attached equipment enclosures as well as some nearby, ancillary enclosures.

The power feed is a ceiling panel which is bonded to the steel facility columns. At this point I am not questioning the effectiveness of the ground path from a safety perspective- I feel it is proper and adequate based on my analysis of the 2003 NEC.

I am, however, questioning the effectiveness of this grounding scheme at reducing the the electical noise that infests these machines. I realize that every ground lead, including the ground source wire from the power drop, can act as an antennae by reacting to the magnetic fields induced by motors and solenoids.

I know this is an absolute can of worms subject, but I'd like to hear what others hve done to minimize the spikes that I am seeing on the signals. More power supply filtering? More shielding? Bigger gound leads? Re-routing the leads?



Grover
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Old December 2nd, 2002, 11:35 PM   #2
KMG
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Grounding

The problem with your system, from a noise standpoint is that you have what sounds more like a spiderís web then a grid. The reason that a spiders web works so well for the spider is that any disturbance on the web is felt everywhere on the web. And that is the same reason why itís not good for a grounding system. In my limited experience the best way to provide many good paths to ground that are very close to the machines. Give any noise source an easy path to ground away from all the other machines. If your machines are on the first floor, then drill through the floor and drive a 8ft ground rod and attach it to the machine. It is overkill for short circuit protection. But not for noise reduction.
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Old December 3rd, 2002, 12:24 AM   #3
rbrown
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Smile Re-Effective Equipment Grounding

I'm an Industrial Electrician for INCO in Thompson, Mb, Canada.

I think you should use the sevices of an Electrcial Engineer.

My solution would be to run bonding conductors, bonded to all your high voltage package machines, These conductors could be bonded to your steel beams. The next step I would take would be to bond grounding rods, driving into the ground outside your building.

Make sure these steel beams are inter connected.

#12 grounds do not offer enough protection in a ground fault or power serge/ground fault situation.


Again seek the advice from an electrical engineer who could provide bond and ground rod sizes for your application.

Safety First

Later
rbrown
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Old December 3rd, 2002, 04:26 AM   #4
sung-ho.song
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communication problem.

Panel view RS-232C port use DH-485 communication
by PV-550 and SLC 5/04
it is panel view 550 and SLC 5/04
I hope pc and panel view 550 communication method
this solve method
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Old December 3rd, 2002, 07:47 AM   #5
David_Emmerich
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Hi group... one of the BIGGEST problems that I have seen in industrial wiring / grounding is the fact that most of the time the electricians that design and/or install them are not INDUSTRIAL electricians, but more use to wiring COMMERCIAL or RESIDENTIAL jobs, and there for not up to date on proper grounding methods for plants. If you check the NEC {I don't remember the section # !!!} the ground wire size is to be LARGER than any CURRENT carrying line. This rule was put in place because with the advent on VFD's and Switching power supplies, the current on the GROUND leg can be up to TWICE the current on any 1 leg. Gone are the days when it was 'OK' to pull a # 12 green w/ 3 250 MCM's and hope for the best.........I hope I have not stepped on anyones toes w/ my triad, and maybe someone can link up the right NEC section......My point is, get enough copper in the ground system, and MOST on your noise problems will go away.


David

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Old December 3rd, 2002, 12:02 PM   #6
Grover
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Fellows,

This is such a wonderful forum. I appreciate being permitted to bring up side topics such as this. (The electrical noise IS affecting our PLC's.)

I have four options at this point.

1. doing what is perfectly right
(getting an EE and doing what he/she says)

vs.

2. doing what seems right by myself
(connect ground conductor through
the floor at the machine)

vs.

3. doing what I need to get by
(oversize conductor to steel beam 12ft above floor)

vs.

4. doing nothing
(after all, it's still working, isn't it?)

Options 1 & 2 are unlikely because of hiring outside help and dealing with downtime associated with a floor penetration (area contamination, cleanup and re-certification). As KMG suggested, this would be the right approach, but "right" at my level is not "right" according to the powers that be.

Option 3 is what I am pursuing at this point. By using a much larger conductor (4AWG) I am hoping to increase the amount of grounded mass, much like David_E suggested. What I don't like about this approach is that it makes for a very long (12ft) run to building beam.

Thanks to both David_E and RBrown correcting me on the #12 wire being adequate for safety grounding. 2002 NEC Section 250 describes equipmment grounding requirements and in the absence of an EE I am trying to parse through it and determine which parts apply. It's in my lap and I want to do it right.

Grover
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Old December 3rd, 2002, 01:35 PM   #7
rsdoran
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You may want to consider getting the NEC 2002 HANDBOOK, it gives detailed explanation with pictures (the part I like best).

Depends on several factors BUT having someone come in and test the ground system (which doesnt always cost anything nor disrupts production) will give you more/better ideas on what may be needed if anything is needed at all. The learning experience is also a benefit. I have gotten companies like Motion Industries, Wesco etc to do testing like this. Talk to some of your suppliers/distributors, many have an Engineering staff that can perform these services.

We recently had our ground system tested and were in bad shape, with the poor ground and harmonics etc we were getting some bad hits. This can cause a woodpecker effect that will ultimately destroy electronic/computer devices. I lost several electronic devices including 4 plc's (2 I didnt know about till later) all in a couple of days during some freak power outages. No storms involved naturally the power company says it wasnt them. The power company will also do testing on incoming power but have a tendency to clean it up if there is a possibility of an issue.

Its also a good idea to monitor usage on your panels, check balancing etc. Since you have no EE these are things to look at to eliminate problems down the road.

We still have some issues with harmonics but we corrected the ground issues.

When you talk to your supplier/distributors you may want to look into any Power Quality seminars that are being given, these can also give detailed info on using analyzers, scopes, meters etc and what to look for that can create problems on the source/distribution system(s).
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Old December 3rd, 2002, 04:45 PM   #8
porky
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Fancy Exclamation

Hello

The way I see it grounding is one thing and earthing is another..

1) seperate your power earths from your signal / PLC earths...
2) Have an earth resistence test carried out on your factory... if the earth resistance is high check on your fault level.. (Sometimes it is suposed to be high.. ie if you have a very high fault level ..a high earth resistance will reduce the fault current hence protecting your transformer.
3) If its not suposed to be high then .. reduce it..
4) Donot let your earth mats / spikes overlap as this may cause circulating currents.
5) your signals to and from your plc should only be earthed at one end.. ie at the PLC or at the instrument.....prevents circulating currents..

Finally donīt guess ...if unsure get someone who is....
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Old December 3rd, 2002, 05:54 PM   #9
Jim Dungar
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The primary thing to remember in grounding for noise reduction is SINGLE reference point. Larger ground (green) conductors are not necessary nor are they required by code. The comment about larger conductors may be true for grounded (white/neutral) conductors in 3 phase 4 wire systems but it is not applicable to VFDs or noise radiation.

Do NOT install a ground rod at each machine unless they are bonded to each other, the building steel, and the electrical system grounding conductors. For electrical safety we want a grid.

For noise reduction we want all related equipment to be connected to everything else only at as few points as possible, ideally one point. Each electrical panel should have a single ground bus. A seperate ground wire should be run from this bus to each device in that panel, do not loop from one device to the next. Remove the paint from all surfaces, especially the back panels, before making any ground connections. Analog signal and communication cables should only be grounded at one end, preferably the least noise sensitive end (i.e. at the field transmitter rather than the PLC).
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Old December 3rd, 2002, 06:04 PM   #10
gse
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grounding

You don't say what type of machines and or controls you are installing at this location. But, it has been my experience that CNC NC and other typical units require grounding bars at each of the machines. A ground for any machine operating with electrical controls should be of the same size as the feeds going to it. Number 12 wire does not sound quite up to code unless they have bonded the conduits etc and are looking at this as systems ground. You might check local codes on what is required in your area, or the NEC book.
Good Luck
GE
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Old December 3rd, 2002, 06:36 PM   #11
harryg
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The existence of two or more grounding systems operating at different potentials contribute to circulating ground currents.
Proper grounding starts with a proper grounding system. Sounds like you could use some PQ testing.
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Old December 3rd, 2002, 06:42 PM   #12
rbrown
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Exclamation Grounding and nosie affecting electronic equipment

Hate to be a pest, but this topic requires another response.

I picked on the grounding issue in my first response, because I see a safety hazard that could result in a fatality. Content of my first reponse stands. In Canada we use 600V to run most 3 phase loads, brushing against one phase 340V to ground feels like someone hitting you with a baseball bat.

In environments where 3 phase power and inductive loads are the norm,
noise will always be a problem.

The cheapest solution would be to install a 120V isolation transformer at each PLC unit. If you have your PLC's in a bank, figure the VA requirments and use a big isolation/power conditioner to power them all.


Later

rbrown
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Old December 3rd, 2002, 06:59 PM   #13
David_Emmerich
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Hi Grover .... I'm just intrested as to what kinds of machines are you dealing with. Are they assembly machines, case erectors and packers, RF sealers, or what ? Is this a wet or dry area? Are the machines hooked up with plug-in twist locks? Do they talk to each other or to a central PC?
We might be able to direct you more w/ some more info...David

PS...I'm glad your are intrested in finding the best way to attack this problem, and I'm sure we will all help out.
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Old December 3rd, 2002, 07:41 PM   #14
Grover
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Hi Guys.

I knew I would get a broad range of very useful input on this topic.

The machine is an old pouching machine that is used to heat seal foil packages which contain over the counter medications. The environement is dry and very clean to comply with various regulations and GMP.

Based on your feedback I am going to bite the bullet and draft a recommendation that we get a professional evaluation done on our facility. I feel confident that my original idea would have improved both the safety and noise aspects of grounding, but the emphatic response from y'all has convinced me that this facility could cause some liablity for my employer, let alone the possibility of someone getting killed.

I have to dash off for today, but keep adding individual two cents, OK? It is really adding up!

Many thanks to all for the help.

-Grover
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Old December 3rd, 2002, 07:48 PM   #15
harryg
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15a - 14ga.
20a - 12ga.
30a - 10ga.
40a - 10ga.
60a - 10ga.
100a - 8ga.
200a - 6ga.
300a - 4ga.
Table 250.122 Minimum Size Equipment Grounding
Conductors for Grounding Raceway
and Equipment.
02 NEC
Quote:
the current on the GROUND leg can be up to TWICE the current on any 1 leg.
Now that's a SERIOUS problem!!

Last edited by harryg; December 3rd, 2002 at 08:05 PM.
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