I sure know about the copper and alu together spells corrosion, from my boating days. (The galvanic corrosion only happens in the presence of moisture.) Brass screws into alu are also bad news when there is sea-water around.

Anyway, whenever we need to put a screw through the end of a wire, we crimp on a lug/terminal, and that is a very standard way of connecting wires to alu. The lugs are plated with a metal other than copper or brass. With the relatively dry control box, I don't see a long term bonding problem . . . . . . I hope.

Gerald,
In the electronics industry, using crimp on terminals and then fastening to aluminum heat sinks or plates is a common practice. Even for the stuff I deal with (Military Electronics) we just do that and then use stainless hardware and we have not seen a problem. Our products are using in marine environments and although the connections are not in water they are in salty/moist environments.

I believe that another area of concern with aluminum is that it expands and contracts more with heat. this allows screws and lugs to loosen more when contacting aluminum than copper...

Bill,
You are right about the thermal expansion. but in practice if you are using stainless hardware with flat and lock washers, I have never seen any problems with hardware coming loose even in military marine environments that have large amounts of vibration. If this was a real problem all the auto engines made these days of aluminum blocks and heads would fall apart in short order.:)

Gerald,
What is your take on fastener holding in aluminum with respect to thermal expansion or otherwise?

Bill, I think we are talking of a different scale of electrics when we are concerned about things connected to/with alu coming loose with thermal expansion/contraction. I think that concern is for high current, self-heating conductors, while we are fiddling around with tiny ground currents that are not going to cause self-heating. Of course, if something goes wrong, we could have a large ground current, but then the GFI unit must trip out. (can't remember now if GFI is the right name over there? We call it earth leakage protection)

If you replace that alu heatsink/ground plate with a copper heatsink/ground plate that would look smart :)

Heatsink compound discussion moved here

When I started this thread, I did not mention the importance of grounding for safety.

Daya in Sri Lanka has just experienced an incident which shocked one of his workers and fried all his expensive stepper motors (not necessarily in that order). This comes as a very abrupt wake-up call to take grounding/earthing very seriously!

Being new here or"wet behind the ears"You guys are going to be all over me on this one.
I have never heard of anyone using an aluminum heatsink or panel as a main ground or for star ground scheme.As Brian mentions of galvanic corrosion problems with the copper/alu,the heatsink to the metal chassis is also prone to corrosion.Down the road the resistance increases and the cables could melt.
The other problem I see is the separate ground wires to theZ,X,Y assemblies .
Looks like ground loops to me.
OK,I am ready for bashing,got my helmet on.
Larry

Please elaborate on what you are seeing, where?

There is no copper/alu connection anywhere. Galvanic corrosion needs moisture - you are supposed to use this stuff in a dry environment.

Larry,
In my day job, we use aluminum panels for assemblies all the time. These panels are used as ground points with good results. We do use plated crimp terminals on the copper wires and stainless steel hardware for all the mounting. Some of these assemblies (military electronics) handle extremely high currents and we have not had problems with this at all. With a semi dry environment as Gerald has mentioned you should be fine.

See no bashing :)

Mike any further comments?

Hi Gerald,
I was just looking at the pictures at the start of the thread and thought the ground wires to the machine frame were separate wires.Upon reading I see there is only one wire,the others are daisy chained which is correct.Sorry.
Larry
I will paste a blurb here for Mike to comment on:

"Another common solution to hum and buzz problems involves disconnecting one end of the shield, even though one can not buy off-the-shelf cables with the shield disconnected at one end. The best end to disconnect is unimportant in this discussion. A one-end-only shield connection increases the possibility of radio frequency (RF) interference since the shield may act as an antenna. The fact that many modern day installers still follow the one-end-only rule with consistent success indicates that acceptable solutions to RF issues exist, though the increasing use of digital technology increases the possibility of future RF problems. Many successfully and consistently reduce RF interference by providing an RF path through a small capacitor connected from the lifted end of the shield to the chassis."
Larry

Wasn't sure to ask this question here or under worst way of wiring. :)

Is this the proper way of connecting the shielding. When I connect the other shield wire, they will touch. Will this cause a ground loop?

Attachment 1374

Greg,

That's similar to the way I did it. I twisted all of the shielding together and then crimped them. I also heat shrinked them so there were no exposed metal.

That's the part I was wondering about. I'll re-do tomorrow.

Thanks Doug.

Greg,
Normally, when we do shielded junctions at work, we use a conductive encloseure and then terminate all the shields to the enclosure. This way the enclosure becomes the shield around all your joints. Your box looks like a plastic of some sort. Just realize that you lose your shielding in that area. In that case just make sure you have all the shields tied together and they dont short to anything else.

Heath,

Thanks. Yes, the E-stop enclosure is plastic.

I am running a large ground wire for the main structure that ties the Z slide, Y car, gantry, and table together. That main ground will terminate inside the metal control box. The metal control box will be grounded to the incoming supply voltage.

Greg I am not sure what others have done but I sank a ground rod as close to the machine as I could get it and I have my large machine ground wires going straight to the ground rod. My grounds in my control box go to the main breaker box which also has a grounding rod. Not sure if it is necessary or if it even makes any differenc but when I bought my huge squaring shear (it has a control box simmilar to what we are doing) they recomended that I do that, so I did the same with the MM.

Ed having two seperate grounds causes a difference of potential in the ground. I'm not an electrician but I would think that would be a big no-no.

If the electric coming from the control box should contact the frame of the mechmate for some reason it will take the easiest path to ground but if it has two paths then you could have a potential fireball.

That is what you want to happen. Electricity will always flow through the easiest path. As long as you have a good ground path, that is all that matters. :)

Yes but if you have two paths to ground you have a difference of potential. Like I said I am not an electrician but when we ground the boxes for the phone lines on the side of your house we are supposed to ground to the common electric ground so as not to create a difference in potential, everything grounded to one place.

I see what you are saying and that is a good point, when I build amplifiers I try not to create any ground loops and stay with one central ground point for the power supply, as not to inject any noise or interference into the signal.

I can already see though with my MM that there is alot of static electricity around the sawdust and wood chips, as I am working or cleaning. That static electricity will take that shortest path to ground. Which hopefully will not be through the sheilding wire or any control wires, but through the MM frame itself. Which to me is a good reason not to connect any cable sheilding wire to the j-boxes that they run through, thinking the box will sheild the circut inside the box. Unless the jboxes are isolated from the MM, doing this will create a ground loop, (one path through the sheilding to the control box and the other through the jbox itself which is bolted to the MM and then through the MM ground wire).

All circuts on mine that runs off the control box, are getting their ground through the main breaker ground rod, all those circuts are (or should be) isolated to the control box. I didn't ground any sheilding to boxes mounted to the MM ( I connected all sheilding inside my J-boxes to each other and tapped them so that they touch no metal inside the box) , they are grounded in the control box only.

Any static electrical discharges around my MM or directly on the metal my MM will go through the MM frame and to the ground rod close to the MM rather than through the control box or through the shielding wire which is very close to my control wires. When I run a vacume near the MM you can feel pulses of static electricity as the wood chips run through the vacume hose.
I know all the wires on the MM are sheilded and the sheilding should take everything to ground, but I just don't like the idea of that much voltage spikes running a few thousanths of an inch from signal wires, or around the BOB or computer, so IMHO I think it would be the lesser of two evils running the seperate ground rod.

Does this make any sense, or have I totally gone nuts:eek:

I am no expert either but there are alot of folk here including Gerald that are more knowedgeble about this, maybe they will chime in on this subject soon.

That point makes sense to me I was thinking more along the lines of if something catastropic happend and the mechmate frame came into contact with power or the router somehow shorted to the frame. I was not thinking of the static build up. I was planning on grounding back to earth with a seperate ground wire going back towards the control box but picking up the ground on the outside of the box where I planned to install a bus bar for the ground.

As I understand Control box and MM is grounded. My question is -

1. If ground is floating?
2. The MM lies on floor and Control box is mounted wall, which are Earth. Is this causing some electric problem?
3. If Earth of mains power line (Green wire) is to be connected to CB or MM?
4. My router has 3 pin connection, one is for Earth, do I have to provide sepearate line for it through mains Power line Earth?
5. PS ground is common via pin 1 and 12 of G203V (Continuity between PS ground, Alu plate and Pin 1,12), it means all metal is having - 70V (PS Ground), does this provide shielding against interference?
6. I have connected all shieldings to Alu plate, it means they all are having PS ground, is it correct way of wiring?

As I don't want expensive smoke, it's better to ask than to regret later.

Thanks,

Relax, ground problems do not make expensive smoke. They can only make cheap smoke. Ground problems make strange movements, and maybe put the cutter deep into the table....cheap smoke! :)

1. If ground is floating? Don't understand the question
2. The MM lies on floor and Control box is mounted wall, which are Earth. Is this causing some electric problem? No
3. If Earth of mains power line (Green wire) is to be connected to CB or MM? To the control box metal
4. My router has 3 pin connection, one is for Earth, do I have to provide sepearate line for it through mains Power line Earth? For safety, you must connect the router earth to the power supply earth via a route of your choice
5. PS ground is common via pin 1 and 12 of G203V (Continuity between PS ground, Alu plate and Pin 1,12), it means all metal is having - 70V (PS Ground), does this provide shielding against interference? Don't really understand your question. Yes, all metal is connected to the negative side of your power supply out - same as the metal parts of your car being connected to the negative pole of the battery
6. I have connected all shieldings to Alu plate, it means they all are having PS ground, is it correct way of wiring? Yes, it is correct. The other end of the shield (furthest from the alu plate) must not be connected to anything.

WOW That's really fast, while I was still browsing for answer.
Thanks Gerald for you INPUT.

It clears (Sigh) all dark clouds.
My main concern was should I connect Earth with this common ground. Now I don't need lengthy Earth cable for router, I can bolt it to MM.

Floating ground - http://en.wikipedia.org/wiki/Ground_...electricity%29
http://en.wikipedia.org/wiki/Floating_ground

Okay, the ground is definitely not floating.

Yes, you can ground the router to the MM frame, provided that you have grounded the MM frame correctly.

See posts 1 and 2 of this thread. That thick ground wire will take your router's earth to the power supply earth.

That's what I was thinking of, thanks.

Another grounding/earthing question.

I know that the shield for the cables must be earthed in the control panel (preferably to the main ground plane - Gecko heatsink) and that the other end of the shield (i.e. at the motor or switch etc) must not be earthed, but is it okay to tie the shields together (but still not earthed) at some intermediate point such as in a junction box on the gantry.

I have a junction box with cables coming from the control box, terminating into DIN connectors then carrying on to their respective destinations. My thinking is to use one or two DIN connectors to connect the shields together.

Richard, Sean, Gerald any comment?

Ideally, a shield or drain conductor should only be connected at one end. The purpose of the shield is to reduce EMI type interference along the entire length of the cable for that one device. By combining shields at a midpoint, you risk the possibility of negating the good that comes from using a shield.

It is more costly to run separate cables for each electrical device, but, on a CNC machine with low voltage signal lines and high voltage motors and spindles, the need is even greater to separate conductors and isolate electrical noise.

On another forum, some users of the Ascension 1000 control box are experiencing tremendous problems. Those control boxes seemed to all work perfectly until spindles were added to the machines and the weather turned hot. Now, several users are having sporadic stepper problems, which seem to be due to electrical noise from the VFD/Spindles. Last night, the consensus from a group e-mail seemed to be that cabling, line/load reactors and EMI filters would be the next things to check/add.

If it makes anyone feel better, running 30 to 60 feet of cable per electronic device creates problems for all types of machinery. What you have, in effect, is a 30 to 60 foot antenna that picks up every bit of electrical noise from your machine as well as all the other machines running in your entire neighborhood.

So, following the best practices is the best policy.

Alan, "Richard"'s first name is Mike :)

I wouldn't risk tying those shields together. When you bend the "rules" a little here and there, and then find some sporadic movements, it is messy to try and remember which rule was bent where. With the table sizes we are building out here, we have some seriously long cables, or "antennae".