Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[andrew beck]

just a update guys.

I forgot to add it to my drawing but I have a big isolator switch of course
on the doors of the machine and the x axis servo has a ground wire.

I forgot to add them to the drawing and Gene mentioned it.

I will also switch the breaker on the shed board off so I have two forms of
protection against unknown power on the machine.

regards

Andrew

On Mon, Dec 30, 2019 at 8:28 AM Nicklas Karlsson <
nicklas.karlsso...@gmail.com> wrote:

> > I'll offer my recently purchased 6040 mill as prime evidence of paint
> > pretty much destroying my ability to ground anything.  And to complicate
> > things even a Q TLO measure is prevented by ceramic bearings in the
> > spindle which are an insulator. ...
>
> Ceramic bearings might be there to prevent bearing currents, have no idea
> if this is a common problem.
>
>
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Nicklas Karlsson]

> I'll offer my recently purchased 6040 mill as prime evidence of paint 
> pretty much destroying my ability to ground anything.  And to complicate 
> things even a Q TLO measure is prevented by ceramic bearings in the 
> spindle which are an insulator. ...

Ceramic bearings might be there to prevent bearing currents, have no idea if 
this is a common problem.


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Gene Heskett]

On Sunday 29 December 2019 13:32:09 John Dammeyer wrote:

> I use
>
> The standard symbols on my drawings to represent what a ground is. 
> The nomenclature is so varied I believe the first decision should be
> how to describe what is what.
>
> For me the EARTH symbol is the green (Green/Yellow) wire that goes
> back to the circuit breaker panel and from there into a ground rod or
> in my case a ground plate in the earth.
>
> At the machine, at only one point, this Earth is connected to the
> frame of the machine.  At that point the symbol in my drawings changes
> to the GND symbol with the horizontal lines.   Any AC powered drives,
> motors etc. also connect their green (green/yellow)  to this single
> point.  I believe the code here specifies that this mounting post must
> either be double bolted or bonded (welded) in such a way that it
> cannot vibrate loose.  The green wires must use ring terminals, not
> spade terminals so a loose nut doesn't allow the wire to vibrate off.
>
> If you have something that has AC (single or multiple phase) in it
> that is metal and could have an AC line short to the metal box, it too
> must have that green wire connect in a non-removable fashion to the
> metal box, and return back to that single point earth point.  Not to
> some other metal part of the machine with hope that it will eventually
> connect to the EARTH connection.Gene mentioned the ramifications
> if it's not.
>
> If you have an isolation transformer from one of the 3 phase legs (or
> two phase in North American 240VAC power) where 240VAC is changed to
> 110VAC with the transformer, the output side of that transformer must
> again be made into a proper neutral with a connection to EARTH to that
> single point EARTH point.  Simply because once it becomes
> Black/White/Green headed out and wired to a standard AC outlet, that
> Neutral has to behave in the same way it would as if it were embedded
> in the wall.  Just because it's isolated from the mains doesn't make
> it any less lethal.
>
> And if the system has been taken apart, cleaned up, painted and
> re-assembled, it's critical that DC continuity is checked between the
> bolted together metal parts.  I've seen systems that worked perfectly
> and then were stripped down, painted, assembled and made ready for
> shipping but developed the most interesting problem with electrical
> noise.  And the cause tracked down to what was a good electrical
> connection now insulated with paint.
>
> IMHO.
>
> My bible for wiring these systems is this:   Electromagnetic
> Compatibility Engineering  By Henry W. Ott published by Wiley.
>
> https://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry
>-2009-08-24/dp/B01FIX96A8/ref=sr_1_2?keywords=Henry+W+Ott
> y-2009-08-24/dp/B01FIX96A8/ref=sr_1_2?keywords=Henry+W+Ott=15776440
>03=8-2> =1577644003=8-2
>
> Page 119 of my copy, Section 3.1.7 is titled Grounding Myths is pretty
> good.
>
> John Dammeyer

I don't have that particular tome John, but everthing you've added is 
valid stuff.

I'll offer my recently purchased 6040 mill as prime evidence of paint 
pretty much destroying my ability to ground anything.  And to complicate 
things even a Q TLO measure is prevented by ceramic bearings in the 
spindle which are an insulator. If I want to position a contact to 
measure TLO, I'll have to rig a contact that touches the nut, or the 
back flange of the collet, grounding it before the tool tip touches the 
contact. Or actually trip a switch with the tool. I'm leaning toward the 
latter but haven't cut anything yet. Need to heal first. My heart attack 
got in the way. But next year promises I'll feel much better than I have 
this past year.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[John Dammeyer]

I use 

The standard symbols on my drawings to represent what a ground is.  The 
nomenclature is so varied I believe the first decision should be how to 
describe what is what.  
 
For me the EARTH symbol is the green (Green/Yellow) wire that goes back to the 
circuit breaker panel and from there into a ground rod or in my case a ground 
plate in the earth.
 
At the machine, at only one point, this Earth is connected to the frame of the 
machine.  At that point the symbol in my drawings changes to the GND symbol 
with the horizontal lines.   Any AC powered drives, motors etc. also connect 
their green (green/yellow)  to this single point.  I believe the code here 
specifies that this mounting post must either be double bolted or bonded 
(welded) in such a way that it cannot vibrate loose.  The green wires must use 
ring terminals, not spade terminals so a loose nut doesn't allow the wire to 
vibrate off.
 
If you have something that has AC (single or multiple phase) in it that is 
metal and could have an AC line short to the metal box, it too must have that 
green wire connect in a non-removable fashion to the metal box, and return back 
to that single point earth point.  Not to some other metal part of the machine 
with hope that it will eventually connect to the EARTH connection.Gene 
mentioned the ramifications if it's not.
 
If you have an isolation transformer from one of the 3 phase legs (or two phase 
in North American 240VAC power) where 240VAC is changed to 110VAC with the 
transformer, the output side of that transformer must again be made into a 
proper neutral with a connection to EARTH to that single point EARTH point.  
Simply because once it becomes Black/White/Green headed out and wired to a 
standard AC outlet, that Neutral has to behave in the same way it would as if 
it were embedded in the wall.  Just because it's isolated from the mains 
doesn't make it any less lethal.
 
And if the system has been taken apart, cleaned up, painted and re-assembled, 
it's critical that DC continuity is checked between the bolted together metal 
parts.  I've seen systems that worked perfectly and then were stripped down, 
painted, assembled and made ready for shipping but developed the most 
interesting problem with electrical noise.  And the cause tracked down to what 
was a good electrical connection now insulated with paint.
 
IMHO.
 
My bible for wiring these systems is this:   Electromagnetic Compatibility 
Engineering  By Henry W. Ott published by Wiley.
 
https://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry-2009-08-24/dp/B01FIX96A8/ref=sr_1_2?keywords=Henry+W+Ott
 

 =1577644003=8-2
 
Page 119 of my copy, Section 3.1.7 is titled Grounding Myths is pretty good.
 
John Dammeyer
 
 
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Peter C. Wallace]

On Sun, 29 Dec 2019, andrew beck wrote:


Date: Sun, 29 Dec 2019 23:19:20 +1300
From: andrew beck 
Reply-To: "Enhanced Machine Controller (EMC)"

To: "Enhanced Machine Controller (EMC)" 
Subject: Re: [Emc-users] looking for advice on best wiring practices and
grounding on cnc mills


SNIP-


and the brake switching system needs a relay I think.  a contact opens in
the drive at whatever timing I set with parameters and that contact will
run another contact cutting the 24 volt power to the brake solenoid.  I
wasn't actually using that.  I just had the brake locked open all the time
while I was testing.  I already had the X and Y axis working fine and was
just connecting up the Z axis when everything went downhill.


If you switch the brake magnet circuit with a relay, You _must_ have a
flyback diode across the brake magnet coil or you will have arcing
at the relay contacts and generate massive amounts of EMI when the brake is 
released...


On Thu, Dec 26, 2019 at 11:53 PM Andy Pugh  wrote:




> On 26 Dec 2019, at 06:49, andrew beck  wrote:
>
> That meant that the brake actually had a lot more than 24 volts in
> it relative to machine earth(like 200v I am guessing, it was a big bang!)

That shouldn??t normally matter. I would be very surprised if the brake
winging insulation wasn??t good for 24V.

I think you should check the brake, make sure that it isn??t leaky. Does
your electrician have an insulation tester?

Is frame ground also a zero-volt reference for logic and field wiring? You
sound to be using the terms semi-interchangeably.

What is the brake switching device in the drive?




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Mesa Electronics

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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Gene Heskett]

On Sunday 29 December 2019 05:37:36 andrew beck wrote:

> Hey everyone
>
> So just getting to the bottom of these emails and thanks so much for
> all the replies.
>
> There is much food for thought.
>
> If you missed it up in the emails here is the current plan for wiring
> the control panel.
>
> yuhai servo drive manual
> w?usp=sharing> Linuxcnc mill control panel drawing
> w?usp=sharing>
>
> All the three phase stuff is pretty standard I think.  The main
> problem I have is that I am not sure how the grounding should work. 
> Eg do I tie the 24 volt powersupplies to ground on the input or output
> etc and any safety stuff I need to make sure I do.

inputs for the 24 volts should be from a 240 hot and neutral. output 
rails minus to the green stuff, by a separate wire for each. + to 
wherever you need it, like field power for the mesa 7i76D. The ground 
symbol terminal on the psu's should goto that common bolt, again by its 
own wire.

> The only opti isolation I have is in the mesa 7i76 card.

Do the motor drivers not have opto's?
>
> So any thoughts feel free to let me know.  I am planning on powering
> this up tomorrow.
>
> Regards
>
> Andrew
>
> On Fri, Dec 27, 2019 at 8:03 AM Chris Albertson
> 
>
> wrote:
> > A ground loop is then a single device is connected to ground more
> > than once.   A good example is a motor driver.   It might in a
> > "power" input called "+" and "-" with the minus side grounded to the
> > AC mains ground or a chassis frame ground.   The in addition
> > there is a logic level control signal that is "signal" and "ground"
> > wires. This is a classic gound loop.
> >
> > How to break it?  Use optical isolation on the signal.  This places
> > an air-gap in the control signal.

The one that counts is in the motor drivers, the + and - signals from the 
mesa card there are both isolated from ground inside the driver. You can 
verify that with a dvm using the ohms scale, it s/b an open circuit to 
anyplace else but its coresponding opposite polarity terminal.
> >
> > Most of the time the system is not so simple as the above but the
> > concept is the same, multiple ground connections are not good.  
> > Why? Because in theory current can flow if you have a loop but can
> > never flow if there is not a closed loop.  Then Ohm's law applies --
> > if there is current flow there is voltage drop.   If the voltage
> > drops across a gound then you have tow "grounds" that are not the
> > same voltage.   This can be really serious if the motors are large.
> >
> > There are a number of conventions that work. but they all do the
> > same thing, they reduce the number of ground connects to one per
> > "part" of the system.
> >
> > All the rules try to do the same thing, connect nuetral to ground
> > ONLY at the building service entrance, use opto's on all signal
> > lines. It is all the same idea
> >
> >
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
Genes Web page 


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Gene Heskett]

On Sunday 29 December 2019 05:19:20 andrew beck wrote:

> Hey Andy
>
> I am just going through all the replies now.
>
> So what I think happened is I put like 300 volts possibly through the
> servo motor.  Not just 24 volts.  as I had a cheap chinese power
> supply that was floating and not tied to ground.  It was a big spark
> that jumped to the steel and it blew the end of the limit switch wire
> to bits and made a big black burn mark on the steel panel.
>
> I will go and check the insulation before I wire it up.  But I think
> it should be all good.
>
> and the brake switching system needs a relay I think.  a contact opens
> in the drive at whatever timing I set with parameters and that contact
> will run another contact cutting the 24 volt power to the brake
> solenoid.  I wasn't actually using that.  I just had the brake locked
> open all the time while I was testing.  I already had the X and Y axis
> working fine and was just connecting up the Z axis when everything
> went downhill.
>
> I am getting confused between the different methods of tying the
> various powersupplies to the frame ground, so I have made a drawing
> here which explains how I think I should be wiring this control panel.
>  If you just have a look at this I think it might simplify things. 
> link to drawing on google drive
> w?usp=sharing>
>
>
> Remembering that I have 400 volts three phase power here in New
> Zealand and 240 volts single phase.  Which you can make by taking a
> one of the three phases and the neutral wire.
>
> here is the servo drive manual.  It is not perfect and is more of a
> general manual so if it looks wrong it probably is.  But then I just
> ask Bill on whatsapp what to do and he asks the engineers.
>
> yuhai servo drive manual
> w?usp=sharing> .
>
> Regards Andrew
>
> On Thu, Dec 26, 2019 at 11:53 PM Andy Pugh  wrote:
> > > On 26 Dec 2019, at 06:49, andrew beck 
> > > wrote:
> > >
> > > That meant that the brake actually had a lot more than 24 volts in
> > > it relative to machine earth(like 200v I am guessing, it was a big
> > > bang!)
> >
> > That shouldn’t normally matter. I would be very surprised if the
> > brake winging insulation wasn’t good for 24V.
> >
> > I think you should check the brake, make sure that it isn’t leaky.
> > Does your electrician have an insulation tester?
> >
> > Is frame ground also a zero-volt reference for logic and field
> > wiring? You sound to be using the terms semi-interchangeably.
> >
> > What is the brake switching device in the drive?

You missed a static (green) ground on the x drive, and you need to add a 
4th wire from that green box (aka your common bolt) back to the static 
ground in the service entrance. Heavy enough that an insulation failure 
will clear that fuse w/o damaging the wire. 4 wire cordage, or better 
yet TW of a suitable gauge in conduit.

Haveing 480 3 phase in that box is a lethal scenario. But you knew that. 

You show fuses, but I'd have an external three phase breaker you can 
padlock in the off position and the only key in YOUR or the electricians 
pocket before touching anything in that box.

I lost a friend in Iron Mountain MI whose $dayjob was as an overhead 
crane operator delivering hot iron from the furnace to the casting floor 
in an iron foundry. The cranes control pendant had 480 in the handpiece 
and had shorted to the box. Touching it and the 2nd floor railing, his 
normal work location was the last thing he did.
> >
> >
> > ___
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Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
 - Louis D. Brandeis
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[andrew beck]

Hey everyone

So just getting to the bottom of these emails and thanks so much for all
the replies.

There is much food for thought.

If you missed it up in the emails here is the current plan for wiring the
control panel.

yuhai servo drive manual

Linuxcnc mill control panel drawing


All the three phase stuff is pretty standard I think.  The main problem I
have is that I am not sure how the grounding should work.  Eg do I tie the
24 volt powersupplies to ground on the input or output etc and any safety
stuff I need to make sure I do.

The only opti isolation I have is in the mesa 7i76 card.

So any thoughts feel free to let me know.  I am planning on powering this
up tomorrow.

Regards

Andrew

On Fri, Dec 27, 2019 at 8:03 AM Chris Albertson 
wrote:

> A ground loop is then a single device is connected to ground more than
> once.   A good example is a motor driver.   It might in a "power"
> input called "+" and "-" with the minus side grounded to the AC mains
> ground or a chassis frame ground.   The in addition there is a
> logic level control signal that is "signal" and "ground" wires.
> This is a classic gound loop.
>
> How to break it?  Use optical isolation on the signal.  This places an
> air-gap in the control signal.
>
> Most of the time the system is not so simple as the above but the
> concept is the same, multiple ground connections are not good.   Why?
> Because in theory current can flow if you have a loop but can never
> flow if there is not a closed loop.  Then Ohm's law applies -- if
> there is current flow there is voltage drop.   If the voltage drops
> across a gound then you have tow "grounds" that are not the same
> voltage.   This can be really serious if the motors are large.
>
> There are a number of conventions that work. but they all do the same
> thing, they reduce the number of ground connects to one per "part" of
> the system.
>
> All the rules try to do the same thing, connect nuetral to ground ONLY
> at the building service entrance, use opto's on all signal lines.
> It is all the same idea
>
>
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[andrew beck]

Hey Gene

thanks for the reply.

I think I follow most of what you said there.
And my neutral and ground will only be tied back at the shed main
electrical box definitely.

I think the main problem I have is how the 24 volt powersupplies should be
wired and connected to frame ground.

I have sent some links in my reply to Andy and have a drawing on there.  If
you have a look I would appreciate the thoughts.

Regards

Andrew

On Fri, Dec 27, 2019 at 1:08 AM Gene Heskett  wrote:

> On Thursday 26 December 2019 01:49:40 andrew beck wrote:
>
> > Hey guys.
> >
> > I have a bit of a story here and some questions..  I Have been seeing
> > the emails coming through and there looks like there is a massive pool
> > of knowledge here in the user list and the forum.  So here it goes
> > hopefully someone can help me.
> >
> > I have a Big 6.5 ton VMC that I have been retrofitting with new
> > chinese servo drives and motors.  3 months ago I wired it up and after
> > a bit of mucking around I got the X and y axis moving fine.  (I am
> > just using step and direction with a mesa  5i25-7i76 combo for now)
> > Then I connected up the Z axis motor and powered the 24v to the brake
> > with a cheap powersupply from aliexpress.
> >
> > I was trouble shooting the limit switches and moving the wires while
> > the machine was live when there was a big bang and the limit switch
> > arced across into the steel cabinet.  It absolutely freaked me out and
> > I haven't been back to the mill since lol.
> >
> > Once I recovered myself I realised that I have blown the Z axis servo
> > drive up.  What I think has happened is the powersupply was a floating
> > powersuppply(I actually knew that but didn't realise what that would
> > mean.)  That meant that the brake actually had a lot more than 24
> > volts in it relative to machine earth(like 200v I am guessing, it was
> > a big bang!)
> >
> > Anyway I think somehow the power backfed via the Z axis servo down the
> > 24 volt brake line and into the servo drive and made the magic smoke
> > come out.
> >
> > They are about $400 usd so I wasn't to happy about that.
> >
> > But the good news is I told my supplier about it and he said they
> > would repair it for free.  they decided it was truely toast when they
> > had a look, so they just gave me a new drive.  which was pretty cool.
> >
> > And after all that I am just getting into connecting this thing up
> > again and I don't want to blow anything up.
> >
> > I will send a diagram later and some photos but for now I have these
> > questions.
> >
> >
> >1. how do I ground the 24 volt switching powersupplies.
>
> Single point bolt, star ground. - rail of all. With only one ohmic
> connection to the buildings static ground at that bolt.Get
>
> >2. Should I isolate the 24volt switching
> >powersupplies from machine
> >ground?  bearing in mind that one of the powersupplies is for logic
> > power and one is just the the servo motor brake.
> >3. The old wiring had a isolating transformer to make 240 V single
> > phase for the switch powersupplies.  They didn't use a neutral back to
> > the shed main board.  Will a neutral help me here?
>
> A neutral is std practice here. No clue, where you are. Recommended by
> grandpa Gene. But keep the neutral separately wired from static ground
> to prevent ground loops.  According to the NEC here, the only place they
> should be common is at the service entrance ground rod connection. Do
> not connect it to your single point ground as that will create a huge
> ground loop just waiting for a nearby lightning strike.
>
> >4. My biggest unknown is not knowing all the best safe practices
> > when working with large voltages.  (my brother is a apprentice
> > electrician which helps but I would appreciate some tips of what not
> > to do and what to do as a checklist or something.
> >
> If he's an apprentice, he should have a copy of whatever serves as the
> NEC in your region.
>
> > Regards
> >
> > Andrew
> >
> > ___
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> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> If we desire respect for the law, we must first make the law respectable.
>  - Louis D. Brandeis
> Genes Web page 
>
>
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[andrew beck]

Hey Andy

I am just going through all the replies now.

So what I think happened is I put like 300 volts possibly through the servo
motor.  Not just 24 volts.  as I had a cheap chinese power supply that was
floating and not tied to ground.  It was a big spark that jumped to the
steel and it blew the end of the limit switch wire to bits and made a big
black burn mark on the steel panel.

I will go and check the insulation before I wire it up.  But I think it
should be all good.

and the brake switching system needs a relay I think.  a contact opens in
the drive at whatever timing I set with parameters and that contact will
run another contact cutting the 24 volt power to the brake solenoid.  I
wasn't actually using that.  I just had the brake locked open all the time
while I was testing.  I already had the X and Y axis working fine and was
just connecting up the Z axis when everything went downhill.

I am getting confused between the different methods of tying the various
powersupplies to the frame ground, so I have made a drawing here which
explains how I think I should be wiring this control panel.  If you just
have a look at this I think it might simplify things.  link to drawing on
google drive



Remembering that I have 400 volts three phase power here in New Zealand and
240 volts single phase.  Which you can make by taking a one of the three
phases and the neutral wire.

here is the servo drive manual.  It is not perfect and is more of a general
manual so if it looks wrong it probably is.  But then I just ask Bill on
whatsapp what to do and he asks the engineers.

yuhai servo drive manual

.

Regards Andrew


On Thu, Dec 26, 2019 at 11:53 PM Andy Pugh  wrote:

>
>
> > On 26 Dec 2019, at 06:49, andrew beck  wrote:
> >
> > That meant that the brake actually had a lot more than 24 volts in
> > it relative to machine earth(like 200v I am guessing, it was a big bang!)
>
> That shouldn’t normally matter. I would be very surprised if the brake
> winging insulation wasn’t good for 24V.
>
> I think you should check the brake, make sure that it isn’t leaky. Does
> your electrician have an insulation tester?
>
> Is frame ground also a zero-volt reference for logic and field wiring? You
> sound to be using the terms semi-interchangeably.
>
> What is the brake switching device in the drive?
>
>
>
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[N]

No. I am talking about voltage drops in cables used to power devices. It might 
also be AC impedance is rather high at frequencies used for communication and 
device use power in smaller or larger bursts.

Problem is there is voltage drop in cable used to power DC and/or AC but no or 
to be exact neglible voltage drop in cables used for communication in between 
devices.


> I think you are confusing ground and neutral. Ground should never
> move off zero.   But the neutral can be up to about 5 volts above
> ground.
> 
> On Thu, Dec 26, 2019 at 2:26 PM N  wrote:
> >
> > Current used to power device will cause some voltage drop in ground so 
> > grond potential at device will be higher. Ground potential will also vary 
> > with power used by device. This higher potential might cause a problem if 
> > there for example is digital communicatin between devices.
> >
> > > A ground loop is then a single device is connected to ground more than
> > > once.   A good example is a motor driver.   It might in a "power"
> > > input called "+" and "-" with the minus side grounded to the AC mains
> > > ground or a chassis frame ground.   The in addition there is a
> > > logic level control signal that is "signal" and "ground" wires.
> > > This is a classic gound loop.
> > >
> > > How to break it?  Use optical isolation on the signal.  This places an
> > > air-gap in the control signal.
> > >
> > > Most of the time the system is not so simple as the above but the
> > > concept is the same, multiple ground connections are not good.   Why?
> > > Because in theory current can flow if you have a loop but can never
> > > flow if there is not a closed loop.  Then Ohm's law applies -- if
> > > there is current flow there is voltage drop.   If the voltage drops
> > > across a gound then you have tow "grounds" that are not the same
> > > voltage.   This can be really serious if the motors are large.
> > >
> > > There are a number of conventions that work. but they all do the same
> > > thing, they reduce the number of ground connects to one per "part" of
> > > the system.
> > >
> > > All the rules try to do the same thing, connect nuetral to ground ONLY
> > > at the building service entrance, use opto's on all signal lines.
> > > It is all the same idea
> > >
> > >
> > > ___
> > > Emc-users mailing list
> > > Emc-users@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/emc-users
> >
> >
> > ___
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> 
> 
> 
> -- 
> 
> Chris Albertson
> Redondo Beach, California
> 
> 
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[N]

> On Thu, 26 Dec 2019 at 19:03, Chris Albertson  
> wrote:
> 
> > All the rules try to do the same thing, connect nuetral to ground ONLY
> > at the building service entrance
> 
> Off-topic, but that isn't the only way to do it.
> https://en.wikipedia.org/wiki/Earthing_system
> Is an interesting read.

Maybe the method with a resistor on protective earth could be rather safe if 
limited to below dangerous level but it will not blow fuse so some eath leakage 
detector is needed. Normally idea is broken conductor come in contact with 
protective earth blowing the fuse but it will not help if you come in contact 
with a conductor, prefer to stay away from grounded equipment then working with 
high voltage because of this.


Regards Nicklas Karlsson


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[andy pugh]

On Thu, 26 Dec 2019 at 19:03, Chris Albertson  wrote:

> All the rules try to do the same thing, connect nuetral to ground ONLY
> at the building service entrance

Off-topic, but that isn't the only way to do it.
https://en.wikipedia.org/wiki/Earthing_system
Is an interesting read.

-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Gene Heskett]

On Friday 27 December 2019 00:04:32 Chris Albertson wrote:

> I think you are confusing ground and neutral. Ground should never
> move off zero.   But the neutral can be up to about 5 volts above
> ground.
>
Which is why, as a CET, I like to specify static ground, which on this 
side of the pond, is the round pin of the duplex socket IF the 
electrician has done it right.  Neutral is the wider flat pin, and AC 
hot is the narrower flat pin.  All control signals should use the static 
ground as a ground reference connected to that single bolt.  On power 
supplies, the ground symbol should also share this bolt, while the 2 
line connections should carry the supplies draw current, and may or may 
not be interchangeable. Switch mode supplies that have a universal 110 
to 240 input will generally be interchangeable.

The input lowside current for 110 volt environments is the neutral from 
the service, and is NOT connected to this static ground at anyplace but 
the common point of the earthen grounds in the service entrance.

The supply outputs can be used as required but should have one terminal 
connected to this static ground bolt for safety reasons.

Relay/solenoid coils being controlled by semiconductor switches in the 
interface card should have a flywheel diode across the coils which is 
reverse biased and therefore non-conductive when the semiconductor 
is "off". This diode should be faster than the semi can switch off for 
best protection of the semi from inductive spikes.

The point of this single bolt common static "ground" connection is that 
it CAN bounce but everything being connected there BOUNCES in unison, 
and when it bounces, carry's all the signal references with it, and 
nothing properly connected to this single bolt sees the bounce even if 
its a direct lightning strike on the substation pole 30 feet away from 
the building.  The operating circuit itself is unaware its just been 
struck by lightning.

When I moved into this house 30 years ago, I lost a modem everytime I 
heard thunder because this house was wired by an idiot. I put 2 and 2 
together and opened up every duplex between this room and the service 
fixing the f-ups as I went, even soldering poorly done static 
connections when they weren't even made up. I have not had a lightning 
damaged piece of gear in this room since, even though I know this whole 
circuit has probably been 100 kv or more from ground hundreds of times.  
Then in 2007 in prep for building the garage, I made this house a legal 
subcircuit of a properly grounded 200 amp service I installed myself.

Ditto for the shed in the back yard. Zero damage from lightning strikes 
since including one hit that blew the fuse link at the transformer pole 
across the street.

If using expander strips to distribute input power, its recommended that 
all the static grounds be broken off but one, and that one is then the 
line feed into the box including the static connection to the house. All 
others s/b terminated at this single bolt by separate wiring so that 
there is just one connection between this bolt and the "house" static 
ground. Break that ground loop before its ever plugged in.

> On Thu, Dec 26, 2019 at 2:26 PM N  wrote:
> > Current used to power device will cause some voltage drop in ground
> > so grond potential at device will be higher. Ground potential will
> > also vary with power used by device. This higher potential might
> > cause a problem if there for example is digital communicatin between
> > devices.
> >
> > > A ground loop is then a single device is connected to ground more
> > > than once.   A good example is a motor driver.   It might in a
> > > "power" input called "+" and "-" with the minus side grounded to
> > > the AC mains ground or a chassis frame ground.   The in
> > > addition there is a logic level control signal that is "signal"
> > > and "ground" wires. This is a classic gound loop.
> > >
> > > How to break it?  Use optical isolation on the signal.  This
> > > places an air-gap in the control signal.
> > >
> > > Most of the time the system is not so simple as the above but the
> > > concept is the same, multiple ground connections are not good.  
> > > Why? Because in theory current can flow if you have a loop but can
> > > never flow if there is not a closed loop.  Then Ohm's law applies
> > > -- if there is current flow there is voltage drop.   If the
> > > voltage drops across a gound then you have tow "grounds" that are
> > > not the same voltage.   This can be really serious if the motors
> > > are large.
> > >
> > > There are a number of conventions that work. but they all do the
> > > same thing, they reduce the number of ground connects to one per
> > > "part" of the system.
> > >
> > > All the rules try to do the same thing, connect nuetral to ground
> > > ONLY at the building service entrance, use opto's on all signal
> > > lines. It is all the same idea
> > >
> > >
> > > ___

Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Chris Albertson]

I think you are confusing ground and neutral. Ground should never
move off zero.   But the neutral can be up to about 5 volts above
ground.

On Thu, Dec 26, 2019 at 2:26 PM N  wrote:
>
> Current used to power device will cause some voltage drop in ground so grond 
> potential at device will be higher. Ground potential will also vary with 
> power used by device. This higher potential might cause a problem if there 
> for example is digital communicatin between devices.
>
> > A ground loop is then a single device is connected to ground more than
> > once.   A good example is a motor driver.   It might in a "power"
> > input called "+" and "-" with the minus side grounded to the AC mains
> > ground or a chassis frame ground.   The in addition there is a
> > logic level control signal that is "signal" and "ground" wires.
> > This is a classic gound loop.
> >
> > How to break it?  Use optical isolation on the signal.  This places an
> > air-gap in the control signal.
> >
> > Most of the time the system is not so simple as the above but the
> > concept is the same, multiple ground connections are not good.   Why?
> > Because in theory current can flow if you have a loop but can never
> > flow if there is not a closed loop.  Then Ohm's law applies -- if
> > there is current flow there is voltage drop.   If the voltage drops
> > across a gound then you have tow "grounds" that are not the same
> > voltage.   This can be really serious if the motors are large.
> >
> > There are a number of conventions that work. but they all do the same
> > thing, they reduce the number of ground connects to one per "part" of
> > the system.
> >
> > All the rules try to do the same thing, connect nuetral to ground ONLY
> > at the building service entrance, use opto's on all signal lines.
> > It is all the same idea
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
>
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-- 

Chris Albertson
Redondo Beach, California


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[N]

Current used to power device will cause some voltage drop in ground so grond 
potential at device will be higher. Ground potential will also vary with power 
used by device. This higher potential might cause a problem if there for 
example is digital communicatin between devices.

> A ground loop is then a single device is connected to ground more than
> once.   A good example is a motor driver.   It might in a "power"
> input called "+" and "-" with the minus side grounded to the AC mains
> ground or a chassis frame ground.   The in addition there is a
> logic level control signal that is "signal" and "ground" wires.
> This is a classic gound loop.
> 
> How to break it?  Use optical isolation on the signal.  This places an
> air-gap in the control signal.
> 
> Most of the time the system is not so simple as the above but the
> concept is the same, multiple ground connections are not good.   Why?
> Because in theory current can flow if you have a loop but can never
> flow if there is not a closed loop.  Then Ohm's law applies -- if
> there is current flow there is voltage drop.   If the voltage drops
> across a gound then you have tow "grounds" that are not the same
> voltage.   This can be really serious if the motors are large.
> 
> There are a number of conventions that work. but they all do the same
> thing, they reduce the number of ground connects to one per "part" of
> the system.
> 
> All the rules try to do the same thing, connect nuetral to ground ONLY
> at the building service entrance, use opto's on all signal lines.
> It is all the same idea
> 
> 
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Chris Albertson]

A ground loop is then a single device is connected to ground more than
once.   A good example is a motor driver.   It might in a "power"
input called "+" and "-" with the minus side grounded to the AC mains
ground or a chassis frame ground.   The in addition there is a
logic level control signal that is "signal" and "ground" wires.
This is a classic gound loop.

How to break it?  Use optical isolation on the signal.  This places an
air-gap in the control signal.

Most of the time the system is not so simple as the above but the
concept is the same, multiple ground connections are not good.   Why?
Because in theory current can flow if you have a loop but can never
flow if there is not a closed loop.  Then Ohm's law applies -- if
there is current flow there is voltage drop.   If the voltage drops
across a gound then you have tow "grounds" that are not the same
voltage.   This can be really serious if the motors are large.

There are a number of conventions that work. but they all do the same
thing, they reduce the number of ground connects to one per "part" of
the system.

All the rules try to do the same thing, connect nuetral to ground ONLY
at the building service entrance, use opto's on all signal lines.
It is all the same idea


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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Gene Heskett]

On Thursday 26 December 2019 01:49:40 andrew beck wrote:

> Hey guys.
>
> I have a bit of a story here and some questions..  I Have been seeing
> the emails coming through and there looks like there is a massive pool
> of knowledge here in the user list and the forum.  So here it goes
> hopefully someone can help me.
>
> I have a Big 6.5 ton VMC that I have been retrofitting with new
> chinese servo drives and motors.  3 months ago I wired it up and after
> a bit of mucking around I got the X and y axis moving fine.  (I am
> just using step and direction with a mesa  5i25-7i76 combo for now) 
> Then I connected up the Z axis motor and powered the 24v to the brake
> with a cheap powersupply from aliexpress.
>
> I was trouble shooting the limit switches and moving the wires while
> the machine was live when there was a big bang and the limit switch
> arced across into the steel cabinet.  It absolutely freaked me out and
> I haven't been back to the mill since lol.
>
> Once I recovered myself I realised that I have blown the Z axis servo
> drive up.  What I think has happened is the powersupply was a floating
> powersuppply(I actually knew that but didn't realise what that would
> mean.)  That meant that the brake actually had a lot more than 24
> volts in it relative to machine earth(like 200v I am guessing, it was
> a big bang!)
>
> Anyway I think somehow the power backfed via the Z axis servo down the
> 24 volt brake line and into the servo drive and made the magic smoke
> come out.
>
> They are about $400 usd so I wasn't to happy about that.
>
> But the good news is I told my supplier about it and he said they
> would repair it for free.  they decided it was truely toast when they
> had a look, so they just gave me a new drive.  which was pretty cool.
>
> And after all that I am just getting into connecting this thing up
> again and I don't want to blow anything up.
>
> I will send a diagram later and some photos but for now I have these
> questions.
>
>
>1. how do I ground the 24 volt switching powersupplies.

Single point bolt, star ground. - rail of all. With only one ohmic 
connection to the buildings static ground at that bolt.Get  

>2. Should I isolate the 24volt switching 
>powersupplies from machine 
>ground?  bearing in mind that one of the powersupplies is for logic
> power and one is just the the servo motor brake.
>3. The old wiring had a isolating transformer to make 240 V single
> phase for the switch powersupplies.  They didn't use a neutral back to
> the shed main board.  Will a neutral help me here?

A neutral is std practice here. No clue, where you are. Recommended by 
grandpa Gene. But keep the neutral separately wired from static ground 
to prevent ground loops.  According to the NEC here, the only place they 
should be common is at the service entrance ground rod connection. Do 
not connect it to your single point ground as that will create a huge 
ground loop just waiting for a nearby lightning strike.

>4. My biggest unknown is not knowing all the best safe practices
> when working with large voltages.  (my brother is a apprentice
> electrician which helps but I would appreciate some tips of what not
> to do and what to do as a checklist or something.
>
If he's an apprentice, he should have a copy of whatever serves as the 
NEC in your region.

> Regards
>
> Andrew
>
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Cheers, Gene Heskett
-- 
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 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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 - Louis D. Brandeis
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Re: [Emc-users] looking for advice on best wiring practices and grounding on cnc mills

[Andy Pugh]

> On 26 Dec 2019, at 06:49, andrew beck  wrote:
> 
> That meant that the brake actually had a lot more than 24 volts in
> it relative to machine earth(like 200v I am guessing, it was a big bang!)

That shouldn’t normally matter. I would be very surprised if the brake winging 
insulation wasn’t good for 24V. 

I think you should check the brake, make sure that it isn’t leaky. Does your 
electrician have an insulation tester? 

Is frame ground also a zero-volt reference for logic and field wiring? You 
sound to be using the terms semi-interchangeably. 

What is the brake switching device in the drive? 



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