Earth grounding question

[plain ol Bill]

I am electrically challenged folks. Now with that said I would like some info on earth grounding. I am building a new 5 x 10 plasma table and will use a Hypertherm plasma. I know everything (plasma, table, computer and anything else that is going to be worked w/ the system) needs to be individually earth grounded to eliminate noise. The plasma will run off 240V single phase - that is 2 hots and a ground back to power panel. How do I hook up an earth ground??? Do I unhook the ground to power cabinet? Do I run another ground wire to the ground lug in the plasma and run it to ground and leave the ground to power cabinet or what????
I run an air hammer in my shop that has a 10 HP single phase motor on the monster. I will also earth ground this equipment the same way I will the plasma. Thanks for any help folks.

[Al_The_Man]

Originally Posted by plain ol Bill I know everything (plasma, table, computer and anything else that is going to be worked w/ the system) needs to be individually earth grounded to eliminate noise. The plasma will run off 240V single phase - that is 2 hots and a ground back to power panel. How do I hook up an earth ground??? Do I unhook the ground to power cabinet? Do I run another ground wire to the ground lug in the plasma and run it to ground and leave the ground to power cabinet or what????

I am not sure what you mean by individual grounded, the general rule is to try to make everything a common ground, i.e. no difference, potential wise between ground points.
Manuf. like Messer MG systems that have used PC control systems and Hypertherm Plasma units with High frequency ignition successfully, and have used the same procedure that I use with my PC based systems.
First, the service ground and the plasma common (table) is usually taken to a ground stake at the table location, using a sufficiently large gauge cable.
The plasma power supply has to be isolated via a transformer in the hypertherm Plasma unit in order to ground the plasma positive electrode and allow it to be common to earth ground and the table, otherwise it would blow the power supply.
In the electrical enclosure, the PC ground and other auxiliary power supply commons,servo supply commons, are connected to a copper ground plate, together with all encoder shields etc.
This is also bonded to the ground stake.
Often the problem comes when an attempt is made to keep everything totally isolated and separate, instead of common bond.
Al.

[Karl_T]

Al, That plasma is going to have both AC nuetral and a ground.

I treat AC nuetral as its own hot wire. They are connected only to the nuetral that goes back to the breaker panel.

AC nuetral carries current. Connecting it to common ground within the machine can cause trouble from my understanding. correct?

Karl

[Al_The_Man]

Originally Posted by Karl_T I treat AC nuetral as its own hot wire. They are connected only to the nuetral that goes back to the breaker panel. AC nuetral carries current. Connecting it to common ground within the machine can cause trouble from my understanding. correct?

I am not sure what you mean by the 'AC neutral as its own hot wire'
The plasma unit is being fed from 240v which is referenced to ground at the grounded neutral point at the panel, whether the neutral is being used or not. In this case it is probably not.
I am not advocating connecting the service ground and neutral at any place other than the panel. So the neutral does not really come into play here as a conductor.
If the table, (Plasma common) is connected to ground then it will be, or should be at the same potential as the service ground.
By bonding all grounds at one point ensures that the ground potential between any ground point is zero.
It is imperative that any ground conductor does not intentionally carry current, the general idea behind grounding is that it creates a stable reference point.
Because a conductor is grounded does not necessarily mean it is carrying ground current.
I found that grounding is one of the least understood aspects of a machine installation.
The Siemens PDF I attached to a recent posting on grounding explains Uni-potential grounding in detail.
Al.

[Karl_T]

Originally Posted by Al_The_Man I found that grounding is one of the least understood aspects of a machine installation. The Siemens PDF I attached to a recent posting on grounding explains Uni-potential grounding in detail. Al.

Al I did a google search and didn't find this post. Could you give me a link to this seimens .pdf?

Karl

[plain ol Bill]

Yes please put a link up to that post for us Al. The more I read the more confuseder I gets. Me thinks I just may have to call a friend that was an electrician in an earlier life.

[Al_The_Man]

I forgot, I put it on a download site because of the size: http://www.divshare.com/download/5002681-38f
Here is the posting http://www.cnczone.com/forums/showthread.php?t=61657
Al.