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I wrote this up in chat gpt pretty quickly I think it just about covers all of the bases here of the project.

CNC Plasma Table – Electrical & Wiring Requirements

Project: Remote design of electrical system + wiring documentation for LinuxCNC plasma table
Client: TCB Metal Works

1. Project Overview

You will remotely design the complete electrical and control system for a custom CNC plasma cutting table powered by LinuxCNC.

You will create:

Complete wiring diagram set (schematic + physical routing)

Full Bill of Materials (BOM) with real part numbers

Wire gauge, shielding, grounding, and EMI mitigation plan

Bulkhead connector list + panel layout

Mesa board selection + full LinuxCNC I/O map

Integration notes for all components

Testing & commissioning checklist

This is a 100% remote engineering job — no physical inspection of hardware is required.

2. Available Power Sources

Near the machine:

220 VAC available

460 VAC available

No dedicated 110/120 VAC, which must be generated using a control transformer if needed

Engineer must design the incoming power strategy and transformer selection.

3. Motion Hardware
3.1 X & Y Axis – AC Servos (Provided)

3× A6 Series 1000W RS485 AC Servo Motor Kits

3000 rpm

3.18 Nm

17-bit absolute encoder

IP67 motors

Axis layout:

Y axis: 2 servos (dual-drive gantry)

X axis: 1 servo

Notes:

Motor-to-drive cables are already supplied by the manufacturer.

You do not need to design or evaluate those cables.

Engineer must:

Design AC mains wiring to each servo drive

Design control, enable, alarm, and ESTOP signal wiring between drives and Mesa

Include needed fuses, breakers, filters, and terminals

Provide cabinet layout and routing plan

Include proper grounding and shielding recommendations

3.2 Z Axis – Stepper Motor (Needs Driver + Cable)

PV267-D2.8AA stepper motor — Oriental Motor

Stepper driver not provided

Stepper motor cable not provided

Engineer must:

Select a compatible stepper driver suitable for PV267-D2.8AA + LinuxCNC step/dir

Define driver voltage supply requirements

Design:

Step/Dir wiring from Mesa

Motor wiring from driver to Z motor

Required cable shielding, gauge, and insulation

Connector type and strain relief

4. Control Electronics (Mesa + Power)

Engineer must select Mesa hardware capable of supporting:

3× servo axes

1× stepper axis

THC-AD

Ohmic sensing

All limit/floating switches

Plasma start / Arc OK

E-stop & safety I/O

Deliverables:

Recommended Mesa board combination (e.g., 7i76E, 7i96S, 7i85, THCAD, etc.)

Justification for chosen hardware

Complete LinuxCNC I/O mapping

Required DC power supplies (24V / 5V / others)

Proper AC distribution, fuses, breakers, and protection devices

5. Torch Height & Ohmic Sensing
5.1 THC-AD Integration

Engineer must design:

Raw arc voltage wiring from Hypertherm HT2000 to THC-AD

THC-AD signal wiring to Mesa

Required shielding and filtering

Scaling notes for LinuxCNC

5.2 Ohmic Sensing (Planned)

Engineer must:

Recommend a compatible ohmic board

Provide wiring diagram for torch → ohmic board → Mesa

Specify cable type and shielding

Document signal polarity & behavior

6. Hypertherm HT2000 Integration

Engineer must design wiring for:

Required signals

Torch start / trigger

Arc OK

Raw arc voltage (+/–) into THC-AD

Required protection

Isolation (if needed)

Surge suppression

Filtering

EMI protection

Routing rules

Arc voltage wiring must be kept separate from low-voltage control wiring

7. Limit Switches & Floating Head
X Axis

2 limit switches:

X-min

X-max

Y Axis (Dual Gantry Drive)

2 limit switches:

Y-min

Y-max

Engineer must propose a reliable gantry squaring / homing method for the two Y motors.

Z Axis

2 end-of-travel limit switches:

Z-min

Z-max

1 floating-head switch (touch-off)

Engineer must:

Select appropriate switch type (mechanical or prox)

Provide wiring diagrams to Mesa

Specify wire gauge, shielding, and cable routing

Provide LinuxCNC input mapping

Include any debouncing/filtering requirements

8. Wiring, Shielding, & EMI

Engineer must specify:

Wire gauges for:

AC mains

Servo drive feeds

Stepper driver feeds

Stepper motor wiring

Limit/floating/ohmic wires

Plasma signals

DC supply lines

Shielding requirements for:

Step/dir

Limits/floating/ohmic

Arc voltage

THC-AD lines

EMI considerations

Cable separation

Ferrite locations

Filtering recommendations

9. Grounding & Bonding

The engineer must design the grounding/bonding approach.

Important physical detail:

The water table, gantry, and control cabinet are three separate physical assemblies.

The engineer must account for this when designing:

Grounding/bonding layout

EMC/EMI mitigation

Plasma return path considerations

Ohmic sensing grounding

No grounding method (star, bus, single-point, etc.) is mandated — the engineer chooses the correct approach.

10. Control Cabinet & Bulkheads

Engineer must design:

Cabinet Layout

AC distribution, transformers, PSUs

Mesa boards

Servo drives

Stepper driver

Fuses, breakers, contactors

DIN rail layout

Ventilation/fans

Bulkhead Connectors

Used wherever practical for:

Servo cables (using glands or pass-throughs)

Z stepper cable

Limit/floating switches

Ohmic sensing

Plasma start / Arc OK

E-stop / operator controls

Ethernet access

Engineer must specify:

Connector type

Pinout

Panel cutout style

Labeling

11. Documentation Package

Engineer must deliver:

11.1 Wiring Diagram Set

Full schematic

Cabinet wiring

Field wiring

Power distribution

Grounding/bonding

Bulkhead connector pinouts

11.2 BOM

Complete list of:

Mesa hardware

Stepper driver

Transformers / PSUs

Switches

Connectors

Wire/cable

Protection devices

Cabinet hardware

11.3 I/O Map

All LinuxCNC inputs/outputs

Axis definitions

THC/ohmic mappings

E-stop & safety signals

11.4 Commissioning Checklist

Power-up verification

Servo enable/jog

Stepper test

Homing / gantry squaring

Z floating-head test

Plasma start / Arc OK

THC test

Ohmic test

EMI/noise checks

There is not much point upgrading from THCAD5 or THCAD10 to THCAD to THCAD2 as it is functionally identical except you can select 0-5v or 0-10 volt scales.

I personally think 150v is a bit low given cutting volts can be up around 130-140 volts. I would set to 180 to 200 volts.

Unser Plasmaschneider Hevy-Metal hat diese Jahr gute Dienste und schöne Ergebnisse geliefert....
Des halb haben wir uns entschlossen das THC nach zurüsten....
Erste Frage da wir damals die falsche Firmware genommen ( 7I96S_7I74 )haben gibt es ein Chaos wenn wir auf 7I96S-dpl gehen ?
Frage zum THCAD2 High isolation A-D:
10 V Full Scale
Wiederstände sind ok
Da der Plasmaschneider etwa 103 V beim Schneiden abgiebt was sich mit den Typenschild decktist die frage kann ich auf 150 V gehen für die Wiederstands berechnung oder sollte man auf 200 V gehen ?
Output Frequency ??Mode F/32 oder weiche für die 7I96S ?
Die Eingänge auf der 7I96S Endcoder-Stecker immer die beiden unteren wie in Beitrag 
MESA THCAD-2 - couple quick questions ?

Das war es fürs erste.

---

Our Heavy-Metal plasma cutter has served us well this year and delivered great results.... Therefore, we've decided to upgrade to the THC....
First question: Since we used the wrong firmware (7I96S_7I74) back then, will there be any problems if we switch to 7I96S-dpl?
Question regarding the THCAD2 High Isolation A-D
10V Full Scale
Resistors are OK Since the plasma cutter outputs about 103V during cutting, which matches the nameplate, the question is: Can I use 150V for the resistor calculation, or should I use 200V?
Output Frequency? Mode F/32 in the THCad 2 for the 7I96S?
The inputs on the 7I96S encoder connector are always the two lower ones, as in the post "MESA THCAD-2 - couple quick questions" ?
That's all for now.

king regard e Juergen

Hi everyone,I’m finishing up my CNC plasma build using a Mesa 7i96s, Spartus ProCut 45PCF, and a THCAD-5 (not yet connected).My issue:
The torch on output (OUT0) from the Mesa won’t trigger the plasma directly.
If I short pin 3 & 4 on the Spartus CNC port manually, the torch fires instantly.
When I run the signal through a relay, it also works fine.
But when I connect the Spartus directly to OUT0+ and OUT0-, (or OUT5) nothing happens — even though the Mesa output LED lights up and I can measure switching.The Arc OK behaves similarly — it only works through a relay. But when i have torch pulse on it stays active. And when cutting a circle is just flashes real quick and torch dies. 
The output LEDs on the Mesa board are about half as bright as the input LEDs.All 0 V lines in my control cabinet go to a common terminal, which is also tied to PE (earth) and the machine frame.
I have 24 V on IN COMMON, and everything else seems correct.Has anyone successfully triggered a Spartus ProCut 45PCF directly from a Mesa 7i96s output (without a relay)?
If so, could you share how you wired OUT0+ / OUT0- relative to the plasma CNC port pins (3–4)?I’ve looked through other wiring diagrams and posts, but haven’t found a clear answer yet.
Any suggestions or example diagrams would be very much appreciated. I will try and make a diagram of mine so you guys can have a look )Thanks!

Long story short, a lot of things were changed before I replaced the the 7i97t. Since then, I have have been cutting with zero issues. The thcad for arc volts is reading accurately while cutting. The thcad for ohmic is not hooked up. I can't get it to work, but maybe that's a good thing because it sounds like it's a bad idea with hf start.

The longer story is that this machine didn't have a home. So while its new home was being built, I set it up temporarily in my shop, so I could attempt to retrofit it with linuxcnc. When I fired up the torch for the first time, it damaged the 7i97t. This was with both ohmic and arc volts hooked up, so its anybodys guess what caused it. I added some grounds and an emi filter and few other things then replaced the 7i97t. Then I got it working great with a non hf plasma(except I didn't hook up ohmic).
Then after it was moved into its new home, we added several ground rods and hooked it up to the hf start plasma the way you had just advised. It's been cutting great. 

I know I ask a lot stupid questions but I do appreciate the help. 

I think there are much bigger issues than ohmic sensing from what you describe, namely bad wiring/shielding/grounding in general, so my strong advice is:
-do not fire the torch before grounding things properly
-make sure the power socket and the machine are grounded and the shop has proper ground rods
-make sure the PC is grounded
-make sure the plasma source is grounded
-disconnect anything ohmic related from Mesa
-disconnect the THCAD from Mesa
-connect THCAD only to plasma source
-wire and test the new Mesa, make sure everything works properly, wire the Torch ON to plasma source
-power on the plasma source and cnc machine and start QtPlasmaC or PlasmaC or whatever you are using
--enable LinuxCNC, jog around a bit, then use the Torch PULSE on screen set to 1 sec (default) ONLY ONCE !!!!!
-did anything move/burn/make strange noise/screen blank/PC turn off or lock/Mesa reset or lost connection/THCAD smoking ?
If any of those is yes, turn OFF everything and go back to wiring/shielding/grounding (goggle Hypetherm grounding they have a nice general guide)
If all above are no, try the pulse again and again, waiting 5 seconds between, make the pulse time 3 seconds and test several times again
If all that goes OK, try to do some manual cutting (use F9 to probe and fire the torch then jog manually), do several short cuts
If all good, power down and wire the THCAD to Mesa, do the same procedure from the line with two - signs above
ONLY if all tests go without issues proceed to wiring and testing Ohmic sensing. Again test from line with two -

Do you have a blinking yellow light on the THCAD?

If you set  the THCAD frequency divider to 1X you can probably
measure a change in the frequency as a voltage change on the F+
or F- relative to ground. Not sure of the polarity but full scale
should be about 2.5V at full scale and maybe 0.3V at 0V

I would need to study a bit about the probe wiring.
 

Since replacing the 7i97t, I haven't had any of the ohmic wired up while the plasma is running. I have only tried to get it working with the plasma off, so the 7i97t encoders should be fine.
I was more referring to the thcad output.
Can measure voltage between f+ and f- with the ohmic circuit open and again with it closed to test the thcad?

For the capacitor you mentioned, would I wire the torch tip to capacitor and the other end of the capacitor to star ground. Then run a separate wire from torch tip to thcad? Or would I wire both the star ground and the thcad to the capacitor?

I am trying to get ohmic sensing to work using a mesa 7i97t, thcad-2(jumpers on low range and 1/32), and a 24v power supply(meanwell hdr-15-24).

I have tried rodw's ohmic comp and ohmic comp3, as well as try many variation in the hal file mentioned in the original ohmic post/thread on this forum.
While I have no doubt there are issues with my hal file, I can't seem to get any response from the encoder in halshow, so I'm starting to wonder if I'm even getting a signal.
I tried using a multimeter to test the thcad outputs, but I don't know what I should be looking for. Is there a good way to test this?

I have it wired up similar to the diagram in the manual. I am using a 370k(or maybe 390k, can't remember) resistor between 24v+ and the thcad.
Since all the controls are on the gantry(this is a retrofit), I connected the 0v on the power supply to the buss bar on the gantry which in turn is wired to the star ground on the frame. I also connected the thcad shield terminal to the same buss bar.

The plasma is a ht hsd130 which uses a high frequency start. I previously damaged a 7i97t(which has been replaced) starting the plasma. I wonder if I could have damaged the thcad, as well. 
How can I protect the mesa boards from the high frequency start? Would a relay between the torch tip and thcad be enough? I assume it would need to be a special relay.

Attached is a hal file I have been using.

 

I'm not good at electronics. i will try implement a hypersensing circuit from plasma-cnc-primer docs with yours schematic. similarly, without surgery in a long cable.

for ohmic sense i only have thcad-10. i have thcad-300 but i used it for THC in this plasma cutter with 1:1 devider.

I found almost all the components (FY0022 + FY0023 connector,24VDC >20A relay ). but i can't find Isolated dc-dc converter with on/off signal.

Yeah the thread is long and full of failed attempts and iterations.
That's my development cycle, sadly.
The last post summarizes it. And this post show the performance forum.linuxcnc.org/show-your-stuff/56269...m-60?start=20#336805 It keeps performing like that even on water and rusty pieces.

Because the torch is the way it is, the ground leads in the torch, used during the arc start, needs to be cut and a small voltage applied which one measure to detect contact with the material. The rest is implementation and packaging in a nice format.
If you are willing to do surgery on the long cable to the torch you can cut it open and access the ground leads in there.
Instead, I made a short extension cable where all modifications were done.

I also used two separate voltage readers but I don't think that is necessary.
One uses the built-in voltage port, one measures directly between material ground and torch tip.
I will cut some parts later today so I can compare the voltage output of the two.
Of course, Mesa's THCAD cards can be used, the full voltage version.

Hi all

i bought a cheap plasma  Herocut Cut55i and i have machine plasma torch IPTM-80 like this
 
 

i try to do ohmic Hypersensing with a MESA THCAD-10 on my cnc table

Can you explain how physicali connect ohmic sensor?

Can i do ohmic ring something like that to the copper shield
 

or it is impossible on this type of torch and all that remains is floating switch?

thank you


 

Yes i am, i have 3 or 4 of those in daily use, 1 with Proma THC150 and others with Mesa THCAD.
I also have a china one with same electronics and pilot arc, the HF type, i intentionally wired the THCAD10 to the main terminals with 1MOhm resistors on each side, still in daily use for nearly a year, no issues.
The thing is, with correct wiring and grounding and shielding, it works fine, but any wiring error will result in burnt electronics the first time the torch fires, hence i refrain from advising such things.

The THC voltage is raw cutting voltage. a THCAD can use this with the right scaling resistors. I would expect there are some resistors between these terminals and the cutting terminals to avoid lethal current! Check with a multimeter.

here the thcad manual is your friend. 200 V full scale will be best but 300v is also Ok

Another cheap option for reading thermistors is LM331, a voltage-to-frequency converter
www.ti.com/lit/ds/symlink/lm331.pdf?ts=1760588182451
Or an industrial solution by Mesa, the THCAD