Big Ohmic Problem ???

Aciera wrote:

As close to torch and table as possible.

What size would you recommend?

CBEAR wrote:

By the way, the colors mean absolutely nothing, I should have used different colors for each wire, but I didn't think about it.

Remove the 24- to shield wire.

EDIT: Per @PCW (much smarter with electronics than I , remove the Shield to Ground wire, leave the -24 to shield.

@snowgoer
I think 500mA should be plenty.

PCW wrote:

snowgoer540 wrote:

PCW wrote:

If you connect the THCAD shield to "Table" you must _not_ have a shield connection to Earth ground
(except via the table connection)

Other wise you could have full plasma current flow in the sense wiring

Well shit. I will remove the blue connection between the -24v and the shield.

The frame/table can stay grounded, correct? Basically the diagram below:

I would do the opposite: Remove the Earth ground from the shield and leave the blue wire (table connection)
as this removes the ground loop but provides better noise immunity

Ok, will do. Thanks for the help.

I do have my THC shield tied with the Ohmic shield too. Is that ok?

Aciera wrote:

The power supply SHOULD be grounded (i.e. for example the metal chassis). Just make sure that the COMM or 0V on the secondary or output side is not connected to earth ground. You can check that with an ohm meter (although really one should use an isolation tester given the high voltages involved in plasma cutting)
And again its usually not wrong to use fuses.

[edit]
To me it actually would make a lot of sense to put a fuse in either sense line. That way even if you have the workpiece not connected to ground earth AND have a ground fault in the sense wiring the cabling is protected from overcurrents.

This is the part that is confusing to me. My table frame is grounded to the electrical box which is grounded to the 110v main ground. As such, so is the water pan.

That means, no matter what, once I hook the -24v to the table, it's grounded by proxy. I can confirm that my power supply IS isolated (there is no continuity between the ground lug, and -24v). However, if I check between -24v and ground, I have continuity (4-5ohm).

I did order the double isolated HDR series PS Rod suggested (somehow I missed that recommendation when I started down this path), but I dont see how that's going to help anything, because as I've said the -24v side is tied to ground through the frame. I also clipped my ground wire that was going to the shield as per Rod's original diagram, based on PCW's new advice.

What I don't want is for my stuff to catch on fire.

rodw wrote:

I would not reccommend adding any fuses etc.

Hard for me to stomach that advice when a guys wiring caught fire...