THC upgrade Miller Spectrum 375 wiring

Lug TE-3 (middle) from the diagram is hook to the red positive terminal

Lug TE-4 (right) from is hooked to the black negative wire terminal

The picture above does show the opposite to that so I assume its wrong. ? look like the op endded up using a different plasma cutter after this post.

a plasma cutter is a constant current electrode negative power supply .

1 Like

if you did get the polarity mixed up you could always swap the leads at the VIM.

If it is KNOWN that the photo in the original post is wrong, it should be flagged as such, either remove the photo or put some BIG text in that post. From your schematic and Tin’s comment RE lugs, I would say it is wrong.

1 Like

Maybe I’ll pull open my 375 again and triple check it?

if @jFab could follow up on his experience with the 375 would be helpful but from his activity history he move to a different plasma cutter short after the post above. .

Maybe the the pic is of a 625x not the 375 ? Looking at the wiring diagram included with the 625 the terminal on the right is the work/clamp which I believe is pos and the terminal in the middle is the torch which is neg unless I am reading the wiring diagram wrong.

1 Like

I only have a 375 so I can’t physically verify for the 625

When I look at the wiring diagrams for each power supply they seem virtually identical.

This is a screenshot from the 625 manual wiring diagram.

Here’s another link from that same topic with a customer who successfully wired his Miller to run with the THC it has some pretty clear photos

Here’s a good tidbit on some of the machines those lugs are reversed…

Of course why would you want the terminals in 2 3 4 order when you could have them in 2 4 3 order, thanks miller?

1 Like



Here is a pic of mine, you can see the bundle from the center terminal (all marked 20) run directly to the torch.

And you can see on mine that they swapped those terminals.

Mine has the ice 27 torch on it. Which sticks into the cabinet longer so there’s a little bit more wire when they move to the bigger torch it looks like it doesn’t stick into the cabinet as much and have shorter wires and it looks like they were forced to switch the terminals from 234 to 243

1 Like

So the take away is dont assume a picture on the interweb is correct and double check the wiring diagram and follow the leads back from the torch plug to the terminal. My 625 has a completely diff plug for the torch than the one in your pic. I assume Miller has used a couple of vendors for these things over the past few years

1 Like

The 625 likely has a removable torch where the 375 is hardwired.

I bought my 375 extreme in 2007 or 2008 I’m sure revisions have been made.

I think their intent though is to have those terminals and right to left order two three four.

And then when they went to that new style torch they realized they didn’t have enough wire to make it to the four terminal so they switched them around.

Physical verification of what you actually have in reality is definitely a good step.

There’s also a couple of Hobart units that are almost identical to the Miller series.

1 Like

Isn’t that the truth.

1 Like

I am new here. I finished installing my table, and installed THC to Miller Spectrum 375 extreme with XT Torch. I installed raw voltage following directions and some of the previous post in this forum. As many said, the wiring is different. See the pic below, I installed the black in the middle machine lugs. I tested the continuity, everything seems to be right. when I try to cut, the plasma is not firing at all. Not sure what I am doing wrong here. Appreciate any help!

@herdemir Welcome to the Forums

How are you currently triggering the torch ? through FireControl?

Yes, using the FireControl.

Where are your trigger wires hooked up ?

hmm, I did not do anything with the trigger wires. is there any directions in the forum on how to do it?

Orange /Purple I believe . Post the model serial number from the bottom of your miller 375 we 'll try to can confirm. Some unit are slightly different .

1 Like

The SN: ND033089P.

375 X-TREME And XT 30 Torch

Owners Manual
Parts Manual

I’ll thumb through it shortly I have a couple chores to take care of .

Here is where you search for miller manuals by serial number

1 Like