Miller Cutmate 375, 120 or 240 Volts

[HAWK]

johns6,

If your wiring supports the 30amp draw, then leave the breaker at 30amps and change out your plug to support 30amps. On the other hand if your machine will not draw more than 20 amps ( plug rating ), then you will be okay as is.

The safe thing to do is match the plug rating to the breaker rating and wire rating. Therefore, if you do not want to change out the plug, then yes change the breaker to a 20 amp.

[Scott V]

It seems kind of odd since the machine is SUPPOSEDLY rated at 5/16, quality,at 3/8 and sever at 1/2. using drag cutting.
Using standoff it's rated at 3/8, Quality at 1/2 and sever at 5/8.
I think the machine is over rated. Before the one i bought broke down (2 days after i bought it). It was having a **** of a time on 3/16 and 1/4. like you already stated. All the cuts looked like they were severd.
Not bashing Miller but i would never get another 375. Thats why i bought a TD 51 **** near for the same cost. $1500.00 out the door. I do like the design of the cases on the Millers though.

Mig,
I will say the 375 I worked worked really well. The most impressive Miller plasma I ran was the 125 c. For 12 amps it really did a good job. I could take or leave the 3050 model. It would do the job, but nothing special like the little one.

[johns6]

It seems kind of odd since the machine is SUPPOSEDLY rated at 5/16, quality,at 3/8 and sever at 1/2. using drag cutting.
Using standoff it's rated at 3/8, Quality at 1/2 and sever at 5/8.
I think the machine is over rated. Before the one i bought broke down (2 days after i bought it). It was having a **** of a time on 3/16 and 1/4. like you already stated. All the cuts looked like they were severd.
Not bashing Miller but i would never get another 375. Thats why i bought a TD 51 **** near for the same cost. $1500.00 out the door. I do like the design of the cases on the Millers though.

Mig,

Thanks for your input, but my Miller dealer who is also a personal acquaintance is the reason for me getting the 375. The service I get is excellent and he is a Miller repair facility. If I am making a mistake it's not the first one. Actually, he likes the Esab 180. Sometimes I think we are splitting hairs around here. But thanks again.

[johns6]

You guys are correct the 120VAC 20amp plug looks similar to the 240VAC plug. However similar they may be, they are not interchangeable. The sideways blade on the 120VAC plug is to assure the operator will use it on a 20+ amp branch circuit. This is of course assuming the proper wiring and breaker are used on the supply circuit.

If you plan to run this machine on 240VAC, then dropping down to a larger size input cable will make a difference in this machine's performance. I am not sure this is listed in the manual, but practical experience has shown this to be true. There are a few posts on this forum regarding this information.

Hawk,
Thanks for the reply. I may not have worded my question correctly, but what I am asking is this. I currently have an 240 outlet with a 6-20p receptecle that is on a 30 amp breaker. My question is should I replace the breaker with a 20 amp breaker ?

Put a bigger cord on it.

[HAWK]

You guys are correct the 120VAC 20amp plug looks similar to the 240VAC plug. However similar they may be, they are not interchangeable. The sideways blade on the 120VAC plug is to assure the operator will use it on a 20+ amp branch circuit. This is of course assuming the proper wiring and breaker are used on the supply circuit.

If you plan to run this machine on 240VAC, then dropping down to a larger size input cable will make a difference in this machine's performance. I am not sure this is listed in the manual, but practical experience has shown this to be true. There are a few posts on this forum regarding this information.

I'm borrowing one from a friend while I build this trailer, its always run on 240v. It cuts 1/8 steel like butter, but 3/16 and 1/4 require alot more skill. I run it at full power all the time.

It seems kind of odd since the machine is SUPPOSEDLY rated at 5/16, quality,at 3/8 and sever at 1/2. using drag cutting.
Using standoff it's rated at 3/8, Quality at 1/2 and sever at 5/8.
I think the machine is over rated. Before the one i bought broke down (2 days after i bought it). It was having a **** of a time on 3/16 and 1/4. like you already stated. All the cuts looked like they were severd.
Not bashing Miller but i would never get another 375. Thats why i bought a TD 51 **** near for the same cost. $1500.00 out the door. I do like the design of the cases on the Millers though.

[johns6]

You're welcome. I hope it made sense.

Regarding the plugs, I don't think the 5-20P and the 6-20P have the exact same physical configuration. On the 5-20P, the horizontal blade is on the right side of the plug (looking at the plug as you face the prongs, with the round ground prong below the other two). On the 6-20P, however, the horizontal blade is on the left. For an example, look at http://www.king-cord.com/ourpro/american.html (scroll down to about the middle of the page).

I think that difference (and the fact the plugs pertain to different supply standards) explains why Miller suggested changing the plug for 230 V operation. BTW, I didn't see explicit references to the 5-20P and the 6-20P in the Miller manual -- just a discussion of changing the plug from the as-supplied 120 V plug to a 230 V plug.

That makes sense. I guess I just didn't look careful enough. Anyway, I have a6-20p I am going to install. Should I drop down from a 30 amp breaker to something smaller for the 375?

As to what comes on the machine, I looked at a new in the box Hobart Airforce 400 which is the same as a Spectrum 375 and it did have a 5-20P.

Thanks Again.

[Scuppers]

Incidentally, johns6, in case you care to know, I think I know the power factor of the Spectrum 375 (you probably won't care if you use residential utility service, but might care if you're a commercial customer).

The numbers in the manual suggest a power factor of 0.95 (the ideal number is 1.00). A number that high makes it more likely that the machine uses active power factor correction, as I wondered in an earlier post.

[Scuppers]

From what the Tech guy told me was that you'll get the same performance on either one as long as you use the right breaker for the job,
30A for 115v
15A for 230v
I do believe he said you'll get better duty cycle using 230 and the machine wont run as hot.
Someone else on this board said the same thing,So i assume they both know what they were talking about.

Hmmm... I wonder whether Miller has changed something in the design or specifications. Otherwise, what the tech guy said doesn't seem to square with Miller's documentation. Looking at both the manual and the specifications, I find a duty cycle of 35%, with no dependence on the supply voltage noted.

As far as the machine running cooler on 230 V than on 115 V, both the manual and the specifications indicate that the machine consumes 3.2 kW, seemingly independent of the supply voltage. That fact suggests that the power dissipation in the machine, and therefore the generated heat, shouldn't change materially between 115 V and 230 V operation.

Theoretically, because the machine draws roughly twice the current at 115 V compared to 230 V (and assuming that it delivers roughly the same power), the power dissipation in the machine and, hence, heat rise, might be slightly higher at 115 V. More specifically, the wires inside the machine have a certain finite resistance. At twice the current, the power dissipation in the wires increases. Also, the power electronics on the circuit board (for example, MOSFETs, diodes, IGBTs, thyristors, etc.) dissipate more power at higher conduction currents. The differences, however, should be relatively small -- especially given the short wire runs in a case that size and the relatively high 2.3 kW input power (without details of what's on the printed circuit board and the resistance of the wires, etc., I can't say with certainty).

[Scuppers]

Scuppers,

Thanks for the information. Can you explain something else to me? I believe the 375 comes ready to run on 120 volts and has a 20 amp rated plug (Nema 5-20 p),one of the blades is turned 90 degrees. This plug is also the same configuration of a 20 amp 250 volt plug (NEMA 6-20P). Since these plugs have the same pysical configuration, why does Miller say that I need to change to the 250 volt plug? I plan on changing it but I am just curious as to why there are both a 120 and a 250 plug with the same configuration. Is it that one is rated for the higher voltage?

You're welcome. I hope it made sense.

Regarding the plugs, I don't think the 5-20P and the 6-20P have the exact same physical configuration. On the 5-20P, the horizontal blade is on the right side of the plug (looking at the plug as you face the prongs, with the round ground prong below the other two). On the 6-20P, however, the horizontal blade is on the left. For an example, look at http://www.king-cord.com/ourpro/american.html (scroll down to about the middle of the page).

I think that difference (and the fact the plugs pertain to different supply standards) explains why Miller suggested changing the plug for 230 V operation. BTW, I didn't see explicit references to the 5-20P and the 6-20P in the Miller manual -- just a discussion of changing the plug from the as-supplied 120 V plug to a 230 V plug.

Scuppers,

Thanks for the information. Can you explain something else to me? I believe the 375 comes ready to run on 120 volts and has a 20 amp rated plug (Nema 5-20 p),one of the blades is turned 90 degrees. This plug is also the same configuration of a 20 amp 250 volt plug (NEMA 6-20P). Since these plugs have the same pysical configuration, why does Miller say that I need to change to the 250 volt plug? I plan on changing it but I am just curious as to why there are both a 120 and a 250 plug with the same configuration. Is it that one is rated for the higher voltage?

I believe you answerd your own question.

I have ordered a new Miller 375 Plasma cutter. Is it an advantage to use it on 240 voltage? I can go either way.

From what the Tech guy told me was that you'll get the same performance on either one as long as you use the right breaker for the job,
30A for 115v
15A for 230v
I do believe he said you'll get better duty cycle using 230 and the machine wont run as hot.
Someone else on this board said the same thing,So i assume they both know what they were talking about.

[johns6]

Scuppers,

Thanks for the information. Can you explain something else to me? I believe the 375 comes ready to run on 120 volts and has a 20 amp rated plug (Nema 5-20 p),one of the blades is turned 90 degrees. This plug is also the same configuration of a 20 amp 250 volt plug (NEMA 6-20P). Since these plugs have the same pysical configuration, why does Miller say that I need to change to the 250 volt plug? I plan on changing it but I am just curious as to why there are both a 120 and a 250 plug with the same configuration. Is it that one is rated for the higher voltage?

[Scuppers]

I have ordered a new Miller 375 Plasma cutter. Is it an advantage to use it on 240 voltage? I can go either way.

Hi johns6:

Unless you don't plan on using the machine's rated capacity (or you have a high-current-capacity 115 V supply), I think you'd be better off running it from a 230 V supply.

I briefly checked the circuit schematic diagram in the Spectrum 375 manual (available at Miller's web site) to see how it handles 115 V/230 V. The machine includes a switch (S2) that switches two windings on the primary of a transformer (T1). With a 230 V supply, the switch connects the primary windings in series. With a 115 V supply, the switch connects the two primary sections in parallel, which should result in twice the current draw compared to the 230 V case. In fact, Miller's input current specifications confirm that conclusion (14 A at 230 V, 28 A at 115 V).

A typical 115 V outlet provides 15 A or 20 A. Unless you don't use the machine's full capacity, you would likely trip the circuit breaker. In fact, Miller's specifications include this note: "Recommended 30 A branch circuit for maximum performance. Performance on 20 A branch service may be limited due to breaker/line fuse. Reducing unit output amperage will minimize nuisance breaker/line fuse tripping."

As an aside, the specifications state that the machine includes power factor correction. The schematics show an inductor (L1) labeled "BOOST." I wonder whether the machine uses a switched-mode boost converter (for example, one that uses the Unitrode UC3854) in order to achieve power factor correction?

If so, it should draw a relatively clean sinewave current from the outlet, with little harmonic content (rather than the clipped-sinewave or spiked waveform without power factor correction) If you're a commercial utlity customer, you probably pay for your electricity at least in part based on the kind of power factor your equipment presents to the utlity grid. If that's the case, this machine should help reduce your electric bill compared to a non-power-factor-corrected machine.

Best of luck.