Hello to all,
I am new to this forum, please excuse me if this question has been answered.

I just bought a Thermal Dynamics Plasma cutter. It has a Nema 50-P plug end on it, which I assume is to be plugged into a Nema 50-R outlet.

In looking in my reference book, this is a 3 wire configuration with a Hot, Hot and Ground and is a 50 amp plug. Perhaps I am wrong, so that may be my first problem.

The Plasma power source is listed as drawing 67amps at full load. The manual says to use 6gauge wire as it can be derated due to duty cycle. Duty cycle is 100% at 45amps output and 40% at 80amps output. The manual also says to protect the plasma cutter with an 80amp circuit breaker.

Aren't I protecting the wiring and not the tool? Why would I want 67 amps going through a 50amp plug and why would I want an 80amp CB on a 50amp receptacle?

I am well versed in AWG, but this combination is throwing me for a loop.

Explanations would be appreciated especially if I can read the explanation in the NEC. I just don't know where to look.

Sorry for the delay, I did not se your question as I usually only monitor the elctrical forum.

The NEMA number you state is missing a number, it should probably read NEMA 6-50, which is 3 wire 250 volt 50 amp, with 2 hotsfor 240 volt and one equipment ground.

R=receptacle P= plug

Did this 50 amp plug come on the unit from the manufacturer?

I would not think so if the instruction manual requires an 80 amp circuit.

A plasma cutter seems to have similar characteristics of a welder, and may be covered by NEC Article 630.

But you will not find anywhere that 67 amps is allowed on a 50 amp circuit.

Tkrussel,

Sorry, you were right, 6-50 is the plug. Yes, it did come installed on my Thermal Dynamics Cutmaster 101 straight from the factory. I consulted the owner's manual and sure enough, it calls for an 80amp CB. The plug is on a cable, I believe it is called an SO cable? It is 6/3, three wire cable.

So, herein lies the rub. How do I correctly install this? I ordered the circuit breaker and it should be here today. Should I install it along with 4awg wire to a receptacle box and then search for a receptacle rated for this along with a new plug? I looked yesterday at my supplier and the only thing I saw was a 60amp 4-wire plug. I doubt I will find an 80 amp unless I step up to a multimillion dollar Appleton connector... sheesh those guys are proud of their product!

I will wait to hear from you before I do anything. I would rather do it right the first time than re-do it later. Or even worse, maybe, cause a fire.

Thanks!:eek:

PS This info is pulled from the Thermal Dynamics Owners Manual 0-2852 on page2-2 of the Introduction for the Thermal Dynamics Cutmaster 101 Plasma Cutting System RevAA.01 Dated October 20, 2006.

Continue with the 80 amp circuit and the NEMA 6-50 R. Anything the manufacturer says in the manual is suppose to be what is followed. I will need to review the Article 630, I don't get to do welders often, and they can be a bit confusing and different to do. I would not worry initially about the cord and plug, since it will be in site when your operating the unit. What you will have no worry about is the proper size circuit that is from panel to outlet.

TKRUSSELL,

Here is what I am doing: Installed the 80amp circuit breaker in the panel, install 1-1/4" Schedule 40 PVC from panel (at rear of my garage) to front of garage, pull two 4awg THHN hot legs and 1 4awg THHN ground, at front of garage I am installing a J-box of adequate volume. Connected in the J-box will be my feeders from the panel and the end of the 4-3 SOOW cord. Coming out of the J-box will be the 4-3 cord with a Hubbel cable sock. The cord will break out into the three wires. I will terminate those three wires with individual female Tweco quick disconnects and color code accordingly. Then I will terminate the cord from the plasma cutter with the male Tweco quick disconnects. This effectively removes the weak link (the 6-50 plug). And maintain an 80amp circuit. I called the manufacturer and he says using a 50amp plug is OK on a 67amp load as long as I don't do it for more than 4 minutes out of 10. But what if someone were to try and do it for longer? That possibility is not one I want to chance.

I did this for a 100 amp Tig Welder because the cost of a 100amp plug and receptacle was outrageous! That was about 5 years ago. So good so far.

Yes pin and sleeve connectors I believe are mined from a special mountain in East Overshoe, by gnomes that are very capitalistic.

I did an data center that needed 100- 60 amp male and female, at about $250 each, so much for volume discount.

OK glad you got in touch with the manufactiurer, and got their reasoning for the small cord, which is rated by the duty cycle, that I know of but needed to review before I offered advice.

FYI, the equipment ground for an 80 Amp circuit can be #8 copper, #4 is not needed. You can if you like, but #8 meets code.