6/2 or 6/3? Purely educational question.


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Old 09-21-22, 05:53 PM
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6/2 or 6/3? Purely educational question.

NOTE: I'm having someone else install this for me so these questions are simply for educational purposes. It drives me nuts not understanding this stuff.

This is the plug for a plasma cutter. Requires 50 amps running all out. Does this need a 6/2 or 6/3 cable and why? It's my understanding the "denominator" on the rating only counts the conductive wires, so with 3 prongs on this thing I should have hot, neutral and ground (with ground being 'non-conductive' right?) ... so 2, right?

As an aside: I've heard that 3 prong, 220-volt connections are a thing of the past (according to https://diy.stackexchange.com/a/214164), should I be pushing for a 4-prong outlet? This stack exchange article has me a tad confused that maybe this setup isn't safe?

Thanks in advance.

 

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09-21-22, 06:29 PM
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That plug tells us you need 240v only. Two hots and a ground. That would be 6/2 w/ground.
If it was 120v only then it would be hot, neutral and ground.... that would also be 6/2 w/ground.
If your device was 120/240v.... then it would need two hots, a neutral and a ground.. 6/3 w/ground.

That stack exchange thread was for a dryer. A dryer is 120/240v and requires four wires.

Let's take a step back.... what is your device....120v or 240v ?
That is not a correct plug.... it says 30A 240v on it. Too small for your use.
Can't read the type off the plug.
 
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Old 09-21-22, 06:29 PM
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That plug tells us you need 240v only. Two hots and a ground. That would be 6/2 w/ground.
If it was 120v only then it would be hot, neutral and ground.... that would also be 6/2 w/ground.
If your device was 120/240v.... then it would need two hots, a neutral and a ground.. 6/3 w/ground.

That stack exchange thread was for a dryer. A dryer is 120/240v and requires four wires.

Let's take a step back.... what is your device....120v or 240v ?
That is not a correct plug.... it says 30A 240v on it. Too small for your use.
Can't read the type off the plug.
 
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Old 09-21-22, 06:31 PM
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3 prong 240V is fine (hot/hot/ground). It's 3 prong 120V/240V (hot/hot/neutral) which is obsolete.
 
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Old 09-21-22, 09:13 PM
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@PjMax:

Let's take a step back.... what is your device....120v or 240v ?
The device is this: https://www.amazon.com/Lotos-LT5000D...004VFJL14&th=1.

Part of the confusion is that you can buy an adapter for it (here: https://www.amazon.com/Lotos-Technol...0NVOW83O/?th=1) to run it off 120 volts. After running it on 120 I'm getting poor performance and want to get 240 into the garage. I'm perfectly capable of running the wiring, but I'll likely hire a friend of mine (an electrician) to hook it up to the panel. I'd like to understand the best outlet + wire to buy before he does so.

​​​​​​​Two hots and a ground.
Oh, duh. The two hots are 120s on separate phases, making the total 240, right? So yes: two hots and a ground. Thanks. I'm dumb.

​​​​​​​A dryer is 120/240v and requires four wires.
This is where I get confused. Are you saying the dryer has 120 volt as well as 240 volt components in it, and that's why there's 4 wires? So, the dryer element itself is probably 240, but the "smarts" of it are standard 120?

​​​​​​​it says 30A 240v on it
Yes, I noticed this as well. This is also part of the source of my confusion. The instructions clearly claim this thing can go up to 50 amps, but it looks like the plug is only rated for 30A.

Thanks for all your help. You're absolutely amazing on here.
 
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Old 09-21-22, 09:14 PM
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3 prong 240V is fine (hot/hot/ground). It's 3 prong 120V/240V (hot/hot/neutral) which is obsolete.
Thanks Luke. That clears up a lot for me.
 
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Old 09-21-22, 10:08 PM
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This is where I get confused. Are you saying the dryer has 120 volt as well as 240 volt components in it, and that's why there's 4 wires?
Yes, most dryers (and most ranges) made for the North America market require both 120V and 240V.

It's kind of dumb because they could easily make them 240V only (that's what most of the world uses, after all), but since 120V is available, they use it.
 
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Old 09-22-22, 12:22 AM
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According to the documentation you linked to, it will need 110V 40A or 220V 20A The voltage drop in the cable will be less at 220 (240) Volts. You need to use 2 wires + ground in both cases.
You may use the calculator here: https://www.calculator.net/voltage-d...y=23&ctype=nec

The voltage drop should be less than 4% at the load of 20A at 220V or 40A at 110V to get it work well.
You will probably need much smaller wire that you started thinking about. The 50 amp rating is the output for the unit.

The plug you pictured will be OK at 240V but it will be smart to use a standard that is easy to get today. My experience is for the most to industrial systems and 3 phase 480V so you will probably get better advice by others. (Or you could do as most of us do: use what you have that is OK, and change when needed, you never know what standard that will pop up next year..)
 
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Last edited by d_s_k; 09-22-22 at 12:29 AM. Reason: adding about plug.
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Old 09-22-22, 12:36 AM
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Looks like the NEMA Designation L6-30R still are OK
 
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Old 09-22-22, 05:03 AM
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It's my understanding the "denominator" on the rating only counts the conductive wires
Not entirely accurate. It counts the insulated conductors. For example an extension type flexible cord with black, white and insulated green ground is called 14/3.
 
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Old 09-22-22, 06:46 PM
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It counts the insulated conductors. For example an extension type flexible cord with black, white and insulated green ground is called 14/3.
That is not true. MC cable that has an insulated ground wire is still called 12/2 cable.
Example: https://www.doitbest.com/shop/electr...4aAt_cEALw_wcB

You are correct about cords. They typically count all conductors inside the jacket.
 
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Old 09-23-22, 10:32 AM
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To address the 3-wire 240v vs 4-wire 240/120v question in general:

It depends on the appliance/device.

Some devices require only 240v such as a pump or welder. Here you'd use 2 wires plus ground (H/H/G) and a 3-prong plug/receptacle. Since there's 240v across the two hots, it's all the motor (or AC unit or whatever) needs.

Other appliances like an oven, need 240v for the heating elements, but use 120v for the clock and electronics. So it requires a 240/120v supply with 3 wires plus ground (H/H/N/G) and a 4-wire plug.

Dryers are just annoying because they have always been 240/120v appliances, but were allowed to be installed with the ground acting as the neutral some time ago. That's why you now have a mix of 3-wire and 4-wire dryers, though 4-wire dryer circuits have been required since the early 2000's (I think).
 
 

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