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Running a 240v circuit for the 3hp/240v single phase lathe, plug questions.

D

DMSentra

Cast Iron
Joined
Sep 12, 2008
Location
Eugene Oregon
I'm thinking this will be a 20a circuit with 3 outlets for various uses also, should the 20a plug be a 4 wire on the lathe for ground included? I don't see many 4 wire 240v plugs so I'm wondering if it's not a thing.
ps. my service is 245v.
 
Go to Home Depot

DMSentra said:
I'm thinking this will be a 20a circuit with 3 outlets for various uses also, should the 20a plug be a 4 wire on the lathe for ground included? I don't see many 4 wire 240v plugs so I'm wondering if it's not a thing.
ps. my service is 245v.
Click to expand...
Every modern electric stove and cloths dryer uses 4 prong plugs. Edwin Dirnbeck
 
edwin dirnbeck said:
Every modern electric stove and cloths dryer uses 4 prong plugs. Edwin Dirnbeck
Click to expand...

Right, but this being a 20a makes no difference?

Second side of this project is moving the 6hp/24.5a/208-230v rated compressor to the back room. Run length from the breaker box will be 80'. Service volts into the main panel is 245v, I'm running 2 cnc machines of 33 and 24 kva requirements on phase matched 20 and 30 hp rotary phase converters through identical SB16N2F buckboosts down to 228v. The compressor has been working fine with +/- 30' of 8-4 SOW-A cable and a 60a breaker. I've been reading that a 25a motor should be good on #10 wire even though up sizing the breaker 250% to compensate for the inrush is allowed, but wonder with adding the additional run length I better stay with #8 wire instead? Can someone confirm this?
 
All plugs are grounded. The difference between 3 wire and 4 wire has to do if you want to include the neutral or not. 3 Wire = hot, hot, ground (hot to hot = 240VC / Ground = safety only). 4 wire = hot, hot, neutral, ground (hot to hot = 240VAC / hot to neutral = 120VAC / Ground = Safety Only). You want to have the 4 wire connector if you are going to use a 120VAC circuit (like a light) on the machine.

I have been standardizing across the shop to the L14-30R/P connectors so I can move things around. R=Receptacle and P=Plug. This is a 30A plug and is sometimes overkill for the 20A 240V machines but that is allowed. This twist-lock is a lot more user friendly than the dryer/oven style 4 wire plugs.
 
Wake up! Pour another cup! And pay attention.

He is talking about THREE PHASE. There is no neutral. Three wires are needed to carry the basic, three phases. A FOURTH wire would be needed to carry a ground to the machine.

And YES, I would strongly recommend having that ground connected to the machine's frame/base. This will provide safety in case of a short between one of the phases and that frame or base.



rwa2004 said:
All plugs are grounded. The difference between 3 wire and 4 wire has to do if you want to include the neutral or not. 3 Wire = hot, hot, ground (hot to hot = 240VC / Ground = safety only). 4 wire = hot, hot, neutral, ground (hot to hot = 240VAC / hot to neutral = 120VAC / Ground = Safety Only). You want to have the 4 wire connector if you are going to use a 120VAC circuit (like a light) on the machine.

I have been standardizing across the shop to the L14-30R/P connectors so I can move things around. R=Receptacle and P=Plug. This is a 30A plug and is sometimes overkill for the 20A 240V machines but that is allowed. This twist-lock is a lot more user friendly than the dryer/oven style 4 wire plugs.
Click to expand...
 
I'm betting the electrical code will require a 4 wire plug. Some 20 years ago I had a contractor come to the shop and add a 100 amp sub panel and 2 circuits to run low hp 240 volt single phase equipment. At that time they wired each circuit with 8 ga. wire and used 20 amp twist lock plugs. A few weeks ago I had another circuit added. This time they used the same 8 ga. wire but used 4 wire plugs due to the change in the code. We also had a kitchen remodel at the house. In that case the contractors changed out the original 3 wire plug for the range to a 4 wire plug to meet code. Fortunately the original contractor had run 4 conductor wire to the outlet. I'm guessing he knew the code would change in the near future and made things easier for future work.
 
DMSentra said:
I'm thinking this will be a 20a circuit with 3 outlets for various uses also, should the 20a plug be a 4 wire on the lathe for ground included? I don't see many 4 wire 240v plugs so I'm wondering if it's not a thing.
ps. my service is 245v.
Click to expand...

Hmm .... I don't believe I've ever seen a plug that does not have a Ground connection other than the older style dryer outlets ....

Yes, you do need to run a ground wire.
 
If you run the power from a Main panel, you need 3 wires, 2 for the 240, 1 grounded conductor

If you run from a Sub Panel, you need 4 wires, 2 for the 240, 1 insulated for the grounding conductor buss, one for the grounded conductor buss

Check with the Authority Having Jurisdiction to find out if the National Electric Code (NEC) is accepted practice and follow appropriate regulations for your location.

While doing electrical work, install a lightning/surge suppressor on your main panel and your sub panels.

Remember that NEC is the minimum standard, you can always do a better job with larger sized conductors, surge suppression, better grounding.
 
APD said:
Title of this thread:

Running a 240v circuit for the 3hp/240v single phase lathe, plug questions.
Click to expand...

No wonder people are so quick to kill each other.
Everyone has their finger on the trigger.
And this is the internet, everything on here DOES NOT MATTER !
Remember that people.

-Doozer
 
The code change from 3 to 4 wire is a result of the appliance industry looking to save a few dollars. It removes the need for a transformer in the appliance to make 120V for lights and other things. It has little to do with safety.

If your equipment does not use 120V, the neutral wire (fourth wire, insulated ground) will do nothing. It does not matter if the feed is from the main or sub panel. Now if you local code requires it then you need the fourth wire even though you will have nothing to connect it to.

My shop built 2 years ago has 3 wires to all the phase converters on the 240V machines. And 80 feet of copper pipe under the slab bonded to the safety ground. Shop has 4 wires back to the main panel. Insulated ground and safety ground are separate until they meet at the main panel.
 
Many coolant pumps, lights/ fans are 120 volts. So I would include a neutral just in case.
For remodels the NEC allows you to add a separate ground wire and run it along side the existing cable for dryers and I think stoves/water heaters.
Bill D
 
The four wires in a single phase 240V circuit are:

1st wire is 240V hot. Usually a red wire.

2nd wire is 240V hot. Usually a black wire.

3rd wire is safety earth ground. Green wire.

Now on to the 4th wire which is neutral (insulated ground) needed for 120V. Usually a white wire. If equipment does not need 120V then you don't need it. But code may require it even thought you don't need it. Blame the appliance industry! This is the return current path for the 120V circuit. It must never be connected to the ground at the sub panel. If it were and the ground wire failed and your equipment has voltage touching the chassis, you now have voltage on the neutral wire back to the main panel, very bad! This wire and the ground wire are connected to each other at the main panel only and then to your water pipe in the building.

Although the neutral and ground may seem to be the same thing, they are not. Neutral is a return current path for 120V. Ground is a return current path if voltage appears on the machines chassis and to save your life! If everything is operating normally, the earth ground wire (green wire) never sees any current flow or voltage on it. In a perfect world the ground wire would never be needed.
 
Last edited:
Just do a web search Hubble makes the plugs and receptacles
Just speck 220v 20 or 30 amp
Put in a couple 4 wire outlets
I put in mostly 30 amp plugs and just one 20 amp.
You don’t have to use all 4 wires just because the plug has them.
Advantage of a 4 wire is you can easily add a 110 outlet at the machine
Say for light and or dro.
 
For residentail wiring there are only three colors. Green(or bare) which is safety ground.
White which is the neutral, used for 120 volts.
Any other color is hot, connected to the power pole.
Bill D.
 
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