Author Topic: 'lectrical question : Using a single phase off of a 240VAC run  (Read 2604 times)

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Offline NM_Shooter

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'lectrical question : Using a single phase off of a 240VAC run
« on: November 01, 2015, 10:16:04 AM »
Since sub panels are effectively setup like this, I think that the answer is "Yes", but since this is not something I have done before I want to ask anyway.

I am setting up a shop in a small cubby area in my garage.  One of the machines (3/4 size knee mill) I am installing is currently wired for 240AC and I want to leave it like that.  I also have some 120VAC items that need power, such as my lathe, bench grinder, compressor.

My plan is to run a 30A 240AC line to the shop cubby area I am building, and have a center outlet in a wall box that is 240VAC.  I plan to run two wall circuits, one on the wall going right, one going left, with one each of those two phases. 

Clearly, I could unbalance the two phases, such as if my mill is running and the compressor is cycling.  However, I think this is okay. 

Thoughts?
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Offline tommytebco

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #1 on: November 01, 2015, 10:34:00 AM »
that's about what I did about 10 years ago. I fed into a small panel. ran one 240 outlet and two 120 lines around the outside of the shop (two outlets each)
Never had any problems

Offline flyingvan

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #2 on: November 01, 2015, 12:11:39 PM »
Kudos for wanting to balance the two phases.  Yes, it's OK, as long as the maximum possible imbalance is no more than the neutral can carry.   It's exactly what's going on in almost every house right now
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Offline DaveOrr

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #3 on: November 01, 2015, 12:30:50 PM »
I did the same thing in our workshop in our last house.
Ran a sub panel off the main with 8 circuits one being 220V for the dust collector and a 220 outlet for other tools that needed it.
The rest of the circuits were for lighting and wall outlets.
Worked perfect!!!   :)
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Offline Don_P

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #4 on: November 02, 2015, 03:51:19 AM »
If I'm understanding the only breaker for that is a 2 pole 30 amp? I don't know, will it trip if there is 40 amps on just one pole?

Offline Dave Sparks

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #5 on: November 02, 2015, 08:47:32 AM »
Forgive me but I did not see if you were running a neutral.  You would have to have one to get 120 from a 30A 240V cable run? Roger?
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Offline Dave Sparks

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #6 on: November 02, 2015, 08:49:41 AM »
If I'm understanding the only breaker for that is a 2 pole 30 amp? I don't know, will it trip if there is 40 amps on just one pole?

It better after a period of time based on the breaker type, it may not for a short overload.
"we go where the power lines don't"

Offline robbicon33

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #7 on: November 02, 2015, 11:04:54 AM »
Hi, all. I'm new to this forum  & have been an electrician for >25 years. I'm hearing 2 plans here: Plan a) is to run a 30 Amp (3-wire + Ground of course) cable to a 240 Volt outlet box & then branch off each phase leg to 2 (or more) 120V/20A convenience outlets. Plan b) is to run the same cable to a small sub-panel that would hold 4 Circuit Breakers that would feed at least 3 receptacles: 1 - 240V & 2 (or more) - 120V branch circuits. Well a) will work & probably never give you trouble, but it's illegal. B) is the proper way to do it. Make sure both the Neutral & the Ground wires are installed to the appropriate buss in the Main CB panel.

Offline NM_Shooter

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Re: 'lectrical question : Using a single phase off of a 240VAC run
« Reply #8 on: November 02, 2015, 04:34:13 PM »
Thanks Robbicon.  That's what I am looking for.  I want to stay legal.

-f-
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