240V underground line to shop?

Hello, all,
I need a 240V circuit in my barn workshop, which is maybe 120' from the house.
Currently, I have (I think) 50A at 120V running from the main panel in
the house, through an underground wire, to a sub-panel in the barn. There is no 240V in the barn, as yet.
I want to have the 240V circuit in the barn to run a 1.5hp table saw (induction motor) that I want to switch over to 240V and an air compressor.
The loads at 240V would be maybe 8A for the table saw (I know its motor uses 15A @ 120V) and 20A for the air compressor.
I would have a hard-wired switch on the compressor such that the table saw and compressor would never run at the same time, so the max load that circuit would ever see would be 20A @ 240V.
Since my "current" setup doesn't bring enough CURRENT (ha ha) to the barn to have a 20A/240V circuit, I will need to run another line from the house panel to the barn, and install another subpanel in the barn, I suppose.
My question is, can I combine two legs of 120V at the house to give 240V and then run the 240V current through a new underground line to the barn? Or must I run another 40A or 50A of 120V to the barn, and then combine the legs in the barn to give 240V?
It seems like if I could run 240V from the house to the barn, I could use lighter wire...does anyone know if this is an option that will meet Virginia Code?
Thank-you for any advice.
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Colonel wrote:

Is this sort of work-around common in the USA?
My arc welder in my barn uses 8kW, just on its own...
My local electircal distribution company only charged 75GBP to drop a 3phase (415v 80A, IIRC) supply from the pole in the field next door, right to a meter in the barn.
--
Sue



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While the upgrade is possible there are a number of issues that you need to clarify to consider this change.
You state that you have a 120 volt 50 amp circuit to the barn. For this to be legal per the NEC the conductors need to be at least #6 copper. Is this the case?
How many conductors are currently being run from the panel to the barn? The minimum for the 120 volt, 50 amp circuit is 2 #6 and 1 #8 ground.
If there are additional conductors it may be possible to legally install the upgraded service without adding conductors.
What would be needed for a 120/240 volt subpanel in the barn would be a three conductor cable with ground sized to work with the breaker in the main panel. Subpanel breakers would typically be a 20 amp, 240 volt for the saw and and a 30 amp 240 volt for the compressor. You will probably be wanting to install several 120 volt 20 amp outlet circuits also.
Minimum sizes for the subfeed and breaker should be as follows. The wire sizes given have been increased one size to minimize the voltage drop due to the distance.
Breaker Wire 240 volt, 30 amp, 3 #8 + 1 #10 Ground 240 volt, 50 amp, 3 #4 + 1 #8 Ground
If this can be accommodated with your current wiring, good. Otherwise I would install a completely new cable run.
Also if it has not already been done I would install a new ground rod at the barn to extend the safety ground to that area. Note that the neutral and ground should not be tied together at the subpanel.
Master Electrician (ret)
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Wow! Thank-you Dave! It sounds like you have it nailed!
It also sounds (unfortunately) like I'm in far over my head...time to call the electrician again!
Thanks again.
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Colonel wrote:

Time to consider a single 60 amp sub-panel for both the 240 and the 120 loads. No matter what you do, you'll need a 120 foot trench (unless you already have conduit and can fish new wiring through) at least 18" deep, and non-metallic conduit. With all that labor, it would be a shame to find you have to do it again in the future.
With a 60 amp sub and # 6 wiring, you can run your 120 V lighting and your 20 amp compressor at the same time, and minimize the voltage drop in the wiring. You'll also have plenty of capability to expand, so you can run your (future) dust collector and table saw and compressor simultaneously, with no need for any lockout switch.
You can consider adding 3-way switch wiring to light the path between the house and the shop and control it from either end, and audio circuits like telephone, intercom, whatever as long as you have that open trench.
Ed
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Leave in a draw wire for the future in case.
--
Stuart Winsor

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wrote:

What do you have for wire now, that will determine what you can do without digging. If you have 3 #6 or larger you can do this. Unitl your AHJ adopts the 2008 code and if they also adopt the removal of 250.32(B)(2), you can use the same wire for neutral and ground (bonding the neutral in the sub)
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