On Tue, Oct 17, 2006 at 03:02:38PM -0500, PicDude wrote:

> Hi all,
> 
> I am looking at purchasing a large-ish CNC mill, but these generally require 
> 220VAC 3-phase, though some require 220VAC 1-phase.  At the same time, I'm 
> also looking into renting an apartment, but finding an attached garage (so I 
> can get 220V from the panel or dryer outlet in the garage) seems to be iffy.  
> Detached garages only have 110V, and I'm not sure if this will be a 
> show-stopper.  This is in the USA, btw.
> 
> First, 220V 3-phase is not a problem to get from 220V 1-phase, using a phase 
> converter.  But 220V 1-phase seems to be a problem...
> 
> If I get 220V from a dryer outlet, I understand that there are grounding 
> differences (dryer outlets are grounded to neutral?) that could be a 
> show-stopper in using the mill, which expect to be grounded to earth.  Is 
> there a fix for this?
> 
> If I get 220V from a breaker panel, is it the same as the dryer outlet?  Or 
> would I be able to get properly-grounded 220V there?
> 
> If I use the 110V outlet, I can step that up using a transformer, but I'm 
> limited to 15A.  That would be ~7A or less at 220V, factoring in transformer 
> inefficiency.  And the mill's spindle motor needs more than that.  However, 
> I'm wondering why the power outlet is limited to 15A?  Is it because of the 
> wiring?  If there are multiple outlets in the garage, and each is rated to 
> 15A, then I should be able to find the "first" outlet in the garage (where 
> the supply wires come into the garage) and wire up a beefier outlet at that 
> point.  The wiring up to that point should be able to handle more current -- 
> theoretically 15A x Num_Outlets.  Is this correct?  I'd also need to change 
> the breaker for this circuit.
> 
> I don't mind getting an electrician in there to add an outlet and run some 
> lines from the breaker panel, etc, but I can't get them to run larger lines 
> into the garage without raising some eyebrows.
> 
> Cheers,
> -Neil.
In the US house wiring is typically brought in from the pole as
center tapped 220V.The center tap is connected to earth ground and 110is
derived from one side of the secondary winding and the center tap. The 220 is
derived from the entire secondary winding and is only 220 across the
winding not to ground.Where dryer outlets are grounded depends on the
local wiring code, it could be either neutral,earth ground or both .The
15A restriction could be because of wiring,outlet capacity or both.You
might check the local library for a copy of the NEC handbook.It can
answer many of your questions with specific examples and many towns base their 
wiring codes on it.
Ray Warren	
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