IANAE, but...

15A is limited by the size of the wire (#14) in the wall.  Your outlets are
all parallel after that.  15A is all you get for *all* outlets.  If you put
a larger breaker in the mains w/out changing out the wiring you will get a
visit from the fire department.

The dryer outlet is your best bet.  240 is essentially 2@120 lines 180
degrees out of phase, so it's not really tied to neutral the same way 120
is, but it is still tied on that third pin.  Neutral is ground for all
intents and purposes, which kind of makes it 2-phase with respect to the
neutral line.  I'm a little hazy on that one.
 
Some of the tools in my shop run on 220 and they are wired no differently
than the dryer is.

DougM

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
PicDude
Sent: Tuesday, October 17, 2006 1:03 PM
To: Microcontroller discussion list - Public.
Subject: [OT]: 110VAC and 220VAC residential power questions

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.
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