Stupid AC wiring question (220-ish Volts...)

Mouse mouse at Rodents-Montreal.ORG
Thu Feb 5 22:16:18 CST 2015

> I picked up a "large" machine* (for certain definitions of large)
> that's currently configured for 220-240V; [...]
> [...]
> So: since all this stuff is in the basement, I'm just about 15 feet
> away from the dryer, [...] since this house was built well before
> 1996 and so the outlet is not grounded; [...]

That does not necessarily follow; I know of at least one house built in
the late '70s that had proper grounding all through it.  (My parents'
place - they and us (then-)kids built it and I learnt about house
wiring from them in the process.)

> there's a neutral lug and two hot lugs (I assume two 120V A/C lines
> out of phase?)

Yes; its all but certain that it's two 120V lines 180 degrees out of
phase with one another, giving 240V between the two, both because
that's usual for electric dryers in North America and because that's
usual for residental power in North America.  (You don't actually _say_
you're in North America, but that's the only place you're likely to be
for which the scenario you describe makes any sense.)

> [...]
> But then, I'm a rank amateur when it comes to house wiring and A/C
> and power supplies and all of that so I thought I'd ask the cctalk
> collective whether this can be made to work [...]

It certainly can be made to work - though finding a decent ground might
be interesting.  It borders on certain that the dryer outlet outlet can
feed it what it wants, if either (a) it doesn't care about ground, (b)
the outlet's box actually is grounded, or (c) you can find a suitable
ground elsewhere nearby.  You probably could even get away with
connecting the machine's ground to the neutral, though I wouldn't be
comfortable doing that for more than a few minutes of testing - ground
is separate from neutral for good reason.

However, there are a lot of ways it can go wrong, and many of them have
disturbingly high chances of being fatal (eg electrocution hazard) or
severely damaging (eg fire hazard) - there's a lot of power lurking
behind that innocuous-looking dryer outlet.  While they are not hard to
avoid for someone used to such things, I would not recommend that "a
rank amateur" try it without someone knowledgeable and experienced on
hand to, at a minimum, give things a look-see before you give it the
juice.  This is definitely a place where Pope's famous line about a
little learning being a dangerous thing is accurate - many things in
this hobby you can fiddle with and the worst that'll happen is you fry
the hardware you're playing with, but mains power, in contrast, can
quite literally kill you on the spot or burn your house down.

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