5 Feb
2015
5 Feb
'15
8:45 p.m.
On 2015-Feb-05, at 8:16 PM, Josh Dersch wrote:
On 2/5/2015 8:00 PM, Brent Hilpert wrote:
If you are convinced it's wired for 240 then yes, you should be able to wire the hots
as you say.
You MUST somehow GND the chassis however, either:
- confirm the dryer receptacle neutral is adequately tied to ground, or
- if the dryer receptacle is wired with armored/BX cable that may be the ground, or
- waterpipe confirmed as adequate ground, or
- connect to a confirmed ground on a normal 120V outlet, although there is a warning
involved in such a scenario,
if the ground conductor is much smaller than the hot conductor, a fault can blow the
ground conductor open,
at which point you have no ground and a live chassis. In theory the circuit breaker
should open before the ground blows, but that's theory.
Alternatively, if you'd like to examine rewiring the machine for 120, we could look at
that, via photos, etc.
(First question would be what are the target power/VA requirements, to consider whether
it's worthwhile on 120).
On 2015-Feb-05, at 7:28 PM, Josh Dersch wrote:
Yes, there's high resistance between both line inputs and chassis ground, higher than
my DVM can measure.
And, let's face it, I'm spoiled and I
demand instant gratification and I'd like to know as soon as possible if this machine
is a basket case or not.
So: since all this stuff is in the basement, I'm just about 15 feet away from the
dryer, which at first glance runs off an outlet that meets my needs. I even have a NEMA
10-30p plug here that I could wire up to the existing power cable for the computer. But
looking into it I have doubts that it's actually that simple; in particular since this
house was built well before 1996 and so the outlet is not grounded; there's a neutral
lug and two hot lugs (I assume two 120V A/C lines out of phase?) and I'm guessing that
might not sit well with the power supply in this computer.
Yes, the two hots are
120VAC to neutral each, 180 degrees out of phase, giving 240 between the two hots.
Yes, you should be able to use those two hots to power the target machine, as long as the
240 input lines for the target are isolated from ground. Normally this will be the case, I
just mention it in case there is some strange circumstance where one side of the target
input is connected to ground. Measure the R between chassis and the two line inputs, it
should be very high R on both.
Is the existing plug/line input to the the target 3-wire (2 hot + GND) or 4-wire (2 hot +
neutral + GND)?
And have you confirmed that one wire IS GND/chassis? (it could conceivably be 2 hot +
neutral).
The existing plug is a 3-wire affair, white/black for hot and green ground using a NEMA
6-20P plug. I have confirmed that ground is wired to the chassis (with the DVM.)
So is it as simple as wiring the white/black wires up to the HOT terminals on the NEMA
connector and leaving the ground disconnected (from the "netural" pole on the
NEMA... or should that be connected as well)? Anything else I should watch out for?