Cray J932SE (was Re: Straight 8 up on Ebay just now)
jonelson126 at gmail.com
Tue Jul 19 14:10:47 CDT 2016
On 07/19/2016 01:41 PM, Fred Cisin wrote:
> 3-phase comes in "delta" or "Wye"("Y")
> some installers don't know the difference!
> I experienced TWO misdone installations. One was an auto garage, and
> resulted in high voltage to the 110 outlets, damaging a bunch of minor
> stuff, such as grinder, space heater, clock, etc.
Oh, it gets much worse. In the US, there is also corner-grounded
open-delta, and center-grounded open delta.
These have some advantages in cases with mixed house/office/industrial
use, but you need to mknow what you have. Corner-grounded open delta has
one of the 3-phase wires grounded. This gives you two hot wires. The
giveaway is that two-pole breakers (or fuses) are used. You get two 230
V hot wires that can be used for any single-phase appliance.
Center-grounded open-delta uses one standard residential transformer,
and has a grounded center tap on that transformer. So, the 3-phase hots
all look normal relative to each other, but have strange readings to
ground. You get two 120 V hot wires, and can run standard home or
office equipment from that, with single or 2-pole breakers. And, you
can run 3-phase loads from the 3 hots.
In most of these cases, the pole equipment is two separate single-phase
These systems are out of favor, but you still run across them in older
> The other was was a PDP installation. After excessive downtime of
> third party disk drive, the community college had sold it to a
> neighboring school district, and bought a roomful of PCs. Microsoft PC
> COBOL and Fortran were crap, but quite adequate for teaching the
> languages, and it was great to have dozens of machines for students to
> use without fear of downtime. PG&E (our power company) agreed to buy
> a new replacement computer, if those involved would go along with the
> fiction that it had been a lightning strike (NOT common here). The
> bad drive ceased to be a problem. Everybody was happy, and PG&E got
> to call it a donation on their taxes.
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