Cray J932SE (was Re: Straight 8 up on Ebay just now)

[Jon Elson]

On 07/19/2016 01:41 PM, Fred Cisin wrote:
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> 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 
transformers.

These systems are out of favor, but you still run across them in older 
mixed-use buildings.

Jon
> 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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