On Mon, 10 Nov 2008 22:48:27 -0500 email@example.com wrote:
| On 11 Nov 2008 02:01:39 GMT, firstname.lastname@example.org wrote:
|>|>If you are building a data center for a large number of computers (lots of
|>|>and server sized PCs, with all the network infrastructure), and this involved
|>|>a large amount of power, and this were in a location where the standard user
|>|>line-to-neutral voltage is 120V, but you could get a line-to-neutral voltage
|>|>of 240V by special order, would you choose the latter to reduce wiring costs
|>|>and I2R losses? If the size matters, where would the point of indecision be?
|>| No question, get 240v wired L/L. That eliminates noise on the neutral
|>| and harmonic problems. Mainframe computer rooms didn't even bring a
|>| neutral into the panels back in the big iron days. Everything was
|>| Virtually all PC system units will switch to 240 and you can order
|>| 240v monitors and other equipment.
|>But not 240V wired L-N (as in 416Y/240) ?
| Why would you want to introduce the noise and harmonic problems you
| get with a neutral load?
These are not really eliminated by L-L loads. All L-N does is concentrate
the issues when you have a shared neutral. You need to have a panels that
handle large neutral current, and wiring upstream from there accordingly.
Branch circuits would have separate, non-shared, neutrals.
|>Many mainframes I worked on back in the day used delta wired motor-generators
|>and produced 400 Hz (I never found out the voltage at this point) for the CPU
| The voltage on IBM systems was 208 on the 400 hz supply
Nice to know. Since it was a derived system, they could have chosen to make
it be whatever they wanted to design their power supplies for.
|>For in home use, where the options are 120 L-N or 240 L-L, I'd like to go with
|>the latter. Proper surge protection and UPS systems are hard to find for that
|>configuration at home usage scale.
| They are availab;e in the commercial market but not normally in the
| residential market
And probably for 208 instead of 240.
| These days data centers are not particularly big power hogs. The Ramac
| racks were the biggest load (A buttload of 3.5" hard drives in a rack)
| Now that multi T-byte drives are in the marketplace, they don't need
| that many drives. I pretty good size "data center" will go in a
| closet. That is one reason I got out of the business. You don't have
| to be an engineer to design a room with two or three racks in it and
| you don't have to be very skilled to fix a machine that has a blinking
| red light on the bad card.
The largest one I worked on was 3600 machines back then when I left in 1997,
and reportedly has broken the 10000 machine barrier. I'm sure it mostly blade
type technology these days, so it could well be a lot less power than before.
But it's no closet operation. Other places I worked on included ISPs with as
many as 20 rows of racks (lots of routers, dial-in boxes, servers, etc).
When I say "big", I don't mean a closet. Most businesses can put their "data
center" in a closet if they are pressed for space (and many more even if not).
I'd rather spread things out if I can for the smaller ones, especially if *I*
am the one that has to get into the machines to do work :-)
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