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RE: 120V from 250V 3 phase?

To: "Brian Kemp" <bk13@earthlink.net>, <shop-talk@autox.team.net>
Subject: RE: 120V from 250V 3 phase?
From: "Ron Schmittou" <rs1121@earthlink.net>
Date: Thu, 2 Oct 2003 10:16:25 -0500
Your right about the three hot legs and one ground.  Each of the hot legs is
a different phase (power generation companies produce 5 phases per
generator)  Normally I have always called this a 440 circuit - no matter
which two hot legs you tap will give you 220v - so you have two 220v taps =
440v.  The third phase is usually marked coming into your panel, and in my
experience you don't want to use this one - most electricians call it the
wild leg because it is generally not as regulated as the first two are, if
you measure the lines coming in to the box you will usually see the
following:

Phase 1 - 110 to ground
Phase 2 - 110 to Ground
Phase 3 - 200 - 250 to ground

The trick will be to identify which phase is which line on your outlet.
Once you have done that you can make a special cord / outlet box that has
one line to the phase 1 and both the neutral and ground wire going to the
ground side of the original outlet.  Most people cringe at wiring the
neutral and ground together, but electrically it makes no difference - they
are always wired together in the breaker panel anyway (unless you are
running an isolated ground setup)

Good luck and wear rubber shoes!


Ron Schmittou
APEX Computer Service
(325) 690-9509 Direct - Forwards to Cell/Voice Mail
(325) 690-9514 Direct Fax
(325) 676-9507 Main Line
(325) 676-9510 Main Fax


-----Original Message-----
From: shop-talk-owner@autox.team.net
[mailto:shop-talk-owner@autox.team.net]On Behalf Of Brian Kemp
Sent: Wednesday, October 01, 2003 6:25 PM
To: shop-talk@autox.team.net
Subject: 120V from 250V 3 phase?



I have a power problem in the office I'm going to be moving into
shortly. I have a rack of computer equipment that needs a dedicated 120V
20A circuit that doesn't exist in the new location. What I do have is a
twist lock 250V 20A 3 phase outlet 4 wire outlet. According to
http://www.diallighting.com/spec0027.htm, it is a NEMA L15-20 outlet.

I'd like to make a cord to plug into this outlet and get a standard 120V
receptacle that I can plug the computer rack into. I expect that this is
possible, but hope someone out there can confirm that it is safe for the
equipment.

I'd try and use an electrician to put on the proper outlet, but the
building is less than helpful and it will take more than a month to
coordinate funding transfers, insurance requirements, and approval.
Management told me I'm moving Monday.

The outlet has 4 slots:
1. prong like a bent "L"
2. narrow slot
3 and 4. wider slots

Thinking a 3 phase system needs 3 "hot" lines leads me to believe I
either have a neutral or ground as the 4th wire. While I know neutral
and ground are probably connected at the breaker box, I'm not going to
chance a bunch of expensive computer equipment on a poor power supply.
So as it is now, I don't think this will work.

I've done enough electrical work to understand what I'm doing, but would
like confirmation from one of the smarter people about this idea. I
looked for a UPS to go into the outlet, but didn't find any with a 3
phase input.

Thanks,

Brian Kemp





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