Negative 48 Volts DC

On Mon, 27 Jan 2020 05:40:04 +0000 (UTC), snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) wrote:


You are right, brain fart on my part.

Yup except it is really the same basic transformer, they just don't connect the center tap.
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On 1/26/20 6:22 PM, snipped-for-privacy@aol.com wrote:

I ran across something while reading ANSI C84.1 Electrical Power Systems and Equipment ? Voltage Ratings (60 Hertz).
Table 1 note d has the following to say about 208Y/120:
(d) A modification of this three-phase, four-wire system is available as a 120/208Y-volt service for single-phase, three-wire, open-wye applications.
I think that exactly describes some of the cabinet distribution units (power strips) at my office; two hots (lines) and ground, for a 208 volt single-phase + ground power feed.
In hindsight, it sort of makes sense that the small number is first, thus indicating single phase, seeing as how it really is feeding a single phase to the equipment.
--
Grant. . . .
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On Sat, 21 Mar 2020 00:42:59 -0600, Grant Taylor

That is the convention. It is similar to 240/120 (3 phase center tapped delta) and 120/240 (single phase center tapped 240). In fact it can be the same service with the 3d phase added by installing one more transformer (open V delta or red leg delta). To get full rated power you really need a 3d transformer tho. It is not commonly done but I have seen it.
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On 3/21/2020 2:42 AM, Grant Taylor wrote:

Hello, and at my place of employment we have devices such as UPSs and test equipment that require a 208 VAC 50A single-phase service. These circuits are gotten from a breaker panel that has an incoming 120/208 VAC 3-phase, 4-wire service. The single phase 208V service is most often terminated in a wall-mounted receptacle that is physically a larger version of the standard u-ground 120 VAC 15A receptacle. Sincerely,
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J. B. Wood e-mail: arl snipped-for-privacy@hotmail.com

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On 1/26/20 4:09 PM, Michael Moroney wrote:

three phase power for irrigation here in central Nebraska. The Y configuration has 277 volts to ground on all three legs. Two lines in any combination read 480. The corner ground delta has two lines reading 480 volts to ground and between each other. The third line reads 0 volts to ground. The center tap delta has one line that reads 415 to ground. The other two lines read 240 to ground. The hot lines all read 480 in any combination to each other. One of those configurations lets the utility use two transformers to supply three phase.
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On Sun, 26 Jan 2020 20:33:41 -0600, Dean Hoffman

You can use 2 transformers on either delta and the center tapped "delta vee" is very popular for industrial bay type operations where a significant part of the load is 120/240 single phase
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???? 25/1/2020 7:24 ?.?., ? Grant Taylor ??????:


I know two examples:on a common microwave oven, so as to avoid the microwave gun being at high voltage potential, it is earthed and the magnetron filaments are being at negative high voltage potential. Also the diode is being earthed. If the oven is not properly earthed there is the danger of electrocution. Also a modern IGBT inverter welding power supply, when welding all electrodes but aluminium, the electrode is on the plus pole and the ground is negative. When welding aluminium the electrode is negative and the ground is positive.
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I'd like to take a moment to thank everybody that has helped me along my journey to learn about Negative 48 Volts DC. I believe that I have learned, and unlearned, enough to have a acceptable decent understanding.
I have learned that the terms "hot" / "common" / "return" / "ground" do not correlate with the polarity without indication of "negative ground" (what I'm used to) or "positive ground".
In a negative ground system, the "hot" wire will be positive compared to "ground" / "return".
In a positive ground system, the "hot" wire will be negative compared to "ground" / "return".
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