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Old 05-10-2011, 04:42 PM   #46
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How To Determine 30A Outlet's Voltage?


I like the term: split phase

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Old 05-10-2011, 05:32 PM   #47
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How To Determine 30A Outlet's Voltage?


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Originally Posted by darkaspitch View Post
Really?...??? This is what I must do? I would have thought I needed to use either black or red into X or Y and then definitely white into the opposite X or Y, no?

No, definitely not. That would give you 120V. Each "hot"/"live"/"ungrounded conductor" is at 120V relative to neutral, and 240V relative to the other hot conductor (they are out of phase).

Doesn't "hot" mean "positively charged"?

No. This is not DC power. I would suggest that you read up on AC circuits - things will make much more sense. Each hot has a voltage that cycles from +170V to -170V and back 60 times per second. The average of the absolute value of this voltage is 120V. At any instant in time, the voltage on one hot conductor is the opposite of the voltage on the other hot conductor. Thus, the voltage between the two conductors varies from +340V to -340V, and the average of the absolute value of that is 240V.

And doesn't a "circuit" need a hot and a neutral wire to function properly?

No. Why would it? What are you envisioning? How do you think it works that leads you to conclude this? You should probably review the basics of electrical circuits (DC and AC) to get a handle on this.

You can't connect two positives ends to a light bulb and light it up - why could I connect two positive ends to my computer PDU and have it give any power?

They are not both positive. When one is positive, the other is negative, and vice versa.

Sorry for all of the questions!
No problem.
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Old 05-10-2011, 06:43 PM   #48
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How To Determine 30A Outlet's Voltage?


Each "hot"/"live"/"ungrounded conductor" is at 120V relative to neutral, and 240V relative to the other hot conductor (they are out of phase).

They in fact are not out of phase, it is single phase. It is the way the POCO's transformer is center tapped to give 120 from one leg to the CT and 240 across the full output of the transformer.


Each hot has a voltage that cycles from +170V to -170V and back 60 times per second. The average of the absolute value of this voltage is 120V. At any instant in time, the voltage on one hot conductor is the opposite of the voltage on the other hot conductor. Thus, the voltage between the two conductors varies from +340V to -340V, and the average of the absolute value of that is 240V.

Almost correct: the voltage does vary from +340 to -340 peak to peak and a meter measures the RMS (root mean square) of the peak voltage. This equates to the average power that can be delivered by the circuit. To go from Peak voltage to RMS voltage multiply the peak voltage by .707 (340 x .707 = 240) (rounded off). For those who remember their High School trig - .707 is the cosine of a 45 degree angle.


You can't connect two positives ends to a light bulb and light it up -


You in fact can connect a light bulb to the 2 hot legs and light a light bulb. If it is a 120 volt light bulb, it will only light for a very short time before it burns out. And a 240 volt light bulb will work very well across the 2 hot legs of a 240 volt circuit.


I Like Nap's suggestion of split phase because in fact that is what it is- split single phase.
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Old 05-10-2011, 07:37 PM   #49
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How To Determine 30A Outlet's Voltage?


Each "hot"/"live"/"ungrounded conductor" is at 120V relative to neutral, and 240V relative to the other hot conductor (they are out of phase).

They in fact are not out of phase, it is single phase. It is the way the POCO's transformer is center tapped to give 120 from one leg to the CT and 240 across the full output of the transformer.


The two hots carry the same waveform, phase shifted by 180 degrees. Thus, they are out of phase. That does not imply that this is a polyphase system. It's not. A polyphase system has signals with at least two different phase angles that are not merely the inverses of one another. Read up on the meaning of phase in this context:
http://en.wikipedia.org/wiki/Phase_(waves)

And see figure 2 in this article, showing the phase diagram for the split-phase system:
http://en.wikipedia.org/wiki/Split_phase

The two hots are out of phase, but since they both lie on the same axis, it is not a polyphase system. If the phase shift were anything other than 180 degrees, it would be polyphase.

Each hot has a voltage that cycles from +170V to -170V and back 60 times per second. The average of the absolute value of this voltage is 120V. At any instant in time, the voltage on one hot conductor is the opposite of the voltage on the other hot conductor. Thus, the voltage between the two conductors varies from +340V to -340V, and the average of the absolute value of that is 240V.

Almost correct: the voltage does vary from +340 to -340 peak to peak and a meter measures the RMS (root mean square) of the peak voltage. This equates to the average power that can be delivered by the circuit. To go from Peak voltage to RMS voltage multiply the peak voltage by .707 (340 x .707 = 240) (rounded off). For those who remember their High School trig - .707 is the cosine of a 45 degree angle.

Yeah, my simplification of RMS measurement was intended to not confuse the guy. The average of absolute value is actually slightly less than the RMS value (about 10% for a sine wave). RMS is really a calculation of the standard deviation of the voltage samples, plus any DC offset if it's not an AC-only measurement. This does not represent the "average power that can be delivered by the circuit." Not sure what that means exactly, but a voltage measurement alone does not convey any information about power or the circuit's capacity. It does represent the equivalent DC voltage that would dissipate the same power in a resistive load. The .707 (1/sqrt2) relationship between peak and RMS values is handy, but only applies to pure sine waves.

You can't connect two positives ends to a light bulb and light it up -

You in fact can connect a light bulb to the 2 hot legs and light a light bulb. If it is a 120 volt light bulb, it will only light for a very short time before it burns out. And a 240 volt light bulb will work very well across the 2 hot legs of a 240 volt circuit.

He was calling the hot conductors "positive", and confusing himself. You can't connect two positive leads (at the same potential) to a light bulb and light it. Since the hot conductors are never both positive at the same time, it works.

Not sure why the whole split-phase-isn't-polyphase thing is so confusing.

Last edited by mpoulton; 05-10-2011 at 07:38 PM. Reason: formatting
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Old 05-10-2011, 10:26 PM   #50
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How To Determine 30A Outlet's Voltage?


Nap have one answer correct a split phase but for me where I am now we call them centre tapped phase due we know the voltage between the centre useally half in most case but if the word " centre " is disappared then it become standard tapped transfomer the voltage will varies depending on where you land the tap is.

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Old 05-11-2011, 02:47 AM   #51
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How To Determine 30A Outlet's Voltage?


Thank you so much for the replies everybody. You have created a new life long member!

I will be creating the adapter tomorrow (as well as hopefully picking up the PDU) so I will post pictures when it's all working soon.
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Old 05-12-2011, 05:44 AM   #52
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How To Determine 30A Outlet's Voltage?


Ok guys, here are the pictures as promised: http://imgur.com/a/o8BXn

As you can see I have:
- taken a standard 4 pronged North American dryer plug
- stripped the wires
- sealed off the white (neutral) wire
- connected the red + black wires to X and Y on my L6-30 female socket
- connected the bare wire to the green/ground terminals on my L6-30 female socket

I then screwed everything into place. Total cost about $60 CAD/USD.

I now have a 4 prong dryer plug (14-30) to 3 pronged server plug (L6-30) adapter so that I can plug my server equipment into my dryer outlet.

...right?! Can I get a confirmation from someone (or two!) that I am not going to burn my house down? There will be ~30A and 240V coming out of this socket now and it's not a fire hazard or anything?

Thanks again everyone!
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Old 05-12-2011, 05:51 AM   #53
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How To Determine 30A Outlet's Voltage?


Looks good to me! Just remember to use only 240V devices on that distribution thingy.
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Old 05-12-2011, 09:12 AM   #54
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How To Determine 30A Outlet's Voltage?


That's correct.
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Old 05-14-2011, 01:50 AM   #55
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How To Determine 30A Outlet's Voltage?


Eureka!

It works!

Thanks a ton everybody.

I have had a computer up and running off of the PDU for the last 15 minutes and everything seems good. No hot wires or anything.

It just so happens that most every PSU (power supply unit) made for computers these days can handle anywhere from 100 to 240 volts. Computers are a global enterprise.

One problem I encountered when adding the female l6-30 socket onto the dryer plug was that since the dryer cord was circular, I was not able to fully close the end of the cable enclosure piece. I screwed the end so tight originally (thinking it had to be completely shut/together) that I ended up breaking through each individual wire's insulation casing and mashing the bare copper wires together. So obviously I cut off that piece and re-did the entire connection. If I had of plugged it in without double checking the wires after I added the plug, it would have shorted immediately.

I will report back if anything else plagues this setup!

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