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Old 05-09-2011, 12:16 PM   #31
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How To Determine 30A Outlet's Voltage?


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Is one of the breakers reserverd to the 120V prong and the other reserved for the 240V prong? Thus giving me me 30A available at 240V or 7,200W maximum?

OR (hopefully) is one of them reserved for the 120V prong and they are both used simultaneously for the 240V prong? Thus giving me 60A available at 240V or 14,400W maximum? As according to ohm's law, when you increase the voltage, you also increase the amperage correct? But wait.. then wouldn't I require a 60A plug + wire to use it to it's full (80%) potential? So confused....
With respect to ground, both hot prongs (call them red and black) are 120 volts (each). With respect to each other (the heater connected to the hot prongs and not the neutral) you get 240 volts.

One breaker is for the red; the other breaker for the black.

A higher voltage does not imply more amperes unless the heater or other device wants more amperes. All the equipment including the breakers is still 30 ampere rated given the size #10 wires.

You can have one allotment of 240 volts at 30 amps, or two allotments of 120 volts at 30 amps (red and white; black and white), or different combinations in between for example drawing 240 volts at 10 amps together with two allotments of 120 volts at up to 20 amps each where in each case each hot wire (red or black) is supplying no more than 30 amps. (30 amps for short periods of time or 24 amps for long periods of time.)

If you draw just 20 amps from red and white, you may not draw 40 amps from black and white to make 60 with; you are still limited to 30 amps on each side.

Yes, theoretically, according to Ohm's Law (volts across any part of a circuit equals amperes flowing through times the resistance of that section), if you double the voltage to some device, the current drawn will also double if the resistance stays the same. In practice the resistance does not stay the same for example for a heater, the resistance increases as the heating element gets hotter, and in turn the current goes down.

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Last edited by AllanJ; 05-09-2011 at 12:30 PM.
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Old 05-09-2011, 01:21 PM   #32
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How To Determine 30A Outlet's Voltage?


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AllanJ;644493]With respect to ground, both hot prongs (call them red and black) are 120 volts (each). With respect to each other (the heater connected to the hot prongs and not the neutral) you get 240 volts.
I know this may come across as picky and anal but, there is not an accurately determinable voltage to ground. The voltage would be from the neutral to the hot legs. The only reason it reads as it does when testing from hot to ground is due to the bonding of the ground and neutral at the service disconnect. While you should have an identical reading to either the neutral or ground, it is only because you are reading to the neutral through the ground conductor.

I told you it was picky but that's just the kind of guy I am.
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Old 05-09-2011, 01:29 PM   #33
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How To Determine 30A Outlet's Voltage?


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I know this may come across as picky and anal but, there is not an accurately determinable voltage to ground. The voltage would be from the neutral to the hot legs. The only reason it reads as it does when testing from hot to ground is due to the bonding of the ground and neutral at the service disconnect. While you should have an identical reading to either the neutral or ground, it is only because you are reading to the neutral through the ground conductor.

I told you it was picky but that's just the kind of guy I am.
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Old 05-09-2011, 02:48 PM   #34
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How To Determine 30A Outlet's Voltage?


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...swooooooosh.... (way over my head) but thanks!

Edit: after re-reading, I think I may have got some of it!?

So I can plug a 10A voltmeter into any wall receptacle and it will give me a proper reading?

And basically what you are saying is... that if my entire apartment is 120 volts, then the dryer receptacle is most likely 120 volts as well..?

There are two dryer plugs actually, so I assume it is 120 volts coming out of there... darn.
you are not checking amps so dont worry about the amp rating of the multimeter. Just make sure you have it on the AC Voltage setting to get a voltage reading.
Just because most of your apartment is 120, it doesn't mean that everything is. Your range and dryer will be 240, unless you have a natural gas or propane dryer, then it is just 120v

Last edited by kawimudslinger; 05-09-2011 at 02:50 PM.
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Old 05-10-2011, 03:23 AM   #35
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How To Determine 30A Outlet's Voltage?


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you are not checking amps so dont worry about the amp rating of the multimeter. Just make sure you have it on the AC Voltage setting to get a voltage reading.
Just because most of your apartment is 120, it doesn't mean that everything is. Your range and dryer will be 240, unless you have a natural gas or propane dryer, then it is just 120v
Natural gas being fed into a hot metal box and then attaching a 30A current to it sounds more like a bomb than a dryer!

Ok guys - thank you again for all of your help - I went out today to purchase a L6-30 female socket end and a NEMA 14-30 male plug with cable attached (just like what is plugged into my dryer now).

I have posted pics to imgur.com of what I have just purchased: http://imgur.com/a/11M6h

Now can anybody direct me as to what wire goes where exactly to get 240V and 30A coming out of that L6-30 female socket?

There are 3 connectors on the L6-30 female socket. One is marked X, Y, and G. I assume that G is the un-insulated ground wire in this particular cable. But what do I use for X and Y? Red, Black or White?

This product's sales page (which is what I am trying to make) seems to tell you which wire goes where on their plug... but how can I tell which color relates to which letter on the 14-30 dryer cord? Am I going to have to plug it in and test it with a voltmeter? Sounds kind of dangerous that...

Should I make this into a separate post? Since this one has derailed so magnificently from it's original title?
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Old 05-10-2011, 04:12 AM   #36
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How To Determine 30A Outlet's Voltage?


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Now can anybody direct me as to what wire goes where exactly to get 240V and 30A coming out of that L6-30 female socket?

There are 3 connectors on the L6-30 female socket. One is marked X, Y, and G. I assume that G is the un-insulated ground wire in this particular cable. But what do I use for X and Y? Red, Black or White?
Black and red are hot. Those two connect to X and Y (they are interchangeable). Green is ground. It goes to G, the terminal that is marked green. White is neutral, and is not used. Cut it off short enough that it doesn't touch the other connections.

I'm not sure this has been covered well in the thread yet: you realize that you will have only 240V available from your power distribution thingy, not 120, right? Since there is no neutral, you cannot connect 120V loads. Every socket will be 240. This is probably fine for servers and such, as long as you set all the power supplies for 240V input. Peripherals and accessories like monitors and networking gear may be tougher since not all of them have multi-input power supplies.
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Old 05-10-2011, 06:59 AM   #37
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How To Determine 30A Outlet's Voltage?


Ooh UK wiring seems so much easier. I'd imagine that 240v is your version of multiphase wiring i.e. two lives and one neutral or do you have two neutrals too on a 240v supply?
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Old 05-10-2011, 07:14 AM   #38
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How To Determine 30A Outlet's Voltage?


You can look at it as 2 phase, though it is not, but it's the easiest way to understand it. The two hots come out of the transformer at 240 volts, and the neutral comes out from the center of the transformer so from neutral to hot it's 120v. While one hot is at 120v the other is at -120v from neutral.
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Old 05-10-2011, 07:43 AM   #39
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How To Determine 30A Outlet's Voltage?


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Ooh UK wiring seems so much easier. I'd imagine that 240v is your version of multiphase wiring i.e. two lives and one neutral or do you have two neutrals too on a 240v supply?
2 lives (ungrounded) and 1 neutral (grounded, but not to be confused with grounding)

We Americans are so silly...
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Old 05-10-2011, 01:27 PM   #40
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How To Determine 30A Outlet's Voltage?


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Ooh UK wiring seems so much easier. I'd imagine that 240v is your version of multiphase wiring i.e. two lives and one neutral or do you have two neutrals too on a 240v supply?
When running a circuit to a device that uses 240 volts only you do not need to include any neutral. A 2 conductor cable with a ground wire will suffice.
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Old 05-10-2011, 02:32 PM   #41
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How To Determine 30A Outlet's Voltage?


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Black and red are hot. Those two connect to X and Y (they are interchangeable). Green is ground. It goes to G, the terminal that is marked green. White is neutral, and is not used. Cut it off short enough that it doesn't touch the other connections.
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?

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

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

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?

Sorry for all of the questions!
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Old 05-10-2011, 02:36 PM   #42
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How To Determine 30A Outlet's Voltage?


Straight 240v, which is what your PDU is wired for, does not have a neutral at all. it is strictly a line to line load.

Don't think of household voltage as positive and negative. you have 3 wires from the power company, 2 hots(Line 1, Line 2) and a neutral(grounded). Between the two hots(Line 1 to Line 2) you have a voltage potential of 240v, between either hot and neutral(grounded)(Line 1 to N, Line 2 to N), you have a potential of 120v.

the box tells you exactly how to connect your cord cap. Black to X, Red to Y, Green/Bare to Green/G cut off the white wire in the dryer cord.

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Old 05-10-2011, 02:57 PM   #43
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How To Determine 30A Outlet's Voltage?


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You can look at it as 2 phase, though it is not, but it's the easiest way to understand it. The two hots come out of the transformer at 240 volts, and the neutral comes out from the center of the transformer so from neutral to hot it's 120v. While one hot is at 120v the other is at -120v from neutral.

I could be wrong. But I believe poly phase is a more accurate description.

They haven't used a true 2 phase anywhere near here for a long long time now.
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Old 05-10-2011, 03:38 PM   #44
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How To Determine 30A Outlet's Voltage?


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Doesn't "hot" mean "positively charged"?
no

Quote:
And doesn't a "circuit" need a hot and a neutral wire to function properly?
no

Quote:
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?
AC power has no positive nor negative as far as the way you are speaking of.
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Old 05-10-2011, 04:01 PM   #45
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How To Determine 30A Outlet's Voltage?


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I could be wrong. But I believe poly phase is a more accurate description.

They haven't used a true 2 phase anywhere near here for a long long time now.
Not poly phase which is 3 or more current carrying conductors.

http://en.wikipedia.org/wiki/Polyphase_system

Single phase is the correct term.

The POCO uses a stepdown transformer to reduce the primary high voltage to 240 volts at the end taps of the secondary side of the transformer. This 240 volts is the single phase. This transformer is also center tapped. The center tap is grounded at the transformer. The service is delivered to your home on 3 wires, the 2 ungrounded conductors (2 hot legs) and the grounded conductor (the neutral). Measuring across the 2 ungrounded conductors (hot legs) you see the full secondary voltage of the transformer - 240 volts. Measuring from the grounded conductor to each ungrounded conductor you see 1/2 the secondary transformer voltage -120 volts.

Do not confuse the grounded conductor (neutral) with the grounding conductor( bare or green wire). The grounding conductor is developed at your home by means of connection to ground rod(s) or metallic water piping. The confusion for many is that the grounded conductor (neutral) and the grounding conductor (ground) are bonded together at the first disconnect point (usually the main breaker).

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