How to wire up a 240VAC receptacle

[Spork Schivago]

I was pointed to this datasheet on page 13: https://cc.cnetcontent.com/vcs/hp-ent/inline-content/SI/6/2/62A6FA74BB1B193CE4C7ABB42D42E37228B9C4A7_source.PDF

This is what they quoted:

Code: [Select]

Input Voltage        Low Line - Rated: 100V - 127V; Min 90V to Max 132V
                     High Line - Rated: 200 - 240V; Min 180V to Max 264V
                     (model 720620-B21 and 720482-B21 supports High Line AC input only)
                     High Line - Rated: 200 - 277VAC; Min 180VAC to Max 305VAC (model 720484-B21 only)

Mine are the 720620-B21.   So do I still insist on those two P9S13A's?

[Monkeh]

I was pointed to this datasheet on page 13: https://cc.cnetcontent.com/vcs/hp-ent/inline-content/SI/6/2/62A6FA74BB1B193CE4C7ABB42D42E37228B9C4A7_source.PDF

This is what they quoted:

Code: [Select]

Input Voltage        Low Line - Rated: 100V - 127V; Min 90V to Max 132V
                     High Line - Rated: 200 - 240V; Min 180V to Max 264V
                     (model 720620-B21 and 720482-B21 supports High Line AC input only)
                     High Line - Rated: 200 - 277VAC; Min 180VAC to Max 305VAC (model 720484-B21 only)

Mine are the 720620-B21.   So do I still insist on those two P9S13A's?

Well, yes, you need 240V. The P9S13A will allow you to use your existing 240V supply.

[Richard Crowley]

I'm trying to understand all this.   How does the 208VAC work exactly?   You say it's phase to phase, that's like my North American Residential Standard Panel Input 240VAC split-phase, right?    240VAC from one 120VAC hot, and from the other 120VAC hot line coming in.   Phase to Neutral is 120. 

Your 120-0-120 split-phases are 180 degrees apart. So when you take "phase-to-phase" you get 120V + 120V = 240V

With 208, you say Phase to neutral is 120.   So the other phase is 88VAC?

Three-phase power is not 180 degrees apart.  The phases are 120 degrees apart 

There is no "other phase" in 3-phase. There are THREE EQUAL phases around the 360 degree phase circle.

Note that 208V is 86% of 240V and the sine of 120 degrees is 0.86  Not a coincidence.

And when a device can run off split-phase, does it combine the two phases internally to get the 240VAC

If by "split-phase" you mean 120-0-120 domestic mains power service, the two "phases" are 240V apart BY DEFINITION.
By connecting from one phase over to the other (ignoring the "neutral") then you have 240V.
You can call that "combining" if you want, but it won't make any sense to an electrician (or electrical engineer).

or does half the circuit use 120VAC and the other half use 120VAC?

240V domestic appliances (water heater, oven, clothes dryer, etc.) have big resistive heating elements that operate directly on 240V
THey make no reference to the "neutral", and there is no "one half" or "other half".
Many older installations didn't even have a neutral wire.  Just L1, L2, and ground.

[Spork Schivago]

I'm trying to understand all this.   How does the 208VAC work exactly?   You say it's phase to phase, that's like my North American Residential Standard Panel Input 240VAC split-phase, right?    240VAC from one 120VAC hot, and from the other 120VAC hot line coming in.   Phase to Neutral is 120. 

Your 120-0-120 split-phases are 180 degrees apart. So when you take "phase-to-phase" you get 120V + 120V = 240V

With 208, you say Phase to neutral is 120.   So the other phase is 88VAC?

Three-phase power is not 180 degrees apart.  The phases are 120 degrees apart 

There is no "other phase" in 3-phase. There are THREE EQUAL phases around the 360 degree phase circle.

Note that 208V is 86% of 240V and the sine of 120 degrees is 0.86  Not a coincidence.

And when a device can run off split-phase, does it combine the two phases internally to get the 240VAC

If by "split-phase" you mean 120-0-120 domestic mains power service, the two "phases" are 240V apart BY DEFINITION.
By connecting from one phase over to the other (ignoring the "neutral") then you have 240V.
You can call that "combining" if you want, but it won't make any sense to an electrician (or electrical engineer).

or does half the circuit use 120VAC and the other half use 120VAC?

240V domestic appliances (water heater, oven, clothes dryer, etc.) have big resistive heating elements that operate directly on 240V
THey make no reference to the "neutral", and there is no "one half" or "other half".
Many older installations didn't even have a neutral wire.  Just L1, L2, and ground.

Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out.   They operate directly on 240VAC.   Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?

Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are.   I take it that's not correct though, I should look at them differently.

If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it?   Because eventually, L1 (240VAC) would be connecting directly to ground.

[IanB]

Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out.   They operate directly on 240VAC.   Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?

Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are.   I take it that's not correct though, I should look at them differently.

If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it?   Because eventually, L1 (240VAC) would be connecting directly to ground.

Let me give you an example. I have a 240 V electric kettle in my kitchen that I have imported from England (I like tea, and I don't want to wait too long for the water to boil).

In the UK, the kettle is wired to a 240 V plug with live, neutral and earth. There is 240 V AC between live and neutral and earth is for safety. It happens that the neutral wire is "neutral", but the kettle doesn't know this. The kettle is a European model that may be sold in many local European markets, and they may not all have the same electrical supply arrangements that the UK has. But I digress...

Here in the USA I have cut off the UK plug and replaced it with a NEMA 6-20 plug (240 V single phase plus ground). In the 6-20 plug I have wired "L" to one pole (L1), "N" to the other pole (L2), and "E" to the ground pin. I plug this into a 6-20 wall socket and I enjoy rapid boiling water from the 3 kW heating element.

The kettle doesn't know that one of the wires isn't neutral, and it doesn't matter because the insulation between the heating element and the rest of the kettle must have been breakdown tested at high voltage to obtain appropriate safety certifications. Some countries in Europe may have a supply where both wires are live just as in North America.

[Richard Crowley]

Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out.   They operate directly on 240VAC.   Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?

No. You may be over-analyzing this.  The first "phase" (L1) goes to one side of the 240V heating element, and the other "phase" (L2) goes to the other side of the heating element.  Simple as that.
The phases "connect" THROUGH the heating element.

Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are.   I take it that's not correct though, I should look at them differently.

That is completely true. But it has nothing to do with getting 240V from 120-0-120 split-phase.

If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it?   Because eventually, L1 (240VAC) would be connecting directly to ground.

No. 240V exists only BETWEEN L1 and L2 (the two "phases" of "split-phase".)
There is no Neutral here.  And Ground is only the safety path to prevent you from being electrocuted, or from setting your house on fire.

[james_s]

It may be easier to visualize this as a transformer with a center tapped secondary, which is exactly what this is. Even simpler you can ignore the center tap because if you want 240V the center tap could be floating or not exist and it would look the same to a 240V load. Consider a single secondary producing 240V, you could ground one end of it to have a Euro-style 240V service, or you could leave it completely floating and have a US style 240V feed. The only difference is that in a real US installation there is a center tap which is tied to ground but that is only relevant when you want to draw 120V from one end or the other to neutral/ground.

[C]

If you split a apple PIE do you get two Pies?
So how do you get two phases?

AC = alternating current

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.[

https://en.wikipedia.org/wiki/Alternator

The hands on a analog clock rotate.
Think of the center of clock as 0 Volts
Max Positive Volts is 12 o'clock.
Max Negative Volts is 6 o'clock.
This makes 3 o'clock & 9 o'clock also 0 Volts as Volts is vertical dimension.

Single phase states you have one hand on clock like hour hand.

60 Hz states that the hand is completing 60 rotations a second.

now when you look at the volt rating is states
RMS

RMS = Root mean square
so if you see "240 Volt RMS"  the peak voltage is 1.414 x 240.
So the 12 o'clock position the max positive = 339.36 volts.

You use the sin table to compute a value based on rotation.

With one end at center you 0 volt connection.
As the hand rotates the other end goes from 12 o'clock around to 6 o'clock and back to 12 o'clock.

So single phase 240 volts is like hour hand rotating.
Going from 9 o'clock (0 volts) to 12 o'clock ( +339.36 volts) and around to 6 o'clock (-339.36 volts) and back to 9 o'clock.
Note that the hand is over 1/2 of the clock so the clock face is 678.72 volts in hight.

 Split-phase is extending the hour hand to other side of circle. When one end of the hand is at 12 o'clock the outer end is at 6 o'clock.
You have three connections. The two hand tips and the center.
Using full clock face you have the clock face 339.36 volts in hight.
Max Positive (12 o'clock) = +169.68 volts
169.68 / 1.414 = 120 volts RMS

Three phase is 3 hour hands 60 degrees apart.

The center of the clock face is the Neutral connecting in above.

The Hour hand tip(s) are the other connection.

Monkeh posted a plot of the voltage vs time which is also a plot of voltage vs rotation.

Have you used a two cell flash light?
The light connects to the two ends of the batteries in series.
Split-phase is adding a connection between the two batteries.

Get out your pencil and paper and make some drawings.

C

 

[Spork Schivago]

Okay, so, for example, my BGA rework station that runs of 120-0-120 from the mains, the heating elements have only two connections, one going in, one coming out.   They operate directly on 240VAC.   Somewhere, in the circuit, before the electricity reaches those heating elements, there must be a connection where the two phases connect to produce that 240VAC, right?

No. You may be over-analyzing this.  The first "phase" (L1) goes to one side of the 240V heating element, and the other "phase" (L2) goes to the other side of the heating element.  Simple as that.
The phases "connect" THROUGH the heating element.

Here, I have always looked at Neutral and Ground as the same, because in my breaker panel, they are.   I take it that's not correct though, I should look at them differently.

That is completely true. But it has nothing to do with getting 240V from 120-0-120 split-phase.

If I were to simply rewire the BGA rework station to have 240VAC going down the L1, ground going down the Earth, and Neutral going down the N, then that would be bad, wouldn't it?   Because eventually, L1 (240VAC) would be connecting directly to ground.

No. 240V exists only BETWEEN L1 and L2 (the two "phases" of "split-phase".)
There is no Neutral here.  And Ground is only the safety path to prevent you from being electrocuted, or from setting your house on fire.

I'm trying to learn, that's why I asked about the Neutral and Ground.   So if L1 and L2 are going into the heating element, where is the completed path?   Where does it go back to Ground?   Electrons are attracted to electrons of the opposite charge, right?   So if I feed a heating element just two 120VAC sources, I wouldn't think it'd heat at all....that's where I'm getting confused here.   I was always taught you need a complete circuit, and without it, you don't get a working circuit.   Each load draws current and has a voltage drop.  By the time we get to ground, that voltage is 0VDC.   But without that ground, where do the electrons go?   Just L1's electrons fly down L2's conducting material and L2's electrons fly down L1's conducting material, even though they're of the same charge?   Or is it because they're not in phase, this works?   If L1 is out of phase with L2, then L1 would be the opposite charge of L2?

[Spork Schivago]

If you split a apple PIE do you get two Pies?
So how do you get two phases?

AC = alternating current

An alternator is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field with a stationary armature.[

https://en.wikipedia.org/wiki/Alternator

The hands on a analog clock rotate.
Think of the center of clock as 0 Volts
Max Positive Volts is 12 o'clock.
Max Negative Volts is 6 o'clock.
This makes 3 o'clock & 9 o'clock also 0 Volts as Volts is vertical dimension.

Single phase states you have one hand on clock like hour hand.

60 Hz states that the hand is completing 60 rotations a second.

now when you look at the volt rating is states
RMS

RMS = Root mean square
so if you see "240 Volt RMS"  the peak voltage is 1.414 x 240.
So the 12 o'clock position the max positive = 339.36 volts.

You use the sin table to compute a value based on rotation.

With one end at center you 0 volt connection.
As the hand rotates the other end goes from 12 o'clock around to 6 o'clock and back to 12 o'clock.

So single phase 240 volts is like hour hand rotating.
Going from 9 o'clock (0 volts) to 12 o'clock ( +339.36 volts) and around to 6 o'clock (-339.36 volts) and back to 9 o'clock.
Note that the hand is over 1/2 of the clock so the clock face is 678.72 volts in hight.

 Split-phase is extending the hour hand to other side of circle. When one end of the hand is at 12 o'clock the outer end is at 6 o'clock.
You have three connections. The two hand tips and the center.
Using full clock face you have the clock face 339.36 volts in hight.
Max Positive (12 o'clock) = +169.68 volts
169.68 / 1.414 = 120 volts RMS

Three phase is 3 hour hands 60 degrees apart.

The center of the clock face is the Neutral connecting in above.

The Hour hand tip(s) are the other connection.

Monkeh posted a plot of the voltage vs time which is also a plot of voltage vs rotation.

Have you used a two cell flash light?
The light connects to the two ends of the batteries in series.
Split-phase is adding a connection between the two batteries.

Get out your pencil and paper and make some drawings.

C

With those batteries though, that connection between them has to return back to either the bottom cell or the top cell to complete the circuit, otherwise, the electrons have no place to go.   That's what I don't understand with the AC, unless I was right about the L1 and L2 being opposite charges, one being +120VAC, the other being -120VAC, and the +120VAC passes through the heating element to the -120VAC, providing a voltage drop of 240VAC total over the heating element....is that correct?

[james_s]

L1 and L2 have 240V across between them, forget about ground, ground is a relative term. With AC the current reverses direction every half cycle, so half the cycle you have current flowing out of L1 and into L2, then the other half cycle it flows out of L2 into L1, there's your complete circuit. If you wanted you could call either L1 or L2 "ground", and you'd be able to connect it to earth ground *except* for the fact that the center tap is already connected to ground so doing this would create a direct short across one half of the transformer secondary.

[james_s]

With those batteries though, that connection between them has to return back to either the bottom cell or the top cell to complete the circuit, otherwise, the electrons have no place to go.   That's what I don't understand with the AC, unless I was right about the L1 and L2 being opposite charges, one being +120VAC, the other being -120VAC, and the +120VAC passes through the heating element to the -120VAC, providing a voltage drop of 240VAC total over the heating element....is that correct?

There's no such thing as +AC and -AC, the polarity is changing 120 times a second. If you were to freeze time at the peak of one cycle then yes you'd see +170V on one of the wires and -170V on the other, but the next half cycle that will reverse. In reality the value is not suddenly flipping (square wave) but is a sine wave, so the RMS value is 120/240 for a peak of 170/340.

[Gregg]

As previously drawn but maybe looking at the power from a different view may help.

The electric utility company has a transformer somewhere near your house; it is wired as shown in the diagram (in the USA).

As you can see the secondary winding is continuous and the output voltage of L1 and L2 are in proportion to the much higher voltage of the primary by the ratio of turns.  In the US it is 240 Volts nominal for most residential services.

The center tap of the secondary is brought out and called Neutral.  It is grounded to the earth near the transformer.  It is called Neutral because it is grounded and because the voltage between the neutral and either L1 or L2 is half the voltage between them, in this case 120 volts to either L1 or L2.  The neutral conductor from the utility carries any imbalance of the two other lines.  For instance, if you had 30 amps load on the 120volt side from L1 to neutral and 20 amps load on the other side from L2 to neutral, the neutral conductor would carry the 10 amp difference back to the transformer.

After the meter at the main disconnect panel (200 amp 2 pole 240v for this discussion) the neutral and ground are bonded together.  This is the only place they should be connected in your house.  The ground wires going to things in your house should not carry any current; they are there for safety reasons such as either L1 or L2 shorted to ground; then the ground wire should be able to carry the fault current long enough for the breaker to trip.

Ground and Neutral are NOT the same thing even though they are connected at the main panel.  Power doesn’t return to ground, it returns to the transformer. 

The potential between Neutral and Ground is very low, depending on resistance of the wiring, current in the neutral conductor and anything that may be leaking to ground (like Y capacitors, but we aren’t going there in this discussion).

[Richard Crowley]

So if L1 and L2 are going into the heating element, where is the completed path?

The path is:  From L1,  through the load (heating element) and returns to L2

Where does it go back to Ground? 

Repeating: 240V exists between L1 and L2.  The current doesn't "go back go ground" (or neutral).

So if I feed a heating element just two 120VAC sources, I wouldn't think it'd heat at all....that's where I'm getting confused here.

What you apparently don't understand is that 120-0-120 ("split-phase") is NOT "just two 120VAC sources."  You have 240VAC coming into your house between L1 and L2 (the two "phases"). It makes absolutely no difference whether L1 is connected to ground, or L2 is connected to ground, or if some point halfway between is connected to ground.  GROUND IS IRRELEVANT.   

If you insist on viewing the L1 and L2 voltages from the perspective of neutral/ground (at the center-tap) you should note that they are 180 degrees out of phase (opposite phases).  You are correct, if L1 and L2 were of similar phase, then there would be no voltage differential between L1 and L2, and no current would flow through your load.

I was always taught you need a complete circuit, and without it, you don't get a working circuit.   Each load draws current and has a voltage drop.  By the time we get to ground, that voltage is 0VDC.   But without that ground, where do the electrons go? 

Current flow does NOT depend on "ground".  Else your cell phone (or flashlight or automobile) would be unable to operate with no connection to "ground".

Just L1's electrons fly down L2's conducting material and L2's electrons fly down L1's conducting material, even though they're of the same charge?   Or is it because they're not in phase, this works?   If L1 is out of phase with L2, then L1 would be the opposite charge of L2?

You are beginning to get it.  L1 and L2 are of opposite "phases" when viewed from that center-tap ground/neutral.  The 240 volts coming into your house is split in half in order to provide 120V branch circuits to power your domestic appliances, lights, etc. 

But you have 240VAC coming into your house.  Your problem here is that it is center-tapped and grounded. But your PDUs want 240-0 (one side grounded, aka. "single-phase"), not 120-0-120 (center-tap grounded, aka "split-phase")  That is why you need a transformer to allow you to ground one side of the 240V to create "single-phase".

You do not have two identical 120V phases coming into your house.  You have 240V which happens to be center-tapped and grounded.  And electricians call it "split" or "two" phases.

[Spork Schivago]

L1 and L2 have 240V across between them, forget about ground, ground is a relative term. With AC the current reverses direction every half cycle, so half the cycle you have current flowing out of L1 and into L2, then the other half cycle it flows out of L2 into L1, there's your complete circuit. If you wanted you could call either L1 or L2 "ground", and you'd be able to connect it to earth ground *except* for the fact that the center tap is already connected to ground so doing this would create a direct short across one half of the transformer secondary.

That's what I've been missing.   I wasn't talking about the transformer here, I was talking about 120-0-120 split-phase that comes into the house, and trying to see how it's equivalent to 240VAC over in Europe.   Because over there, they'll have L1 and then Neutral hooked to the heating elements, which would still give the 240VAC.   I think I understand now fully how the AC works.

Now, why would connecting earth ground to a 240VAC source that comes from 120-0-120VAC USA split-phase or whatever you want to call it cause a short there?   It's because L1 and L2 are reciprocals of each other, right?  When one is 120VAC, the other is -120VAC.   When one is 75VAC, the other is -75VAC.   When one is zero, the other is zero.   If we added a ground, when either where anything other than 0VAC, we'd have our direct connection to ground, which would be horrible.   Am I finally understanding this?

[Spork Schivago]

With those batteries though, that connection between them has to return back to either the bottom cell or the top cell to complete the circuit, otherwise, the electrons have no place to go.   That's what I don't understand with the AC, unless I was right about the L1 and L2 being opposite charges, one being +120VAC, the other being -120VAC, and the +120VAC passes through the heating element to the -120VAC, providing a voltage drop of 240VAC total over the heating element....is that correct?

There's no such thing as +AC and -AC, the polarity is changing 120 times a second. If you were to freeze time at the peak of one cycle then yes you'd see +170V on one of the wires and -170V on the other, but the next half cycle that will reverse. In reality the value is not suddenly flipping (square wave) but is a sine wave, so the RMS value is 120/240 for a peak of 170/340.

Yes, I realize it's changing so fast we can't see it, but that doesn't really mean it's not there.   I think I have a good understanding of it now, except  for the RMS.   I have a true RMS DMM, so when I measure the voltage from my receptacles, I see 120VAC.   I don't see 170VAC.   When the sine wave is at the peak, you're saying for 120VAC, it's really 170VAC +/- ?   And for 240VAC, it's really 340VAC +/-?   RMS = Root Mean Square.   The RMS value is 120/240, as you say...even my old analog volt meter that isn't true RMS measures it at 120VAC though.... so I'm still missing some pieces to this, but I'm getting there.   I don't understand why we use the RMS and not just the peak value when measuring or talking about the voltage sources.   Why use the RMS value?   Why not just call it 170VAC or 340VAC?

With the European 240VAC, don't they generally have 240VAC going down L1 and Neutral to Neutral, Ground to Ground (where Neutral would be connected to Ground, like in my breaker panel)?   If so, wouldn't they receive a short if they tried hooking my BGA rework station (which is wired with L1 = 120VAC, L2 = 120VAC, N = Neutral, E = Earth) directly into their outlets, just by changing the NEMA L6-30P I wired to the end of it?   We still have the sine wave, where it's going from positive to negative for one wave cycle right?   But now, because they're using 1-phase 240VAC, they don't have the L1 and L2, where the AC goes into L1, then back into L2, and so on and so forth...the heating elements would be wired up so 240VAC was feeding directly through the heating element and then to ground.   I guess that wouldn't cause a short though, would it?   The heating element would still be the load and would still have a voltage drop of 240VAC.   So nothing would change there I guess....hrmm.

I'm trying to think if there's any cases where just switching the plug on one of our devices that is made for our 240VAC to fit into their receptacles over there would cause damage.   I know we can do it here, most of the time, but does it usually work the same over there?

[Spork Schivago]

As previously drawn but maybe looking at the power from a different view may help.

The electric utility company has a transformer somewhere near your house; it is wired as shown in the diagram (in the USA).

As you can see the secondary winding is continuous and the output voltage of L1 and L2 are in proportion to the much higher voltage of the primary by the ratio of turns.  In the US it is 240 Volts nominal for most residential services.

The center tap of the secondary is brought out and called Neutral.  It is grounded to the earth near the transformer.  It is called Neutral because it is grounded and because the voltage between the neutral and either L1 or L2 is half the voltage between them, in this case 120 volts to either L1 or L2.  The neutral conductor from the utility carries any imbalance of the two other lines.  For instance, if you had 30 amps load on the 120volt side from L1 to neutral and 20 amps load on the other side from L2 to neutral, the neutral conductor would carry the 10 amp difference back to the transformer.

After the meter at the main disconnect panel (200 amp 2 pole 240v for this discussion) the neutral and ground are bonded together.  This is the only place they should be connected in your house.  The ground wires going to things in your house should not carry any current; they are there for safety reasons such as either L1 or L2 shorted to ground; then the ground wire should be able to carry the fault current long enough for the breaker to trip.

Ground and Neutral are NOT the same thing even though they are connected at the main panel.  Power doesn’t return to ground, it returns to the transformer. 

The potential between Neutral and Ground is very low, depending on resistance of the wiring, current in the neutral conductor and anything that may be leaking to ground (like Y capacitors, but we aren’t going there in this discussion).

We gotta back up the train here a bit.   I understand the purpose of the neutral and ground in the house.   If we have a short, we want that current and voltage to go to the path of least resistance, hopefully back to the breaker, to trip it.

The transformer at the pole though....you said, "For instance, if you had 30 amps load on the 120volt side from L1 to neutral and 20 amps load on the other side from L2 to neutral, the neutral conductor would carry the 10 amp difference back to the transformer."

Where are these loads coming from?    Some place in the transformer, or in the house?   Why would there ever be an excess of current?   A 60 watt bulb will always draw 60 watt, even if you have it hooked to a 200-amp breaker.   So how could you ever have an excess of current?   Even if you were to directly wire hot to neutral or hot to ground, if neutral and ground are at 0V, wouldn't there be an instant volt drop where they connected and a lot of heat generated?   I had an old camaro and the ignition went bad.   I had to hot wire it.   I'd use the fuse panel.   I'd hook to a 12V source, then use a wire to tie into the fuse for the Ignition.   Then I'd hook into the 12V source and tie into the starter, but just long enough to get running.   One day, I was a little careless and grounded that 12V source.   The wire evaporated in my hand and left a white indent.   At first it didn't hurt, then it hurt real bad.   But there wasn't no excess current that just traveled safely back to the cells in the battery.   Wouldn't an excess current be called a short?

Also, how come our neutrals and grounds in the house are tied together?   Why can we not have it like the transformers on the poles where neutral is seperate from ground?   Actually, I probably could, couldn't I?   Outside, there's a grounding wire that's buried in the earth that hooks to the panel.   If I separated the ground and neutral buss-bars in the breaker panel, and made sure my ground buss-bar went to the grounding wire outside, and the neutral went back to the pole, I'd essentially have the same setup as the pole.   Someone in this thread mentioned in their house they'd never have the ground tied to the neutral.   But in every home I've seen, this is how it's always setup.   Is there any dangers to doing what I just described?

[IanB]

With the European 240VAC, don't they generally have 240VAC going down L1 and Neutral to Neutral, Ground to Ground (where Neutral would be connected to Ground, like in my breaker panel)?   If so, wouldn't they receive a short if they tried hooking my BGA rework station (which is wired with L1 = 120VAC, L2 = 120VAC, N = Neutral, E = Earth) directly into their outlets, just by changing the NEMA L6-30P I wired to the end of it?

You have listed four wires (L1, L2, N, E), but in the L6-30P there are only supposed to be three wires (L1, L2, E). There is no neutral.

Your BGA rework station is only supposed to have three wires too. In the European outlet there are two wires carrying 240 V between them, and a third wire for safety ground. In the USA the L6-30 receptacle has two wires carrying 240 V between them and a third wire for safety ground. So the situation is really the same in Europe as it is here from an electrical perspective. It is only the safety arrangements that differ.

We call a wire "hot" or "live" because it is effectively hot and will hurt you if you touch it. We call a wire neutral because--theoretically--it won't hurt you if you touch it (but don't rely on this). There is no difference between live and neutral as far as carrying electric current is concerned, there is only a difference with regard to safety and protection arrangements.

[Spork Schivago]

So if L1 and L2 are going into the heating element, where is the completed path?

The path is:  From L1,  through the load (heating element) and returns to L2

Where does it go back to Ground? 

Repeating: 240V exists between L1 and L2.  The current doesn't "go back go ground" (or neutral).

So if I feed a heating element just two 120VAC sources, I wouldn't think it'd heat at all....that's where I'm getting confused here.

What you apparently don't understand is that 120-0-120 ("split-phase") is NOT "just two 120VAC sources."  You have 240VAC coming into your house between L1 and L2 (the two "phases"). It makes absolutely no difference whether L1 is connected to ground, or L2 is connected to ground, or if some point halfway between is connected to ground.  GROUND IS IRRELEVANT.   

If you insist on viewing the L1 and L2 voltages from the perspective of neutral/ground (at the center-tap) you should note that they are 180 degrees out of phase (opposite phases).  You are correct, if L1 and L2 were of similar phase, then there would be no voltage differential between L1 and L2, and no current would flow through your load.

I was always taught you need a complete circuit, and without it, you don't get a working circuit.   Each load draws current and has a voltage drop.  By the time we get to ground, that voltage is 0VDC.   But without that ground, where do the electrons go? 

Current flow does NOT depend on "ground".  Else your cell phone (or flashlight or automobile) would be unable to operate with no connection to "ground".

Just L1's electrons fly down L2's conducting material and L2's electrons fly down L1's conducting material, even though they're of the same charge?   Or is it because they're not in phase, this works?   If L1 is out of phase with L2, then L1 would be the opposite charge of L2?

You are beginning to get it.  L1 and L2 are of opposite "phases" when viewed from that center-tap ground/neutral.  The 240 volts coming into your house is split in half in order to provide 120V branch circuits to power your domestic appliances, lights, etc. 

But you have 240VAC coming into your house.  Your problem here is that it is center-tapped and grounded. But your PDUs want 240-0 (one side grounded, aka. "single-phase"), not 120-0-120 (center-tap grounded, aka "split-phase")  That is why you need a transformer to allow you to ground one side of the 240V to create "single-phase".

You do not have two identical 120V phases coming into your house.  You have 240V which happens to be center-tapped and grounded.  And electricians call it "split" or "two" phases.

I had temporarily moved away from the transformer for the PDU.   I understand completely why I need a transformer for the PDU and why I could never power it with just a double pole breaker hooked to my panel.   What I wasn't getting (but am now) is that the current for AC flows forwards and backwards, not just forwards like DC.   I had said early on I understood DC fairly well, it was the AC I struggled with, but now I feel I have a pretty good grasp of how the 240VAC works in the USA.   Still not sure about 1-phase 240VAC that is used in other parts of the world, or that would be used with my transformer.    Because we don't have an L1 and L2, because the 240VAC is on the same phase, where do the electrons go if they're not hooked to a neutral or ground to complete the circuit?    Somehow they have to make it back to the breaker, correct?   I use the word ground, but all I mean is a completed circuit.   I know and understand that a completed circuit doesn't need a ground or a voltage potential of 0V.   I could technically power a circuit where the supply is 24V and the return is 12V.   So long as the return is at a lower voltage potential than the supply, we can have the electrons moving.

Using the water analogy that everyone seems to like to use, we have our "pump" (the transformer I'd buy for the PDU, for example).   The "water" (electrons) flow out of L1 into the PDU.   But then what?   They need to make it back to the "pump" (transformer) somehow.    I know you say ground / neutral is irrelevant, but in this case, I cannot imagine how those pesky little buggers would make it back to complete the circuit without using one of those other wires that are at 0V potential.    The components inside the PDU would be the loads and by the time the current / electricity had passed through the entire circuit and was ready to leave the PDU, it surely wouldn't just be traveling up the L1 wire again, would it?   We'd have to use one of the additional neutral / ground wires in that instance.   Just like if we're dealing with 120VAC receptacles.   We cannot just hook up the hot wire.   That wouldn't do diddly squat.   We'd still have to hook up the neutral so the electrons could make it back to the panel.

With the 120-0-120, I understand how it works now.   I also understand why if I were to not use a double pole breaker but tried wiring up a NEMA L6-30R using a 30-amp single pole breaker in slot 1 and slot 2 (opposites sides of the panel), it wouldn't work.   I'd have 120VAC, not 240VAC.

[IanB]

Also, how come our neutrals and grounds in the house are tied together?   Why can we not have it like the transformers on the poles where neutral is seperate from ground?

Let me say something that will seem funny at first. If you take a transformer, any transformer, like the one at the top of the utility pole, or like the one earlier in this thread that might go in your basement, it doesn't matter. Anyway, if you take a transformer with two wires coming out of it carrying voltage, then at this point no wire is "neutral" and no wire is "hot". There is no neutral. Neutral is created by connecting one wire to a rod in the ground. Until we do that there are just two wires with voltage between them.

Think about an analogy with a 3 ft rule. First hold it up in your hand. The ruler is 3 ft long (240 V), but it is floating and not grounded. This is like the transformer with two wires 240 V (3 ft) apart.

Next stand it upright on the ground. Now the lower end (0 ft) is grounded, and the other end (3 ft) is 3 ft up in the air, but the ruler is still 3 ft long. You could call the lower end of the ruler "neutral".

Next, dig a three foot deep hole and drop the ruler down it. Now the top end (3 ft) is level with the ground and the bottom end (0 ft) is 3 ft below ground. The ruler is still 3 ft long, but now the top end is grounded. You could call the top end of the ruler "neutral" because there is no distance to fall between that end and ground level.

Lastly, dig a  1½ ft hole and stand the ruler in that. Now the ruler is half above ground and half below ground. It is still 3 ft (240 V) long, but now the middle is grounded. This is what split phase is like. The maximum distance to fall to ground level is 1½ ft (120 V), which makes it a bit safer.

[IanB]

I could technically power a circuit where the supply is 24V and the return is 12V.

No, in a two wire system it is not possible "to have one wire at 24 V and the other at 12 V". Voltage is defined as the difference in potential between two wires. No single wire can ever have a voltage on it in isolation. Every time you talk about a voltage you have to talk about the voltage between this wire and that wire. So all you can say about two wires is that "they have a voltage of 12 V". All you can say about a single wire is "we don't know anything about voltages because there is only one wire". (Sometimes the other "wire" can be ground, or a water pipe, or something, but this is still a "wire" from an electrical and safety perspective.)

With the 120-0-120, I understand how it works now.   I also understand why if I were to not use a double pole breaker but tried wiring up a NEMA L6-30R using a 30-amp single pole breaker in slot 1 and slot 2 (opposites sides of the panel), it wouldn't work.   I'd have 120VAC, not 240VAC.

No, you don't seem to understand. You would have 240 V AC, which is exactly what the computer power supplies want. The reason you can't hook up your existing PDU to the L6-30R receptacle is one of safety. It doesn't comply with North American electrical standards. It was designed for another system, outside North America.

[Spork Schivago]

With the European 240VAC, don't they generally have 240VAC going down L1 and Neutral to Neutral, Ground to Ground (where Neutral would be connected to Ground, like in my breaker panel)?   If so, wouldn't they receive a short if they tried hooking my BGA rework station (which is wired with L1 = 120VAC, L2 = 120VAC, N = Neutral, E = Earth) directly into their outlets, just by changing the NEMA L6-30P I wired to the end of it?

You have listed four wires (L1, L2, N, E), but in the L6-30P there are only supposed to be three wires (L1, L2, E). There is no neutral.

Your BGA rework station is only supposed to have three wires too. In the European outlet there are two wires carrying 240 V between them, and a third wire for safety ground. In the USA the L6-30 receptacle has two wires carrying 240 V between them and a third wire for safety ground. So the situation is really the same in Europe as it is here from an electrical perspective. It is only the safety arrangements that differ.

We call a wire "hot" or "live" because it is effectively hot and will hurt you if you touch it. We call a wire neutral because--theoretically--it won't hurt you if you touch it (but don't rely on this). There is no difference between live and neutral as far as carrying electric current is concerned, there is only a difference with regard to safety and protection arrangements.

I'm sorry, I haven't gotten a lot of sleep lately, but yes, you are correct.   The NEMA L6-30P / L6-30R only has 3 wires, not four.    So in Europe and other parts of the world that use 240VAC, it's just like ours, where 120V goes down one wire, 120V goes down another?   This is what my European friend was talking about I think when he said it was a language barrier and that Neutral was meant to be hot.   If that's the case though, and they have two wires carrying the 240V load, then my PDU wouldn't work over there either, would it?   Because we still have single pole breakers.   They'd need 1-phase 240VAC, not two-phase.

This guy I know had me come to his house to fix his electricity.   He's really intelligent, but should not be messing with this stuff, and I stressed that many times, but he said if his house burned up with him in it, he'd be happy.   Anyway, he had a furnace in his basement and lives downstairs.   He wired up some sort of forced air, which was just pure genuis, but he wired the receptacle incorrectly and it didn't trip a breaker, but sparked.   Then none of the loads on the circuit worked.   So I went through and probed them with my multimeter and I have a small device I plug in to show me if they're wired correctly, and a no-contact voltage detector.

I'm working my way backwards, right?   I get to this receptacle, plug my device in, nothing, but the no-contact voltage detector says there's juice.   I put my DMM on there, 14VAC.   I'm like what the heck?   I know it was dumb, but I had to check.   I touch the receptacle, and sure enough, a bit of a tingle.    I go down stairs, trace the wire, and come to a junction box.   This is where it gets real bad.    He tied into 12-gauge wire using 14-gauge wire and ran it to the new receptacle he installed for his forced air hookup.

Every outlet in the house had no ground wire hooked up, and this is why it never tripped the breaker.   In the actual junction box, the wirenut had actually partiatially exploded.   Some of it was melted.   I told him this is why you need to not be doing this.   I can show you how to do it safely, but you cannot have this type of setup, you're going to get hurt or killed.   That's when he said he didn't care, so I didn't know what to do.   I fixed it, but said he shouldn't be using the 14-gauge.   It's a danger.   He needs to switch it out with 12-gauge.   I tried telling him, how would you feel if you was at work and your house burned down and your dogs couldn't get out?   I dunno if he ever switched it out or not.   He got real paranoid after that and started talking about cameras in the tree's and the FBI watching him or something so I left.

[Spork Schivago]

I could technically power a circuit where the supply is 24V and the return is 12V.

No, in a two wire system it is not possible "to have one wire at 24 V and the other at 12 V". Voltage is defined as the difference in potential between two wires. No single wire can ever have a voltage on it in isolation. Every time you talk about a voltage you have to talk about the voltage between this wire and that wire. So all you can say about two wires is that "they have a voltage of 12 V". All you can say about a single wire is "we don't know anything about voltages because there is only one wire". (Sometimes the other "wire" can be ground, or a water pipe, or something, but this is still a "wire" from an electrical and safety perspective.)

With the 120-0-120, I understand how it works now.   I also understand why if I were to not use a double pole breaker but tried wiring up a NEMA L6-30R using a 30-amp single pole breaker in slot 1 and slot 2 (opposites sides of the panel), it wouldn't work.   I'd have 120VAC, not 240VAC.

No, you don't seem to understand. You would have 240 V AC, which is exactly what the computer power supplies want. The reason you can't hook up your existing PDU to the L6-30R receptacle is one of safety. It doesn't comply with North American electrical standards. It was designed for another system, outside North America.

No, I do understand.    slot 1 and slot 2 are on the same phase, from the panels perspective.   Take two computer PSUs.   Strip the 12V wire from each of them.   Tie them together.   Plug both into the same outlet.   Measure the voltage in reference to ground.   What do you get?   24VDC?   No.   12VDC.    Now, do the same, but plug one of the PSUs into a circuit powered by the other mains coming into the house.   What do you get?   Should be 24VDC, not 12VDC.

I'm tired, I did a horrible job, I was trying to give a simple analogy of something we call differential signaling, but after I get some sleep, I'll come back and update it proper like.   I have been awake for over 36 hours now.   I gotta go to bed, but I love talking to you guys and learning this stuff.   So hard to walk away.

[IanB]

With that in mind, if you were me, would you take the chance and send the PDU back and order the other two, plus the additional equipment to get it running?  Or would you just purchase the transformer and new breaker panel?

I would send the PDU back and order the other two PDUs. The reason being that that other PDUs are designed and specified for installation in North America and they comply with the electrical and safety requirements of the North American electrical code.

Your existing PDU is not code compliant and is not suitable for connection to a North American electrical supply. It is intended for another market elsewhere in the world. This is why it has a strange plug on it and why electricans don't want to touch it.

You could, theoretically, install the transformer and the sub-panel, but it's going to be really complicated getting it to pass inspection because it will be a strange and abnormal setup.

If you don't want to take the responsibility of ordering the other PDUs just on the advice of this forum, you should find someone in your line of business to consult who can offer appropriate expert advice. I do not think you have been well advised by the HPE sales consultants in your journey so far.

[IanB]

slot 1 and slot 2 are on the same phase, from the panels perspective

No, slot 1 and slot 2 are on the opposite phase, from the panel's perspective. That is why slot 1 and slot 2 have 240 V between them.