shopman
Solar Enthusiast
They have pills for that.
Electrical question
- Thread starter Bluedog225
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peakbagger
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To really confuse things, at one point there were two phase power systems and a few are still running. I used to have to mess with them on rare occasions at the papermill I worked at. I also ran into 40 cycle AC systems at a very old papermill, I have a couple of solenoid valves that are rated for 40 cycle kicking around the house.
The idea that the ends of a single phase system are 180 degrees out of phase is wrong, but it is understandable. They aren't out of phase, therefore it is geometrically incorrect to describe it that way. But they are opposite in polarity, so they are "180 degrees different" like you might say night and day are "180 degrees" apart. Ya know?
I’m guessing you might be referring to an ungrounded system? Popular in the cities from the 30-60s, it was cheap to install but deadly AF as fault current didn’t have a good path to ground/source.
Also you can operate a three phase system/motors with only two phases, it’s called open delta. It works but is a but def a unique system and is probably only grandfathered in.
Bluedog225
Texas
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I’m still trying to wrap my head around the wire cost savings for split phase.
It looks like one more conductor for split phase.
When looking up voltage drop for a split phase run of about 100’, do I use the 240 volt difference between L1 and L2 or do I use the 120 volt measured between each line and neutral.
With single phase, I get that more volts means less amps for a given watts. But with split phase, more volts compared to what?
Thanks
It looks like one more conductor for split phase.
When looking up voltage drop for a split phase run of about 100’, do I use the 240 volt difference between L1 and L2 or do I use the 120 volt measured between each line and neutral.
With single phase, I get that more volts means less amps for a given watts. But with split phase, more volts compared to what?
Thanks
No, he's talking about a true two-phase system, where the phases are 90 degrees apart. They came in three flavors, 3-wire, 4-wire, and 5-wire. They were quickly overtaken by 3 phase. The only two phase system still in operation is in Philadelphia.
Which was my point. I started off by explaining that the supply in was 1 phase (to the central tapped transformer). Anyone that understands the design of a generator head understands how phases are created through the use of magnetic poles and windings. As the rotor spins against the stator the magnetic flux induces a voltage that corresponds to the windings passing the North or South pole. Thus a sine wave. It rises from zero as the pole is directly against the windings and drops off as the rotor turns and than rise as it passes the opposite magnetic pole but in a 180 degree opposite direction. A 3 phase genrator head has 2 more sets of windings and poles that are built into the generator that creates their own set of outputs.
The video I linked to showed a O-scope trace of both legs to neutral of a 240vAC split phase setup. It can not be argued that the sine waves are 180 degrees apart. It just can't. However as I already stated that if you read between the two hot legs you have only one sine wave.
The problem that Tim has is he refuses to acknowledge the apparent 180 degree.
I say this not to confuse anyone.
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There can be a good argument made for the European single phase 230v setup (though 50hz is a poor choice).
You should find that for a given current at 120vAC the voltage drop is the same as 1/2 the current in a 240vAC split phase setup.
Incidently America likes spending money. No cheaping out on conductors for us.
Hedges
I See Electromagnetic Fields!
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Split phase lets you have 120V for some loads, also 240V for larger loads.
If all your loads were 240V (e.g. European) you would just use 2 wires for 240V.
But in the U.S., many loads are 120V.
If you have 120V only, between two lines, a 12V IR drop is 10%
If you have 240V only, 12V IR drop is 5%.
For same gauge wire, 12V IR drop would come from same current, regardless if 120V, 240V, or other.
Most load are either 120V or 240V. Some motors can be wired to run either way, like my 2 HP air compressor.
Assume it draws 10A at 240V, or 20A at 120V. Either way, Amps x Volts = 2400 VA.
Assume 0.6 ohms from a long run of wire. 20A x 0.6 ohms = 12V drop, which is 10% of 120V.
Alternatively, 10A x 0.6 ohms = 6V drop, which is 2.5% of 240V.
Because it draws 5x as much current when first starting, the lower voltage drop works much better. Also less energy wasted.
Too much voltage drop and an induction motor won't turn, just overheat.
2400 | W load | |
120 | 240 | V supply |
20 | 10 | A drawn by motor (rewired for given voltage) |
0.6 | ohms wire | |
12 | 6 | V drop in wire |
10.0% | 2.5% | of supply voltage |
Bluedog225
Texas
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I think I follow. IR is internal resistance of the wire, right?
In terms of sizing wire for a split phase run of 100’, I need to size them for a 3% drop for 120 volt uses, right? And that will necessarily cover the lower amperage 240 volt loads.
I read some info indicating that smaller conductors could be used for split phase. But I think those savings don’t come into play if I have both 120 volt and 240 volt loads. Am I close?
In terms of sizing wire for a split phase run of 100’, I need to size them for a 3% drop for 120 volt uses, right? And that will necessarily cover the lower amperage 240 volt loads.
I read some info indicating that smaller conductors could be used for split phase. But I think those savings don’t come into play if I have both 120 volt and 240 volt loads. Am I close?
Because he is absolutely correct.
The phases are not 180⁰ opposite each other... there is only a single 240V phase.
The split point gives 1/2 the phase to each line relative to neutral.
He is stuck on the fact that the phase is not two different opposing phases...
However...
Even with true 3 phase... ALL PHASES ARE GOING THE SAME DIRECTION.
In 3 phase, they are seperated each by 120⁰, but they are all going the same direction... how else could they be... I mean, 3 phase isn't three different generators, it is one generator with three poles...
They ALSO have a center tapped neutral by the way... that produces 120V as well...
Anybody thinking split phase has two phases needs to explain how 3 phase gets 120V to neutral... is that then six phases? No, of course not...
Hedges
I See Electromagnetic Fields!
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"IR" in the context of "IR drop" means V = I x R
("IR" means internal resistance in the context of battery cells.)
Sizing wires for maximum current causing voltage drop no more than 3% of 120V would be good.
Each circuit L1 & N, L2 & N, L1 & L2 needs to be sized for about 3% or less voltage drop in both wires combined (1.5% of supply over the length of the wire.)
3.6V drop in L and N of a 120V circuit, 7.2V drop in L1 and L2 of a 240V circuit.
If your inverter can deliver 25A at 120V and 25A at 240V, size all three wires L1, L2, N according to 25A at 120V.
If your inverter can deliver 50A at 120V and 25A at 240V, size all according to 50A at 120V.
This could be the case with transformer type, or if 240V output of inverter goes to a transformer making 120/240V.
Once it goes through a breaker panel and has multiple circuits coming off it, each of those would be sized according the breaker amperage.
No he is not correct. Absolutely not. Simply because I was not and never have argued that there is 2 phases. Or that the two traces you see on the O-scope are indicative of 2 phases. Read though every post I made about the subject and if you can find me stating that it is 2 phases I will immediately apologize and never post to this Forum again. I am about at that point anyway. I absolutely hate to be mis-characterized or misconstrued deliberately.
Funny enough but 3 phase is similar to 3 generators.
Getting into all the ways that you can create different voltages from combinations of using those 3 phases is lengthy and and I must admit it has been a long time since I took training in motor, generator theory.
Oh, I highly doubt he is responding to ONLY you in all his responses.
And I don't think you ever said two phases either.
I am good at noting patterns. It is what helps in troubleshooting.
timselectric
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Correct
And I don't think so, either.
timselectric
If I can do it, you can do it.
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And I'm glad that all of that is almost gone.
Delta high leg is also being phased out. At least in my area.
208/120 you get 120 for phase to phase voltages not phase to neutral. Just like a leg of 240 to neural is 120v just with some phaser math involved.
No one is talking about 3 phase so it’s best to not muddy the waters.
Hedges
I See Electromagnetic Fields!
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When I saw 12kV 3-phase on the cross street two houses away, I was excited.
I requested 120/208V 150A service upgrade (to replace 120/240V 100A.)
Visiting the site, a PG&E guy said it might cost $15,000.
I said, "That's maybe twice what the transformer costs."
He later emailed and said I wasn't eligible to request 3-phase. Because my loads weren't 75 kVA.
That would have been for 120/208Y. Reading their rules, I pointed out that a 3 HP motor was sufficient for me to demand 120/240V high-leg, and they acquiesced.
However, the next person (in the list of people to wear me down), called and gave an estimate of $150,000.
Two trucks with crews, two days, at $25,000 per truck per day. Shut down the power line. Install one 3-phase transformer on a pole and string 200' of wire to it (then the drop to my house.)
No thanks, I said. I'll just install PV, a 3-phase inverter, and disconnect from PG&E.
(In reality, what I'll do is get 120/240V 200A upgrade. Since multiple customers will be served, even if they have to upgrade transformer it should be all their cost.)
Oh, and after I paid $150k (if I did), they would own the asset, probably claim on the books it was $150k worth of material and installation. Then they could collect 8% = $12,000 annually in income, declining as it was depreciated. Pretty good racket for a transformer and wire worth about $12k total, huh?
See there’s your problem, one 3phase xfrmr is way more $$$ than 3 single phase xfrmrs wired up. Only 3phase single units we install are pad mounts.
Did you contact a third party electrical outfit for a quote? It seems to be the cheapest option around here. You still have to cut a check to the utility to take over ownership for maintenance costs but is worth it once everything is added up.
Also they did the numbers on your usage, a low hitting low KWhr usage customer like you gets the shaft of your were an actual industrial customer with serious useage they will probably be able to write off 90% the install because they’ll make it up in kwhr sales over the lifetime of the install.
