Why Is American 220v Not Considered 2 Phase?

Yup, you guys are spot on. That's what I get for post at 1 in the morning. My apologies for any confusion.


Oh, and unless you have an isolation transformer, or your scope is so coupled internally, best not to probe the socket your scope is plugged into. Or use a battery operated portable scope. So I've heard.....never smoked a scope yet.
 
Hmmm...
Letting the magic smoke out of a scope...
Would be a real mistake... :eek:
Much worse than letting the smoke out of a sawzall or a drill... :(
 
I hope ya'll know that was a joke about measuring the 7200 V lines!
Actually we live in a neighborhood built in 1920 and we have tons of overhead high voltage lines just waiting to break. Last year I had to call about a tree on fire from arcing. Fortunately the rain put it out 'cause they showed up the next day to check it out. Good ole Duke Power.
R
 
It's easy to see that 3 wires could be considered 3-phase but it's a US problem. Most countries that provide only 240 volts have 2 service wires, but if they had 3 service wires it would most likely be 3 phase. In the US we couldn't decide whether we liked 120 or 240 volts so we decided to have both - we have one phase and 3 wires (120v to neutral, 240v between L1 and L2 - the third one is a neutral/ground). To confuse things further if you order 3 phase in the US you may get grounded delta 3 phase with one leg neutral/grounded, 3 phase delta with all phases above neutral, or 3 phase wye all phases above neutral.
 
I hope ya'll know that was a joke about measuring the 7200 V lines!
Actually we live in a neighborhood built in 1920 and we have tons of overhead high voltage lines just waiting to break. Last year I had to call about a tree on fire from arcing. Fortunately the rain put it out 'cause they showed up the next day to check it out. Good ole Duke Power.
R

Yeah... Definitely not a good idea to climb the pole to measure voltage...
As I understand it... it is a federal offense (terrorism) for an un-authorized person to climb a utility poll...

About a year or so ago... they changed the Xformers in my neighborhood... was chatting with the line guys...
They said the current service 'was' 8700 volts, however it was gonna change to 12K volts.
There is 3 phase at the head of my subdivision on the boulevard... none in the neighborhood.
Surprising... one leg (one line) serves close to 100 homes.
 
Ahh man, I really wanted to check out the high voltage lines. I downloaded the oscilloscope app for my I phone, and duct tapped my 20 foot aluminum ladder to the end of my 30 foot aluminum ladder. I figured with the light rain we are having, no one would see me climb up a,d check out the wave forms.

Ohh well, I'll just drink another beer instead.

:big grin:
 
OK, some additional info on 3 and split phase. 208 3 phase is 208 and NOT 240 because the phases are not 180 degrees out of phase. Since the phases are 120 degrees out of phase the maximum leg to leg RMS voltage is 208. RMS is something else. Since we have now drug o-scopes into this discussion. The actual PEAK voltage to neutral is actually 169 volts and not 120. 120 is the RMS voltage that what was adopted to refer to it. Did you ever wonder why you needed to use 370 volt caps for a RPC? That would be it. the Peak voltage on 240 is actually 338 volts. So while a regular volt meter will show 240 a scope which shows peak voltage would indicate 338 volts.

More confusion
 
OK, some additional info on 3 and split phase. 208 3 phase is 208 and NOT 240 because the phases are not 180 degrees out of phase. Since the phases are 120 degrees out of phase the maximum leg to leg RMS voltage is 208. RMS is something else. Since we have now drug o-scopes into this discussion. The actual PEAK voltage to neutral is actually 169 volts and not 120. 120 is the RMS voltage that what was adopted to refer to it. Did you ever wonder why you needed to use 370 volt caps for a RPC? That would be it. the Peak voltage on 240 is actually 338 volts. So while a regular volt meter will show 240 a scope which shows peak voltage would indicate 338 volts.

More confusion
Not quite, or maybe I don't understand what you're saying. 208 three phase will always be a wye connected secondary with 120v phase to ground. If the voltages are the difference of 1.73 (√3) they are always wye connected. 240/120 is always delta connected as it is 1/2 ratio. phase to phase is 240 and phase to ground is 120, it's a 4 wire system. Phase angles are 120° apart in all instances. RMS has nothing to do with 208v systems.
 
That's actually one way to do it: you get 208 phase to phase and 120 phase to neutral. It isn't common in residental distribution but you will find it in some large buildings such as hospitals. In residential distribution they normally just connect the primary of your pole pig phase to neutral (with adjacent pole pigs going on different phases to balance the load). If you are out near the end of a branch like we are there may only be one phase up on the poles.
Here in NYC its not uncommon for residential buildings to have 3 phase service, especially new or renovated buildings. The main reason is for elevators and air conditioning. However, most apartments will only have a single phase (two of the three phases) sub panel. 208v phase to phase 120v to the neutral.
 
Here in NYC its not uncommon for residential buildings to have 3 phase service, especially new or renovated buildings. The main reason is for elevators and air conditioning. However, most apartments will only have a single phase (two of the three phases) sub panel. 208v phase to phase 120v to the neutral.
By residential I meant single-family.
 
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