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Author Topic: Sparky Language Lesson  (Read 11305 times)

TJ (Tom) Cornish

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Re: Sparky Language Lesson
« Reply #40 on: June 26, 2015, 02:11:31 pm »

More dead horse flogging: Can we agree to call the 120/240V grounded center tap service prevalent in the US "120/240V single-phase" or "125/250V single-phase"? It is not split-phase or two-phase. (Look what it says on the nameplate.) A legitimate use of two-phase is in the context of certain AC-servo motors (that went out of style in the 1960s) where the two phases are 90 deg, not 180 deg, apart. Anyhow, Ivan will argue that it's polarity, not phase   :)
Good luck with that, and as relatively few of us are linemen rather than users, I would argue that two-phase is the most-accurate description for what we are actually using, from a branch distribution point of view (yes I understand that it is derived from one phase up on the pole). 

At least we're largely done with the whole "grounding", "grounded", "ungrounded" naming cluster.
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Stephen Swaffer

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Re: Sparky Language Lesson
« Reply #41 on: June 26, 2015, 02:15:43 pm »

Yes please.

And Ivan would be correct since the 2 legs of a 120/240 single phase service are the same (single) phase but 180 out of polarity.

Mac

Of course this is correct, IF you in fact have a single phase/center tapped transformer.  Just to make life complicated I have installed nominally 120/240 single phase services that were fed off a 3 phase transformer network in which case you actually have 120/208 with phases 120 deg out of phase.
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Steve Swaffer

TJ (Tom) Cornish

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Re: Sparky Language Lesson
« Reply #42 on: June 26, 2015, 02:21:39 pm »

Of course this is correct, IF you in fact have a single phase/center tapped transformer.  Just to make life complicated I have installed nominally 120/240 single phase services that were fed off a 3 phase transformer network in which case you actually have 120/208 with phases 120 deg out of phase.
Which is the majority condition for commercial buildings, and what folks in our industry will mostly encounter.
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Mac Kerr

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Re: Sparky Language Lesson
« Reply #43 on: June 26, 2015, 02:27:14 pm »

Of course this is correct, IF you in fact have a single phase/center tapped transformer.  Just to make life complicated I have installed nominally 120/240 single phase services that were fed off a 3 phase transformer network in which case you actually have 120/208 with phases 120 deg out of phase.

If you have installed a service that has 2 hot legs and they are from different phases, as in part of a 120/208 3 service, it is clearly not (nominally or otherwise) a single phase 120/240V service, and has no access to 240V.

Mac
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Timothy J. Trace

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Re: Sparky Language Lesson
« Reply #44 on: June 26, 2015, 02:33:43 pm »

Can we agree to call the 120/240V grounded center tap service prevalent in the US "120/240V single-phase" or "125/250V single-phase"? It is not split-phase or two-phase.

"120/240V single-phase:" Does this always describe a three-wire service, two live and a neutral, with 120V across each live and neutral?
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TJ (Tom) Cornish

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Re: Sparky Language Lesson
« Reply #45 on: June 26, 2015, 02:34:55 pm »

If you have installed a service that has 2 hot legs and they are from different phases, as in part of a 120/208 3 service, it is clearly not (nominally or otherwise) a single phase 120/240V service, and has no access to 240V.

Mac
Which is semantics in the vast majority of cases.  NEMA plugs don't differentiate between 208 and 240 volts, and very few products care.  Those that do can be internally adjusted.
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TJ (Tom) Cornish

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Re: Sparky Language Lesson
« Reply #46 on: June 26, 2015, 02:36:52 pm »

"120/240V single-phase:" Does this always describe a three-wire service, two live and a neutral, with 120V across each live and neutral?
That always describes a service with 3 current carrying conductors (hot, hot, neutral), and one ground conductor.  Whether you consider this a 3-wire service or a 4-wire service depends on if you're buying SOOW cord (you count the ground conductor), or if you're buying NM cable (you don't count the ground conductor).  More confusing fun. 
« Last Edit: June 26, 2015, 02:38:53 pm by TJ (Tom) Cornish »
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Timothy J. Trace

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Re: Sparky Language Lesson
« Reply #47 on: June 26, 2015, 02:57:45 pm »

....a 50 amp load will have a 32 volt drop and the end of your assembly. To keep within the 5% voltage drop guideline #6 maxes out at roughly 60 feet.  Or 200 feet maxes out at 18 amps.  Your continuous load will be ok-but what happens to your amps when the subs quick in?

Unlike most of this topic, I can speak to this part with confidence.

My four sub amps draw 7.5A 1/8-power in 4-ohm bridge. My two FR amps draw 8A, same spec. My two monitor amps, of which I only need one these days thanks to IEMs, draw 9A, same spec. I estimate my all-digital FOH at 3A, and my smallish all-LED light show at 5A. I estimate backline at 7A, everyone uses a modeler but we love our personal cooling fans.

When running full-out for an outdoor event with my distro, I put two sub amps, one FR amp, the monitor amp and FOH on one line. The other line gets everything else. This ends up being a well-balanced ~35A load per line.

I can think of only one time in the last decade that I've run out all 200' of cable. It was to a 100kVa generator, of which I'd directed the promoter to move it away from the stage as it was nowhere near to being a show-quiet model. I distinctly recall bumping the generator output to give a solid 120V at the stage under full system output. I'm completely ignorant of whether that's a "kosher" way to solve such problems, but the show went off without incident. Perhaps coincidentally, I think this show was the best my system has ever sounded. Great power, very light breeze, October sunshine on an uncovered stage in a huge university stadium parking lot, with no hard reflective surfaces inside of a quarter-mile in any direction. But I digress.

More often, I only need the 25' tails or the 50' cable, and I can't recall having to tweak anything under those circumstances.

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Jeff Bankston

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Re: Sparky Language Lesson
« Reply #48 on: June 26, 2015, 03:33:12 pm »

I agree. I find it strange how "110 Volts" just won't go away. Even stranger is how (on electric vehicle forums, in particular) I often see "110V" right next to "240V".

While we're on terminology, "split-phase" has no meaning in the world of power. There is single-phase and three-phase and that's it. Some services offer multiple voltages by virtue of being derived from transformer windings that are tapped, and sometimes the center taps are grounded. It's still single-phase.

Split-phase refers to a starting strategy used in certain single-phase induction motors in which a second "starting" winding that has a different inductance and resistance from the main winding is engaged by a centrifugal switch during start in order to provide the necessary rotating field.

-F
it is around 118 volts on the Fluke here in los angeles
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Stephen Swaffer

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Re: Sparky Language Lesson
« Reply #49 on: June 26, 2015, 04:06:09 pm »



I can think of only one time in the last decade that I've run out all 200' of cable. It was to a 100kVa generator, of which I'd directed the promoter to move it away from the stage as it was nowhere near to being a show-quiet model. I distinctly recall bumping the generator output to give a solid 120V at the stage under full system output. I'm completely ignorant of whether that's a "kosher" way to solve such problems, but the show went off without incident.

That is essentially what the POCO does with transformer taps-and why most distribution transformers have multiple taps.  How else do you get consistent voltage across hundreds of miles?

The only downside to fixing it this way is a bit of inefficiency due to voltage drop-but that is an insignificant consideration for a temp setup.

As to the voltage nuances and sparky speak.  Almost always I look at 208-220-230-240 as "nominally" the same.  Unless I have a motor that calls out a 208 vs 230 rating, etc.  Yes, those voltages give me clues as to the distribution behind it that I understand-and I do take them into consideration when necessary, but if a non-sparky asks for single phase any of the above, I will give him whatever I have available without comment.  If it matters to you clarify, because I likely will assume you don't know the difference (sorry :))
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Steve Swaffer

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Re: Sparky Language Lesson
« Reply #49 on: June 26, 2015, 04:06:09 pm »


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