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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Timothy J. Trace on June 25, 2015, 01:54:42 pm

Title: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 01:54:42 pm
Coming from a guy with my mileage...sheesh.

How do I clearly, and concisely, ask an electrician for lugs to tie in my two 50A legs of 110VAC single-phase on a common, bonded neutral and ground?

I typically say, "50A single-phase, please." Industry sparkies immediately grok my needs, yet I often confuse uninitiated commercial electricians.

I'm hoping for a lesson today in how to more clearly express my desires to a wider audience.

Thanks.
Title: Re: Sparky Language Lesson
Post by: Mark Cadwallader on June 25, 2015, 02:33:45 pm
May I respectfully suggest that this question should be moved or reposted in the AC Power sub-forum?  Lots of sparky-types over there.
Title: Re: Sparky Language Lesson
Post by: Andrew Broughton on June 25, 2015, 02:44:26 pm
I would say:
"50A single-phase 4-wire".

If you don't say 4-wire, the electrician doesn't know that you want 2 hots instead of 1.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 03:47:53 pm
May I respectfully suggest that this question should be moved or reposted in the AC Power sub-forum?  Lots of sparky-types over there.

Mods, please.
Title: Re: Sparky Language Lesson
Post by: Tim McCulloch on June 25, 2015, 04:00:18 pm
I would say:
"50A single-phase 4-wire".

If you don't say 4-wire, the electrician doesn't know that you want 2 hots instead of 1.

50 amp 120/240v single phase with ground (3 wires plus ground, 4 wires total).

I've found that non-entertainment electricians do not consider the EGC to be "a wire".  The 120/240v designation SHOULD tell the electrician that we want split-phase, not 240v service.

When specifying 3 phase power I've found it necessary to call out WYE service, as in "200 amp 120/208v 3 phase wye, 4 wires plus ground (5 wires total)."
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 04:44:47 pm
50 amp 120/240v single phase with ground (3 wires plus ground, 4 wires total).

I've found that non-entertainment electricians do not consider the EGC to be "a wire".  The 120/240v designation SHOULD tell the electrician that we want split-phase, not 240v service.

That's quite helpful, Tim. Thank you. Two follow-on q's which I know will be a cakewalk for you LOL ---

Title: Re: Sparky Language Lesson
Post by: Mark Cadwallader on June 25, 2015, 05:17:26 pm
That's quite helpful, Tim. Thank you. Two follow-on q's which I know will be a cakewalk for you LOL ---

  • How does this sound? "50A split-phase 110V phase-to-neutral, 3 wires plus ground, 4 wires total, for connecting a tail set or an L5-50P."  ....or did I get too wordy?
  • Forgive my ignorance, must the two hot conductors always be fed from separate lines of the split-phase, or may they draw from the same phase if the individual upstream breakers equal each conductor's ampacity?

Perhaps you made a typo, but an L5-50P is for one 125v leg, not two. The NEMA designation for two legs (125/250 v) is 14-(amps).  I have seen 14-50p (straight blade range plug), but never an actual L14-50p. There is a 125/250 3 pole, 4 wire device, but it is the "CS" (California standard) series. (Namely the CS 6365.). The L15-50p is for 3 phase,250 volts only.
Title: Re: Sparky Language Lesson
Post by: Andrew Broughton on June 25, 2015, 05:18:02 pm
Forgive my ignorance, must the two hot conductors always be fed from separate lines of the split-phase, or may they draw from the same phase if the individual upstream breakers equal each conductor's ampacity?

I think you would need a double-sized neutral for that to be legal.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 05:40:52 pm
Perhaps you made a typo...there is a 125/250 3 pole, 4 wire device, but it is the...CS 6365.

Thanks much, Mark. You're being generous by calling it a typo :)  I was outright mistaken.

These are functionally similar to my cables: http://www.motionlabs.com/pm-240-1-64-50a-125250v.aspx .

Is this better? "50A split-phase 110V phase-to-neutral, 3 wires plus ground, 4 wires total, for connecting a tail set or a CS6365C." I want to be concise as possible, so if I'm saying too much, please let me know.

Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 05:42:23 pm
I think you would need a double-sized neutral for that to be legal.

Thanks. Can you help me understand how this is different than having two branch circuits drawing off the same line? Is it because we're dealing with portable distribution?
Title: Re: Sparky Language Lesson
Post by: Rob Spence on June 25, 2015, 05:45:26 pm
That's quite helpful, Tim. Thank you. Two follow-on q's which I know will be a cakewalk for you LOL ---

  • How does this sound? "50A split-phase 110V phase-to-neutral, 3 wires plus ground, 4 wires total, for connecting a tail set or an L5-50P."  ....or did I get too wordy?
  • Forgive my ignorance, must the two hot conductors always be fed from separate lines of the split-phase, or may they draw from the same phase if the individual upstream breakers equal each conductor's ampacity?

Just say what Tim said.

120/240 50a 4 wire. 3 wires plus ground.

Use all the words as written. Don't get cute with it.

Since you said lugs, don't confuse it with connector types.

Go study a NEMA chart so you get your designations right. Your lack of knowledge about even what connectors to use is scary.




Sent from my iPad using Tapatalk HD
Title: Re: Sparky Language Lesson
Post by: Rob Spence on June 25, 2015, 05:50:22 pm
I note that the various posters used 110, 120 and 125 (and the associated double).

As far as I know, 110 has fallen out of common usage and while NEMA identifies connectors as 125/250, the most seen usage seems to be 120/240.

Comments?

Sent from my iPad using Tapatalk HD
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 05:54:40 pm
Just say what Tim said. 120/240 50a 4 wire. 3 wires plus ground. Use all the words as written. Don't get cute with it. Since you said lugs, don't confuse it with connector types.
Fair enough. Respectfully, no one has yet used the word "lugs," except me. Is that the correct term to use which should be understood by a commercial electrician in this context, "lugs?"

Go study a NEMA chart so you get your designations right. Your lack of knowledge about even what connectors to use is scary.
I did, Rob. Right here: http://www.stayonline.com/reference-nema-locking.aspx ...and became confused, which serves as an explanation as to why I'm here seeking assistance.

ETA: And now, thanks to Mark's help, I see the NEMA L14-50 on that chart and the cross-ref to the CS6365C. Nice!
Title: Re: Sparky Language Lesson
Post by: Andrew Broughton on June 25, 2015, 06:02:53 pm
Thanks. Can you help me understand how this is different than having two branch circuits drawing off the same line? Is it because we're dealing with portable distribution?

I'll leave that to the experts, but it would be necessary in the case that the 2 hots were being tied into 2 50a breakers on the same phase. If you tied both conductors into 1 50a breaker, you'd probably be fine (someone can correct me if I'm wrong), but you'd only be able to draw 1/2 the amperage that you would if the 2 hots were on opposite phases.
Tying the 2 hots into anything larger than a 50a breaker of course would still be illegal.
Title: Re: Sparky Language Lesson
Post by: Tim McCulloch on June 25, 2015, 06:28:13 pm
That's quite helpful, Tim. Thank you. Two follow-on q's which I know will be a cakewalk for you LOL ---

  • How does this sound? "50A split-phase 110V phase-to-neutral, 3 wires plus ground, 4 wires total, for connecting a tail set or an L5-50P."  ....or did I get too wordy?
  • Forgive my ignorance, must the two hot conductors always be fed from separate lines of the split-phase, or may they draw from the same phase if the individual upstream breakers equal each conductor's ampacity?

"50A 120/240v split (aka single) phase, 3 wires plus ground, terminated to Hubbell CS6369 or to lugs in a fused disconnect switch."

When you specify 120/240v service it requires (or at least infers) that the 2 hot legs are 180 apart, with the center tap acting as Neutral.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 06:36:24 pm
"50A 120/240v split (aka single) phase, 3 wires plus ground, terminated to Hubbell CS6369 or to lugs in a fused disconnect switch."

When you specify 120/240v service it requires (or at least infers) that the 2 hot legs are 180 apart, with the center tap acting as Neutral.

Thanks, Tim. Does "fused" include enclosed circuit breaker disconnects by implication?
Title: Re: Sparky Language Lesson
Post by: Stephen Swaffer on June 25, 2015, 06:51:21 pm
50 amp 120/240v single phase with ground (3 wires plus ground, 4 wires total).

I've found that non-entertainment electricians do not consider the EGC to be "a wire".  The 120/240v designation SHOULD tell the electrician that we want split-phase, not 240v service.

When specifying 3 phase power I've found it necessary to call out WYE service, as in "200 amp 120/208v 3 phase wye, 4 wires plus ground (5 wires total)."

+1

FWIW, as an electrician the context is important.  3 phase/4 wire when talking a panel or service implies 3 phases plus a neutral-because 3 phases without a neutral is common in industry.  When dealing with portable cord 3 phase 4 wire implies 3 phases plus a ground because we are usually dealing with a 3 phase load.  So the context determines whether or not a wire is "counted".  Why make it easy?  So yes all of the wording is important.

I would prefer to see "breaker or fused disconnect" just because there times where fuses (specifically fast blow) are mandated so while a breaker and a fuse are both acceptable by code for overcurrent protection they are not always equivalent so tell me its "OK". 
Title: Re: Sparky Language Lesson
Post by: Frank DeWitt on June 25, 2015, 07:34:16 pm

Your lack of knowledge about even what connectors to use is scary.


It is good that he is gaining knowledge.  I am much more worried about people who don't want to learn.
Title: Re: Sparky Language Lesson
Post by: Mike Sokol on June 25, 2015, 08:58:53 pm
"50A 120/240v split (aka single) phase, 3 wires plus ground, terminated to Hubbell CS6369 or to lugs in a fused disconnect switch."

When you specify 120/240v service it requires (or at least infers) that the 2 hot legs are 180 apart, with the center tap acting as Neutral.

Actually, in addition to 180 degree phases, the latest code revision allows you to connect an RV plug to 2 hot legs that are 120 degrees out of phase, basically 2 legs of a 3-phase Wye service. But as you stated, you can't use the same phase to feed both legs. That's because the neutral current will then be additive rather than subtractive. Basically, if you feed both legs of the plug with a common phase, then you can easily get 60, 70, 80 or even 100 amps flowing though a neutral wire and connection only rated for 50 amps.

Here's what a 50-amp NEMA 14-50 plug looks like when its neutral tried to carry more than 50 amps due to both hot legs being connected to the same phase. It ain't pretty...
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 25, 2015, 09:44:33 pm
Basically, if you feed both legs of the plug with a common phase, then you can easily get 60, 70, 80 or even 100 amps flowing though a neutral wire and connection only rated for 50 amps.

Thanks,  Mike!
Title: Re: Sparky Language Lesson
Post by: Mark Cadwallader on June 25, 2015, 11:24:37 pm
I recently discovered that while the Hubbell CS6364/6365 series devices only accept up to 6 AWG, the Leviton version accepts 4 AWG. For longer runs, other than cost and weight, it seems like 4 AWG wire would be the way to go. Am I missing anything?

Edit: correct Hubbell wire size. Doh!
Title: Re: Sparky Language Lesson
Post by: Rob Spence on June 25, 2015, 11:57:49 pm
"50A 120/240v split (aka single) phase, 3 wires plus ground, terminated to Hubbell CS6369 or to lugs in a fused disconnect switch."

When you specify 120/240v service it requires (or at least infers) that the 2 hot legs are 180 apart, with the center tap acting as Neutral.

While I like Hubbell, I would not restrict it. There are other brands I like better but as long as it meets the CS6369 spec, I don't much care.


Sent from my iPad using Tapatalk HD
Title: Re: Sparky Language Lesson
Post by: Jeff Bankston on June 26, 2015, 03:17:02 am
i'm a commercial electrician. just ask for lugs for the wire gauge you need. For 50 amp ask for #6 lugs. #8 will work but its easier to put it in the larger #6 hole.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 10:07:20 am
50A 120/240v split (aka single) phase, 3 wires plus ground, terminated within 125' of the stage to CS6369 or #6 lugs in an overload-protected disconnect switch.

How's that look to your experienced eyes?
Title: Re: Sparky Language Lesson
Post by: Frank Koenig on June 26, 2015, 10:26:52 am
I note that the various posters used 110, 120 and 125 (and the associated double).

As far as I know, 110 has fallen out of common usage and while NEMA identifies connectors as 125/250, the most seen usage seems to be 120/240.

Comments?

Sent from my iPad using Tapatalk HD

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
Title: Re: Sparky Language Lesson
Post by: Frank DeWitt on June 26, 2015, 10:42:06 am
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".
-F

OK I know it was 110 (That was Edisons standard.  Now it is 120 or 125  but who said?  who is in charge? When did it change? why.

BTW  In the beginning Edison set out some goals.  He wanted bulbs as bright as good residential gas lighting (because that was what he planned to compete against.)  He decided that that would require 100 watts.  He felt that 1 amp per lamp would allow for reasonable wiring so that meant 100 volts He added 10 volts to take care of losses and we got 110 volts.

At the time there was already some wiring in cities, both for telegraph and for arc street lighting.  Te street lighting voltage was very high.



Title: Re: Sparky Language Lesson
Post by: Stephen Swaffer on June 26, 2015, 11:01:26 am
i'm a commercial electrician. just ask for lugs for the wire gauge you need. For 50 amp ask for #6 lugs. #8 will work but its easier to put it in the larger #6 hole.

If you are using portable cord you need at least #6 for 50 amps-in some cases #4 is required. Most lugs for #4 will be fine with #6.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish on June 26, 2015, 11:07:57 am
OK I know it was 110 (That was Edisons standard.  Now it is 120 or 125  but who said?  who is in charge? When did it change? why.

BTW  In the beginning Edison set out some goals.  He wanted bulbs as bright as good residential gas lighting (because that was what he planned to compete against.)  He decided that that would require 100 watts.  He felt that 1 amp per lamp would allow for reasonable wiring so that meant 100 volts He added 10 volts to take care of losses and we got 110 volts.

At the time there was already some wiring in cities, both for telegraph and for arc street lighting.  Te street lighting voltage was very high.
I did some research on this a while back.  As you mention, 110v was a historical maximum: 100V + 10% allowable, which was revised in 1954 (ANSI C84) to the current US voltage standard of 120v +/- 5%.  Plugs and receptacles are often rated at 125V/250V, which allows for the high side of the allowable range - i.e. the maximum allowable voltage, not the nominal.  Other oddball voltages like 115 or 117 volts often appear on motors, and this was to indicate the expected voltage at the motor - 120V minus a few volts for distribution wiring.

If you actually measure voltage above 125V, there's either a loose neutral, or a buck/boost transformer that's set too high.  Neither are good situations.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 11:14:42 am
If you are using portable cord you need at least #6 for 50 amps-in some cases #4 is required. Most lugs for #4 will be fine with #6.
My cords are #6, 4-wire.

So ... "50A 120/240v split (aka single) phase, 3 wires plus ground, terminated within 125' of the stage to CS6369 or #4 lugs inside an overload-protected disconnect switch."

LOL! So much discussion to get to this, but it seems a good time was had by all ;)    .....and I've learned things in the process. Win.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish on June 26, 2015, 11:22:05 am
My cords are #6, 4-wire.

So ... "50A 120/240v split (aka single) phase, 3 wires plus ground, terminated within 125' of the stage to CS6369 or #4 lugs inside an overload-protected disconnect switch."

LOL! So much discussion to get to this, but it seems a good time was had by all ;)    .....and I've learned things in the process. Win.
You'll probably be OK with that terminology, but asking with the right words is no guarantee you'll get what you need.  Testing is necessary.  Your #6 cables are fairly commonly used for 50A distribution, however technically they are illegal.  A picky inspector may ding you on that.  For future cable purchases, move up to #4 cabling for 50A.  You'll have less voltage drop, and less to worry about from inspectors.
Title: Re: Sparky Language Lesson
Post by: Frank DeWitt on June 26, 2015, 11:55:21 am
I did some research on this a while back.  As you mention, 110v was a historical maximum: 100V + 10% allowable, which was revised in 1954 (ANSI C84) to the current US voltage standard of 120v +/- 5%.

Wow, that was quick.  Thanks.   BTW Just for fun I checked some manuals and advertising for Kohler light plants  (Generator)
1920  - 110
1926 -  110
1924 - 110
1228 -  110
1937  - 115
1941 - 115
1945 -  115
1947 -  115

I have a 1947 It is rated at 115 Volt, A C  I am going to readjust it for 120.  I take it to engine shows and use it to make coffee and waffles in the morning so the faster cook time will be welcome.  (Grin)  BTW The waffle iron is marked 110 V and is around 1920.  No I am not serious about worrying about this
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 11:57:39 am
Testing is necessary.

Always!

Your #6 cables are fairly commonly used for 50A distribution, however technically they are illegal.  A picky inspector may ding you on that.  For future cable purchases, move up to #4 cabling for 50A.  You'll have less voltage drop, and less to worry about from inspectors.

Better, then, to spec 45A service?    --- I'm trying to interpret NEC Table 400.5(A).
Title: Re: Sparky Language Lesson
Post by: Ray Aberle on June 26, 2015, 12:21:59 pm
Always!

Better, then, to spec 45A service?    --- I'm trying to interpret NEC Table 400.5(A).

It will be a LOT more common to find 50A/220V service (breakers, outlets) then 45A/220V whether installed or available to be installed by whomever you are sending the requirements to.

-Ray
Title: Re: Sparky Language Lesson
Post by: Tim McCulloch on June 26, 2015, 12:24:41 pm
Always!

Better, then, to spec 45A service?    --- I'm trying to interpret NEC Table 400.5(A).

Asking for 45 amp service will make them think you're crazy.

From the practical standpoint, you're unlikely to have an inspector reject your use if the rest of your electrical distribution is safe and compliant.  I'm with TJ - bigger wire is always better :)
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 12:33:12 pm
Asking for 45 amp service will make them think you're crazy.

Tim, we established YEARS ago that guys named "TJ" are indeed crazy.  ;)

....and that's exactly the kind of thing I wanted to learn from this topic. How to not act crazy in front of the grown-ups. So, thank you.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish on June 26, 2015, 12:50:08 pm
Tim, we established YEARS ago that guys named "TJ" are indeed crazy.  ;)

....and that's exactly the kind of thing I wanted to learn from this topic. How to not act crazy in front of the grown-ups. So, thank you.
Indeed.  :)

I wouldn't sweat your #6 wire if the rest of your distro equipment is high quality, but going forward, it's a worthy investment to get the right wire.  Incidentally, 8/4 is a better choice for 30A two-phase cables than 10/4, and 8/5 is DEFINITELY better than 10/5 for 3-phase L21-30 stuff.
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 12:56:12 pm
I wouldn't sweat your #6 wire if the rest of your distro equipment is high quality...

My cable assemblies (125', 50') and 25' tails are well-built and maintained. My box is a Motion Labs 3-space Rac Pack in a roto molded rack. I've got 30' of Guard Dog 3-channel drop-in protectors and another 30 feet of 2-channel drop-over protectors. I think it looks good when deployed.


Title: Re: Sparky Language Lesson
Post by: Stephen Swaffer on June 26, 2015, 01:29:05 pm
Everybody sweats ampacity-depending on whether or not the neutral "counts" # requires a 45 amp breaker or a 60 breaker (rounded up to next standard size which are 45,50, 60...)

However 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? 
Title: Re: Sparky Language Lesson
Post by: Frank Koenig on June 26, 2015, 01:40:16 pm
Wow, that was quick.  Thanks.   BTW Just for fun I checked some manuals and advertising for Kohler light plants  (Generator)
1920  - 110
1926 -  110
1924 - 110
1228 -  110
1937  - 115
1941 - 115
1945 -  115
1947 -  115

I have a 1947 It is rated at 115 Volt, A C  I am going to readjust it for 120.  I take it to engine shows and use it to make coffee and waffles in the morning so the faster cook time will be welcome.  (Grin)  BTW The waffle iron is marked 110 V and is around 1920.  No I am not serious about worrying about this

You beat me to it. I was going to ask what is the age of the NEWEST piece of (US configured) gear anyone knows about that says 110V on the nameplate. For me it's an amp I used to have (6V6 push-pull, no negative feedback) that was late 1930s.

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   :)

-F

PS: Your cook time should vary as roughly the inverse square of the voltage. Waffles. Yum.
Title: Re: Sparky Language Lesson
Post by: Mac Kerr on June 26, 2015, 02:04:50 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   :)

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
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish 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.
Title: Re: Sparky Language Lesson
Post by: Stephen Swaffer 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.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish 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.
Title: Re: Sparky Language Lesson
Post by: Mac Kerr 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
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace 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?
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish 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.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish 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. 
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace 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.

Title: Re: Sparky Language Lesson
Post by: Jeff Bankston 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
Title: Re: Sparky Language Lesson
Post by: Stephen Swaffer 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 :))
Title: Re: Sparky Language Lesson
Post by: John Roberts {JR} on June 26, 2015, 04:29:31 pm
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.
The main problem with doing that is what happens when you are not drawing full system output? Your 200' going, and coming, through wire, is no longer dropping the same voltage it was at full current.

As long as you don't exceed the over voltage spec for your gear you are Ok...  I'd measure the no-load voltage and if too scary maybe split the difference... 

JR
Quote
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.
Title: Re: Sparky Language Lesson
Post by: TJ (Tom) Cornish on June 26, 2015, 04:45:39 pm
The main problem with doing that is what happens when you are not drawing full system output? Your 200' going, and coming, through wire, is no longer dropping the same voltage it was at full current.

As long as you don't exceed the over voltage spec for your gear you are Ok...  I'd measure the no-load voltage and if too scary maybe split the difference... 

JR
This is good advice.  Also keep in mind that if the generator is marginal or if voltage regulation is poor, when the load is suddenly removed - turning lighting off, the end of an intense song, voltage may spike above the no-load level.

What's the opposite of a brown-out?  A white-out?  A blue-out?
Title: Re: Sparky Language Lesson
Post by: Timothy J. Trace on June 26, 2015, 05:04:58 pm
Thanks, guys. Good advice from all.

I can tell you that the generator was a nice CAT, from a well-known rental supplier ---- it just wasn't a noise-dampened model. It was nicely fly-wheeled and regulated, and easily sustained delivery while my subs were cranking.

I don't precisely recall the idle voltage, but I'm sure I metered it, and I'm sure it wasn't high enough to trip any alarms in head....or on my Furmans.