New Fixture AC Power

[macsound]

Yes, of course, AV should be separate. But thinking about the catwalks in the theatres I've worked in:
The stage pin cables were for lighting, the edison AC hidden in a raceway was for worklights and any other visible plug was for any networking, opto, audio or effect gear. The audio guys never had the opportunity to plug into the wrong circuit.
In building out a new space and all the plugs look the same to a teenager, training only goes so far. The trained electricians know what relay circuit to use, the audio guys will probably scope out any circuit that is the same as theirs and cover with gaff, but there are still plenty of opportunity for mistakenly plugging in the wrong outlet.
How do we plan for that?

 

[MNicolai]

Erich, I believe you may be referring to "balanced Power " specifically operating at 120V line-to-line, and 60V to ground. This is not simply single-phase power, but a separately derived system where a 120V secondary has a grounded center tap. It is covered by NEC article 647-- Sensitive Electronic Equipment.

Balanced power is different from what Erich is referring to. Audio wants to be on a single leg of power or on split phase with each leg 180° apart where the leakage currents at least somewhat cancel each other out.

From Middle Atlantic's research on this subject:

Phasing of Supply Conductors

When designing power distribution systems, electrical engineers will typically balance the loads among all the phase conductors in order to reduce the load on individual phase portions of transformers and circuit breaker panels. This is not always the best design for AV systems.

Three Phase electrical service is most commonly found in commercial and industrial buildings where there are motors, air conditioners and lighting controllers. Due to leakage current and grounded filter capacitors found in most equipment, loads on each phase usually couple a small amount of noise onto the ground circuit. Any device that draws a pulse of current for less than the entire voltage wave generates harmonics. Because the phase conductors are separated by 120 degrees, some of the harmonic current in the neutral conductor combines in phase (adds), rather than canceling, as in the case of the 60Hz fundamental current. The problems with three phase service are mostly from harmonic-generating devices sharing the same neutral as the AV system. A shielded isolation transformer minimizes the coupling of these harmonics to the signal path by deriving a new neutral and neutral-ground bond point.

Single-Phase 120/240V electrical service is most commonly found in residences and smaller commercial buildings, and is commonly used to feed AV equipment. One key advantage that single phase has over three phase is that while harmonic currents are still present, only even order harmonics can add in the shared neutral, and they are uncommon, since the waveform would be asymmetrical. In addition, use of single-phase 120/240V can result in at least a 6dB reduction in noise floor as compared to three phase if the capacitances of the connected equipment are relatively well balanced. Furthermore, if a signal cable is connecting two pieces of ungrounded equipment powered from opposite phases, the leakage current flowing in it will increase (causing more noise) as compared to powering the equipment from the same phase.

Further elaborating on the problem with 3-phase, here are Bill Whitlock's comments from a thread over at SynAudCon.

Now (finally!) to your questions. Putting all AV equipment on the same branch circuit, twisting the L and N conductors (don't include the G conductor) along the entire path back to the panel, keeping fast switching loads off the branch circuit and out of "your" conduit run, and even using an isolated ground system on the branch circuit are all things that will minimize ground loop issues. Be aware that unbalanced audio interconnects may still be a problem - only a few tens of microvolts of ground voltage difference can cause significant noise in such interfaces - video is much more forgiving. "Balanced power", since it addresses only leakage current issues that are generally insignificant compared to the "conduit transformer", is IMHO a waste of money.

Using legs of 3-phase power to operate single-phase circuits is *not* recommended - largely because nullifying the effect of the conduit transformer requires that *all* the phase conductors and the neutral be twisted (or, at least in the same conduit) for the entire run from panel to destination. If separate, single-phase circuits break away, cancellation in the remaining conductors will *not* occur. I always recommend a separately-derived transformer create the single-phase and locate it (and its new N-G bond) as close to your system as possible.

----

Yes, of course, AV should be separate. But thinking about the catwalks in the theatres I've worked in:
The stage pin cables were for lighting, the edison AC hidden in a raceway was for worklights and any other visible plug was for any networking, opto, audio or effect gear. The audio guys never had the opportunity to plug into the wrong circuit.
In building out a new space and all the plugs look the same to a teenager, training only goes so far. The trained electricians know what relay circuit to use, the audio guys will probably scope out any circuit that is the same as theirs and cover with gaff, but there are still plenty of opportunity for mistakenly plugging in the wrong outlet.
How do we plan for that?

In my projects all of the AV receptacles are usually orange as isolated ground receptacles, and I require that the faceplates are engraved "AUDIO/VIDEO ONLY". They're are also parked next to all of the AV connector panels so you have convenient AV power wherever you can plug a stage box or a console in.

 

[teqniqal]

Erich, I believe you may be referring to "balanced Power " specifically operating at 120V line-to-line, and 60V to ground. This is not simply single-phase power, but a separately derived system where a 120V secondary has a grounded center tap. It is covered by NEC article 647-- Sensitive Electronic Equipment.

ST

No, I was specifically referring to 240/120 single phase power.

• When you have harmonic generating loads (just about everything these days) and power them on a three-phase system, the harmonics don't all cancel-out at the common neutral, thus the reason for K-rated transformers, oversized neutrals, and other harmonic mitigation schemes.
  
  
• When you have harmonic generating loads and power them on a single-phase system, the harmonics all cancel-out at the common neutral. In the diagram below, the middle tap of the 240/120V windings would all be tied together so as to derive the common neutral and ground reference between everything.

You get electrically quieter systems as a result, and they don't back-feed noise upstream that can affect other systems. Historically, the lighting industry has just loaded-up each of the three phase legs at 120 volts to neutral, but you can use transformers that transfer each phase's power to a 240/120 single phase output. This increases the number of panelboards and dimer racks, as you would need three single-phase panelboards in lieu of one three phase panelboard, or three smaller single-phase dimmer racks in lieu of one bigger three-phase rack. In a small system this seems like a lot more gear, but in a large system the panelboard or dimmer rack count is about the same, it's just a different layout.

 

[BillConnerFASTC]

I have been using L5-20R twist locks for relay and 5-20R for constant but break that rule sometimes an parallel a 5-20R off a relay circuit. But I did that for a few dimmed circuits too, when I did dimners. They are graphically "connected" on plate. That, good labels, and orange for av seems workable.

 

[STEVETERRY]

No, I was specifically referring to 240/120 single phase power.

• When you have harmonic generating loads (just about everything these days) and power them on a three-phase system, the harmonics don't all cancel-out at the common neutral, thus the reason for K-rated transformers, oversized neutrals, and other harmonic mitigation schemes.
  
  
• When you have harmonic generating loads and power them on a single-phase system, the harmonics all cancel-out at the common neutral. In the diagram below, the middle tap of the 240/120V windings would all be tied together so as to derive the common neutral and ground reference between everything.

You get electrically quieter systems as a result, and they don't back-feed noise upstream that can affect other systems. Historically, the lighting industry has just loaded-up each of the three phase legs at 120 volts to neutral, but you can use transformers that transfer each phase's power to a 240/120 single phase output. This increases the number of panelboards and dimer racks, as you would need three single-phase panelboards in lieu of one three phase panelboard, or three smaller single-phase dimmer racks in lieu of one bigger three-phase rack. In a small system this seems like a lot more gear, but in a large system the panelboard or dimmer rack count is about the same, it's just a different layout.

View attachment 17608

Very interesting! I'm not aware of any dimming systems installed with this arrangement. Has anyone done a power quality analysis to see exactly what the THDv and THDi waveforms look like on this type of system? It would be especially interesting to see what 3rd, 5th, 7th and 11th harmonics propagate upstream through the delta primary, or between single-phase secondaries.

Also, as far as isolating THDi and preventing THDv from propagating from a phase control dimming system, I wonder what the cost and performance comparison is between this arrangement and a three-phase zig-zag harmonic-mitigating transformer? I smell a research project and an article!


Thanks!

ST

 

[teqniqal]

I have been using L5-20R twist locks for relay and 5-20R for constant but break that rule sometimes an parallel a 5-20R off a relay circuit. But I did that for a few dimmed circuits too, when I did dimmers. They are graphically "connected" on plate. That, good labels, and orange for av seems workable.

Be aware that 2014 NEC Article 406.3(E) introduced a new requirement that 5-15R and 5-20R receptacles that are remotely switched must have clear marking that the device is 'Controlled'. See the attached data sheets for examples. Hubbell, Legrand, and Leviton also offer a nice twist on this, too, as they have 'Controlled' tamper-resistant devices which are not required in schools, but certainly a consideration. Using black devices on upstage walls reduces the visual distractions, too. Now, if we can just get 'Controlled' tamper-resistant Surge Protected IG GFCI devices . . .

Side note: Of interest is that Leviton also offers RF remote-controlled marked switched receptacles, which could be useful in mobile set pieces. Look at their WattStopper line for info.

 

[macsound]

@teqniqal Ah that's great and exactly what I was looking for.
I mean the idea that audio circuits are adjacent to xlr connectors helps alot, but yes, this permanently labeled marking so people know what will and won't turn off is huge.
Seriously, I can imagine someone plugging into a relay outlet and wondering why there's no DMX in the catwalk until the sound guy comes in, because he chose the wrong hole.

 

[BillConnerFASTC]

Be aware that 2014 NEC Article 406.3(E) introduced a new requirement that 5-15R and 5-20R receptacles that are remotely switched must have clear marking that the device is 'Controlled'. See the attached data sheets for examples. Hubbell, Legrand, and Leviton also offer a nice twist on this, too, as they have 'Controlled' tamper-resistant devices which are not required in schools, but certainly a consideration. Using black devices on upstage walls reduces the visual distractions, too. Now, if we can just get 'Controlled' tamper-resistant Surge Protected IG GFCI devices . . .

Side note: Of interest is that Leviton also offers RF remote-controlled marked switched receptacles, which could be useful in mobile set pieces. Look at their WattStopper line for info.

All remotely controlled or just automatically controlled receptacles? A circuit breaker allows remote control of a receptacle. Not at my desk but I only found automatically controlled on line, and no definition.

 

[RonHebbard]

Balanced power is different from what Erich is referring to. Audio wants to be on a single leg of power or on split phase with each leg 180° apart where the leakage currents at least somewhat cancel each other out.

From Middle Atlantic's research on this subject:



Further elaborating on the problem with 3-phase, here are Bill Whitlock's comments from a thread over at SynAudCon.




----



In my projects all of the AV receptacles are usually orange as isolated ground receptacles, and I require that the faceplates are engraved "AUDIO/VIDEO ONLY". They're are also parked next to all of the AV connector panels so you have convenient AV power wherever you can plug a stage box or a console in.

View attachment 17606

@MNicolai I trust you've seen the Hubble IG duplexes in brown rather than orange with a tiny green marking on them for a more discrete look on US walls.
Toodleoo!
Ron Hebbard

 

[teqniqal]

All remotely controlled or just automatically controlled receptacles? A circuit breaker allows remote control of a receptacle. Not at my desk but I only found automatically controlled on line, and no definition.

I interpret it to mean controlled remotely by a switch or relay (contactor), with the exception of just manually toggling the circuit breaker handle. This would include a receptacle controlled (switched) by an energy management system, a timer, a stage lighting system, a photo-eye, and an A/V controller (like Crestron or AMX).

I spec these for the power receptacles along a make-up counter, too, since there are specific requirements (NEC 520.73) for switching and monitoring them.

 

[BillConnerFASTC]

I think the code says "automatically" but needs checking. I don't think a relay controlled stage lighting circuit qualifies. Woe be to the stage hand that plugs his fridge into a stage lighting circuit and his lunch spoils.

 

[teqniqal]

I think the code says "automatically" but needs checking.

NEC section 406.3(E) requires that "All nonlocking type 125-volt, 15- and 20-ampere receptacles, that are controlled by an automatic control device, or that incorporate control features that remove power from the receptacle for the purpose of energy management or building automation, shall be permanently marked with the symbol ( ' ) and located on the controlled receptacle outlet [face] where it is visible after installation." The word “controlled” on the receptacle face is optional, but the manufacturers have added it to many of the products for clarity (yes, there are many people that do not know what the ( ' ) symbol means). Receptacles for wall switch controlled outlets for a light is excepted, but I'd do it anyway.

I don't think a relay controlled stage lighting circuit qualifies.

NEC section 406.15 Dimmer Controlled Receptacles requires that "Receptacles supplying lighting loads shall not be connected to a dimmer unless the plug/receptacle combination is a nonstandard configuration type that is specifically listed and identified for each such unique combination." So I think only dimmed outlets are covered here. If you have 5-15R and 5-20R receptacles you are feeding power to ANY type of load via a remote control (not manually switching the circuit breaker handle) device, then 406.3(E) applies. Not to worry Bill, I spec switched 3-phase receptacles with duplex receptacles beside them just like you do, but I do now spec the 5-15R / 5-20R's to be marked controlled types. It couldn't hurt to put the ( ' ) symbol and 'controlled' text on the panel adjacent to the switched 3-phase receptacle, it just isn't required.

 

[BillConnerFASTC]

, that are controlled by an automatic control device, or that incorporate control features that remove power from the receptacle for the purpose of energy management or building automation,

Doesn't sound like stage lighting receptacles but interpretations will vary.

 

[MNicolai]

I expect context clues play a role here -- in a theater circuits labeled R## or D## are already understood to be controlled by the people using these rooms. In the coming years that may change as relay systems become the norm and are so transparent to users that they may forget they switch off from time to time.

The genesis of this code development is that energy code requirements for places like offices now require 50% of the receptacles be controlled for energy conservation. When my Tampa office relocated into a new suite this resulted in a lot of people plugging PC's or conference room TV's into receptacles that would automatically switch off on them at a certain time of day or in response to occ sensors. All of the switched receptacles were labeled "CONTROLLED" as required but that didn't make a difference because people aren't used to looking for that information. Even the electrical engineers who designed those power plans forgot to check which receptacles they were plugging into.

Fast forward a few years and the increasing reach of energy code will have more people looking for those clues as to what they should or should not plug into. Got a fan under your desk or desk lamps? That's going on the controlled receptacle. Looking for a place to plug in a phone or your PC? Better make sure that's not controlled.

 

[STEVETERRY]

NEC section 406.3(E) requires that "All nonlocking type 125-volt, 15- and 20-ampere receptacles, that are controlled by an automatic control device, or that incorporate control features that remove power from the receptacle for the purpose of energy management or building automation, shall be permanently marked with the symbol ( ' ) and located on the controlled receptacle outlet [face] where it is visible after installation." The word “controlled” on the receptacle face is optional, but the manufacturers have added it to many of the products for clarity (yes, there are many people that do not know what the ( ' ) symbol means). Receptacles for wall switch controlled outlets for a light is excepted, but I'd do it anyway.


NEC section 406.15 Dimmer Controlled Receptacles requires that "Receptacles supplying lighting loads shall not be connected to a dimmer unless the plug/receptacle combination is a nonstandard configuration type that is specifically listed and identified for each such unique combination." So I think only dimmed outlets are covered here. If you have 5-15R and 5-20R receptacles you are feeding power to ANY type of load via a remote control (not manually switching the circuit breaker handle) device, then 406.3(E) applies. Not to worry Bill, I spec switched 3-phase receptacles with duplex receptacles beside them just like you do, but I do now spec the 5-15R / 5-20R's to be marked controlled types. It couldn't hurt to put the ( ' ) symbol and 'controlled' text on the panel adjacent to the switched 3-phase receptacle, it just isn't required.

There is no longer a section 406.15. It went in to the 2014 NEC and was removed in the 2017 edition. During the three years it was in the NEC, it was subject to two Tentative Interim Amendments (TIA's) specifically exempting article 520 and 530 occupancies from its requirements.

The proposal to kill 406.15, which I wrote and CMP 18 agreed with, contained the following justification:

"This section should be deleted in its entirety. This new section sought to correct incompatibilities between certain types of dimmer and certain cord-connected loads. Such incompatibilities are currently dealt with in the listing of specific load types and the listing of specific dimmer types. That is the correct way to prevent unsafe incompatibilities between certain types of loads and certain types of dimmers. To prevent these incompatibilities by mandating an undefined "non-standard" connector creates more problems than it solves.

The current wording of the section contains a number of major flaws:

1. "Non-standard" is not defined with regard to plug/receptacle combinations. Does this mean a locking-type connector not normally used in a residential application is "non-standard" in such an application? Or does it mean that the connector in question must not mate with any existing NEMA type?

2. The section requires that a plug/receptacle combination be "specifically listed and identified for each unique combination". Does this mean we need a different unique connector pair for each combination of dimmer and dimmable load or load type that is compatible with that dimmer? Clearly, this is preposterous--there are not enough unique listed connectors available to satisfy this requirement--there are simply too many combinations of dimmer types (forward phase control, reverse phase control, sine wave--to name just a few) and safely dimmable loads and load types (halogen, fluorescent, magnetic ballasts, electronic transformers, LED drivers etc.).

3. This section sought to correct a specific problem: incompatibility between certain types of LED under-cabinet lighting and dimmers. The section wording tried to do this with a broad, sweeping requirement by requiring a new, undefined type of connector pair unrelated to load vs. dimmer incompatibility. This has two negative results:
A) The problem will not get fixed. The same specifiers and installers that ignored the listing requirements of specific dimmers and LED loads will ignore this section.
B) There will be far-reaching unintended consequences in a wide variety of safe applications of dimmers with receptacles. This section has already resulted in TIA's on NEC sections 520.45 and 530.21(A). The TIA's exempt these sections from section 406.15. There are many other safe applications of cord-connected loads to dimmers that will be negatively affected by the wording of section 406.15 for no good safety reason.

Clearly, the creation of this section was an attempt to solve a specific problem associated with an emerging and evolving new technology: LED's. But the wording of section 406.15 will not solve that problem, it will simply create additional new problems."

ST