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Author Topic: 2-phase hum?  (Read 6571 times)

Mike Sokol

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Re: 2-phase hum?
« Reply #10 on: February 11, 2016, 03:46:53 pm »

Using only one side of the distro (phase, if you want to misuse that term) kind of cripples why you have it in the first place.

Not to throw gas on the fire, but what should we call the two sides of the distro, if not phase?
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Mike Sokol
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Mike Sokol

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Re: 2-phase hum?
« Reply #11 on: February 11, 2016, 03:59:11 pm »

I just read this article posted on PSW about chasing hum in a church sound system. http://www.prosoundweb.com/article/accidental_electrician_eliminating_dreaded_sound_system_hum_buzz/

So I sent an email with our concerns to the editor of PSW, and he's pulled the article due to inaccuracy. That's one reason I like e-zines rather than paper magazines. We can easily correct mistakes.

Now it looks like I get to write a primer on hum and buzz issues. Don't worry, I won't say "phase" except when referring to 3-phase power.  ;D
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Jonathan Johnson

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Re: 2-phase hum?
« Reply #12 on: February 11, 2016, 04:51:40 pm »

Not to throw gas on the fire, but what should we call the two sides of the distro, if not phase?

Poles.

It could be a 120/240V single-phase, double-pole system with a center-tapped secondary with the center tap bonded to ground. You have two hot/live/line poles, and one neutral pole.

It could be a 120/208V three-phase, triple-pole system with a common-neutral secondary (common bonded to ground). You have three hot/live/line poles and one neutral pole.

In wiring in the United States, the hot/live/line poles are often referred to as line conductors. You may notice that wiring devices are often labeled L1, L2, (L3,) N, G. That's three "LINE" conductors (which are live), one NEUTRAL conductor, and one GROUND conductor. Sometimes instead of L1, L2, (L3,) N, G you have X, Y, (Z,) W, G -- X, Y, and Z are the line conductors, W is the neutral conductor (W for WHITE), and G is the ground (G for "green" probably). Of course, L3/Z are only used with 3-phase power.
« Last Edit: February 11, 2016, 05:00:53 pm by Jonathan Johnson »
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John Roberts {JR}

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Re: 2-phase hum?
« Reply #13 on: February 11, 2016, 04:54:43 pm »

Poles.
+1 polarity.... 

as if phase isn't complicated and misused enough in audio, power distribution gives it even more nuanced meanings.

JR
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Jonathan Johnson

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Re: 2-phase hum?
« Reply #14 on: February 11, 2016, 05:03:53 pm »

"So the original system installer (OI) had specified that the circuits needed to be all on the same phase. My guess is that some well-meaning electrician had thought it would be smart to group the circuits together during one of the church expansion projects. I returned the circuits to their original spacing.

Having all the power circuits on an identical phase is important for minimizing the possibility of an inter-chassis current in a ground loop.


This portion you quoted indicates that the troubleshooter changed the configuration of the POWER wires to fix a GROUND LOOP problem. Did they change anything with the ground conductors?

That's a bit like switching brands of gasoline to fix a flat tire.
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Jerome Malsack

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Re: 2-phase hum?
« Reply #15 on: February 11, 2016, 05:47:00 pm »

All true on the polarity and will it make a difference.  However Mike if you put a computer UPS system in front of the digital mixer you have the added complexity. 
Especially when the S16 and Behringer X32.  If the S16 is connected to the stage power and not back to the UPS then what will this do when the power is pulled down enough to cause the UPS to switch onto the battery ?  Now the S16 is at a different power source than the X32.  Add in the Ethernet cable is shielded ? 
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John Roberts {JR}

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Re: 2-phase hum?
« Reply #16 on: February 11, 2016, 06:37:20 pm »

All true on the polarity and will it make a difference.  However Mike if you put a computer UPS system in front of the digital mixer you have the added complexity. 
Especially when the S16 and Behringer X32.  If the S16 is connected to the stage power and not back to the UPS then what will this do when the power is pulled down enough to cause the UPS to switch onto the battery ?  Now the S16 is at a different power source than the X32.  Add in the Ethernet cable is shielded ?

Which brings us back around to equipment design... The more bits we try to send down network cables the easier it is to confuse it. I like the concept of running equipment off the same power drop because they all see the exact same ground corruption, but there is no theory to support this, just practice.

JR   
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Rob Spence

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Re: 2-phase hum?
« Reply #17 on: February 11, 2016, 06:55:49 pm »

Which brings us back around to equipment design... The more bits we try to send down network cables the easier it is to confuse it. I like the concept of running equipment off the same power drop because they all see the exact same ground corruption, but there is no theory to support this, just practice.

JR

I like digital mixers that use UTP cable to connect to the stage. Well designed category cable interfaces that are static resistant mean there is no ground connection through the snake cable to contribute to problems.

I agree with others that is simply good practice to bring power to foh so all are on the same ground. However,  much of the entry level gear is used without following this practice and having a ground in the connection to the stage box creates problems.



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Stephen Swaffer

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Re: 2-phase hum?
« Reply #18 on: February 11, 2016, 11:17:13 pm »

Poles.

It could be a 120/240V single-phase, double-pole system with a center-tapped secondary with the center tap bonded to ground. You have two hot/live/line poles, and one neutral pole.

It could be a 120/208V three-phase, triple-pole system with a common-neutral secondary (common bonded to ground). You have three hot/live/line poles and one neutral pole.


I would agree that this terminology seems to be correct and fit with code usage.

Practically speaking, in most cases, using "Phase A & B or Phases A, B & C" is the common language.  Most people when the ask for a "coke" are content with whatever cola is available-we use dozens of common nicknames on a daily basis-how many if us actually answer to our given names (unless its mom's voice)?  When troubleshooting industrial controls we use the term "contact" to refer to a physical contact or a logical bit without explanation, the potential ramifications are understood. I feel like, if people are working at a level that it really matters, they need to take the time to understand. Perhaps a "white paper" explaining the situation is in order-but it you go asking a the average electrician what "pole" this circuit is connected to, he is going to be trying to figure which structural pole the conduit containing that circuit is attached to.
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Steve Swaffer

Mike Sokol

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Re: 2-phase hum?
« Reply #19 on: February 12, 2016, 08:11:20 am »

+1 polarity.... 

But I see this term mis-used in the RV industry all the time when swapped Hot and Neutral wires are referred to as "reverse polarity". Of course, AC power in the US swaps polarity 120 times a second (60 Hz). Sadly, many so called RV "experts" think it causes an RV hot-skin voltage, which isn't true.

So what do we call swapped Hot and Neutral wires?
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Mike Sokol
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Re: 2-phase hum?
« Reply #19 on: February 12, 2016, 08:11:20 am »


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