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Author Topic: Distributed Power  (Read 16920 times)

Mike Sokol

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Re: Distributed Power
« Reply #20 on: December 20, 2013, 07:00:06 pm »

This means that if the neutral wire is loose, high resistance, or broken, it may not be able to carry the current imbalance between phases. In that situation, the 240 or 208 volts is divided between your gear in proportion to your equipment's apparent impedance. For example, if you have a 1000 par can on one leg and a 100 watt mixer on the other leg, the par can will take 21 volts, and the mixer will then receive 219 volts from a 240 volt service. This is really bad.

Yup, that's the point. When you're into extension cord mode, a lost neutral just shuts down the power to a piece of gear. However, when you're running a 240 or 208 volt distro that splits down to 120-volts, if a neutral then fails then you'll likely create an over-voltage condition on the less loaded side of the distro split. And few pieces of audio gear will sustain 200 volts AC for even a few seconds.

This just means that your 120/240-V AC distro wiring has to be perfect and properly maintained. No cuts or pulled out wires, no corroded connectors allowed. I always checked the lug screws in my power distro gear at least once a year. Funny how 10,000 miles in the back of a truck loosens everything up. That's because a loose neutral lug can cost you lots of money in a heartbeat. Don't get me wrong, 240-volt split-phase or 208-volt 3-phase distro is great. You just have to respect that's you're playing with a lot more power.

When you get into camlocks and 2/0 cable, then it's very serious power and you really need to up your game. At that point arc-flash explosions became a real possibility. I'm putting together a recommended list of PPE gear for sound and lighting crews connecting to these high amperage systems and should have an article published early in the new year.
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Rob Spence

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Re: Distributed Power
« Reply #21 on: December 20, 2013, 07:38:31 pm »

I hadn't seen a commercial product of this.  It's interesting - they list as a "feature" that you can un-bond the grounds between sections.  Not sure why that's a good idea.  Presumably this is not a listed product.  Hopefully they've done the math and some testing to be sure that their circuit board traces and fast-on connectors are suitable for the full 20A load.

I have a single section version (1 in, 3 out) that they gave me since I had documented my build of one using many parts from them. The unit is built with up to 3 modules and the ground ties between are external (on the rear) jumpers. The "feature" is simply a byproduct of the manufacturing.
Internally (not easy to open up) the PC board is well made with very wide, heavy traces.


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Jared Koopman

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Re: Distributed Power
« Reply #22 on: December 20, 2013, 08:36:18 pm »


NEC is pretty clear on this - must be totally enclosed in metal. A wood rack is not sufficient.

So a metal chassis mounted in a wood rack is ok since the electrical bits are enclosed within the chassis?
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Jared Koopman

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Re: Distributed Power
« Reply #23 on: December 20, 2013, 08:38:33 pm »


This means that if the neutral wire is loose, high resistance, or broken, it may not be able to carry the current imbalance between phases. In that situation, the 240 or 208 volts is divided between your gear in proportion to your equipment's apparent impedance. For example, if you have a 1000 par can on one leg and a 100 watt mixer on the other leg, the par can will take 21 volts, and the mixer will then receive 219 volts from a 240 volt service. This is really bad.

Thanks.

Is this something measurable that can be detected before plugging in anything to the circuit?

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Jared Koopman

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Re: Distributed Power
« Reply #24 on: December 20, 2013, 08:42:16 pm »

So in the other threads I see everyone cramming everything in a single rack space. Any reason a 2u enclosure can't work?

This looks like something we could use and simple enough to craft.
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TJ (Tom) Cornish

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Re: Distributed Power
« Reply #25 on: December 20, 2013, 10:12:24 pm »

So a metal chassis mounted in a wood rack is ok since the electrical bits are enclosed within the chassis?
Correct.
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TJ (Tom) Cornish

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Re: Distributed Power
« Reply #26 on: December 20, 2013, 10:12:58 pm »

Thanks.

Is this something measurable that can be detected before plugging in anything to the circuit?
Absolutely.
http://soundforums.net/hub/1856-basic-receptacle-testing.html
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TJ (Tom) Cornish

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Re: Distributed Power
« Reply #27 on: December 20, 2013, 10:13:48 pm »

So in the other threads I see everyone cramming everything in a single rack space. Any reason a 2u enclosure can't work?

This looks like something we could use and simple enough to craft.
No reason it can't work - just takes more rack space.
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Jared Koopman

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Distributed Power
« Reply #28 on: December 20, 2013, 10:39:24 pm »

So the stage stringer I have shares a neutral between the two circuits "12/4" with pigtail of two Edison plugs.

http://www.ampshop.com/distro.html

When using this type of poor mans district, is there any danger to plugging in both circuits of the stringer to the same "circuit" on the distro when venue source is limited to one circuit? (Equivalent to plugging both pigtail ends into the same Edison duplex)
« Last Edit: December 20, 2013, 10:48:38 pm by Jared Koopman »
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Tim McCulloch

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Re: Distributed Power
« Reply #29 on: December 20, 2013, 11:02:18 pm »

Thanks.

Is this something measurable that can be detected before plugging in anything to the circuit?

You need a load (a 1000w PAR can or shop floodlight will do nicely) and your voltmeter.

For single (split) phase, after verifying no-load voltages to be acceptable, plug the load into a circuit on, say, the Black leg.  Meter the voltage between neutral and the RED leg.  It should be 120v-ish, now meter the voltage on the Black leg... should also be 120v-ish.  Measure between the Black and RED leg and see if you have 240v.  Whatever you read, you should have HALF that voltage (a volt or 2 difference wouldn't worry me) between neutral and Black/neutral and RED.  If you don't, you have a neutral problem.  Switch the load to the RED leg.  Does the voltage difference follow?

Like Mike suggests, once a year we go through every AC connector we have and check for arcing, corrosion and terminal torque.  Distro (outlets, breakers, lugs) cables, quad boxes... everything.  Unless every AC cable in the shop has molded connectors, you (yes, all of you) should be doing this.  It's common to find a few screws that needed a quarter-turn or more to be snug again.
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

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Re: Distributed Power
« Reply #29 on: December 20, 2013, 11:02:18 pm »


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