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Author Topic: Distributed Power  (Read 16922 times)

Mike Sokol

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Re: Distributed Power
« Reply #30 on: December 20, 2013, 11:04:31 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)
At first look I believe the real danger comes when both Edison plugs are connected to two separate branch circuits of 20-amps each, but on the same phase (L1 or L2). Under those conditions the neutral currents are additive rather than subtractive. So you can easily exceed the 20-amp limit of the neutral by a significant amount. For instance, 20 amps on each pigtail connected to the same phase on two circuits would not subtract to zero amps as it does on two different phases of a 120/240-v circuit. That 40 amps in the neutral can be a problem if neutral paths aren't double-sized to handle the extra current and overheating can result.

Now maybe I'm misunderstanding this hookup, so please correct me if I'm thinking about this incorrectly.
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Jared Koopman

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Re: Distributed Power
« Reply #31 on: December 20, 2013, 11:11:28 pm »


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.

Thanks Tim

Maybe it's me but I check my power cable connections before they go out for every gig.
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Jared Koopman

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Distributed Power
« Reply #32 on: December 20, 2013, 11:17:18 pm »

At first look I believe the real danger comes when both Edison plugs are connected to two separate branch circuits of 20-amps each, but on the same phase (L1 or L2). Under those conditions the neutral currents are additive rather than subtractive. So you can easily exceed the 20-amp limit of the neutral by a significant amount. For instance, 20 amps on each pigtail connected to the same phase on two circuits would not subtract to zero amps as it does on two different phases of a 120/240-v circuit. That 40 amps in the neutral can be a problem if neutral paths aren't double-sized to handle the extra current and overheating can result.

Now maybe I'm misunderstanding this hookup, so please correct me if I'm thinking about this incorrectly.

So the cable I have has an l14-20 on an adapter that converts that into two Edison  pigtail.

So are you saying that plugging them both into the same circuit it is additive due to the shared neutral? And therefore shouldn't be done? I should only plug in one half of the pigtail?
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Mike Sokol

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Re: Distributed Power
« Reply #33 on: December 20, 2013, 11:20:37 pm »

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?


Good advice. In fact, I used to build an AC voltage panel meter into my early 120/240-v distros. I also added a rotary switch which allowed me to check voltage between neutral to leg-1 or neutral to leg-2 as well a leg-1 to leg-2. If you don't want to risk blowing up a PAR, a little 1,200 watt ceramic heater is a good load. Or you could mount 3 separate panels meters to monitor all 3 voltages if you wish.  I found some really cool imported fluorescent AC panel meters for $6 each including shipping from China. They work great and can easily be seen from across the room, even by my aging eyes.

With portable 120/240-volt split-phase or 3-phase power distro, the neutral is really the most important connection. Lose that, and you can lose a lot of gear.
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Mike Sokol
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Mike Sokol

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Re: Distributed Power
« Reply #34 on: December 20, 2013, 11:23:03 pm »

So the cable I have has an l14-20 on an adapter that converts that into two Edison  pigtail.

So are you saying that plugging them both into the same circuit it is additive due to the shared neutral? And therefore shouldn't be done? I should only plug in one half of the pigtail?
Draw me a simple picture and I'll tell you for sure. I want to make sure I understand the hookup.
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Corey Scogin

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Re: Distributed Power
« Reply #36 on: December 20, 2013, 11:46:02 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.

I'm considering purchasing or building option 3 that Tom mentioned above.  A 50A Cali plug was one of the line side connectors.  As far as I can tell, that plug is a 240V 3 wire setup X-Y-G -- so no neutral.

**Edit: I saw after posting this that some of those connectors have a ground around the outside for a 4 wire setup.  I was looking at a different pinout previously that didn't show that.  Sorry for the stupid question. **
**Edit2: Removed the "dangerous question" portion **
« Last Edit: December 26, 2013, 08:49:21 pm by Corey Scogin »
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Doug Johnson

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Re: Distributed Power
« Reply #37 on: December 21, 2013, 08:59:00 am »

 >:(
I'm considering purchasing or building option 3 that Tom mentioned above.  A 50A Cali plug was one of the line side connectors.  As far as I can tell, that plug is a 240V 3 wire setup X-Y-G -- so no neutral.  I'm assuming the load-side neutral will be bonded to the line side ground at the distro.

If I'm plugging an unbalanced load to this, how does the ground on the line side keep from becoming a current carrying conductor?

**Edit: I saw after posting this that some of those connectors have a ground around the outside.  I was looking at a different pinout previously that didn't show that.  Sorry for the stupid question. **
The 50 amp CALI connectors come in several voltages, and both single and three phase.  The CS6375, CS6365c and the CS6364c are the 125/250v 3 pole, 4 wire configuration.
« Last Edit: December 21, 2013, 05:16:04 pm by Doug Johnson »
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Geoff Doane

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Re: Distributed Power
« Reply #38 on: December 21, 2013, 02:22:06 pm »

At first look I believe the real danger comes when both Edison plugs are connected to two separate branch circuits of 20-amps each, but on the same phase (L1 or L2). Under those conditions the neutral currents are additive rather than subtractive. So you can easily exceed the 20-amp limit of the neutral by a significant amount. For instance, 20 amps on each pigtail connected to the same phase on two circuits would not subtract to zero amps as it does on two different phases of a 120/240-v circuit. That 40 amps in the neutral can be a problem if neutral paths aren't double-sized to handle the extra current and overheating can result.

Now maybe I'm misunderstanding this hookup, so please correct me if I'm thinking about this incorrectly.

The other reason that such an adapter (two Edisons into an L14-20) is a bad idea, if not illegal, is that if there is a 240V volt load across the two hots, once you plug one Edison in, the line blade of the second one will have 120V on it, and that is a shock hazard.  In most cases, you only have 120V loads on the stringer, so it's not a problem, but since that isn't guaranteed, such adapters are frowned upon (although they certainly exist  ::) ).

If you have to use such an adapter, just build it with a single Edison feeding both hots in the L14-20.  You can only supply  half the power, but you can't overload the neutral, and there can't be any exposed live terminals.

GTD
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Rob Spence

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Re: Distributed Power
« Reply #39 on: December 21, 2013, 04:17:02 pm »

I'm considering purchasing or building option 3 that Tom mentioned above.  A 50A Cali plug was one of the line side connectors.  As far as I can tell, that plug is a 240V 3 wire setup X-Y-G -- so no neutral.  I'm assuming the load-side neutral will be bonded to the line side ground at the distro.

If I'm plugging an unbalanced load to this, how does the ground on the line side keep from becoming a current carrying conductor?

**Edit: I saw after posting this that some of those connectors have a ground around the outside.  I was looking at a different pinout previously that didn't show that.  Sorry for the stupid question. **

How did you conclude the CS connector was 3 wire?
If you had looked where the wires go you would see 4 connections.
 It has X, Y, N & G.

/Snark coming...

 Why did you not use this great internet to actually look up the connector rather than take the time to write down for all to see that you are clearly not qualified to be building any electrical gear. Buy a properly built distro before you kill some one.

End snark\

And, yes, I am not having a happy day

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Re: Distributed Power
« Reply #39 on: December 21, 2013, 04:17:02 pm »


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