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[TJ (Tom) Cornish]

Read this overview on Triplen Harmonics. http://blog.powermonitors.com/blog/understanding-triplen-harmonics

It's relatively easy to generate significant odd-order Triplen harmonics using Triac lightning dimmers or switch mode power supplies on a 3-phase Wye connected system. And the math proves you can generate up to 173% of the line current on the neutral. Many old factories with a lot of 3-phase electric motors would routinely undersize the neutrals to save money on copper. So that's double whammy that can easily cause the neutral wires to burn up.

I think we're getting off into the weeds a bit for Neil's usage, but this is another reason why its desirable to run as much gear as you can at 208/240v.  If you aren't using the neutral wire for some things, that part of your load can't contribute to triplen currents.

I did an inventory of my equipment and found that other than dimmers and stage power, I could run almost everything else at 208v/240v, since nearly all my gear has universal power supplies - all my power amps, powered speakers, LED lighting, and movers are good to go. 

The way I am implementing this change is to move to Powercon distribution for a chunk of my cable infrastructure, and then depending on power availability, all I need to change are the input cords - regular Edison to blue Powercon when I am using standard circuits, or L14-20 to blue Powercon wired HHG when I'm using my own distro equipment.  Sticking with L14-20 receptacles means I don't need to do any remote breaker step-downs, and I can still use #12 cabling for everything.

[John Daniluk (JD)]

There is another interesting thing about 3 phase tie in.  Some locations, older buildings, have a 3 phase with a high leg  ie l-1 120v, l-2 120 v  l-3 220v +- 

I had a hotel give the convention a 3 phase 120v breakout,  the one with the red, blue, black female outlets.  One of the outlets was 220v, magic smoke appeared.   It seems the hotel upgraded the ballroom ac and no one bothered to verify the ac.  I now verify EVERY outlet I use for correct voltage and wiring.
I would advise checking the current on the neutral.   I do this on all single and 3 phase systems. 
There are several good books about working with ac in the production world.
Spend $100.00 and get a volt/amp/ohm meter to use on your shows.  I use a cheap rv volt, wiring checker, simple to use and has an edison m plug, I also carry a standard volt/amp and a rms volt/amp meters.

[Neil Sakaitis]

I am going to be adding 2 volt/ammeters, and hopefully I can just connect each one to hot plus neutral, and if both sides read 110-120, I am good to go. Then I will meter the individual Edisons as well but they should match what the meters read. I was only going to add coils around the 2 hots for the 2 ammeters, but based on all this feedback about the neutral, might add a 3rd coil around the neutral to monitor it with a 3rd meter.

I know I should not assume, but the hall is quite modern, and not some beat-up thing from decades ago. So I am confident that my metering will show what I am expecting to find and see.

Tom, while you own most of your inventory, and can have 2 sets of Powercon connector cables, not so with me. My LED PARs are pre-wired for 110v, as well as all my DJ stuff (controller, PCs, strobes, smoke, etc), And the rental place where I am getting my MAC250's and bigger sound kit all runs off of 120v, even though I am sure I could ask them for a 220v hook-up, but then it would get messy.

My distro is wired for 110v completely, and all my gear is wired for 110v. I won't be using any lighting dimmers, it's only the movers, couple of Atomics, smoke, LEDs and that is it.

You know, reality is that this hall has all kinds of circuits lining the walls and stage, but I just was lazy and did not feel like running circuits all over this hall in every corner and wall, thought it would be easier to just slap my distro near the DJ table or under the flown truss. Makes for a neater and more controlled run of AC. I sure hope this all works out for me, and that I don't have to worry about the neutral carrying high current, or unbalanced legs, or something funky because I am not using that 3rd leg......

I guess my meters will be my best friend that night....

[Cailen Waddell]

Popping back in here. A single phase distro using two of the three hots on a 3 phase distro can create the 173a of neutral current.   Whether you are using the 3rd phase or not, you are creating an unbalanced load which can overload your neutral...  I would strongly consider an amp meter on the neutral if you will approach capacity and use a 3 phase distro.


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[Tom Bourke]

I know I should not assume, but the hall is quite modern, and not some beat-up thing from decades ago. So I am confident that my metering will show what I am expecting to find and see.

They built a brand new PAC where I use to live.  First show comes in and meters, voltage was WAY high.  Turns out the electrical engineering firm did not know anything about stage power.  They looked at a long life lamp and ordered the transformers tapped at 130 or 135V to match.  I think it was so bad that they had ordered special transformers to hit the wrong voltage!

[Neil Sakaitis]

Hey Cailen,

For argument sakes, let's say that even though I am more or less balanced on both legs of my 1-phase hookup to the 3-phase panel, and I end up with 173A on my neutral, assuming a #2 neutral capable of 190A (ideal temp), where is my worry then ?? My distro should be fine, and so should the 3-ph 100A panel, no ??

Not challenging anything here, just trying to understand where is the worry in this scenario ??

And I think the previous example that got us to 173A on the neutral was me using the full 100A on each leg, which I doubt I will. I think I might be somewhere between 60-70A max per leg.

Thanks !!

They built a brand new PAC where I use to live.  First show comes in and meters, voltage was WAY high.  Turns out the electrical engineering firm did not know anything about stage power.  They looked at a long life lamp and ordered the transformers tapped at 130 or 135V to match.  I think it was so bad that they had ordered special transformers to hit the wrong voltage!

[Cailen Waddell]

Hey Cailen,

For argument sakes, let's say that even though I am more or less balanced on both legs of my 1-phase hookup to the 3-phase panel, and I end up with 173A on my neutral, assuming a #2 neutral capable of 190A (ideal temp), where is my worry then ?? My distro should be fine, and so should the 3-ph 100A panel, no ??

Not challenging anything here, just trying to understand where is the worry in this scenario ??

And I think the previous example that got us to 173A on the neutral was me using the full 100A on each leg, which I doubt I will. I think I might be somewhere between 60-70A max per leg.

Thanks !!

It's not a worry - sorry to give that impression.  Something you said earlier made me think you misunderstood the neutral implications.  I wanted to make sure you understood that being balanced on your single phase distro doesn't equal low neutral current on a 3 phase tie in. 

Anyway - I think I may have steered this a bit away from your original objective.   


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[Neil Sakaitis]

While still waiting for all of my distro parts (mostly distro blocks), to beef up my 1-phase distro, in preparation to use it at a big event with 3-phase tie-ins, I came across something interesting on this forum, that I was not aware of. Up until now, most of you are saying that I can somewhat safely tie in my 1-phase distro to a 3-phase panel, so long as I measure and monitor my voltage on both legs, and try to balance the current on both sides. Fine.

BUT, I stumbled across a post on here, that talked about a guy ordering a 3-phase distro from Motion, for use on 1-phase, and that they were using phase conversion to tie the blue leg to the black and red. I am assuming that, if my distro only houses 16 X 20A Edisons, then the "phase conversion" is nothing more than tapping a couple of Edisons off of the Blue leg, to balance out the 16 Edisons across the 3 legs, correct ??

Now, this would change everything for me in my setup, and get more costly of course. My feeder cable is 1-phase, I would have to order another length of #2 SC, as well as Blue Cams. Then, I just ordered a 100A 2-pole main breaker, and am having a custom breaker panel made to house that main as well as 16 QCF breakers. If I were to take advantage of using 3-phase, I would now have to call Jim at AmpShop and hope that it is not too late to change out that main for a 3-pole, probably too late by now, panel already cut and main breaker already purchased. But no harm in asking.

And of course, the final thing is that I really don't need the extra 100A on the Blue leg of the 3-phase feed, I have plenty of juice on the 2 legs. So I would be going thru all this trouble and cost for the sake of balancing things across the legs, and making it look like I am using 3-phase for how it was intended, with all 3 legs.

Thoughts ?? Worth it for peace of mind ??

Thanks
Neil

[TJ (Tom) Cornish]

While still waiting for all of my distro parts (mostly distro blocks), to beef up my 1-phase distro, in preparation to use it at a big event with 3-phase tie-ins, I came across something interesting on this forum, that I was not aware of. Up until now, most of you are saying that I can somewhat safely tie in my 1-phase distro to a 3-phase panel, so long as I measure and monitor my voltage on both legs, and try to balance the current on both sides. Fine.

BUT, I stumbled across a post on here, that talked about a guy ordering a 3-phase distro from Motion, for use on 1-phase, and that they were using phase conversion to tie the blue leg to the black and red. I am assuming that, if my distro only houses 16 X 20A Edisons, then the "phase conversion" is nothing more than tapping a couple of Edisons off of the Blue leg, to balance out the 16 Edisons across the 3 legs, correct ??

Now, this would change everything for me in my setup, and get more costly of course. My feeder cable is 1-phase, I would have to order another length of #2 SC, as well as Blue Cams. Then, I just ordered a 100A 2-pole main breaker, and am having a custom breaker panel made to house that main as well as 16 QCF breakers. If I were to take advantage of using 3-phase, I would now have to call Jim at AmpShop and hope that it is not too late to change out that main for a 3-pole, probably too late by now, panel already cut and main breaker already purchased. But no harm in asking.

And of course, the final thing is that I really don't need the extra 100A on the Blue leg of the 3-phase feed, I have plenty of juice on the 2 legs. So I would be going thru all this trouble and cost for the sake of balancing things across the legs, and making it look like I am using 3-phase for how it was intended, with all 3 legs.

Thoughts ?? Worth it for peace of mind ??

Thanks
Neil

What does phase conversion mean?  Short or a rotary phase converter or inverter-based unit, there isn't any way to passively convert single phase to three phase power.

A few distros have a switching mechanism that can be switched so that in "single phase mode" the z phase is split half on each leg. Leprecon makes one like that.

[jason misterka]

What does phase conversion mean?  Short or a rotary phase converter or inverter-based unit, there isn't any way to passively convert single phase to three phase power.

A few distros have a switching mechanism that can be switched so that in "single phase mode" the z phase is split half on each leg. Leprecon makes one like that.

I believe that is what he is referring to.

In my opinion, as an "audio-only" system provider, there are two reasons to build your systems with three phase or switching PD.

1. You use three phase motors

2. You want to be able to use smaller generators and run them more happily in three phase mode.

If you provide large lighting systems as well and need the current capacity, then certainly go three phase.   Otherwise, you can run some pretty large shows on a 100 amp single phase.

Jason

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