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[Nathan Riddle]

It's fine as long as everything you're connecting only needs 120v. If you have 208v or 3-phase motors, obviously it won't work.

Company I used to work for ran into situations often that required single-phase power, so when they re-did their distros, they made them switchable. They're very slick and completely legal. I've never seen another one like them.

That's very neat. Essentially what I want to be able to do. But manually.

[Mac Kerr]

Either way, I understand that I'll be limited to the maximum supply of a single phase.
240v may or may not work if I'm bridging the wrong circuits.
I can possibly damage 3Ø (phase) equipment.

Also remember that in a 3Ø panel as you will find in the entertainment industry there is no 240V. Each leg is 120V to N, and 208V to each other. For 240V you need single phase, 120V to N, 240V to each other. In industrial use 3Ø is often 240V or 400V phase to phase to power motors wired for those voltages.

Mac

[Scott Holtzman]

Also remember that in a 3Ø panel as you will find in the entertainment industry there is no 240V. Each leg is 120V to N, and 208V to each other. For 240V you need single phase, 120V to N, 240V to each other. In industrial use 3Ø is often 240V or 400V phase to phase to power motors wired for those voltages.

Mac

Mac is of course correct Nathan and in older industrial buildings (many up here in rust belt) you have to be on the lookout for high leg delta systems.  This is two 120v legs and one 208V.  I believe the industrial application was motor starters.

With the high leff system you have one 208v to neutral and two 120v.  You still have the single phase 240v available phase to phase on the regular legs.  The high leg is essentially unusable.

[brian maddox]

.....you have to be on the lookout for high leg delta systems.....

Ah, can't get more than a page or two into a Distro thread before the mystical High Leg Delta raises it's ugly head.   

[Art Welter]

Look at the table for SC cable, that table refers to THHN and other types. That's why I gave the note and reference.

Though, I'm never anywhere near that load and won't run anything even remotely close to 90c and even considering the lower 130A #2 rating my distro is only 100A per phase so I have headroom.

Nathan,

My mistake, forgot the higher ampacity rating of the individual SC cable.
Even at 100A per phase, voltage drop using #2 could still be a concern if you are using the typical 125 feet of feeder and tails fed at some distance from the mains transformer, then adding the usual distance of lighter cable to lights and amplifiers. 

Art

[Frank Koenig]

Mac is of course correct Nathan and in older industrial buildings (many up here in rust belt) you have to be on the lookout for high leg delta systems.

You don't have to be in the Rust Belt. The San Francisco Bay Area is rife with them. It's an economical way to get light duty 3-phase and 125/250 single-phase into a building with just 4 wires. And by using "open leg delta" the PoCo only needs to put 2 transformers on the pole. When I ride the train to SF from Palo Alto I pass through miles of light industrial up around San Carlos and every pole has a big pot with 3 secondary wires and a little pot with 2. I assume all those are open and high-leg delta. One gig I do every year in East Palo Alto has such power. Fortunately, these days, I run off a couple of 120 V branch circuits and don't need to muck around in the panel.

--Frank

[Nathan Riddle]

Also remember that in a 3Ø panel as you will find in the entertainment industry there is no 240V. Each leg is 120V to N, and 208V to each other. For 240V you need single phase, 120V to N, 240V to each other. In industrial use 3Ø is often 240V or 400V phase to phase to power motors wired for those voltages.

Mac

Mac is of course correct Nathan and in older industrial buildings (many up here in rust belt) you have to be on the lookout for high leg delta systems.  This is two 120v legs and one 208V.  I believe the industrial application was motor starters.

With the high leff system you have one 208v to neutral and two 120v.  You still have the single phase 240v available phase to phase on the regular legs.  The high leg is essentially unusable.

Not to split hairs, but I was referring to 240v in a single phase source scenario.

But yes, thanks for the clarification both of y'all for anyone "following along at home."

And I am aware of the infamous high leg delta systems We have a few around here too actually.

Nathan,

My mistake, forgot the higher ampacity rating of the individual SC cable.
Even at 100A per phase, voltage drop using #2 could still be a concern if you are using the typical 125 feet of feeder and tails fed at some distance from the mains transformer, then adding the usual distance of lighter cable to lights and amplifiers. 

Art

Hey Art,

I don't know... plugging the numbers into calculators on the internet could yield poor results. But this seems to indicate otherwise (5% voltage drop).

[John Sulek]

Ah, can't get more than a page or two into a Distro thread before the mystical High Leg Delta raises it's ugly head.   

Just be happy we aren't talking about Denmark or parts of Spain. 

[Art Welter]

Hey Art,

I don't know... plugging the numbers into calculators on the internet could yield poor results. But this seems to indicate otherwise (5% voltage drop).

Assuming (an assumption that generally won't be true) that your service entrance maintains a full 120 volts under load, using 125' of #2 loaded at 99 amperes the voltage drops 5% to 114volts. The starting voltage for your cords leading to the distribution panel is 114 volts, using a 75' #12 drawing 19 amps the end of the line voltage drops another 5%, down to 108.3 volts.
Everything may still work OK at the lower voltage, but generally lights will be dimmer and amplifiers will put out less power at the lower voltage when peak power is used.

Art

[Nathan Riddle]

Assuming (an assumption that generally won't be true) that your service entrance maintains a full 120 volts under load, using 125' of #2 loaded at 99 amperes the voltage drops 5% to 114volts. The starting voltage for your cords leading to the distribution panel is 114 volts, using a 75' #12 drawing 19 amps the end of the line voltage drops another 5%, down to 108.3 volts.
Everything may still work OK at the lower voltage, but generally, lights will be dimmer and amplifiers will put out less power at the lower voltage when peak power is used.

Art

You're right, I forgot to take into account distro > device. Thanks.

---

So to sum up this thread. There's nothing code wise wrong with it. And there's nothing wrong with it if I'm all 120v.
Inspectors might look sideways, but it's probably okay with them.

I'll use this.
https://www.gencable.com/product/16-series-cam-soft-tapping-tee/

Oh and as always, beware of delta squad 

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