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Author Topic: When to 3 phase?  (Read 890 times)

Dave Guilford

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When to 3 phase?
« on: June 26, 2018, 11:14:13 am »

Been renting small MQ15kVA generators for a few years.  Got lined up at another rental co and the smallest they offer is a 25kVA. Same price too, and about 30 mins closer to their shop.

Their 25kVA has 3-phase option.  When / why would I do that?  What benefits do I get from 3 phase versus regular ass 1 phase. 

And what about 240 vs 120.  I think virtually all my gear is “universal power supply” type where it’ll take 100-250v or whatever. 

Teach me.
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TJ (Tom) Cornish

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Re: When to 3 phase?
« Reply #1 on: June 26, 2018, 11:17:05 am »

Been renting small MQ15kVA generators for a few years.  Got lined up at another rental co and the smallest they offer is a 25kVA. Same price too, and about 30 mins closer to their shop.

Their 25kVA has 3-phase option.  When / why would I do that?  What benefits do I get from 3 phase versus regular ass 1 phase. 

And what about 240 vs 120.  I think virtually all my gear is “universal power supply” type where it’ll take 100-250v or whatever. 

Teach me.
What did Guitar Center say?
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John Daniluk (JD)

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Re: When to 3 phase?
« Reply #2 on: June 26, 2018, 12:23:19 pm »

the 25kw will give you more amperage in single phase than you have now.   3 phase gives you 1/3 more amperage to use. 

Basically if a generator is 3 phase  the KW power is rated for 3 phase.   When you set it for single phase you loose one leg of power or 1/3  of your available amps.

For example a generator rated for 25kw at 3 phase is a basically 70 amps per phase giving you 210 total amps.  when you change the generator to single phase you have around 140 amps available for use.   ALL of this is depends on how the generator monitors the legs for over current and voltage.

If you change your equipment to 208v I think you will be changing them back and forth for smaller shows.   Leave them at 120v and get a AC distro.  If you get a 3 phase distro, mark which outlets are on each phase.  This helps when you can only get single phase.

I have I did not confuse you....

jd
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Dave Guilford

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Re: When to 3 phase?
« Reply #3 on: June 26, 2018, 07:29:34 pm »

Great reply and thank you.  The last thing you mentioned was building distro for 3phase. 

But when I use it for single phase, as you mention, what happens?  “When you can only get single phase power”. Does that mean 1/3 if my outlets won’t work?
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Dave Guilford

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Re: When to 3 phase?
« Reply #4 on: June 26, 2018, 07:31:50 pm »

But basically the answer to “when to 3-phase” is “whenever you can”.

I’ve been renting from UR and Sunbelt and the like.  They provide those ugly yellow spider boxes.  Those probably don’t denote which circuits are on which legs, do you suspect?

Usually it’s california type 50a feeder
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David Sturzenbecher

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Re: When to 3 phase?
« Reply #5 on: June 26, 2018, 07:40:14 pm »

But basically the answer to “when to 3-phase” is “whenever you can”.

I’ve been renting from UR and Sunbelt and the like.  They provide those ugly yellow spider boxes.  Those probably don’t denote which circuits are on which legs, do you suspect?

Usually it’s california type 50a feeder

Don't use three phase unless you have a three phase distro.
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Erik Jerde

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Re: When to 3 phase?
« Reply #6 on: June 26, 2018, 11:19:31 pm »

Don't use three phase unless you have a three phase distro.

Yep, this.  Unless you have the distro for it 3p is useless to you.
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Tom Bourke

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Re: When to 3 phase?
« Reply #7 on: June 27, 2018, 01:44:17 am »

the 25kw will give you more amperage in single phase than you have now.   3 phase gives you 1/3 more amperage to use.

Basically if a generator is 3 phase  the KW power is rated for 3 phase.   When you set it for single phase you loose one leg of power or 1/3  of your available amps.

You don't normally loose power that way on a truly switchable generator.  Typically they have some multiple of 6 poles and maybe some center taps to switch around depending on the voltage and phase  settings.

The important thing to do is meter your outputs to make sure you're getting what you expect based on the connected distribution. I have seen over 170V on a 120V connection to a generator.  That is not counting the times a tech set the generator for 480 3 phase when we expected 120/240V single phase.
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Ray Aberle

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Re: When to 3 phase?
« Reply #8 on: June 27, 2018, 09:30:35 am »

Let's take a minute to step back and address something critical that's possibly being overlooked. My apologies if everyone knows this and is assuming as such, but I want to make certain the OP is aware of this when deciding whether to run single or three phase on the generator.

If you are renting diesel generators, ONLY in 1Ø mode are those 50A twist locks connections available. If you set the unit to 3Ø, those twist locks will NOT be functioning. So, 3Ø will not get you "more power" to the twist-locks, and "some outlets (on the spider boxes) will not be functioning" will not be the case.

The lugs (for attaching cams to) will work in either 1Ø or 3Ø. There's silk-screen graphics indicating as to which two lugs to connect to when only running 1Ø; you hit all three for 3Ø. If your rented unit has cam lugs bolted to the body (for ease of connections; often these are fed with internal cabling to the aforementioned lugs, and are usually after-market installs... not sure if Cat, MQ, etc, offer that as an option from the factory) then those cams are going to always be hot whether the generator is running 1Ø or 3Ø.

Breakers: Everything is still covered by the main breaker in the control panel. On a 25kW unit, its typically 60A. On a 45kW usually 110A. It's a three-pole breaker, but covers the system regardless of whether it's in 1Ø or 3Ø mode. So, JD was on the right track when he said that 3Ø would give you more amperage than you have now (technically a 50% increase from 120A to 180A; 120A IS a 1/3 hit from 180A but blah blah math and being pedantic ;) ) -- but again, when you are in 1Ø mode, that extra "power" for being in 3Ø mode just isn't available. This is why I mentioned the use of spider boxes- changing to 3Ø mode isn't going to free up that extra power for use with spider boxes. 1Ø is only pulling from the U & W legs (they're marked "U," "V" and "W.").

What's also important to keep in mind is that in 1Ø mode, when you're breakered at 60A (on that 25kW unit), that's covering BOTH 50A twist locks. So, even though in your mind you have 100A/220V (2-50A circuits) you are still going to be restricted by the 60A MAIN breaker. (60A per leg/220V.)

Finally, spider boxes normally come with an L6-30 30A/250V (H-H-G) as one of the circuits. Some rental shops converted those to L14-30, which can be useful for you. It's never a bad idea to ask if your rental shop has some of those converted boxes, and if they don't (and you know you'll be using them regularly) to make you one or two.

-Ray
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Ray Aberle

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Re: When to 3 phase?
« Reply #9 on: June 27, 2018, 09:43:18 am »

The important thing to do is meter your outputs to make sure you're getting what you expect based on the connected distribution. I have seen over 170V on a 120V connection to a generator.  That is not counting the times a tech set the generator for 480 3 phase when we expected 120/240V single phase.
"Gosh, Tom, how does the voltage get changed?"

PICTURE TIME! (I wish I had already gotten my generator wrapped with my company logo and such, so it'd look way cooler than it does.... alas.)

1) (45kW.jpg) Here's a typical 45kW WhisperWatt.

2) (LookHere.jpg) This is the side panel you'll probably need to open.

3) (Inside.jpg) Here's what it looks like inside.

4) (ModeSelect.jpg) This is the voltage selection switch. THE ENGINE MUST BE OFF WHEN CHANGING THIS SWITCH.

5) (lugs.jpg) The graphics on the lugs, showing you which lugs to connect to based on the output you want. We have cam tails attached to the generator permanently, so I don't have to futz with these anymore. When someone has 1Ø cams/distro (a distro with 1Ø cams) I attach to my black and blue cam tails, that are wired to "U" and "W" respectively.

-Ray
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Tim McCulloch

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Re: When to 3 phase?
« Reply #10 on: June 27, 2018, 10:27:25 am »

"Gosh, Tom, how does the voltage get changed?"

PICTURE TIME! (I wish I had already gotten my generator wrapped with my company logo and such, so it'd look way cooler than it does.... alas.)

1) (45kW.jpg) Here's a typical 45kW WhisperWatt.

2) (LookHere.jpg) This is the side panel you'll probably need to open.

3) (Inside.jpg) Here's what it looks like inside.

4) (ModeSelect.jpg) This is the voltage selection switch. THE ENGINE MUST BE OFF WHEN CHANGING THIS SWITCH.

5) (lugs.jpg) The graphics on the lugs, showing you which lugs to connect to based on the output you want. We have cam tails attached to the generator permanently, so I don't have to futz with these anymore. When someone has 1Ø cams/distro (a distro with 1Ø cams) I attach to my black and blue cam tails, that are wired to "U" and "W" respectively.

-Ray

The voltage fine adjustment is not pictured and that's where I find changes have been made by the previous user.

Voltage drop over 300ft of #16 orange extension cords?  Turn up the voltage rather than use larger wire or moving the genset.  I had one rental unit show up with the correct selection switch setting but putting out 156v on the Edison convenience outlet.  A screwdriver fixed that in 15 seconds.

Next item- NEVER trust the volt meters on the genset.  No horror story of my own but have heard enough about guys/gals mis-reading or blindly trusting them and not noticing 140v instead of ~120v.
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Tim McCulloch

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Re: When to 3 phase?
« Reply #11 on: June 27, 2018, 10:29:12 am »

Been renting small MQ15kVA generators for a few years.  Got lined up at another rental co and the smallest they offer is a 25kVA. Same price too, and about 30 mins closer to their shop.

Their 25kVA has 3-phase option.  When / why would I do that?  What benefits do I get from 3 phase versus regular ass 1 phase. 

And what about 240 vs 120.  I think virtually all my gear is “universal power supply” type where it’ll take 100-250v or whatever. 

Teach me.

If you don't have a 3 phase distro and 3 phase rackpacks and 5 conductor wiring, you use single (split) phase.  That's it.
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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

John Fruits

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Re: When to 3 phase?
« Reply #12 on: June 27, 2018, 10:54:42 am »

First  of all, a "LIKE" to Ray.
More fuzziness in my head, re: the mode select image, it says "3 phase, 240/139V" Somebody please explain.
Thanks
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Ray Aberle

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Re: When to 3 phase?
« Reply #13 on: June 27, 2018, 11:15:14 am »

The voltage fine adjustment is not pictured and that's where I find changes have been made by the previous user.
Here's the back panel of a typical WhisperWatt. (Controls.jpg) (Why yes, the same one from before. haha.) As Tim mentioned, you can see "Voltage Regulator" at the top of the controls. The meter next to it is Hertz (frequency), so you need to look down for the "V" meter.

Here's a closer look at that Voltage Meter (VoltageMeter.jpg). Note the black knob to the left. That allows you to chose which legs you are measuring between. It's set for W-U right now, since it's in 1Ø mode. This selection knob will let you measure between the other leg if you change to 3Ø mode. To be candid, it's always in W-U since whether we're in 1Ø or 3Ø, that setting is always measuring.

Next item- NEVER trust the volt meters on the genset.  No horror story of my own but have heard enough about guys/gals mis-reading or blindly trusting them and not noticing 140v instead of ~120v.
Yep.

As you adjust the Voltage Regulator at the top, you will see this "V" meter change. Best Practice would be to have someone at your spider box/distro with a meter, and they call the change, "up," "down," "bump a bit," and "perfect." This way you are allowing for any voltage drop over the cable (as opposed to metering the generator courtesy outlets) and getting the optimal voltage at your gear.

Side note: Newer generators have a "Reduced power" setting. I guess it's beneficial to the engine to start it in "low power," and then wait for it to warm up before going to "full power?" That reduced power will affect the voltage though! I had a rental unit at a show once where I was measuring about 70V leg-to-neutral. I was wondering what-the-eff was wrong with it, when I saw the "low power" setting engaged. Disengaged it, and it throttled right up to full power and voltage!

Take away: ALWAYS inspect all settings before starting the generator. :)

Bonus points: I've not touched anything on my WhisperWatt since it was used on Sunday, other than opening the panel. Can you see what is "not a best practice" that's shown in these pictures?

-Ray
« Last Edit: June 27, 2018, 11:17:56 am by Ray Aberle »
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Ray Aberle

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Re: When to 3 phase?
« Reply #14 on: June 27, 2018, 11:20:59 am »

First  of all, a "LIKE" to Ray.
Thanks. :)

More fuzziness in my head, re: the mode select image, it says "3 phase, 240/139V" Somebody please explain.
I know 139V is a factor somewhere (I think because it's part of the 3Ø equation?), I just can't state exactly what. That top position, though, is what we use for 3Ø operation, where it measures 120V leg to G/N and 208V leg-to-leg. (139V is 2/3 of 208V...)

I've never used it in 3Ø 480/277 mode.

-Ray
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TJ (Tom) Cornish

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Re: When to 3 phase?
« Reply #15 on: June 27, 2018, 11:54:01 am »

Thanks. :)
I know 139V is a factor somewhere (I think because it's part of the 3Ø equation?), I just can't state exactly what. That top position, though, is what we use for 3Ø operation, where it measures 120V leg to G/N and 208V leg-to-leg. (139V is 2/3 of 208V...)

I've never used it in 3Ø 480/277 mode.

-Ray
If you regulate your voltage so you get 240v leg to leg, then your leg to neutral voltage will rise to 139v.  This is not desirable if you are using line to neutral loads, as 139v is way above spec, but is apparently provided for motor loads that require 240v instead of 208v.

This is a good example of why metering is essential.
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John Daniluk (JD)

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Re: When to 3 phase?
« Reply #16 on: June 27, 2018, 12:41:23 pm »

ray  I like your post

A little note on setting voltage.  There may be a high voltage shutdown on the generator....I try and not exceed 120v at generator.   If you have low voltage at distro you may need to get larger feeder cable. 

When using a single phase distro on 3 phase,  monitor the neutral current (amps)  you will see significant amperage,  do not exceed the current capability of the wire used for the neutral.

inside the generator there is usually a hidden reset button.  If you do not have ac out look at the instructions on the control door/panel to know where it is.   

learn how to balance power on the various legs.

My suggestion for you is to talk to your generator provider.  Get some hands on instruction on the generator(s) you are using.  Discuss with them what you are trying to do and they will help you plan for your power growth. 

There are many safety issues with distros, commercial ac, generators, grounding, etc. 

off topic but the schools for our industry do not teach enough about working with ac.

jd



   
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Tim McCulloch

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Re: When to 3 phase?
« Reply #17 on: June 27, 2018, 03:52:02 pm »

Take away: ALWAYS inspect all settings before starting the generator. :)

Bonus points: I've not touched anything on my WhisperWatt since it was used on Sunday, other than opening the panel. Can you see what is "not a best practice" that's shown in these pictures?

-Ray

Yes.  The main circuit breaker is in the "on" position which means it was likely disconnected with the breaker in the same operational state.
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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

Ray Aberle

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Re: When to 3 phase?
« Reply #18 on: June 27, 2018, 03:55:30 pm »

Yes.  The main circuit breaker is in the "on" position which means it was likely disconnected with the breaker in the same operational state.
Thar be it. My team shut it down without killing the main breaker first. Best Practices is to shut off main breaker, and then let the generator run for a few additional minutes at no load for a "cool down" period.

(Don't worry, I'll fire everyone involved.)
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Rob Spence

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Re: When to 3 phase?
« Reply #19 on: June 27, 2018, 05:06:27 pm »

I have only used 35kw and 45kw units.
I remember that the 35 had 2 California connectors but I think the 45 had 3. Would the 45kw still be limited to 60a across all three?


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Ray Aberle

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Re: When to 3 phase?
« Reply #20 on: June 27, 2018, 05:32:34 pm »

Any generator is limited by the mains breaker. My 45kW has a 110A/3Ø mains breaker.
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Stephen Swaffer

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Re: When to 3 phase?
« Reply #21 on: June 27, 2018, 07:49:25 pm »

480/1.73=277
240/1.73=139
208/1.73=120

Just math and simple physics
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Re: When to 3 phase?
« Reply #22 on: June 27, 2018, 08:05:39 pm »

I love picture time, hehe. Thanks Ray, and everyone else!
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Tom Bourke

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Re: When to 3 phase?
« Reply #23 on: June 28, 2018, 05:18:03 pm »

The voltage fine adjustment is not pictured and that's where I find changes have been made by the previous user.

Voltage drop over 300ft of #16 orange extension cords?  Turn up the voltage rather than use larger wire or moving the genset.  I had one rental unit show up with the correct selection switch setting but putting out 156v on the Edison convenience outlet.  A screwdriver fixed that in 15 seconds.

Next item- NEVER trust the volt meters on the genset.  No horror story of my own but have heard enough about guys/gals mis-reading or blindly trusting them and not noticing 140v instead of ~120v.
The most memorable time was 150V to the food service trucks.  The cooks commented how FAST everything was cooking!

I was told by the generator company that many of the construction crews turn it up to get more zip out of their power tools.
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