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Author Topic: Need help with panel  (Read 3377 times)

Doug Fowler

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Need help with panel
« on: August 23, 2014, 12:53:21 am »

I have to use this panel tomorrow, have not yet metered it.

See photos, trying to make sense of the "B phase high leg" bit.

Note voltages labeled on the camlocks.

I can use 208 (2 legs of it) but prefer 240v for our 4 wire distro.  Amp racks are wired to run amps on 240 (or 208 if necessary)

???

TIA
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Scott Holtzman

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Re: Need help with panel
« Reply #1 on: August 23, 2014, 01:06:59 am »

I have to use this panel tomorrow, have not yet metered it.

See photos, trying to make sense of the "B phase high leg" bit.

Note voltages labeled on the camlocks.

I can use 208 (2 legs of it) but prefer 240v for our 4 wire distro.  Amp racks are wired to run amps on 240 (or 208 if necessary)

???

TIA

High Doug, something I can actually help with and give back.  The high leg Delta is called a four wire because it adds the Neutral.  It allows you to have multiple single phase voltages on the secondary of the service transformer.

Any phase to Neutral should be 120, high leg to any other phase will give you the 240 single phase that you are looking for.

Does that make sense?

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Mike Sokol

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Re: Need help with panel
« Reply #2 on: August 23, 2014, 06:20:10 am »

I have to use this panel tomorrow, have not yet metered it.

See photos, trying to make sense of the "B phase high leg" bit.

Note voltages labeled on the camlocks.

I can use 208 (2 legs of it) but prefer 240v for our 4 wire distro.  Amp racks are wired to run amps on 240 (or 208 if necessary)

???

TIA

This is a high-leg Delta setup (also called "wild-leg" or "red-leg"). It was done in a lot of earlier industrial power that needed mostly 3-phase 240-volt power for motors, while also
needing 120-volts for office power.

So do you REALLY have power amps wired for 240 volts? If so, then any phase-to-phase will give you 240-volts, neutral to the orange "high-leg" will give you 208 volts, and neutral to the blue or black phases will give you 120-volts. See http://en.wikipedia.org/wiki/High-leg_delta

I'm heading out a 6:30 AM to setup for a gig today so I can't think about this more for now, but be REALLY sure of your connections with this since I've seen a lot of 120-volt sound and lighting systems blown up by connecting to the "high leg" accidentally.
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Mike Sokol
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Doug Fowler

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Re: Need help with panel
« Reply #3 on: August 23, 2014, 10:55:01 am »

This is a high-leg Delta setup (also called "wild-leg" or "red-leg"). It was done in a lot of earlier industrial power that needed mostly 3-phase 240-volt power for motors, while also
needing 120-volts for office power.

So do you REALLY have power amps wired for 240 volts? If so, then any phase-to-phase will give you 240-volts, neutral to the orange "high-leg" will give you 208 volts, and neutral to the blue or black phases will give you 120-volts. See http://en.wikipedia.org/wiki/High-leg_delta

I'm heading out a 6:30 AM to setup for a gig today so I can't think about this more for now, but be REALLY sure of your connections with this since I've seen a lot of 120-volt sound and lighting systems blown up by connecting to the "high leg" accidentally.

Yes, amps run from 2 hot legs;  Speakerpower 12Ks.

I will be triple-metering just to be sure.

Thanks guys.
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Stephen Swaffer

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Re: Need help with panel
« Reply #4 on: August 23, 2014, 03:08:49 pm »

I have always been told that you should never use a single phase load from neutral to the high leg.  In a set up like Mike's drawing it should be just fine; however, one reason it is used (at least around here) is the POCO can get 3 phase with just 2 transformers (and less $$$)-they leave out the "b" to "c" transformer.  It works fine on the 120-N-120 loads and 3 phase, but the neutral to high leg can vary depending on loads.  Personally, I wouldn't trust it.
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Mike Sokol

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Re: Need help with panel
« Reply #5 on: August 23, 2014, 09:34:33 pm »

I have always been told that you should never use a single phase load from neutral to the high leg.  In a set up like Mike's drawing it should be just fine; however, one reason it is used (at least around here) is the POCO can get 3 phase with just 2 transformers (and less $$$)-they leave out the "b" to "c" transformer.  It works fine on the 120-N-120 loads and 3 phase, but the neutral to high leg can vary depending on loads.  Personally, I wouldn't trust it.

Yeah, I've heard that as well, but I have no personal experience with open delta, high-leg service. I found this quote about high-leg to neutral currents which confirms your statement about limiting high-leg to neutral currents.

Commonly there is a High-leg to neutral load limit.[5] One transformer manufacturer's page suggests that High-leg to neutral loading to not exceed 5% of transformer capacity.[6]
« Last Edit: August 23, 2014, 10:04:24 pm by Mike Sokol »
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Mike Sokol
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Jeff Bankston

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Re: Need help with panel
« Reply #6 on: August 24, 2014, 01:01:39 am »

i would not connect anything to "B" phase(Orange). use only "A" and "C" phase(Black and Blue) for 240.
« Last Edit: August 24, 2014, 03:23:24 am by Jeff Harrell »
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Mike Sokol

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Re: Need help with panel
« Reply #7 on: August 24, 2014, 08:22:21 pm »

i would not connect anything to "B" phase(Orange). use only "A" and "C" phase(Black and Blue) for 240.

I would agree with that. Stay away from the "high" leg.
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Mike Sokol
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Tim McCulloch

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Re: Need help with panel
« Reply #8 on: August 24, 2014, 09:02:56 pm »

I would agree with that. Stay away from the "high" leg.

Yup.  You never know what it might be smokin'...

/double or triple entendre
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Jeff Bankston

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Re: Need help with panel
« Reply #9 on: August 24, 2014, 09:48:42 pm »

i wired up a lot of businesses that had High Leg service. and in california the High Leg is on C phase at the service and it switches to B phase at the panels.
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ProSoundWeb Community

Re: Need help with panel
« Reply #9 on: August 24, 2014, 09:48:42 pm »


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