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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Doug Fowler on August 23, 2014, 12:53:21 am

Title: Need help with panel
Post by: Doug Fowler 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
Title: Re: Need help with panel
Post by: Scott Holtzman 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?

Title: Re: Need help with panel
Post by: Mike Sokol 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.
Title: Re: Need help with panel
Post by: Doug Fowler 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.
Title: Re: Need help with panel
Post by: Stephen Swaffer 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 $$$)-they leave out the "b" to "c" transformer.  It works fine on the 120-N-120 loads and 3 phase, but the neutral to high leg can vary depending on loads.  Personally, I wouldn't trust it.
Title: Re: Need help with panel
Post by: Mike Sokol on August 23, 2014, 09:34:33 pm
I have always been told that you should never use a single phase load from neutral to the high leg.  In a set up like Mike's drawing it should be just fine; however, one reason it is used (at least around here) is the POCO can get 3 phase with just 2 transformers (and less $$$)-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]
Title: Re: Need help with panel
Post by: Jeff Bankston 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.
Title: Re: Need help with panel
Post by: Mike Sokol 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.
Title: Re: Need help with panel
Post by: Tim McCulloch 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
Title: Re: Need help with panel
Post by: Jeff Bankston 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.
Title: Re: Need help with panel
Post by: Doug Fowler on August 25, 2014, 02:08:09 pm
All good, A and C phases got it done.

Later I found a PostIt note on the floor that read "DO NOT USE THE B PHASE".

Thanks everyone.
Title: Re: Need help with panel
Post by: Lee Buckalew on August 25, 2014, 03:26:40 pm
All good, A and C phases got it done.

Later I found a PostIt note on the floor that read "DO NOT USE THE B PHASE".

Thanks everyone.

Post It's are the universally recognized safety standard for transmitting warning information.  :-)

Lee
Title: Re: Need help with panel
Post by: Cailen Waddell on August 27, 2014, 08:06:51 am
So, a question about this situation I have been thinking about for a couple days. 

Are the hot legs still 120 degrees out of phase with eachother?  With where the neutral is derived and the phase relationship of the hot legs, are neutral currents on a 120v/240v split phase distro a concern?  Is my actual capacity lower so I don't overload my neutral?

Thanks for the consideration....


Sent from my iPhone using Tapatalk
Title: Re: Need help with panel
Post by: Mike Sokol on August 27, 2014, 11:18:02 am
So, a question about this situation I have been thinking about for a couple days. 

Are the hot legs still 120 degrees out of phase with eachother?  With where the neutral is derived and the phase relationship of the hot legs, are neutral currents on a 120v/240v split phase distro a concern?  Is my actual capacity lower so I don't overload my neutral?

Thanks for the consideration....


Sent from my iPhone using Tapatalk

The 120-volt phases on a high-leg delta are actually at 180 degrees phase, forming what works and measured like a standard 120/240-volt feed. So its neutral current will be totally subtractive, just like any single-phase feed in the USA.

Just stay away from that "high-leg" since it's 208 volts from the neutral. Plus the POCO doesn't want any current drawn between the high-leg and neutral since that will cause all sorts of unbalancing to happen in the transformers.
Title: Re: Need help with panel
Post by: Stephen Swaffer on August 27, 2014, 11:30:34 am
The 2nd transformer will not affect the relationships on the split phase transformer. I have a customer with a an open delta-the POCO used a regular split phase transformer for that portion and just added a transformer for the wild leg.

Only 3 phase or phase to phase should use the wild leg-so they should not contribute to neutral currents.

If you use only the 240 volt split phase transformer to feed your gear, I see no significant issues.