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Old 07-02-2016, 08:49 AM   #1
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Default A true '2phase' system?

We have a delta high leg system on one of our buildings to run the chillers. Then they derive a 2 phase system off of a and c to feed the outlets and lights. Would that series of panels be a two phase system or is my terminology wrong.
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Old 07-02-2016, 09:02 AM   #2
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Well, you have 2 - 120V separated by 180˚

Technically not 2 phases, just one phase of a 3 phase system with a center tap.
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Old 07-02-2016, 09:55 AM   #3
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We have a delta high leg system on one of our buildings to run the chillers. Then they derive a 2 phase system off of a and c to feed the outlets and lights. Would that series of panels be a two phase system or is my terminology wrong.
To make it clear...

The A - C phase is 240 volts..

Now between A-C phase is a mid tap which it is 120 volts phase to netural..

This is common arrangement on 4 wire ∆ system ...

However there is one serious warning...

Do not connect 120 volt load to B phase - netrual.

That called wild leg .. And yuh there are other name for that..

Anyway B phase to netural will read 208 volts ...

That is smoke making leg or phase...

But for straight 240 volt loads like water heater or single phase 240 volt motor.

That can be on any phase.

Of course ya can have 3 phase motor on it..
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Old 07-02-2016, 09:55 AM   #4
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If you have two hots and a neutral from a single transformer winding then it's split-phase. It's still a single phase system.

Now, we do often feed loads with two 208V windings and a neutral. For reasons that have never been explained to my satisfaction we also call this "single phase" despite that it's clearly two phases.
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Old 07-02-2016, 06:06 PM   #5
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If you have two hots and a neutral from a single transformer winding then it's split-phase. It's still a single phase system.

Now, we do often feed loads with two 208V windings and a neutral. For reasons that have never been explained to my satisfaction we also call this "single phase" despite that it's clearly two phases.
Maybe the term was used to differentiate it from a 3phase circuit. Anyways, if you saw a picture of a 2phase distribution system it would look like 2 single phase systems side by side IIRC.
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Old 07-02-2016, 10:17 PM   #6
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Maybe the term was used to differentiate it from a 3phase circuit. Anyways, if you saw a picture of a 2phase distribution system it would look like 2 single phase systems side by side IIRC.
Yes it is and it come in 3,4.5 wire verisons...

The last one do have netrual. The line to netrual is typically 120 volts on correct phase but if you read on different phase it can go up a bit depending on which phase legs you are hittng it can be 120 or 148 or 240 volts..
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Old 07-04-2016, 08:44 AM   #7
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I wasn't sure if it counted, I know the residential ones are split phase but didn't know if these sub panels would since they are fed off a delta system
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Old 07-04-2016, 10:29 AM   #8
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I wasn't sure if it counted, I know the residential ones are split phase but didn't know if these sub panels would since they are fed off a delta system
A center tapped delta IS a split-phase system -- as the only potential it 'sees' is that between A and C phases -- 240 VAC -- and they are grounded half-way between -- giving you your classic 120 VAC line-to-neutral voltage.

Such schemes invariably use an OPEN delta transformer set up -- oft termed a 'stinger' -- to generate the B phase.

You can spot them, often enough, by staring at the pigs on the pole. You'll see what appears to be a very hefty split-phase transformer -- with a modest side-buddy -- the stinger -- side by side.

Such Services are out of favor with EUSERC -- so one can only spot them in the older industrial and commercial parts of town -- out here.
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Old 07-04-2016, 06:10 PM   #9
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Philadelphia still has some 2 phase distribution. Other than that I don't think there is any remaining. Niagara Falls generating station was originally two phase but that is long gone.
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Old 07-04-2016, 06:19 PM   #10
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A center tapped delta IS a split-phase system -- as the only potential it 'sees' is that between A and C phases -- 240 VAC -- and they are grounded half-way between -- giving you your classic 120 VAC line-to-neutral voltage.

Such schemes invariably use an OPEN delta transformer set up -- oft termed a 'stinger' -- to generate the B phase.

You can spot them, often enough, by staring at the pigs on the pole. You'll see what appears to be a very hefty split-phase transformer -- with a modest side-buddy -- the stinger -- side by side.

Such Services are out of favor with EUSERC -- so one can only spot them in the older industrial and commercial parts of town -- out here.

So rather than 3 trans formers to produce a 3phase wye you use 2 one center tapped for a/c and the other straight up 208?
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Old 07-05-2016, 02:38 PM   #11
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Elsewhere in the world (Germany in particular), they sometimes use the term "2 phase" to refer to "two-out-of-three phases", but that's because outside of those selective areas of the US (Philadelphia and upstate New York), TRUE 2-phase systems don't exist. So because we actually HAVE true 2-phase systems, we don't refer to two-out-of-three phases as anything other than "single phase".
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Old 07-07-2016, 08:03 PM   #12
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Elsewhere in the world (Germany in particular), they sometimes use the term "2 phase" to refer to "two-out-of-three phases", but that's because outside of those selective areas of the US (Philadelphia and upstate New York), TRUE 2-phase systems don't exist. So because we actually HAVE true 2-phase systems, we don't refer to two-out-of-three phases as anything other than "single phase".
Unless you are overly pedantic and anal as I used to be.

Me 15 years ago " it's not single phase it's two phases of a three-phase system!"

Me now. "Run a single phase circuit out of that 240 panel"

You can't beat the ignorant sheep, eventually you just have to join them.

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Old 07-07-2016, 08:06 PM   #13
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A center tapped delta IS a split-phase system -- as the only potential it 'sees' is that between A and C phases -- 240 VAC -- and they are grounded half-way between -- giving you your classic 120 VAC line-to-neutral voltage.

Such schemes invariably use an OPEN delta transformer set up -- oft termed a 'stinger' -- to generate the B phase.

You can spot them, often enough, by staring at the pigs on the pole. You'll see what appears to be a very hefty split-phase transformer -- with a modest side-buddy -- the stinger -- side by side.

Such Services are out of favor with EUSERC -- so one can only spot them in the older industrial and commercial parts of town -- out here.
Did you mean to use the term invariably? That can't be right as you don't HAVE to use an open delta to get a center tapped phase.

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Old 07-07-2016, 08:24 PM   #14
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So rather than 3 trans formers to produce a 3phase wye you use 2 one center tapped for a/c and the other straight up 208?
Yes... I think. I'm not actually sure what you are asking but yes to the two transformers. An open delta is a cheaper way to get 3 phase transformation as it only uses two windings on each side instead of three. It's not as efficient but for a small customer that won't generate much revenue it's how my local poco does it. At least they used to, as Telsa said it's kinda out of favour now.

Can also be used in an emergency if one coil of a three phase system fries. Depending on the load being served being light enough.

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Old 07-07-2016, 09:42 PM   #15
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So rather than 3 trans formers to produce a 3phase wye you use 2 one center tapped for a/c and the other straight up 208?
While the stinger phase is 208 VAC relative to the GEC System -- the real aim is to have the B tap 240 VAC away from BOTH A and C taps.

It's expected that all loads tapping "B" will be three-phase ( balanced ) loads.

No one-phase 208 VAC loads are to be wired up back at the panel.

Such Services are obvious at the panel -- as plenty of blanks cover the "B" phase when the adjoining A and C phases are busy with 1-pole breakers.

Even 240VAC two-pole loads are best fed from A & C phases. ( water heaters, etc. )

EUSERC utilities will simply not install center-tapped delta Services any more.

Standardizing on 208Y120 and 280Y277 three phase Services hugely simplifies inventory control and emergency repairs.

Everywhere, EUSERC wants pad mounted transformers. They are safer for the crews and much more earthquake resistant. Pole mounted pigs go flying during earthquakes.

If they don't fly off their mountings -- they can still take the entire pole down to the ground.
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Old 07-07-2016, 10:37 PM   #16
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But... EUSERC is not universally adopted by all utilities around the country. Here in the west, yes, because that's where EUSERC originated, but elsewhere, no. It was a shock to me actually when I found out, I had always thought (growing up here) that EUSERC was the governing body for the entire electric utility industry, but a friend got a job at Tampa Electric as a distribution engineer and does things I have never seen. When I mentioned it not conforming to EUSERC, he said "What's that?"
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Old 07-08-2016, 06:25 AM   #17
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We have a delta high leg system on one of our buildings to run the chillers. Then they derive a 2 phase system off of a and c to feed the outlets and lights. Would that series of panels be a two phase system or is my terminology wrong.
Quote:
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I wasn't sure if it counted, I know the residential ones are split phase but didn't know if these sub panels would since they are fed off a delta system
Quote:
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So rather than 3 trans formers to produce a 3phase wye you use 2 one center tapped for a/c and the other straight up 208?

Spend a little time looking around these pages for different transformer configurations.

Roger
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Old 07-08-2016, 07:32 AM   #18
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While the stinger phase is 208 VAC relative to the GEC System -- the real aim is to have the B tap 240 VAC away from BOTH A and C taps.

It's expected that all loads tapping "B" will be three-phase ( balanced ) loads.

No one-phase 208 VAC loads are to be wired up back at the panel.

Such Services are obvious at the panel -- as plenty of blanks cover the "B" phase when the adjoining A and C phases are busy with 1-pole breakers.

Even 240VAC two-pole loads are best fed from A & C phases. ( water heaters, etc. )

EUSERC utilities will simply not install center-tapped delta Services any more.

Standardizing on 208Y120 and 280Y277 three phase Services hugely simplifies inventory control and emergency repairs.

Everywhere, EUSERC wants pad mounted transformers. They are safer for the crews and much more earthquake resistant. Pole mounted pigs go flying during earthquakes.

If they don't fly off their mountings -- they can still take the entire pole down to the ground.
Sounds like you are talking about any center tapped delta and not necessarily an open delta?

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Old 07-08-2016, 07:47 AM   #19
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Elsewhere in the world (Germany in particular), they sometimes use the term "2 phase" to refer to "two-out-of-three phases", but that's because outside of those selective areas of the US (Philadelphia and upstate New York), TRUE 2-phase systems don't exist. So because we actually HAVE true 2-phase systems, we don't refer to two-out-of-three phases as anything other than "single phase".
Never come across two phase in upstate NY or the Philly area. Wasn't aware the systems were in existence really.
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