2 Phase 4wire

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domnic

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Electrical Contractor
I'm looking for a wiring diagram for a 2 phase 4 wire and a 2 phase 3 wire transformer.
 
2 phase 2 wire source, 3 phase 4 wire

2 phase 2 wire source, 3 phase 4 wire

if the source is a 2 phase, 2 wire system and the load is 3 phase 4 wire, which type of transformer should i use on that configuration? open wye - open delta? 13.8/0.48 kV

i got to design 5 feeders at 480 V (1000 KVA) for industrial purposes, one of those feeders is at 207 V for offices (3913 ft^2). im having trouble to decide what diversity factor should i use? does anybody know?
 
StephenSDH said:
Scott-T Transformer if you mean 2-phase 4 wire to 3-phase 3 wire

I had to buy one for philadelphia

http://en.wikipedia.org/wiki/Scott-T_transformer
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Sorry for a repeat post here....but still trying to figure this out. We are starting the design on a retail store (120 KVA connected load estimate) in Philly and the service planner sent us an email stating the service is 2-phase, 5-wire. He didn't list a voltage but I have to assume it is 240V. I am very unfamiliar with what 2-phase, 5-wire means. Am I getting a red-leg delta system that will have ability for 3-phase and 1-phase loads, or does Philly truly have a very old 2-phase system where I am only going to get 240V, 1-phase and 120V, single phase? In that case, how do you serve large roof top units that are large enough that they need 3-phase power? Finally....what are each of the 5-wires for? appreciate any help!
 
gravy said:
Sorry for a repeat post here....but still trying to figure this out. We are starting the design on a retail store (120 KVA connected load estimate) in Philly and the service planner sent us an email stating the service is 2-phase, 5-wire. He didn't list a voltage but I have to assume it is 240V. I am very unfamiliar with what 2-phase, 5-wire means. Am I getting a red-leg delta system that will have ability for 3-phase and 1-phase loads, or does Philly truly have a very old 2-phase system where I am only going to get 240V, 1-phase and 120V, single phase? In that case, how do you serve large roof top units that are large enough that they need 3-phase power? Finally....what are each of the 5-wires for? appreciate any help!
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If it really is 2-phase 5-wire, you essentially have two single phase systems tied at their center-tap point. The two single phase systems have a 90 degree displacement.

Imagine a center-tapped 120/240 single phase system. Take a second center-tapped 120/240 single phase system and give it a 90 degree displacement from the first system. Tie the two neutrals together. You will now have a 2-phase 5-wire system.

Since these systems are so rare today, I would have to pay a visit to the site to see what was really there.

Can you get a contact number for someone at the serving POCO? They will know for sure.
 
mivey said:
If it really is 2-phase 5-wire, you essentially have two single phase systems tied at their center-tap point. The two single phase systems have a 90 degree displacement.

Imagine a center-tapped 120/240 single phase system. Take a second center-tapped 120/240 single phase system and give it a 90 degree displacement from the first system. Tie the two neutrals together. You will now have a 2-phase 5-wire system.

Since these systems are so rare today, I would have to pay a visit to the site to see what was really there.

Can you get a contact number for someone at the serving POCO? They will know for sure.
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thanks mivey. Yes, I am gearing up to call PECO...but wanted to get smart on this system in advance. two separate 1-phase center tapped systems? wow....that's a first for me. so the 5 wires comes from: two phase conductors (from first system), two phase conductors (from the second system), and the center tapped grounded neutrals (tied together)? so looks like I can only serve 240V, 1-phase and 120V, 1-phase loads. For large HVAC units....would I be looking at providing phase convertors as part of Tenant work?
 
gravy said:
thanks mivey. Yes, I am gearing up to call PECO...but wanted to get smart on this system in advance. two separate 1-phase center tapped systems? wow....that's a first for me. so the 5 wires comes from: two phase conductors (from first system), two phase conductors (from the second system), and the center tapped grounded neutrals (tied together)? so looks like I can only serve 240V, 1-phase and 120V, 1-phase loads. For large HVAC units....would I be looking at providing phase convertors as part of Tenant work?
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You can serve single-phase or 2-phase loads with that service. You might could make 3-phase loads run, but I would not do it. I wonder if there are any 2-phase loads still there.

They are not two completely separate supplies (depends on your definition of supply, I guess) and I suspect they come from a set of 2 transformers similar to post #2. In the 5-wire case, the two transformers have their center lowside terminals tied together with the 5th wire (not shown it post #2).

If that is what you have, you will have to either provide a phase converter to get three phase (like the two transformers mentioned before), or have the POCO supply a 3-phase service.

It is not very efficient to take 3-phase, convert it to 2-phase, then convert it back to 3-phase. I would talk to the POCO about a 3-phase service.

Perhaps you will find the customer no longer needs 2-phase and you can sell them an upgrade.

Add: Yes, it is 2 phase conductors from one system, 2 phase conductors from the other system, and they share a common point.
 
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mivey said:
You can serve single-phase or 2-phase loads with that service. You might could make 3-phase loads run, but I would not do it. I wonder if there are any 2-phase loads still there.

They are not two completely separate supplies (depends on your definition of supply, I guess) and I suspect they come from a set of 2 transformers similar to post #2. In the 5-wire case, the two transformers have their center lowside terminals tied together with the 5th wire (not shown it post #2).

If that is what you have, you will have to either provide a phase converter to get three phase (like the two transformers mentioned before), or have the POCO supply a 3-phase service.

It is not very efficient to take 3-phase, convert it to 2-phase, then convert it back to 3-phase. I would talk to the POCO about a 3-phase service.

Perhaps you will find the customer no longer needs 2-phase and you can sell them an upgrade.

Add: Yes, it is 2 phase conductors from one system, 2 phase conductors from the other system, and they share a common point.
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thanks again. this is a complete gut of the space....so we won't have any 2-phase loads. requesting a 3-phase service is looking like my best option. was trying to avoid since PECO will require a transformer vault be constructed in our basement, and we'll have to pay for trenching in the street for new primary conduits over to some manhole that I am sure is farther down the street in order to get the preferred 120/208V, 3-phase, 4-wire system. But it will be worth it for our customer in the long run...it's a long lease.

just for curiosity sake....for the 2-phase, 5-wire service....the main service entrance distribution panel would consist of just one panel (hmmm...how to you land all those conductors)? it seems like you would need two 240V, 3-ph, 3-wire service entrance panels with two meters? just keeps getting uglier.....
 
gravy said:
just for curiosity sake....for the 2-phase, 5-wire service....the main service entrance distribution panel would consist of just one panel (hmmm...how to you land all those conductors)? it seems like you would need two 240V, 3-ph, 3-wire service entrance panels with two meters? just keeps getting uglier.....
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It will be a 2-phase panel or switchgear. There will be four bus bars instead of three like in a 3-phase panel.
zbang said:
If you have a chance to get into the space and take some photos of the existing metering, switchgear, etc, I'd love to see them.
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Me too.
 
mivey said:
It will be a 2-phase panel or switchgear. There will be four bus bars instead of three like in a 3-phase panel.Me too.
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I'm trying like heck to not continue this as I'm sure we all have actual work to do, but:

I've never seen a panel like this with 4 busses plus a neutral....do they even still make them? I guess they need to make it bulletproof so nobody could ever install a 3-phase breaker by accident? All breakers would be 2-pole from this panel (either across A-B or C-D busses)? And all lighting and receptacle panels would be 1-ph, 3-wire loadcenters?

thanks again for all this info....big fan of the site (more of a lurker though).
 
A Scott-T can change a 2 phase service into a 3 phase service

Try pricing a Scott-T transformer, sized for your loads, it might be cheaper then the POCO trenching in the street up, sounds like a downtown old installation.

if going the Scott-T route, strip out the old service except the main disconnect, and hit the Scott-T from there, and run your 3 phase from the Scott-T

See post #2 or #3 for the wire up.

But I agree for the long run the building needs to be updated, and you need to be able to give the owner all the options.
 
gravy said:
I'm trying like heck to not continue this as I'm sure we all have actual work to do, but:

thanks again for all this info....big fan of the site (more of a lurker though).
Click to expand...

Oh but please keep this thread going, I would love to hear the outcome of this one. never ran into a 2 phase feeding a building before, just old draw bridges, and we used a Scott-T to get 3 phase to power the new drive motors when they up graded the drive.:D

Oh and pleanty of photos is a must:D
 
hurk27 said:
A Scott-T can change a 2 phase service into a 3 phase service

Try pricing a Scott-T transformer, sized for your loads, it might be cheaper then the POCO trenching in the street up, sounds like a downtown old installation.

if going the Scott-T route, strip out the old service except the main disconnect, and hit the Scott-T from there, and run your 3 phase from the Scott-T

See post #2 or #3 for the wire up.

But I agree for the long run the building needs to be updated, and you need to be able to give the owner all the options.
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thanks wayne- are you really saying that I can specify as part of my Tenant work a transformer (the Scott T is also new to me.....man I feel like a freshman at college again 20-years ago....just without the mullet) that will essentially turn my service into a 120/240V, 3-phase system where I can supply 120V 1-phase, 240V 1-phase, and 240V, 3-phase loads? I just googled this and it looks like a strange arrangement with a 50% tap on one winding and an 86.6% tap on the other. my overall building load (NEC connected) is 120 KVA.....do they make a 112KVA or 150KVA size for this as a standard?

I have been trying to post a couple JPEG's but have not been successful....any tips on how to do this?

thx
 
gravy said:
I have been trying to post a couple JPEG's but have not been successful....any tips on how to do this?

thx
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after you have hit the "REPLY" button, scroll down below the text box (the box you type in) and you will see the file manager, just click on "Manage Attachments" and in the next window at the top you will see where you can upload a file to here, one at a time point to the file and click the upload button, then repeat for the next file, then close the window. and make sure you include a message in the regular text box, as the forum has a minimum letter count to post,
 
gravy said:
thanks wayne- are you really saying that I can specify as part of my Tenant work a transformer (the Scott T is also new to me.....man I feel like a freshman at college again 20-years ago....just without the mullet) that will essentially turn my service into a 120/240V, 3-phase system where I can supply 120V 1-phase, 240V 1-phase, and 240V, 3-phase loads? I just googled this and it looks like a strange arrangement with a 50% tap on one winding and an 86.6% tap on the other. my overall building load (NEC connected) is 120 KVA.....do they make a 112KVA or 150KVA size for this as a standard?
thx
Click to expand...

I would say if this is not going to be the only tenant, and there is other loads on the existing 2 phase service, then your going to have to do a build from your allowed point of service, but if your tenant is taking the whole building then it would be up to the tenant and the owners of the building as to what they are going to allow? I would get everything together for all the options including the new 3 phase service from the POCO.

Then sit back and let them decide which way they want to go, the owner might even kick in and cover some of it, just to get the building service updated?

as far a sizes go I remember the Scott-T was very large, because it had to handle 2 200hp motors, and some other loads, but to say what is available now, I wouldn't have a clue?:confused:
 
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