Delta

[walkerj]

First:
I am wiring a machine in a marble shop.
The machine says 115v 3 phase Y and the control panel has a spot to land 3 hots, one neutral, and one ground.
Three of the motors are 120v.
The building's service is 240v 3 phase.
120v A-N and C-N.
208 B-N and 240 phase to phase.

What are my options on powering the equipment?
The current system will not work, correct?

Second:
Only two pole mounted transformers serve the building.
The transformers are only tapped off of two off the primary phases.
How does this work exactly?

 

[iwire]

What are my options on powering the equipment?

I think your only option is a 240 delta to 208Y/120 transformer.

The current system will not work, correct?

I would think one third of the motors would let out smoke. :wink:

 

[walkerj]

Thank you.
That is what I thought.

 

[LarryFine]

Second:
Only two pole mounted transformers serve the building.
The transformers are only tapped off of two off the primary phases.
How does this work exactly?

You have what is known as an open-Delta service. The 120/240 portion is supplied by a single 240v center-tapped secondary, exactly like the service in your home.

The third line, aka the 'high leg', comes from the second transformer, and is there to supply only 3-phase loads when used with the other two lines, without the neutral.

 

[Besoeker]

First:
I am wiring a machine in a marble shop.
The machine says 115v 3 phase Y and the control panel has a spot to land 3 hots, one neutral, and one ground.
Three of the motors are 120v.
The building's service is 240v 3 phase.
120v A-N and C-N.
208 B-N and 240 phase to phase.

How do you get 120V phase to neutral from a 240V 3-phase service?
A bit off topic....
You have 115V, 120V, 208V, and 240V.
Other systems have a high leg delta, center-tapped 240V for domestic.
At best, it is complex rather than complicated.

By comparison, in the UK it is so much simpler.
LV is 400V 3-phase and 230V single phase (phase to neutral of the 400V)
Just one system.
Domestic installation has just one 230V input. Appliances from lighting to washing machines are all 230V.
Light industrial and commercial might take the 400V 3-phase. Office equipment is fed from 230V phase to neutral with the loading distributed across the three phases.

As an electrical engineer, using two different supply voltages into a domestic residence just doesn't sit well with me when one could get the job done.

 

[iwire]

As an electrical engineer, using two different supply voltages into a domestic residence just doesn't sit well with me when one could get the job done.

My home is supplied by one voltage system, it happens to be one 120/240 system.

 

[iwire]

How do you get 120V phase to neutral from a 240V 3-phase service?

From here ECN

OK, so maybe we do have some odd set ups :grin: but at least we drive on the right side of the road.

For what it's worth I don't run into the open delta service in my area, predominately all Wye services.

 

[LarryFine]

Looking at the pic in Bob's post, notice that the bottom half is exactly the same as a 120/240v 1ph service. If you scroll the image up so the top half is cut off by your monitor, you'll see it easier.

Bob's comment about seeing mostly Y systems reflects newer services at a majority of his jobs. Open-Delta systems originated as 3-ph modifications to existing 1-ph services for new machinery.

Nobody would specify an open-Delta service today, but you have to remember that electrical distribution has evolved over many years. One uses what's available when one installs a new service.

 

[iwire]

Larry I don't think any of our local power companies provide open delta. :smile:

Here are my choices from one of the local large utilities.

• Single phase, 3 wire, 120/240 volts
  
• Single phase, 3 wire, 120/208 volts
  
• Three phase, 3 wire, 240 volts, Delta
  
• Three phase, 3 wire, 480 volts, Delta
  
• Three phase, 4 wire, 120/208 volts,Wye
  
• Three phase, 4 wire, 277/480 volts,Wye

 

[peter d]

My home is supplied by one voltage system, it happens to be one 120/240 system.

Big deal...my home is supplied with a direct 7,200V connection.

 

[peter d]

Larry I don't think any of our local power companies provide open delta. :smile:

Here are my choices from one of the local large utilities.

• Single phase, 3 wire, 120/240 volts
  
• Single phase, 3 wire, 120/208 volts
  
• Three phase, 3 wire, 240 volts, Delta
  
• Three phase, 3 wire, 480 volts, Delta
  
• Three phase, 4 wire, 120/208 volts,Wye
  
• Three phase, 4 wire, 277/480 volts,Wye

They still provide delta for a new service? Weird.

 

[iwire]

They still provide delta for a new service? Weird.

I have not done one but think industrial.

 

[LarryFine]

Larry I don't think any of our local power companies provide open delta. :smile:

Here are my choices from one of the local large utilities.

• Single phase, 3 wire, 120/240 volts
• Single phase, 3 wire, 120/208 volts
• Three phase, 3 wire, 240 volts, Delta
• Three phase, 3 wire, 480 volts, Delta
• Three phase, 4 wire, 120/208 volts,Wye
• Three phase, 4 wire, 277/480 volts,Wye

That's now. I'm talking about neighborhoods that are 100 years old and the like. Remember, I'm in one of the oldest cities in the USA. I see a lot of open-Delta systems in older parts of Richmond. I have done new services on them, usually with separate 1ph and 3ph panels.

I bet Paul A. has seen plenty of them since he's been here. He even inspected one of mine that I did exactly what I just described.

 

[iwire]

That's now. I'm talking about neighborhoods that are 100 years old and the like. Remember, I'm in one of the oldest cities in the USA.

So you have 100 year old services?

When it's time to update a commercial service here it will likely be updated to a wye. The power company will replace their end. I am sure somewhere near me is a open delta service but they are as rare as a dodo bird. :smile:

When I started in the trade Boston still had some DC services, that would not mean you could update them, they would be terminated if modified. :smile:

 

[subtech]

Of the above listed services, either of the three phase, three wire services could be served by an "open delta" bank. (two transformers, not three)
An open delta bank is often preferred by many power companies when three phase loads are relatively small. The bottom line is, two transformers cost less than three.

 

[LarryFine]

So you have 100 year old services?

I think so. Some of them are pretty old.

When it's time to update a commercial service here it will likely be updated to a wye. The power company will replace their end.

Oh, they will here, too, but at the customer's expense. Same here. If you need new service, you can't get a high-leg Delta.

I saved one customer about $6K by re-using the existing high-leg service and the two fusible mains; a 125a 3ph and a 200a 1ph.

I am sure somewhere near me is a open delta service but they are as rare as a dodo bird. :smile:

I can take you to any of hundreds of alleys and show you the two transformers.

When I started in the trade Boston still had some DC services, that would not mean you could update them, they would be terminated if modified. :smile:

They only recently got rid of the last DC systems in Richmond within the last five years or so, if I'm not mistaken.

 

[hillbilly1]

They still do open deltas here, Still common in rural areas. The POCO saves having to buy one more transformer for relatively small services, such as gas stations, irrigation pumps, sewage lift stations, and the like. You still may be able to use the delta service, but you will have to know if any of the 120 volt loads are on the high leg. Some equipment only use the neutral with only two of the legs. You will have to check the wiring schematics to verify this. The high leg will make toast out of anything 120 (short of a water heater or resistance heating).

 

[LarryFine]

You still may be able to use the delta service, but you will have to know if any of the 120 volt loads are on the high leg. Some equipment only use the neutral with only two of the legs.

Actually, you must make sure than no load that has a neutral connection also connects to the high leg. That's the main reason I prefer separate 1ph and 3ph panels.

You can connect line-to-line 240v loads between any two lines, even the open side, as long as you don't overload it.

 

[hillbilly1]

Actually, you must make sure than no load that has a neutral connection also connects to the high leg. That's the main reason I prefer separate 1ph and 3ph panels.

You can connect line-to-line 240v loads between any two lines, even the open side, as long as you don't overload it.

I thought that's what I said?

 

[LarryFine]

. . . you will have to know if any of the 120 volt loads are on the high leg.

It sorta looked like you were saying it's okay as long as you're aware of it.