convert delta service to wye

[electrofelon]

I have a 120/240 high leg delta service serving a building that has 5 accounts/meters. Three dwellings, a deli, and a club. The club's service is three phase but I think all the others are single phase. The clubs disconnect has all three phases run to it, but no fuse on the B phase and no wire run from the load side of the disco to the 200 amp panel. The only line to line load in the club is a walk in cooler. The client wants to add a grow room fed off the clubs panel. I did a load measurement while the club was up and running and its going to be close with this grow room added. Actually it will be fine most of the time but now and then when they have a real big act, they run extra lights and sound and that's what I am worried about. This got me thinking - probably more of an academic questions at this point but: What if I had the utility change the service to a 120/208Y? Any implications/ramifications that I am missing? Here is what I have come up with:
1. The club's meter and maybe socket would need to be changed, not sure about the other 4 single phase, depends on their meters I guess...?
2. Obviously lower wattage for ranges and water heaters - no biggie. Maybe would want to look at equipment in the deli to see if ok with 208
3. Un-identify the high leg

That's all I have, am i missing something or would it actually pretty much turn key after the utility does their end?

The theory is that this would free up space in the panel and things could be balanced out nicely.

 

[kwired]

I have a 120/240 high leg delta service serving a building that has 5 accounts/meters. Three dwellings, a deli, and a club. The club's service is three phase but I think all the others are single phase. The clubs disconnect has all three phases run to it, but no fuse on the B phase and no wire run from the load side of the disco to the 200 amp panel. The only line to line load in the club is a walk in cooler. The client wants to add a grow room fed off the clubs panel. I did a load measurement while the club was up and running and its going to be close with this grow room added. Actually it will be fine most of the time but now and then when they have a real big act, they run extra lights and sound and that's what I am worried about. This got me thinking - probably more of an academic questions at this point but: What if I had the utility change the service to a 120/208Y? Any implications/ramifications that I am missing? Here is what I have come up with:
1. The club's meter and maybe socket would need to be changed, not sure about the other 4 single phase, depends on their meters I guess...?
2. Obviously lower wattage for ranges and water heaters - no biggie. Maybe would want to look at equipment in the deli to see if ok with 208
3. Un-identify the high leg

That's all I have, am i missing something or would it actually pretty much turn key after the utility does their end?

The theory is that this would free up space in the panel and things could be balanced out nicely.

Balancing the load can be an issue. Are you changing all the single phase panels to three phase in all the spaces?

The delta system is nothing more than a single phase transformer and the third phase may only be derived from a smaller transformer as it has little load on it. By changing to a 208/120 system they will likely all be same sized windings and if you have all that single phase load connected between just two phases you will need oversized units to prevent overloading them, and the third will have little load on it.

Conductor derating for multiwire branch circuits can change as the neutral of a 120/208 three wire circuit is considered a current carrying conductor where on a 120/240 circuit it is not a current carrying conductor for deration purposes.

 

[augie47]

I'm a bit confused. If there is no wire connected to the load side of the disconnect is the panel not a single phase panel ? I don't see where you gain anything by changing to 208 ?
As far as the wattage change being "no biggie", the folks using appliances might tend to disagree

 

[electrofelon]

Balancing the load can be an issue. Are you changing all the single phase panels to three phase in all the spaces?

The delta system is nothing more than a single phase transformer and the third phase may only be derived from a smaller transformer as it has little load on it. By changing to a 208/120 system they will likely all be same sized windings and if you have all that single phase load connected between just two phases you will need oversized units to prevent overloading them, and the third will have little load on it.

I would not be changing any panels out, just energizing the currently unused phase in the club panel. The meters all come off a big buss bar box so it should be easy to re-phase the single phase panels to get the B phase in on the action. Plus the club is the largest load by far so being able to balance that out would be most of the battle. Im not sure I Agree with your statement about the delta system transformers. Of course it could be set up a number of ways, it could be an open delta, but it could be set up to serve mostly line to line loads and have equal capacity on all legs. Isnt the textbook general assumption that a Delta would have mostly line to line loads with minor line to neutral loads?

Conductor derating for multiwire branch circuits can change as the neutral of a 120/208 three wire circuit is considered a current carrying conductor where on a 120/240 circuit it is not a current carrying conductor for deration purposes.

Thats a good one. I knew there must have been some conductor or derating thing I was missing. Although I dont think there are any multiwires that would have non linear loads on them here. Actually dont recall seeing any multiwires at all.

I'm a bit confused. If there is no wire connected to the load side of the disconnect is the panel not a single phase panel ? I don't see where you gain anything by changing to 208 ?
As far as the wattage change being "no biggie", the folks using appliances might tend to disagree

the panel is three phase but no conductor is run to the B phase. As it is under worst case usage, A and C get uncomfortably close to 200 A so if some loads could be moved over to the B phase and balanced out, I would have more capacity - that is the theory.

 

[kwired]

I would not be changing any panels out, just energizing the currently unused phase in the club panel. The meters all come off a big buss bar box so it should be easy to re-phase the single phase panels to get the B phase in on the action. Plus the club is the largest load by far so being able to balance that out would be most of the battle. Im not sure I Agree with your statement about the delta system transformers. Of course it could be set up a number of ways, it could be an open delta, but it could be set up to serve mostly line to line loads and have equal capacity on all legs. Isnt the textbook general assumption that a Delta would have mostly line to line loads with minor line to neutral loads?



Thats a good one. I knew there must have been some conductor or derating thing I was missing. Although I dont think there are any multiwires that would have non linear loads on them here. Actually dont recall seeing any multiwires at all.




the panel is three phase but no conductor is run to the B phase. As it is under worst case usage, A and C get uncomfortably close to 200 A so if some loads could be moved over to the B phase and balanced out, I would have more capacity - that is the theory.

If you currently have a high leg delta system and the high leg has very little load, there is a pretty good chance the POCO either has open delta with reduced capacity transformer for the high leg. There are also full delta systems out there that still have a large pot for the 120/240 phase and two smaller pots for the other two phases because they do not anticipate them to be loaded as much as the 120/240 phase. Only time I really ever see full delta with three equal sized transformers is when lighting loads are minimal and power loads are the majority of load. Like a place that has mostly larger motor loads. A club probably has mostly line to neutral loads and maybe a three phase AC is only reason for the third phase.

As far as multiwire circuits non linear circuits is not the issue here. A MWBC consisting of two phase conductors and the grounded conductor on a wye system is three current carrying conductors for ampacity adjustment regardless of what the load is.

On a single phase system (or the single phase portion of a delta connected system) the neutral carries only unbalanced current. On a wye system it only carries unbalanced current if it is carrying current from all three phases. If you only have two phase conductors and the neutral and a load of say 10 amps on each phase, the neutral will be carrying about 10 amps also. That means more heat is produced in the raceway and the reason you have to count it for deration purposes.

 

[hbendillo]

Changing the service out to 208-volt would not be very cost effective unless the building were undergoing a major renovation. I don't think the power company would want to accommodate such a change based on what you are doing. Although most modern appliances and equipment are designed to operate effectively at a range of 208-230 volts, you may run into an old piece of equipment that requires 230-volts. One thing that would definitely be affected is equipment with electric heating coils in the HVAC system. Heating coils are rated to produce the necessary heat based on the delivered voltage. Reducing the voltage roughly reduces the heating capacity by the ratio of the square of the two voltages I think.

As far as balancing loads, if I were too change out a service like this I would connect the single-phase panel loads to different phases. Panel 1 to phases A-B, Panel 2 to phases B-C and Panel 3 to Phases A-C. I think the idea of adding the phase to the existing three-phase disconnect and reworking that service would be the best approach.

 

[electrofelon]

If you currently have a high leg delta system and the high leg has very little load, there is a pretty good chance the POCO either has open delta with reduced capacity transformer for the high leg. There are also full delta systems out there that still have a large pot for the 120/240 phase and two smaller pots for the other two phases because they do not anticipate them to be loaded as much as the 120/240 phase. Only time I really ever see full delta with three equal sized transformers is when lighting loads are minimal and power loads are the majority of load. Like a place that has mostly larger motor loads. A club probably has mostly line to neutral loads and maybe a three phase AC is only reason for the third phase.

As far as multiwire circuits non linear circuits is not the issue here. A MWBC consisting of two phase conductors and the grounded conductor on a wye system is three current carrying conductors for ampacity adjustment regardless of what the load is.

On a single phase system (or the single phase portion of a delta connected system) the neutral carries only unbalanced current. On a wye system it only carries unbalanced current if it is carrying current from all three phases. If you only have two phase conductors and the neutral and a load of say 10 amps on each phase, the neutral will be carrying about 10 amps also. That means more heat is produced in the raceway and the reason you have to count it for deration purposes.

While i agree in theory, and sorry if I wasnt real clear on it, the service predates the club by a lot so the service design as nothing to do with the existing setup and occupants.

On the MWBC's, yes definitely. I was thinking of a 4-wire Wye MWBC, and there wouldnt be a 4-wire MWBC on the current system and if there was, someone would be do something very strange.

Changing the service out to 208-volt would not be very cost effective unless the building were undergoing a major renovation

Well that is really the whole discussion: the theory that there would be hardly anything to change, other than maybe a meter socket. Unless you are talking about the utility work which is certainly a consideration as to what they would charge.

I think the idea of adding the phase to the existing three-phase disconnect and reworking that service would be the best approach.

Problem is there is only one line to line load so there is no reworking/balancing that can be done to the high leg.

I think i will investigate getting a 6th meter and give the grow room their own 100 amp supply Having their own meter is a plus too.

 

[hbendillo]

Don't know whether to start a new thread but just hours after I was on this forum, we got a call from a building owner and electrician about changing and old coca cola bottling plant service from 240/120 volt, three-phase delta to 120/208 volt wye. The power company wants to get rid of the old service and transformers and provide a pad mounted transformer for the facility. The existing service uses three-pole mounted transformers mounted in a concrete block enclosure on timbers on ground. There is a main panel on the outside wall next to the enclosure. Conduits run through the wall into the enclosure, terminate with weather heads, tie into secondary. Conversion will remove existing service and Install new underground service to a pad mounted transformer.

Now I am left to consider any implications for making the change in service. I have frankly never done this unless the whole building was being renovated and everything was replaced.

 

[hbendillo]

Don't know whether to start a new thread but just hours after I was on this forum, we got a call from a building owner and electrician about changing and old coca cola bottling plant service from 240/120 volt, three-phase delta to 120/208 volt wye. The power company wants to get rid of the old service and transformers and provide a pad mounted transformer for the facility. The existing service uses three-pole mounted transformers mounted in a concrete block enclosure on timbers on ground. There is a main panel on the outside wall next to the enclosure. Conduits run through the wall into the enclosure, terminate with weather heads, tie into secondary. Conversion will remove existing service and Install new underground service to a pad mounted transformer.

Now I am left to consider any implications for making the change in service. I have frankly never done this unless the whole building was being renovated and everything was replaced.

Sorry everyone, I started and new thread. Didn't mean to try and hijack this one.

 

[ggunn]

I have a 120/240 high leg delta service serving a building that has 5 accounts/meters. Three dwellings, a deli, and a club. The club's service is three phase but I think all the others are single phase. The clubs disconnect has all three phases run to it, but no fuse on the B phase and no wire run from the load side of the disco to the 200 amp panel. The only line to line load in the club is a walk in cooler. The client wants to add a grow room...

Is anyone else curious?

 

[eHunter]

Is anyone else curious?

Yes.

 

[electrofelon]

Yes.

Washington state. Its legal