240V Delta/120V 3-Phase, 4-Wire to 208Y/120V 3-Phase, 4-Wire

[HG_Phenom]

Stuck in a real quagmire of a situation. Hoping there is a solution that someone can think of or can shed some light on their experience and thoughts in making this work.

We have a 30-unit affordable multifamily apartment project going in Los Angeles that requires all systems to be electric. Due to significant site conditions and constraints, off-site transformation is needed from service coming from the utility company, DWP. Unfortunately, the utility company is insisting that the best they can offer through underground service from their transformer is a 240 Delta/120V 3-Phase, 4-Wire service to the project site at a maximum of 1000 Amp (initially they only would allow a max of 800 Amps). Their max threshold for providing off-site transformation is at 288 kVA with 240 Delta service and after that, it would be 208Y service but will require on-site transformation and installation by them with extremely onerous requirements that cannot be met in our case.

On the house/common area side, there is only a 15HP elevator, 2 small 6 Amp sump pumps, and general corridor lighting and ventilation, in TOTAL about 30kW demand.

The remaining units' demand load, when applying NEC 220.84 optional demand factor, is a TOTAL of about 250 kW. (Note, with the 240 Delta service they are providing, this load calc becomes based on single-phase instead of three-phase we could use with the 208Y service).

Is there any way for us to set up a system (Buck, step down, inverter, transformer???) to convert and get from the utility transformed and provided 240V Delta 3-Phase, 4-Wire service to a 208Y 3-Phase, 4-Wire service on our site so that we can provide the entire building demand (units and house area) 208Y 3-Phase service altogether in order to achieve the efficiencies of the true Y and 3-phase service transformation (being able to utilize the 3-phase efficiency at 1.732) across the entire load demand so that it could significantly drive down our entire building load to meet the 1,000 Amp limitation on the 240 Delta service they are providing?

 

[winnie]

A standard 240V delta to 208V wye transformer will do the conversion you are asking for.

You might also consider using separate single phase transformers to create 120/240V systems. You could use the 'native' 120/240V from the incoming delta for some of the units, and single phase 120/240V transformers to put load on the other legs of the delta.

But before looking at transformers you need to ask who is doing the metering, who is paying for the electricity, and where the meters will go. The utility probably won't want meters after a customer owned transformer.

Jon

 

[augie47]

Is it possible to use what they are providing by supplying each unit with 3 phase 240/120 utilizing the high leg for the 240v loads ?

 

[winnie]

Is it possible to use what they are providing by supplying each unit with 3 phase 240/120 utilizing the high leg for the 240v loads ?

This is certainly possible, but IMHO a very bad design choice. It would put a 3 phase high leg panel in a residence, which makes it very likely that someone down the road will try to connect a single phase load to the 208V leg.

-Jon

 

[hillbilly1]

They must have an existing delta service they don’t want to, or can’t change, (other customers on it most likely) or all they have left in the yard? A 480 volt service with a step down to 120/208 wye would be the easiest and most efficient, given the circumstances, but then there would be a metering nightmare. Another option would be three separate 400 amp single phase meter banks, with the poco transformers connected as single phase (they can still use the three phase HV line, but just in a single phase capacity, assuming it’s a new install, not existing.)

 

[ptonsparky]

This is certainly possible, but IMHO a very bad design choice. It would put a 3 phase high leg panel in a residence, which makes it very likely that someone down the road will try to connect a single phase load to the 208V leg.

-Jon

We've determined, through experience, that this usually happens only once.

 

[hillbilly1]

We've determined, through experience, that this usually happens only once.

Until the next guy……..LOL!

 

[kwired]

Stuck in a real quagmire of a situation. Hoping there is a solution that someone can think of or can shed some light on their experience and thoughts in making this work.

We have a 30-unit affordable multifamily apartment project going in Los Angeles that requires all systems to be electric. Due to significant site conditions and constraints, off-site transformation is needed from service coming from the utility company, DWP. Unfortunately, the utility company is insisting that the best they can offer through underground service from their transformer is a 240 Delta/120V 3-Phase, 4-Wire service to the project site at a maximum of 1000 Amp (initially they only would allow a max of 800 Amps). Their max threshold for providing off-site transformation is at 288 kVA with 240 Delta service and after that, it would be 208Y service but will require on-site transformation and installation by them with extremely onerous requirements that cannot be met in our case.

On the house/common area side, there is only a 15HP elevator, 2 small 6 Amp sump pumps, and general corridor lighting and ventilation, in TOTAL about 30kW demand.

The remaining units' demand load, when applying NEC 220.84 optional demand factor, is a TOTAL of about 250 kW. (Note, with the 240 Delta service they are providing, this load calc becomes based on single-phase instead of three-phase we could use with the 208Y service).

Is there any way for us to set up a system (Buck, step down, inverter, transformer???) to convert and get from the utility transformed and provided 240V Delta 3-Phase, 4-Wire service to a 208Y 3-Phase, 4-Wire service on our site so that we can provide the entire building demand (units and house area) 208Y 3-Phase service altogether in order to achieve the efficiencies of the true Y and 3-phase service transformation (being able to utilize the 3-phase efficiency at 1.732) across the entire load demand so that it could significantly drive down our entire building load to meet the 1,000 Amp limitation on the 240 Delta service they are providing?

One has to ask what their reasoning would be to not provide you with 208/120 Y for this? On the surface it doesn't make any sense at all. You are not going to use buck boost setups to make that 208 high leg into a 120 volt leg, not without creating other issues with it, main one being it is just not a great idea to use this leg for line to neutral loads whether they are direct 208 volt loads or some other arrangement. the return current if it is closed delta will split two ways, if open delta it only has one choice which way to go and adds to what is already connected to the closed side of the delta.

On top of that say you only use the high leg for line to line and three phase loads (if any) you will be unbalancing the system with the bulk of your loads simply by not utilizing one phase hardly at all.

some immediate issue they don't want to do it for becomes a longer term problem I would think.

Also if they are directly metering this they are either using 120/240 single phase meters and not utilizing the high leg which goes back to the unbalancing issues or are going to have to use three phase meters, which will cost them more and they probably still end up with a fair amount of the unbalancing issues.

We also have an affordable housing project yet POCO possibly wants to force them to pay a base service rate for three phase commercial power arrangements I guess? Thirty customers all on one transformer is still cheaper for them to provide their services than thirty customers spread out over larger area on multiple transformers.

 

[hillbilly1]

I’m betting other customers are already on this service, and the poco would have to build a new service along with having the old. Until the op gets back on that, I’m only guessing.

 

[kwired]

I’m betting other customers are already on this service, and the poco would have to build a new service along with having the old. Until the op gets back on that, I’m only guessing.

But why can't or won't they build the new service? If there is literally no place to do it that can be a little understandable, but yet at other places they find a way. Worst case why not require customer to install a vault to put POCO equipment in and bring primary voltage and a transformer within the building? If they can't get the transformer desired at the time - welcome to the current times, you might just have to wait until it becomes available or find alternate supplier or method?

 

[HG_Phenom]

All great feedback and questions/comments. As a preface for those of you who don't know, but this POCO is the DWP, notoriously corrupt and plays by its own rules regardless of what the Mayor or other City departments try to ask them to allow.

There is no rhyme or reason to them as to why they don't build new service or at least allow us to pay for it when we have requested to do so and put a street vault (even when we understand it would be a sizable cost).

To answer and clarify some other questions ask:
1. Yes, this is a new construction building

2. POCO "supposed" liability mandate since 2019 allows them to only provide you off-site transformer through public ROW street/side-walk vaults or pole-mounted at max service size of 240 Delta 3-phase 4-wire up to max 800 Amp or 300kVA. I already have finally got them to allow this service to at lease 1,000 Amps. All other services, 208Y and above they consider as "high voltage" and require the transformation on your premises.

3. Although ideally, we want individual metering, I do agree with you and think private metering is the only possible solution in order to make this work, but still unsure.

I was thinking of using something like this, https://store.maddoxtransformer.com/products/240-delta-208-y-120?variant=45588273993, but not sure if this would work and would be allowed.

 

[winnie]

That would be a fine transformer for your application. You would need a 250 or 300kVA unit.

As I previously suggested, you might consider using a pair of these:

Maddox Industrial Transformer

New and reconditioned commercial and industrial grade transformers. Build a quote or call 1-866-984-1856 to talk to us.

store.maddoxtransformer.com

You would use two 75kVA or 100kVA units.

Assuming phase B is the high leg, with both A and C sharing the center tap, then one transformer would be connected B to A, and the other would be connected B to C. Each transformer would feed 9 units, 12 of the units would be supplied from A to C without a transformer.

The house panel and elevator motor would get three phase.

One significant benefit of multiple smaller transformers is reduced fault current. Depending on the available fault current you might want all three legs to have transformers.

Jon

 

[robertd]

All great feedback and questions/comments. As a preface for those of you who don't know, but this POCO is the DWP, notoriously corrupt and plays by its own rules regardless of what the Mayor or other City departments try to ask them to allow.

There is no rhyme or reason to them as to why they don't build new service or at least allow us to pay for it when we have requested to do so and put a street vault (even when we understand it would be a sizable cost).

To answer and clarify some other questions ask:
1. Yes, this is a new construction building

2. POCO "supposed" liability mandate since 2019 allows them to only provide you off-site transformer through public ROW street/side-walk vaults or pole-mounted at max service size of 240 Delta 3-phase 4-wire up to max 800 Amp or 300kVA. I already have finally got them to allow this service to at lease 1,000 Amps. All other services, 208Y and above they consider as "high voltage" and require the transformation on your premises.

3. Although ideally, we want individual metering, I do agree with you and think private metering is the only possible solution in order to make this work, but still unsure.

I was thinking of using something like this, https://store.maddoxtransformer.com/products/240-delta-208-y-120?variant=45588273993, but not sure if this would work and would be allowed.

>but this POCO is the DWP, notoriously corrupt

You weren't kidding when you wrote that:

https://www.justice.gov/usao-cdca/pr/former-head-ladwp-sentenced-six-years-federal-prison

Former Head of LADWP Sentenced to Six Years in Federal Prison
...Wright, who is the first defendant to be sentenced in the LADWP corruption cases...

I'm not sure what kind of logic you use to label a 120/208Y service as "high voltage", but a 120/240 High Leg Delta service as not "high voltage".

 

[kwired]

>but this POCO is the DWP, notoriously corrupt

You weren't kidding when you wrote that:

https://www.justice.gov/usao-cdca/pr/former-head-ladwp-sentenced-six-years-federal-prison

Former Head of LADWP Sentenced to Six Years in Federal Prison
...Wright, who is the first defendant to be sentenced in the LADWP corruption cases...

I'm not sure what kind of logic you use to label a 120/208Y service as "high voltage", but a 120/240 High Leg Delta service as not "high voltage".

Same here.

That said electrical industry in general considers anything under 1000 to be low voltage, inside wiring guys may not always see it that way but the utility companies definitely consider that to be low voltage.

 

[zbang]

Context matters- we also talk about low-voltage as being below 50 volts or for comms/network/etc cabling, then line-voltage, medium-voltage, etc.

 

[synchro]

As I previously suggested, you might consider using a pair of these:

Maddox Industrial Transformer

New and reconditioned commercial and industrial grade transformers. Build a quote or call 1-866-984-1856 to talk to us.

store.maddoxtransformer.com

You would use two 75kVA or 100kVA units.

Assuming phase B is the high leg, with both A and C sharing the center tap, then one transformer would be connected B to A, and the other would be connected B to C. Each transformer would feed 9 units, 12 of the units would be supplied from A to C without a transformer.

Another obvious benefit of this is that L-L loads in the apartments for HVAC and appliances would have 240V vs. 208V.

 

[kwired]

Another obvious benefit of this is that L-L loads in the apartments for HVAC and appliances would have 240V vs. 208V.

Air conditioning - will still work just fine, a little less line losses on in conductors for equipment that still otherwise capable of delivering same output rating at either voltage. Resistance heating appliances - will take longer to do same work, but unless marginally sized user probably won't ever really know any difference.

still will have a lot of 120 volt loads that will either be placed on the two 120 volt to neutral lines or if using transformation to get 120 out of the high leg, will have increased losses even if the transformer(s) are idle. Heat given off by transformers is real power losses.

 

[ggunn]

We've determined, through experience, that this usually happens only once.

It happened here in Austin a few years ago. A large apartment complex was wired with individual panels for every unit having two phases of a 208/120V service, and then the utility came in and installed a 240/120V high leg transformer. Two thirds of the unit panels had 120V on one busbar and 208V on the other. Oops.

 

[kwired]

It happened here in Austin a few years ago. A large apartment complex was wired with individual panels for every unit having two phases of a 208/120V service, and then the utility came in and installed a 240/120V high leg transformer. Two thirds of the unit panels had 120V on one busbar and 208V on the other. Oops.

I had a somewhat large cattle feed yard with three different services in three different areas of the place. One on the "far end" had somewhat limited load and even though when new was full delta bank had been changed to open delta. Underground primary feeding this one - but ran up a pole and had pole top transformers. That primary was getting older and occasionally would have a failure, POCO would swap effected line with unused line to get them going and make repairs to the faulted cable at their convenience.

One time they made their swap after a failure, the guys (POCO) checked for proper rotation after they were done but never paid attention to position of the high leg. About only three phase load was a couple submersible well pumps and everything else was 120/240 single phase. They had a lot of mercury vapor (been a while ago) lights on poles for the pens at night, quite a few of them did not survive being on the high leg, as well as some items in a shop building close to the main pole. Bad thing was I had just recently gone through the pen lights just a couple weeks before this happened and repaired any not working, which we kind of normally did on an annual basis, then I got to kind of do it all over again.

It wasn't too much longer after that they finally just replaced those old underground primary lines with new ones.

 

[synchro]

Another obvious benefit of this is that L-L loads in the apartments for HVAC and appliances would have 240V vs. 208V.

still will have a lot of 120 volt loads that will either be placed on the two 120 volt to neutral lines or if using transformation to get 120 out of the high leg, will have increased losses even if the transformer(s) are idle. Heat given off by transformers is real power losses.

Of course a 240V delta - 208Y120 transformer to distribute the single-phase loads across the phases of the 240V high leg delta service will also have such losses.