What was done to fix it?
240V Delta/120V 3-Phase, 4-Wire to 208Y/120V 3-Phase, 4-Wire
- Thread starter HG_Phenom
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electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Maybe I'm missing something, but sounds like you are right about there even if you take the 1000A 240 three phase service and only serve the apartments with single phase. Send three phase to a few of the apartments if need be. Also maybe double check your calcs, they seem kinda high to me.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I would have no concern whatsoever. OP said this is a "affordable multifamily apartment" so it seems highly unlikely someone will be fiddling around in the panel. Even if they do so what, there are 1001 ways an idiot can get into trouble messing with something they shouldn't be messing with. I wouldnt fret about what ifs.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
yes, that is why you request the 208/120 as the service voltage in the first place, so you don't need said transformers and the up front cost plus the idle losses over time.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I have had a few affordable housing clients that are at least partially government funded in their operations. Sometimes there is a maintenance man that can find a way to mess with things, though can't recall encountering something where they added more breakers. A common thing I have seen is replacing receptacles and not realizing what a MWBC is about and that you at very least need to break tab off on duplex receptacles that were fed with both legs.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Also, I know some electricians find high leg deltas very foreign, and thus probably have some irrational hesitation or fear of them. I run across them all the time, believe it or not probably more than 208Y/120, to me it's just another electrical panel and system.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I can sort of say the same thing. Local electricians here are used to high leg systems, but have seen cases over the years when a contractor outside the area comes in and doesn't seem to know anything about them.
When I was still an apprentice our local school had outside of area contractor(s) installing an elevator. Their electrician moved things around in main gear to feed that elevator. Was in summer when school was not in session, but we got called in sometime shortly after with lots of things in kitchen not working - 120 volt loads ended up on high leg from whatever they did. I wasn't involved in main gear to see what was actually done, my boss said he tried to explain to them what they did and they acted like they never heard of such a thing, is about all I recall other than me repairing or replacing items that were damaged on the other end of the feeder.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
And I have fried more things by accidentally giving a 120V load 240 (in a regular single/split phase panel) than I have by giving a 120V load 208 from the high leg.....just sayin'
HG_Phenom
Member
- Location
- Los Angeles
- Occupation
- Contractor
lol, ya I wish I was joking and that's just the tip of the iceberg, he is just the beginning.
when using the phrase "high voltage" I'm using their stupid verbiage and jargon where they consider 208Y high but not 240V Delta at the same 1000amps
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
The easiest way, of course, would have been for the utility to come back with a 208/120V replacement transformer. There was much wailing and gnashing of teeth, but I don't know who ultimately won that fight.
HG_Phenom
Member
- Location
- Los Angeles
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- Contractor
Trust me, we have ran the numbers more than 50 times in so many different scenarios. You are right, we almost got there with that latest calc I shared, about 33 or 50 amps over 1,000 amp board requirement which jumps us up to a 1,200amp board.
I somewhat understand what you, synchro, and others have mentioned here to try but what I'm struggling to understand here and from other consulting engineers we have hired who are failing to explain clearly to us other than saying "it can't be done," is why can't we simply take the max service the POCO is willing to provide us from their off-site transformer which at this point is a 240V Delta/120V 3-phase 4-wire up to 1,000amps and convert/transform it privately on our site to become the same or similar 208Y/120V 3-phase, 4-wire (subject to some loss) service to the house meter items and each apartment meter loads so that all loads can utilize 3-phase power to drop the amps down on the 208Y 3-phase transformer before it gets to the main utility service transformer providing 240V delta?
If I'm not mistaken, in the case of the POCO transforming and providing us directly with 208Y/120V 3-phase, 4-wire service, the 3-phase calc (square root of 3) can be applied across the board, to the tenant meter loads and to the house loads.
Why is that not the case in what we are recommending and proposing here and everything for the tenants load has to go to 1-phase?
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Almost always residential units get 'single phase' power. Possibly simply because 3 phase panels are more expensive.
In large groups of residential units such as apartments, this 'single phase' is simply two out of the three legs of a three phase wye service.
So the _building_ gets 3 phase wye service and the individual units are distributed across all three phases. The entire building is a 3 phase load and the 1.732 factor applies. This is totally normal, and if you could get it what you want the power company to provide.
You've made it clear that what you really want (208/120 wye from the power company) is not available. The question is how to best make due with what they will supply.
The simplest concept is exactly what you suggest: take the 240V delta and use a full capacity transformer to get 208/120V wye. But everything you can do to minimize the size of the necessary transformer and minimize the power going through that transformer is money saved.
As I see it your options are:
1) run the three phase high leg delta to each apartment. Most HVAC loads are straight 240V, so other than more expensive panels and the confusion that high leg delta can cause some non-professionals, this is viable. This would have the benefit of letting the utility meter each individual apartment....if they have a tariff for 3 phase residential meters.
2) install a big 240V to 208/120V 3 phase transformer. Then run pseudo single phase 120/208V to each unit. You would have one meter from the power company and would sub meter to the tenants (if allowed), and would have to deal with the losses in the transformer.
3) Serve most of the tenants using the 120/240V single phase power of the high leg delta, but put some of the tenants on a transformer to distribute the load.
As a random thought, I wonder if the POCO would provide 3 separate 600A 120/240V single phase services rather than the equivalent power in the form of a 1000A 240V delta.
Jon
In large groups of residential units such as apartments, this 'single phase' is simply two out of the three legs of a three phase wye service.
So the _building_ gets 3 phase wye service and the individual units are distributed across all three phases. The entire building is a 3 phase load and the 1.732 factor applies. This is totally normal, and if you could get it what you want the power company to provide.
You've made it clear that what you really want (208/120 wye from the power company) is not available. The question is how to best make due with what they will supply.
The simplest concept is exactly what you suggest: take the 240V delta and use a full capacity transformer to get 208/120V wye. But everything you can do to minimize the size of the necessary transformer and minimize the power going through that transformer is money saved.
As I see it your options are:
1) run the three phase high leg delta to each apartment. Most HVAC loads are straight 240V, so other than more expensive panels and the confusion that high leg delta can cause some non-professionals, this is viable. This would have the benefit of letting the utility meter each individual apartment....if they have a tariff for 3 phase residential meters.
2) install a big 240V to 208/120V 3 phase transformer. Then run pseudo single phase 120/208V to each unit. You would have one meter from the power company and would sub meter to the tenants (if allowed), and would have to deal with the losses in the transformer.
3) Serve most of the tenants using the 120/240V single phase power of the high leg delta, but put some of the tenants on a transformer to distribute the load.
As a random thought, I wonder if the POCO would provide 3 separate 600A 120/240V single phase services rather than the equivalent power in the form of a 1000A 240V delta.
Jon
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yes, you can buy your own 240-208Y/120V step down transformer. It will likely not be able to be cost justified, but you can do it.
The building owner will be absorbing the losses of the transformer for the entire life of the facility.
The tenant metering and monthly billing will have to be done by the owner unless the electricity is included in the rent.
Many municipalities and states do not allow a profit to be made on the resale of electricity provided by a regulated utility.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I am still confused. If you are a mere 30-50 amps away, it seems like there are numerous ways to squeeze it in. Just feed a few units with three phase and load up the line the line loads on the high leg as much as you can, you slightly smaller elements in the water heaters, get creative with the calcs, drop a couple ranges and say they are getting gas ranges....
You DO NOT want to buy a 225 KVA or larger transformer, pay for the losses and deal with sub metering.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Just going back to the original post to point out an error in the understanding of 3-phase power.
The factor of 1.732 does not indicate improved electrical efficiency. It simply indicates that with the 3rd wire carrying current you have more power delivered with the same current on each wire.
With two wires 240V apart, each carrying 100A, you deliver 24000 VA to the load.
With 3 wires 240V apart (delta), each carrying 100A, you deliver 41600VA to the load.
You don't want the 208/120V service for improved efficiency; you want it because at the 1000A limit the power company sets, you need it to meet the 280kVA load requirement.
Jon
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Along those lines, consider having 3 of the 30 tenants on a 25 kVA single-phase transformer fed by phases A-B (i.e., A and the high leg), and another 3 tenants on a 25 kVA fed by B-C. The remaining 24 tenants would be put on A-C of the 4-wire delta service. It appears this would reduce the line currents on A and C drawn by the apartments from 1040A down to 890A. There would be 181A on the high leg phase B feeding the two transformers.
Doing this would reduce the total required transformer kVA by a factor of 5 from that of a 240V delta - 208Y120V transformer that feeds all of the apartments.
The transformer kVA's mentioned above are minimum required values.
HG_Phenom
Member
- Location
- Los Angeles
- Occupation
- Contractor
Of course we would love the utility to meter each unit individually so tenants pay direct since in LA we can't charge back affordable housing tenants if submetered except partially for water. However I think that ship has nearly sailed and have to accept it as this is our last go around in trying to make individual meters work by getting loads down and at the very least master metering and getting the project to at least come to fruition.
Option 1, is exactly what we've been doing with our calcs but still coming just short of the threshold, however I do think you're forgetting with option 1 about the three phase house items, ie, elevator, etc. It's not just individual tenant units.
Option 2 seems to be possibly the only avenue and where we will have to end up, but again I believe when we ran this scenario we were just at the threshold w 99% efficiency and not taking into account the losses which most likely would put us over the building department's threshold which would require type 1 masonry construction for most of the first floor.
Problem with option 3 would be you lose the NEC 220.84 demand factor of 0.32 which would put us wayyy above the load threshold.
I do like your random thought and will be proposing that as we finally have another call set up with the supervisor of the supervisor, pretty much the head that can say yay or nay to see what he says. Much appreciate all the commentary and feedback here. I really need to make this work for our group.
HG_Phenom
Member
- Location
- Los Angeles
- Occupation
- Contractor
We have cut everything down to the bare bones. Using commercial water heater at 4,000 watt non-simultaneous dual elements. We have even looked at just going gas on the water heaters which the skinny couch assume one gas boiler and no electric.
Also from what you mentioned, unfortunately what you're missing is all these are including NEC 220.84 demand factor of 0.32. once you feed other units differently, you lose the low demand factor and assumed load goes much higher. Same goes for dropping ranges. I wish we could but the same NEC requires all electric ranges and if not, then you can calculate using the same code section I mentioned but assume the non-existing range (that's now gas) is at 8,000 Watts and you get to choose the lower of the two calculations, under the standard calc or the optional which is 220.84 which we have done to no avail. Some real BS, I know :/
HG_Phenom
Member
- Location
- Los Angeles
- Occupation
- Contractor
Correct and I thought I cleared this up the other day. Efficiency was absolutely not the correct word to use. Definitely did not explain it as eloquently as you just did, but yes you are correct and understood.
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