nosratrouhani
Member
- Location
- Las Vegas
Is permitted by NEC to serve a dwelling unit with 3-phase power say 208Y/120V
3-phase power to Dwelling Units
- Thread starter nosratrouhani
- Start date
- Status
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Sure, but ya gotta get POCO to agree to provide it and it probably will not be cheap.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
There are lots of apartments supplied with 2/3 of a 120/208v 3-ph service.
nosratrouhani
Member
- Location
- Las Vegas
we do have 3-phase power coming to our current project and project we have developed in the past. But we have been traditionally just using 2 legs of 3-phase to feed each apartment. I have a project (227 units, one building) where it makes scene to feed the apartment with 3-phase feeder (apartments are all electric), however a colleague contractor who installs a lot of apartments tells me that NEC does not allow it and i cannot find such a thing anywhere in NEC.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Ask them for the cite? Anyway, 1-phase panels are a fair bit cheaper than 3-phase, and if there aren't any 3-ph loads, there isn't much point in using the more expensive panel. (I don't know of any code requirement, either.)
What about feeding the apartment with 208Y/120 3PH 4W makes sense... over 120/208 1PH 3W?
Assuming you can balance the load, the smaller wire that you can use is usually offset cost wise with having to run an extra wire... and then as already mentioned, the cost of the panel. I haven't actually run the numbers, but I have to assume that many already have and that's why many apartments are powered 120/208.
Iron_Ben
Senior Member
- Location
- Lancaster, PA
I live in a humongous apartment building. It's served by 8 three phase padmount transformers, each around 2,000 kva. (Told you it was humongous). My apartment has a full three phase 208Y/120 service.
nosratrouhani
Member
- Location
- Las Vegas
thanks everyone for your valuable inputs. our project will be served by (4) 2500A, 208Y/120V services at 4 different locations. I think I will propose the 3-phase option, especially that i will be running a larger (300 Amps) riser to feed 5 stacked units (5-story Building) and tap-off at each level with smaller feed to each apartment panel (80A 3-phase or 125A 1-phase)
kwired
Electron manager
- Location
- NE Nebraska
In many instances there likely isn't enough load in each individual unit to justify cost of three phase gear for individual units and there almost is never any three phase loads to feed within the dwelling units themselves. But you do have larger conductors to run for feeders if only supplying same VA with single phase - but in many cases still will be 100 or 125 amp panelboards just with one less bus. Put in a 60 or 80 amp main you still likely have 100 or 125 amp bus as that is typically all they make for them.
Before you mentioned this will be a multifamily dwelling I was thinking on the lines of you asking whether or not you can run 3 phase to a single family dwelling - probably does happen with the "Mc Mansion" type of dwelling, if anything because of the size of the place and the HVAC loads along with pools, spa's other loads that either are not present or at least at lesser levels in other dwellings are at a high enough level it is worth consideration - IDK never really worked at one. Have done a few homes with 600 amps single phase service capacity, but if one were to need much more capacity then that I think three phase is worth looking into as an option.
My first though would be the availability of a service drop. A dwelling unit usually is located in a residential neighborhood and if 3ph would even be available where an apartment complex may be more in an industrial commercial area where 3ph is available.
It is of my opinion that Bering allowed is not the issue but sourcing the 3ph to begin with.
- Location
- Massachusetts
How are you metering if using common feeders?
Here the law requires individual metering for each dwelling unit.
Iron_Ben
Senior Member
- Location
- Lancaster, PA
Perhaps they are unmetered, as are all the apartments here. Our monthly fee includes water, sewer, and electric. Everything but phone and Internet. It surprised me too.
- Location
- Massachusetts
That is common here in old buildings but not new ones.
kwired
Electron manager
- Location
- NE Nebraska
The capacity of service he mentioned in post 8 isn't all that likely to just tap on to some already existing POCO secondary conductors, unless it is an existing building being renovated.
Why wouldn't there be three phase primary in a residential neighborhood? May not be present adjacent to each lot but chances are it isn't too far away.
- Location
- Massachusetts
We have many residential areas around me with only single phase running down the street.
But I do agree, this is not an issue in the OPs case.
kwired
Electron manager
- Location
- NE Nebraska
Same here, but if a customer is willing to add the load to the system they will build it - may be some cost to the user though. This is nothing inside a city or small town compared to when some rural customers need such improvements to get what they need for power. If they run three phase primary down the road they will alternate phases when connecting single phase loads to balance the system, so it is not like they are using those extra conductors for just the one customer.We have many residential areas around me with only single phase running down the street.
But I do agree, this is not an issue in the OPs case.
You also have the occasional non residential property that is surrounded by primarily residential property like a small store, church, school...
I guess big cities have much larger residential areas with little or no non residential properties in that area, especially for more recently developed areas, but I can't imagine they would serve the entire area off one single phase line either.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
I know of an apartment building near here that had a 240V 3P high leg service but when it was being built the electricians wired it as if it were 208/120, i.e., 1/3 of the units had the B (high leg) phase with the neutral from the A and C center tap. Oops.
kwired
Electron manager
- Location
- NE Nebraska
We get that kind of thing around here when some electrician from a bigger city comes out here for a project - some seem really baffled at the concept of the high leg.
Been 25 - 30 years ago but had an elevator contractor install an elevator at a local school, provided their own electrician from big city. They did this during summer months when there was little/no activity at the school. When they tied into the main gear to supply the elevator they moved some things around and put the high leg for some existing feeders where it didn't belong.
Because school was out for summer my boss never got a call for those problems they created for days or weeks when they were finally discovered. I was kind of still pretty green, but had been pretty exposed to high leg systems at that time. I remember my boss saying that when he talked to the other contractor they acted like they never heard of such a system. I don't know exactly what they did at the main gear as I wasn't really involved in discovering what happened, but I remember replacing many lighting ballasts in the effected areas.
If 3ph were not too far away theoretically you could run/bury a line specifically for a single customer with the common sresidential ervice drop being 120/240 where would 208y/120 be sourced? Unless the pri dist was 3p, such as 2300v, 4160v we here you could add a 3ph transformer it isn't going to happen. I would conceed that if money was no object it wouilkd not be an impossibility.
With overhead service I haven't seen 3ph in a residential neighborhood. With underground service padmounts are 1ph.
With either s loop are radial feed primary I am not aware on any that feed 1ph trasnsformers.
It would be great if we got some input from someone we go in familiar with how a POCO distributes power.
JFletcher
Senior Member
- Location
- Williamsburg, VA
We have 3ph overhead powerlines here in our neighborhood. I believe they are 4160-4400V. It's uncommon tho (aerial, anyway).
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