Is There Such A Beast?

zuhow

Long time lurker, first time poster here:

I am wondering if there is such a thing as a 480/277 Wye to 120/240 Delta transformer.

I'm doing some investigation into a proposed condo. The condo would need 480/277 3 phase for the elevator and 120V single phase for the garage/site lighting and what not.

How would you arrange this supply so it's all on one meter to be billed to the condo association. Should it be 2 seperate services?

I'd appreciate any opinions on the best way to get there.

Thanks in advance

Mike

mdshunk

There's no reason to ever feed the primary of a 3 phase transformer with the neutral also, just the three hot legs. Thus, the primary is neither functionally "delta" or "wye" connected. Even if you have a 480 wye service, the primary of the step down transformer you use will be called "delta" because you won't be using the neutral. This referrs to how the coils are arranged inside that transformer, and not your service type. http://www.phaseconverter.com/tptransformer2.html

If you only need a single phase secondary, I might not even use a 3 phase transformer. Just use a 480 x 240/120 transformer. That's a pretty ordinary transformer. (translate that into relatively cheap, as far as transformers go). What's the single phase 240/120 load total? Could you be talked into using 277 or 480 for your exterior site lighting? Most wall packs and parking lot lights are already set to accept 277 or 480 (they have multi tapped ballasts), so that translates into smaller conduits and smaller wire sized and that equals cost savings. Same with most parking garage lighters. You can just save the 120 lighting for hallways, stairwells, and little accent lights.

zuhow

MD thanks for the quick reply.

The 120V total load is small - 4 20A circuits, plus a spare- call it 10kVA.

the elevator is a 40 hp motor, plus (1) 15 A lighting circuit

mdshunk

No kidding? Yeah, for sure I'd just use a little 480x240/120 transformer, single phase only. You'd be a hero. No real need for 3 phase at that lower voltage, so it seems. Keeps the costs down if you don't need 3 phase.
http://www.phaseconverter.com/sptransformer.html

zuhow

Ok please contribute a bit more to my education, my electrical skills are more or less limited to DC and electronics.

Is my understanding of this situation correct:
The Utility supplies 3 phase into the building to a panel "A", from that circuits 1/3/5 (3 poles) go to the elevator and circuit 4 (1) pole goes to the xformer and then to panel "B" with it's 5 circuits?

mdshunk

Very good, with one exception. That breaker feeding your transformer would be a 2 pole breaker (480, single phase). If you use a one pole breaker, you'd only have 277.

On 480, between any two hot legs is 480, single phase. If you have all three hot legs, you have 480, three phase. Between any one hot leg and neutral, you have 277. If you have all three hot legs and the neutral, you have 480/277 three phase, which is unuseful for anything except feeding an additional panel.

Yes, in your case you'd have a three pole breaker for the elevator pump, and a two pole breaker to feed the transformer.

How big of a building is this, anyhow? Is there some overwhelming reason you must use a 480 elevator? What I mean to say is, your common area lighting load seems so low, this can't be that big of a place. Can't you spec a 208/120 service, and get a 208 elevator? A 208 elevator isn't really odd at all. That saves you from bringing in 480 (cost savings) and saves you from needing a transformer for your lighting load (more cost savings). Seems a real waste to bring in 480 for one piece of equipment that can be installed to operate at a more cost effective voltage.

zuhow

It's tiny- 3 floors w/ a garage under it.

Cost is the driver on the elevator. A single phase elevator is good for 5+ stops and starts at 125K. the 3 phase hydraulic is 80K (so says Otis sales rep). No need for 480, but I do need the 3 phase- and my (admittedly shallow) understanding is that my choices are pretty much 120/240 3 wire single pahse or 480/277 4 wire 3 phase from the utility. It's an existing (older) neighborhood of row houses where the prospective site is.

I thought that 208/120 was the way to go- but I was told that 480/277 was a better way (easier supply from the utility). Hence why Im here asking. The gent who said use 480/277 said the 1st post about the xformer. I fiigured i'd get a sanity check here first.

mdshunk

Sounds reasonable enough, then. That's a dandy cost savings on that elevator to serve it at 480 then, so it seems. Thanks for that information. By the way, ETI (Elevator Technologies, Inc.) in Hagerstown MD will beat the socks off Otis and TyssenKrupp on price every time on the same elevator specs. I see you're just down the road, in Annapolis. Otis is definately the Cadillac. Not sure what type of a buiding this will be. Maybe it is a Cadillac building? I know I'm sticking my nose into design here a little bit, but I like to take advantage of engineers when I have their ear, and ask questions too.

zuhow

Well, feel free to pick my brain whenever you want- I'll be happy to repay the favor. Feel free to contact me directly.

So answer me this- is 208/120 3 phase typically available from the overhead lines?

thanks for the tip on the supplier -oddly enough most of my work is in hagerstown/frederick but typically I don't do condo's. I'm just trying to develop a cost estimate.

mdshunk

Depends on the neighborhood. The voltage isn't the issue... 3 phase is the issue. If three phase is available, you can have it at 208/120 or 480/277. Your choice. One is not easier than the other, from the utility standpoint. It's just a matter of what transformer(s) they will hang on the pole or plop on the padmount. If all three phases are in that neighborhood, you have your choice of the supply voltage. For a condo complex, you'd want three phase available, so that you can distribute each condo's power supply evenly amoung all three phases. Keeps the meter stack feeder more reasonably sized.

zuhow

well then, here's my dilema. I need 10 individually metered services ( each of 9 units and 1 for the bldg/elevator).

I thought the way to go was bring in 2 services (1) 3 phase and (1) single phase.

the single phase would be routed through a panel with 9 seperate metered 175A services- 1 to each unit.

Would it make more sense to bring in (1) 3 phase main and then break it up from there? I'm hung up on making sure evey unit is independently metered and a seperate "address" for the utility.

mdshunk

It would be most normal to bring in a large 208/120 3 phase to a meter stack for the units. If you need 480 for the elevator and house loads, then that would be a seperate service. No big deal. Pretty normal. I'd buck for two, 3 phase laterals or aerial drops. One at 480, for the house, and one at 208 for the tennant meter stack.

A "meter stack" is also called a multi unit meter. http://www.geindustrial.com/cwc/prod...MSM&lang=en_US

zuhow

Well the untis need 120/240V. The waterheaters and particularly the HVAC supplemental electric heaters must have the 240V. I can't get by with 208 there.

So it seems that a 3 phase drop and a single phase are the way to go, no?

zuhow

and thanks again MD, you've been a big help. Hope I can pay it back!

mdshunk

Yup, but water heaters and heat pump backup heat dataplates do have 208 listed on the dataplate. It's just a smidge less wattage. For 9 units, it's not a big deal. Probably better to go ahead with single phase for the tennant meters to keep your full wattage ratings. For much more than 9 units, you'd definately be looking at a 3 phase lateral. You just size water heaters and resistance heating with the 208 in mind when you have 208/120. Same with any electric ranges. I can assure you that the tennants won't know the difference.

Sparky Joe

Wow, way too many posts, where have I been? Forgive me for not reading through them all, so here's what I have to say.

Why do you need 240 for the condo and why not 208?
Delta secondary's are very uncommon for new installations.

And your elevator is much more complicated than you propose (1 120 circuit)

mdshunk

No, Joe. His elevator will operate at 480

Sparky Joe

Yeah I understand that, who's seen a 120v elevator.

I think he proposed 1 120 circuit, when in fact he'll need at least 3. 1 for the car, 1 for the pit, and 1 for the room. And the 120 for the car needs a fused disconnect directly adjacent to the 480 disconnect. He will also need 2 phone lines to the room, a fire alarm initiating loop to the room and the top of the shaft, and everything in these 2 fire rated areas needs to be in conduit and penetrations need to be fire caulked or fire taped.

Sparky Joe

And a pull station next to the elevator doors on each floor and a visible horn strobe, and an emergency light (night light with battery backup) at each floor and a visible exit light.

A lot of **** to remember with these beasts, and because I've never heard of an elevator contractor that wasn't union, that means their code is nationwide.

I could go on. But feel I'm wasting my breath to the OP question, I mean why would someone want a center tapped Delta for 5 120 volt circuits?