help...480/277 transformer ???

[nickforn]

i have a 3 phase 480/277 volt service coming into my new building. (600 amp)this power was brought in to power a large mahine we bought and had wired for that voltage.
my electrician has now told me i need a tranformer to step down to 120v for the light switches, fans etc, in the building. he is offering a 30kva transformer with a 100amp panel to power 32 receptacles, 2 bathrooms and 25 large 250 watt ballust lights like you see at home depot . there will be alot of hand tools and things plugged in simaltaneusly. i don't know anything about eletrical and feel i am not getting enough info from him on the limitations of the 30kva/ 100 amp panel. can some one please help?

thanks,nick

 

[amazingmg]

Oh, and as a registered Engineering business we are required to have a PE. We keep him in a cage out back.

 

[EEJaime]

Your electrician is right. Your loads you have listed are about 15 kVa and with allowances for the tools and such you mentioned, a 30kva transformer is about what I would recommend. It has a secondary current rating of 83 amps, so a 100 Amp panel and feeder are appropriate. You will have a 40 Amp, 3-pole circuit breaker in your 480v panel, feeding the transformer with a 3/4" conduit and 3 # 8awg (plus 1 # 10 ground),conductors. To your 30kVa, 480v. Delta to 208y/120v. 3phase, 4 wire transformer. Connecting the secondary with 4 # 2awg plus 1 # 8 ground to the Main circuit breaker of your 100 Amp, 3ph, 4 wire panel.

Your lighting can be fed from either your service entrance panel at 277v., or from your 120V. panel. (At 277v, you will only need 3-20A circuits, at 120 v you will need 5 or 6 circuits).

Hope that helps a little.

 

[ScottI2R]

Amzingmg,
I was thinking of applying for a position with a company as a PE ( assuming that is "project engineer") which we have noticed at my present company, stands for "point man engineer." One question: Is that cage padded?

Scott

In a hundred years, it isn't going to matter anyway.

 

[EEJaime]

In my area, a licensed contractor with a C-10 license is able to stamp and sign any commercial project to "design-build" a project. The only time this is not allowed and we need to have our PE stamp on the drawings is in the design of healthcare work which is reviewed by OSHPD, (Office of Statewide Health Planning and Development), or Educational institutions, which are reviewed by DSA, (Division of the State Architect). Also some municipalities, Los Angeles, San Francisco, etc.... will require PE stamps for high rise work, large industrial, etc....

 

[mc5w]

Electronic ballasts on 277 volts can have terrible inrush current and reliability problems. Please see

http://home

dot earthlink dot net/~mc5w/badnewsballasts.txt . I am talking about say 1200% inrush current! There is only so much that you can expect from cheap Chinese junk and not quite so cheap or junky Mexican stuff.

If you do use 277 volts ballasts stick with electromagnetic ballasts.

 

[EEJaime]

We specify and supervise the installation of several hundred million dollars worth of construction annually. Electronic ballasts are energy efficient, reliable and inexpensive. Electro-magnetic ballasts are dinosaurs, whose day is done. They do not meet most current energy codes. Most reputable lighting fixture manufacturers are phasing them out. One can still get them at the local hardware store, but for large projects, they are passe'.

 

[mc5w]

I have a customer that has a very high failure rate for General Electric electronic fluorescent ballasts in their building that underwent a total electrical renovation 2 years ago. I did an autopsy on a failed ballast and the design violates several design rules for power electronics and power supplies. These ballasts have a design flaw that makes them incapable of operating on 305 volts as advertised when the system voltage is a little high, which is one of this customer's problems. A power quality study showed that the high voltage problem would not be killing ballasts unless the ballasts were CRAP. The bulbs also are having a high failure rate because of instant starting rather than programmed rapid starting with filament heating and because the ballasts are driving the bulbs at 115% of nameplate rating.

When the bulbs do go the ballsts internally fails because there is no internal dummy load to bleed off excess voltage from the power supply capacitor. What that means is that spikes charge up the capacitor until the capacitor blows.

I am also still in the middle of replacing all of the lampholders and about 3/4 of the ballasts in some outdoor compact fluorescent fixtures that I installed 2.5 years ago. The only environmental factor is that sulfuric acid from automotive catalytic converters caused the wire connections at the lampholders to oxidize rapidly. The only explanation for ballast failures are that they are cheap Chinese CRAP!

I know enough people who have so many problems with electronic ballasts that the only kind that I recommend are the one that are part of self contained fluorescent refit bulbs. Hardwired electronic ballasts are just not ready for prime time - a large part of the problem is that new construction is invariably done by the lowest bidder. As long as the emphasis is on cheap rather than quality electronic ballasts will still continue to be unreliable.

 

[itsmoked]

mc5w: So far my experience in using compact fluorescents has been abizmal.

I don't think they are ready for prime time YET!

Last June I decided after looking at a $295 power bill for one month, that it was time to change over from incandescents... What a mistake.

I replaced 16 incandescents. I used seven different types of compacts by five different makers. Bought them on the WEB. The boxes even have pictures of how many incandescaents they replace (10-20) because "they last so long".

By April all of them had failed but three. None of them ran more than 300 hours. The biggest a 80Watt died in 4 days.

I really wish they worked as advertized.

 

[alehman]

The office building in which I work (designed by my company) has over 100,000 square feet of floor space lit entirely by fluorescent (32W T8) and compact fluorescent lamps with electronic ballasts. In the four years since construction there have been only a few ballast failures. We specified a good quality (pricy) U.S. ballast manufacturer however. I guess this is indicative of the range of quality still in the marketplace.

We have had no particular problem with the compact fluorescents other than fairly short lamp life, which is expected.

 

[mpparent]

I'm in about a 2.5 million sq ft facility, and when we can, we go to compact fluorescent and T8's. No real problems to report and we do use 20%THD electronic ballasts.

Mike

 

[mc5w]

We have some compact fluorescent refit bulbs in our house that run 24/7 and they last about 2 years in that kind of service. Where I bought them was at Kmart. The ones that run 12/7 or 4/7 have very reasonable life. One of my customers have some ( refit bulbs ) in some outdoor ceiling fixtures in an open entrance canopy that I installed 2 years ago and they still work. I bought those at Home Depot. You do not necessarily get a good buy over the internet.

I have a hard time believing that there is a plant in the U.S. that makes electronic ballasts. Every electronic ballasts that I have touched was made in China or Mexico. Until you name a specific manufacturer I am not willing to believe that any electronic ballasts are made in the U.S.

The electromagnetic ballasts are very efficient if they are of the filament disconnecting type that shut off the rapid start filaments after the bulbs warm up. Electromagnetic ballasts seem to be more tolerant of power quality problems particularly voltage swells.

You can also just about double the efficiency of a fluorescent fixture that uses a prismatic lens by turning over the lens so that it is prism side up. Prism side down does a better job of hiding the lamps but 2/3 of the light is trapped inside of the fixture. The effect is very dramatic. Prism side up does just as much light diffusion and you can save energy by deenergized about 1/2 of the ballasts.

Also, there have been some explosive failures of the power supplies in electronic revenue meters when energized on 277Y480 volts or 480 volts delta. There will soon be ANSI form numbers for meters that are wired for separate 120 volt power for the power supply using 1 or 2 extra meter prongs. The reason why Hunt will not make a Turtle automatic meter reading transmitter for 277 volts is that finding reliable power supply components for that voltage is very difficult due to the demise of small signal vacuum tubes.

 

[EEJaime]

When you have to design office space to 1.3 watts/sf,(including an assumed 0.2 watts/sf for "portable lighting"), you learn to utilize the most efficient lighting sources around. That is where the specifications become paramount. Specifying very specific ballast and lamp combinations by manufacturer will guarantee that you don't get these ridiculous offshore products which fail at very high rates. If you get Motorola, Sylvania, or Phillips ballasts and lamps as a system, you will not experience the failures you mentioned. That is why it is important to write a tight spec, and hold to it.

We have many, many, compact fluorescent installations built. Some of the early versions had problems, including "end of life catastrophic failure", (ELCF). That was a condition wherein the lamp would fail, but the ballast continued to power it sometimes to the point of overheating it so much it would start a fire. Current versions include an 'end of life relay' which cuts off power to the ballast. These work fine. I personally do not like the "double-D" flat lamp, but the triple and quad tube lamps are very reliable and provide a good lumen/watt ratio and decent lamp life.