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help...480/277 transformer ???

help...480/277 transformer ???

help...480/277 transformer ???

(OP)
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

RE: help...480/277 transformer ???

nick: there are others here who can probably say YEA/NAY on the sizing.

What I would do, is sketch your facility on a large piece of paper then mentally walk through it and put in a mark for every light and every bathroom fixture then make a list of all the expected tools.

Next jot down the watts each item will use.  There are lots of web sites that will tell you the power used by all your tools.

Once you've put numbers on everything, add them all up.

Decide if the future holds any major possibilies like a bunch more tools or lots of computers etc.

Based on the numbers you have come up with and the chances of increased load the other guys on this site will quickly tell you the rule of thumb to use and you will have the transformer size you should use.

Compare that with the electrician's suggesting.


RE: help...480/277 transformer ???

Typically, anytime you change/add to your existing electrical infrastructure, it must be engineered by a licensed professional and then submitted to an AHJ for permit.  I would not install anything without a load study being done by an engineer.

Mike

RE: help...480/277 transformer ???

AHJ ?

RE: help...480/277 transformer ???

Nick
I would have the electrician use 250 watt lights that can be connected to the 277/480 volt service. The ballast come rated for several voltages. Then the 30kva transformer would be more that adequate. 30 kva at 208 3 phase is 83 amps.

RE: help...480/277 transformer ???

Just a couple of quick comments.

First, I don't know of any Industrial or Commercial customer that calls for an inspection and permitting everytime they add something or change something in their plant. Are you in the USA? Are you on this planet? Major new construction (like a whole new section of the plant) sometimes gets permitted (sometimes not). Oh, and a load study? by a professional Engineer? for adding a Transformer and a lighting panel? LOL! <Shrug> Just my experience.

Second, 480/277V lighting is fine, unless your the poor SOB working on it! I would much rather work on 120V lighting than 480V! Sure, sure, the power should be off, but you never know what you are going to get into. Many, many maintenance departments require 120V lighting for safety reasons.

480/277V is a very common for plant distribution. So is transforming down to either a 120/240V single phase or 120/208V three phase panel for lighting, receptacles, etc. So, basically he is telling you right. Electricians are notorious for undersizing things though, so I understand your concern about the 30KVA Xfmr.

Three phase will get you more power so that sounds good. The only problem I've had with that is if you have a load that will be affected by the 208V rather than 240V, like heaters for instance. Other than that, I think 120/208V is great.

A 30KVA 120/208V Transformer will be a 45A Primary with a 100A Secondary. Ok, sounds good. 30KVA is good for 100A.

Loads:
32 receptacles x 1.5A = 48A
25 Lights (250W add 20% for ballast) x 3A = 63A
2 Bathroom Fans? X 3A = 6A
Bathroom Lights? Maybe another 10Amps?

127Amps

Now that is over the 100A but with some diversity of the loads you could still be ok. A judgement call. In other words, all 32 receptacles will never be used at once, will they? How many drills and small tools could be used at once? If a lot then I would go to a 45KVA Xfmr (I probably would anyway).

Hope that helps.







RE: help...480/277 transformer ???

32 receptacles at 180VA each = 5760 VA
25 lights @ 300 VA each = 7500 VA
Need to know the load for the fans, but for here say 360VA each = 720VA

Total = 14 kVA.

If the transf. is 3-phase 208/120 volts that would be 39 amps. If it is 1-phase 240/120 volts, 59 amps.

NEC says you can load a panel up to 80% of it's rating (for continuous loads, which lights and recepacles are).

The transformer must have overcurrent protection per the NEC. The basic rule for secondary protection is a maximum of 125% of the transformer rated secondary current. That can be exceeded if the transformer primary is protected at less than 125% of the primary rating. The transformer secondary X0 must be grounded as well. The NEC specifies the method and conductor size. It's basic stuff, but the person doing it must know how.

That's why you need a PE and a permit. Many electricians have PE's on staff who can handle basic design such as this and obtain the required permit.

RE: help...480/277 transformer ???

AHJ = Authority Having Jurisdiction


Mike

RE: help...480/277 transformer ???

amazingmg,

Yes...I'm on this planet.  Yes...I'm in the US.  As alehman points out, additions/changes made to ANY existing system must be engineered, stamped by a PE, etc. to obtain permit.  That's just my experience...I've only been doing this stuff for 15 yrs.  Does that qualify?

Mike

RE: help...480/277 transformer ???

Aleman,

Obviously I was thinking all 120V 1ph. Sorry to confuse the issue. My only excuse is too many hours and not enough sleep. Major goof.

mpparent,

Sorry to rub you the wrong way. I think that additions and changes being engineered, stamped by a PE, etc. are the exception, not the rule. Maybe that's not the way it should be, but....

<slinks off stage right to get some sleep...>

RE: help...480/277 transformer ???

amazingmg,

No problem.  I've never been in a municipality that didn't require a stamped set of professionally designed drawings to obtain an electrical permit for any type of alteration, etc of an existing system or the construction of a new one.  Period.  It may be the case in some areas (the midwest where I'm originally from), that an engineered set of drawings isn't required.  But, I would think from a liability perspective, any owner of a building, etc. would want that to ensure no "consequences" later.

Mike

RE: help...480/277 transformer ???

To add another final point,

I don't know of many electrician's (I do know a couple that could), that would be able to calculate the fault current at any point in any given electrical system and then have the knowledge of applying X/R values at that point to come up with an equipment rating.  I think many people think that slapping in a panel here and there is no big deal, but at some point, that thinking is dangerous and could get someone seriously hurt, not to mention it is a part of the NEC to ensure proper bracing.  This is just one example.  That's why I think careful consideration should be given when installing electrical equipment.

Mike

RE: help...480/277 transformer ???

mpparent: Thanks for the definition.

Sorta like "no controllng authority".

I would have to agree with amazingmg.  Of all the "additions" I have ever seen in a large tannery, perhaps 30 over 100KW I have NEVER seen a hint of any drawings and certainly no PE stamps.

Most companies I've seen would rather "take a risk" to avoid yet more taxation.

Just my experience.

RE: help...480/277 transformer ???

mpparent has a good point about fault current. 480V systems of this size could easily exceed the capacity of a typical cheap 14kAIC 480V breaker. That won't be a problem until the breaker has to open a fault. Then there's a good chance of an explosion.

Yes, you can do it the "cheap" way. Maybe I've seen too many burn-downs, but it would scare me. Even if you don't want to pay for a permit, at least get a qualified engineer to review what you're doing.

RE: help...480/277 transformer ???

alehman:  Very good point.  I'm sure it never crossed their minds.

RE: help...480/277 transformer ???

mpparent,

Actually, in some states (like Oregon), electricians are permitted to design systems 600V and below up to a certain ampere rating.  No PE stamp is required.  

Engineers? We don't need no stinking engineers!

RE: help...480/277 transformer ???

"Engineers? We don't need no stinking engineers!"

BAZZZZUUUUUUUUUMMPHKAAAPOW!

RE: help...480/277 transformer ???

Let’s compare apples to rotten tomatoes.
If a request is for the utility to change/add to the service feeding the customer, then a PE is required in most municipals.
If the customer wants to change/add anything on the load side of the point-of-service (generally the billing meter), then “What is an engineer?”

RE: help...480/277 transformer ???

dpc,

I'll remember not to buy any commercial property in Oregeon.

:)


Mike

RE: help...480/277 transformer ???

Well, in all fairness, we don't do any municipal work and very little commercial. Our customers are all industrial type facilities.

I'm certain municipalities required permits which in turn required a stamp if it's of any significant size.

RE: help...480/277 transformer ???

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

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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....

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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'.

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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

RE: help...480/277 transformer ???

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.

RE: help...480/277 transformer ???

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.

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