How convert three-phase power to single-phase?

Your questions could be answered easily once the voltage is known.

277-480, 120-208, 120-240, 377-600 these are all pretty common in north America.

| We're just moving into some new office space, and among the things that we | inherited was some three-phase power. I haven't actually seen what the | outlets look like, because the person who knows where it is isn't in this | week, but I was kind of curious if there's any way that we can utilize any | of that? We're a typical office environment, and all of our equipment | (workstations, servers, etc.) are single-phase.

Larger UPS systems use three-phase power to keep the batteries charged and power the DC to AC conversion. Some can be had that then produce only single-phase, but most of them produce three phase back out. But that's not a big deal as they can all be had with 120 volts.

| To go from the three-phase power to single-phase, is it simply a matter of | creating three single-phase outputs from the one three-phase (i.e., | A+neutral, B+neutral, and C+neutral), and then we can just plug | (independent) equipment into each of the 3 single-phase outputs?

It depends on what kind of three phase power you have. If you have what is known as "208Y/120" then what you describe gets you 120 volts. But if you have "240 delta center tapped", then A+N and C+N gets you 120 volts but B+N gets you 208 volts. With 208Y/120, A+B or B+C or C+A gets you

208 volts, while with 240 delta, A+B or B+C or C+A gets you 240 volts.

You could have another three phase system or voltage, in which case you likely have a transformer or three changing the voltage so you can get something at 120 volts. The power coming in from the electric company could be in "480Y/277", "600Y/347" (primarily in Canada), "480 delta", or some others. You would have multiple fuse boxes or breaker panels to support the high and low voltage circuits in these cases.

If you have no transformers, you're probably getting one of the first two I described. In some locations you might be getting "216Y/125" or "220Y/127".

| Also, if we do that, from a power standpoint, do we end up with each of the | single-phase outputs just being 1/3 of the power rating for the original | three-phase power?

The way you just described, yes. A phase-to-phase connection, which gets a different voltage, could have a higher capacity, since it is using two of the phases and thus gets a higehr voltage with no reduction in current (unless something else uses up some of the capacity).

If you have 208Y/120, you will most likely have circuits distributed over the three phases in a circuit breaker panel designed to interleave the three phases at every 3rd row. A 1-pole breaker gets 120 volts at the phase it is plugged in to. A 2-pole breaker gets 208 volts (this would have been 240 volts if it were single phase), but can be used with 120 volt loads. A 3-pole breaker gets the full three phases.

Whatever the amperage rating of a breaker is, you get that much power at each of the poles/wires coming from it, however many that is. So if you have a 20 amp 1-pole breaker, it can provide 2400 watts to 120 volt loads. If you have a 20 amp 2-pole breaker, it can provide 4800 watts total to

2 sets of 120 volt loads, or 4156 watts to 208 volt loads. A 20-amp 3-pole breaker would let you have a total of 7200 watts for 3 sets of 120 volt loads. 3 sets of 208 volt loads could use up to 4156 watts each as long as the total of 2 does not exceed 4800 watts and the total of all 3 does not exceed 7200 watts. And of course it can supply a real three phase load up to 7200 watts. Electrical codes generally require planned loads to not exceed 80% of capacity, so derate the above figures to determine what you could plan for.

There are PDUs (power distribution units, or power strips) for computer rack cabinets that plug into a three phase receptacle and provide three sets of 120 volt outlets. If everything is rated 20 amps, you'd have that 20 amps three times (16 amps maximum planned usage on each set). You might want to check what you can, or are, doing with a UPS, before jumping into how power is fed to your computers.

| As often happens, I'm probably asking what might seem like dumb/naive | questions, but I'm really glad to have found this NG :)!

You're well ahead of most. The first big step is knowing you needed to ask.

Try to find out what kind of three phase power it is, and the voltages, so we can focus on your real options. Also, if you can, find out what type(s) and size(s) of circuit breaker panel(s) you have.

One important thing to remember is that in a situation outside of an owner-occupied single family house, virtually every jurisdiction does require using the services of a licensed electrician to do any work. People here can give you hints, advice, general direction, and explain your options. But wiring the building is not a do-it-yourself project; not even changing out a receptacle or light switch.

Phil and SQLit,

I'll have to get more details that you mentioned from someone else who isn't at the office today. Will post back next week sometime.

And Phil, it's not my intention to do any of the actual wiring or whatever, I'm mainly trying to gain an understanding so I can be a little more knowledgeable about what our options might be.

Thanks, and have a great weekend!

Jim

Depending on your jurisdiction (I don't think you said what country you're in, which sometimes makes a big difference) this could well be illegal. It may happen on construction sites with special splitter boards, but is probably not at all appropriate for an office environment. Systems of supply and protective arrangements (fuses, CBs etc) that may be safe and legal in one environment may not be, in another.

The voltages and the way phase, neutral and earth wiring is arranged is also important. Your best solution is to call an electrician to check this out with certainty. Only then will you be sure that what you want to do is both safe and legal in your particular region.

1/3 of the "power" rating yes, but exactly the same "current" rating. Which of these were you meaning?

Newsgroups are not a safe place to be asking these sorts of questions unless you are already very knowledgeable about electrical distribution and safety.

This is good advice, but you could still end up getting the wrong advice because the information you provide may be incomplete or even wrong, despite your own best efforts. Your comment about asking "someone who isn't at the office today" gives me considerable concern.

If you get the wrong advice because the advisors don't have the full or accurate picture, it could cost you a whole lot more than just getting in an electrician to look at it in the first place. Any advice you get on here can only be based on what you tell people here, which is likely to be incomplete, and may be inaccurate if the people that you're talking to don't know as much as you thought they did.

Electrical safety is too important to leave to chance. Sorry if this sounds negative, but for this sort of thing you need an electrician not a Newsgroup.

My thoughts fwiw.

Moving into a new office is always a great experience, starting from scratch is a great way of getting things organised in ways that you probably couldn't justify changing in an existing office. Good luck with your project. Hope it goes really well for you.

|> snipped-for-privacy@ipal.net wrote: |> > | To go from the three-phase power to single-phase, is it simply a | matter of |> > | creating three single-phase outputs from the one three-phase (i.e., |> > | A+neutral, B+neutral, and C+neutral), and then we can just plug |> > | (independent) equipment into each of the 3 single-phase outputs? | | Depending on your jurisdiction (I don't think you said what country you're | in, which sometimes makes a big difference) this could well be illegal. It | may happen on construction sites with special splitter boards, but is | probably not at all appropriate for an office environment. Systems of | supply and protective arrangements (fuses, CBs etc) that may be safe and | legal in one environment may not be, in another.

Are you referring to things like rack PDUs?

| Newsgroups are not a safe place to be asking these sorts of questions unless | you are already very knowledgeable about electrical distribution and safety.

In which case he would have no questions to ask.

|> > One important thing to remember is that in a situation outside of an |> > owner-occupied single family house, virtually every jurisdiction does |> > require using the services of a licensed electrician to do any work. |> > People here can give you hints, advice, general direction, and explain |> > your options. But wiring the building is not a do-it-yourself project; |> > not even changing out a receptacle or light switch. | | This is good advice, but you could still end up getting the wrong advice | because the information you provide may be incomplete or even wrong, despite | your own best efforts. Your comment about asking "someone who isn't at the | office today" gives me considerable concern.

The advice here should be on the order of things like what you might be able to do that no one told you about otherwise because they didn't think of it or didn't know about it.

For example, you can probably find as many electricians who will tell you that 240 volt appliances on 208 volts is fine as you can who will tell you that you will have problems with that. It's good to get a 2nd opinion (which in the case of getting it here, would be the 1st opinion).

Of course, never trust anyone here. It's like medical advice. You can find _someone_ that will tell you HOW to do surgery on yourself. There are crackpots in all fields (especially computers).

|> And Phil, it's not my intention to do any of the actual wiring or |> whatever, I'm mainly trying to gain an understanding so I can be a |> little more knowledgeable about what our options might be. | | If you get the wrong advice because the advisors don't have the full or | accurate picture, it could cost you a whole lot more than just getting in an | electrician to look at it in the first place. Any advice you get on here | can only be based on what you tell people here, which is likely to be | incomplete, and may be inaccurate if the people that you're talking to don't | know as much as you thought they did. | | Electrical safety is too important to leave to chance. Sorry if this sounds | negative, but for this sort of thing you need an electrician not a | Newsgroup.

You need an electrician, period. But electricians, despite being licensed, have their faults, too. The best of the advisors on the newsgroup will exceed the median of electricians. What that means is, if the electrician does anything you don't understand, ask for an explanation both from the electrician as well as here. Whenever there is a conflict, get it resolved. I've seen and/or read of cases where licensed electricians did things totally stupid and created very hazardous conditions. One I read about was the guy who put in a three phase panel for 240 delta center tapped, and filled it up with single pole breakers for all the branch circuits (there were no three phase loads). So some of the receptacles or lights had 208 volts. Then there was the electrician who installed grounded outlets in a house and wired all the grounds to the box and neutral because the existing wiring did not have a separate grounding wire. I'm sure many others have some horror stories in this regard.