# How convert three-phase power to single-phase?

Discussion in 'Electrical Engineering' started by nntp.ext.ray.com, Aug 6, 2004.

1. ### nntp.ext.ray.comGuest

Hi,

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.

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?

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?

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

Jim

nntp.ext.ray.com, Aug 6, 2004

2. ### SQLitGuest

"nntp.ext.ray.com" <> wrote in message
news:TENQc.2\$...
> Hi,
>
> 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.
>
> 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?
>
> 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?
>
> As often happens, I'm probably asking what might seem like dumb/naive
> questions, but I'm really glad to have found this NG !
>
> Jim

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

SQLit, Aug 6, 2004

3. ### ohayaGuest

wrote:
>
> On Fri, 6 Aug 2004 11:46:28 -0400 nntp.ext.ray.com <> wrote:
>
> | 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
>
> 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

ohaya, Aug 6, 2004
4. ### MilesGuest

"ohaya" <> wrote in message news:...
>
> 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.

> > 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.

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.

> > | 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?

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

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

Newsgroups are not a safe place to be asking these sorts of questions unless

> > 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
office today" gives me considerable concern.

> 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.

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.

Miles, Aug 7, 2004