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Home > Archive > Electrical Engineering > April 2007 > 208Y/120 to single phase 120
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208Y/120 to single phase 120
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| Howdy -
We're in an industrial park where our space is supplied with 208Y/120
3phase power. My understanding is that any phase taken to the fourth wire
neutral gives 120V. And any phase taken to any other phase gives 208V. My
question is about the amps available on any given phase - neutral (120V)
connection. The service is 120/208@100A . Is it so that three feeds of
120V (A - Neutral, B - Neutral, and C - Neutral) would each be able to carry
100A?
I guess, in other words, what I am trying to ask.. is that from a 120V
perspective.. is 208Y/120 @ 100A equivalent to three 120V @100 single phase
circuits?
Thanks
-M
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| Ben Miller 2007-02-12, 9:25 am |
| "Mike" <mike@not.for.mail.com> wrote in message
news:mKmdne5OlYJNgk3YnZ2dnUVZ_tqnnZ2d@giganews.com...
> Howdy -
>
> We're in an industrial park where our space is supplied with 208Y/120
> 3phase power. My understanding is that any phase taken to the fourth wire
> neutral gives 120V. And any phase taken to any other phase gives 208V.
> My question is about the amps available on any given phase - neutral
> (120V) connection. The service is 120/208@100A . Is it so that three
> feeds of 120V (A - Neutral, B - Neutral, and C - Neutral) would each be
> able to carry 100A?
>
> I guess, in other words, what I am trying to ask.. is that from a 120V
> perspective.. is 208Y/120 @ 100A equivalent to three 120V @100 single
> phase circuits?
>
> Thanks
> -M
Yes. Each phase can provide 100 amps, regardless of whether you connect
loads as three-phase, single-phase line to line, or single-phase line to
neutral (or any combination).
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
| |
| phil-news-nospam@ipal.net 2007-02-12, 5:25 pm |
| On Mon, 12 Feb 2007 07:37:15 -0600 Ben Miller <benmiller@worldnet.att.net> wrote:
| "Mike" <mike@not.for.mail.com> wrote in message
| news:mKmdne5OlYJNgk3YnZ2dnUVZ_tqnnZ2d@giganews.com...
|> Howdy -
|>
|> We're in an industrial park where our space is supplied with 208Y/120
|> 3phase power. My understanding is that any phase taken to the fourth wire
|> neutral gives 120V. And any phase taken to any other phase gives 208V.
|> My question is about the amps available on any given phase - neutral
|> (120V) connection. The service is 120/208@100A . Is it so that three
|> feeds of 120V (A - Neutral, B - Neutral, and C - Neutral) would each be
|> able to carry 100A?
|>
|> I guess, in other words, what I am trying to ask.. is that from a 120V
|> perspective.. is 208Y/120 @ 100A equivalent to three 120V @100 single
|> phase circuits?
|>
|> Thanks
|> -M
|
| Yes. Each phase can provide 100 amps, regardless of whether you connect
| loads as three-phase, single-phase line to line, or single-phase line to
| neutral (or any combination).
That would be for one single phase load. Multiple L-N loads work out easy
because you just add up the amps separately on each phase. It gets more
complicated when dealing with a couple of L-L loads because the amps don't
add straight on the common wire for the loads in different phases. If all
the L-L loads are equal, you can run them up to 57.735 amps and will see
the 100 amps on the actual phase lines. But as long as your loads are all
just 120 volt, they are all L-N, and it's simple: you get 100 amps on each
wire relative to neutral, and (short of harmonics or certain weird reactive
combinations) the neutral balances out.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-02-12-1326@ipal.net |
|------------------------------------/-------------------------------------|
| |
| Ben Miller 2007-02-12, 5:25 pm |
| <phil-news-nospam@ipal.net> wrote in message
news:eqqfcf0ppo@news3.newsguy.com...
> On Mon, 12 Feb 2007 07:37:15 -0600 Ben Miller <benmiller@worldnet.att.net>
> wrote:
> That would be for one single phase load. Multiple L-N loads work out easy
> because you just add up the amps separately on each phase. It gets more
> complicated when dealing with a couple of L-L loads because the amps don't
> add straight on the common wire for the loads in different phases. If all
> the L-L loads are equal, you can run them up to 57.735 amps and will see
> the 100 amps on the actual phase lines. But as long as your loads are all
> just 120 volt, they are all L-N, and it's simple: you get 100 amps on each
> wire relative to neutral, and (short of harmonics or certain weird
> reactive
> combinations) the neutral balances out.
Phil
All true, but none of that matters when considering the question of maximum
supply current. For that supply system, 100 amps is the maximum total
current that you can draw on any line, regardless of how you connect the
loads.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
| |
|
| Hi Phil -
Thanks for the answer. In the L-L case that you mentioned, how does one
calculate the 57.735A value you gave? To clarify my understanding of that
case.. I could pull 208V @57.735A from all combinations of A-B, B-C, and C-A
simultaneoulsly from the given 208Y/120@100A supply?
-Jim
<phil-news-nospam@ipal.net> wrote in message
news:eqqfcf0ppo@news3.newsguy.com...
> On Mon, 12 Feb 2007 07:37:15 -0600 Ben Miller <benmiller@worldnet.att.net>
> wrote:
>
> | "Mike" <mike@not.for.mail.com> wrote in message
> | news:mKmdne5OlYJNgk3YnZ2dnUVZ_tqnnZ2d@giganews.com...
> |> Howdy -
> |>
> |> We're in an industrial park where our space is supplied with 208Y/120
> |> 3phase power. My understanding is that any phase taken to the fourth
> wire
> |> neutral gives 120V. And any phase taken to any other phase gives 208V.
> |> My question is about the amps available on any given phase - neutral
> |> (120V) connection. The service is 120/208@100A . Is it so that three
> |> feeds of 120V (A - Neutral, B - Neutral, and C - Neutral) would each be
> |> able to carry 100A?
> |>
> |> I guess, in other words, what I am trying to ask.. is that from a 120V
> |> perspective.. is 208Y/120 @ 100A equivalent to three 120V @100 single
> |> phase circuits?
> |>
> |> Thanks
> |> -M
> |
> | Yes. Each phase can provide 100 amps, regardless of whether you connect
> | loads as three-phase, single-phase line to line, or single-phase line to
> | neutral (or any combination).
>
> That would be for one single phase load. Multiple L-N loads work out easy
> because you just add up the amps separately on each phase. It gets more
> complicated when dealing with a couple of L-L loads because the amps don't
> add straight on the common wire for the loads in different phases. If all
> the L-L loads are equal, you can run them up to 57.735 amps and will see
> the 100 amps on the actual phase lines. But as long as your loads are all
> just 120 volt, they are all L-N, and it's simple: you get 100 amps on each
> wire relative to neutral, and (short of harmonics or certain weird
> reactive
> combinations) the neutral balances out.
>
> --
> |---------------------------------------/----------------------------------|
> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
> |
> | first name lower case at ipal.net / spamtrap-2007-02-12-1326@ipal.net
> |
> |------------------------------------/-------------------------------------|
| |
| Don Kelly 2007-02-13, 8:25 pm |
| ----------------------------
"Mike" <mike@not.for.mail.com> wrote in message
news:fLmdnfGyAu_070zYnZ2dnUVZ_uuqnZ2d@giganews.com...
> Hi Phil -
>
> Thanks for the answer. In the L-L case that you mentioned, how does one
> calculate the 57.735A value you gave? To clarify my understanding of that
> case.. I could pull 208V @57.735A from all combinations of A-B, B-C, and
> C-A simultaneoulsly from the given 208Y/120@100A supply?
>
> -Jim
-------------
For a delta connected balanced 3 phase load, drawing 57.7A at 208V, the line
current will be the phasor sum of the currents in the two connected legs.
This would be 57.7*root(3)=100A
Note that the total power is 57.7*208*3 =3.6KW vs 3*120*100 =336KW for a Y
load. No difference.
--
Don Kelly dhky@shawcross.ca
remove the X to answer
> <phil-news-nospam@ipal.net> wrote in message
> news:eqqfcf0ppo@news3.newsguy.com...
>
| |
| Ben Miller 2007-02-15, 1:25 pm |
| "Don Kelly" <dhky@shaw.ca> wrote in message
news:HouAh.991581$R63.662529@pd7urf1no...
> Note that the total power is 57.7*208*3 =3.6KW vs 3*120*100 =336KW for a
> Y load. No difference.
36kW ?
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
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"Mike" <mike@not.for.mail.com> wrote in message
news:fLmdnfGyAu_070zYnZ2dnUVZ_uuqnZ2d@giganews.com...[color=darkred]
> Hi Phil -
>
> Thanks for the answer. In the L-L case that you mentioned, how does one
> calculate the 57.735A value you gave? To clarify my understanding of that
> case.. I could pull 208V @57.735A from all combinations of A-B, B-C, and
> C-A simultaneoulsly from the given 208Y/120@100A supply?
>
> -Jim
>
>
> <phil-news-nospam@ipal.net> wrote in message
> news:eqqfcf0ppo@news3.newsguy.com...
Over complicated.
It's simple. You can't go over 100 Amps on ANY hot leg in ANY combination.
Mike R
Electrical Contractor
Northern CA
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| Paul Hovnanian P.E. 2007-04-08, 9:25 pm |
| Ben Miller wrote:
>
> <phil-news-nospam@ipal.net> wrote in message
> news:eqqfcf0ppo@news3.newsguy.com...
>
> Phil
>
> All true, but none of that matters when considering the question of maximum
> supply current. For that supply system, 100 amps is the maximum total
> current that you can draw on any line, regardless of how you connect the
> loads.
I'd add one small caveat to that. Its possible that the panel feeder may
have been sized to supply a group of balanced three phase in addition to
single phase loads. Under certain conditions, the NEC will allow the
neutral to be reduced so long as it can carry the maximum unbalanced
load. In such a case, loading one phase to its maximum capacity will
overload the neutral.
Generally, I don't downsize neutrals serving tennant spaces. Even if the
original design includes significant 3 phase balanced loads, one can
never be certain what the next tennant will modify.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
I think you left the stove on.
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"Paul Hovnanian P.E." <paul@hovnanian.com> wrote in message
news:46199F7D.F0ED4407@hovnanian.com...
> Ben Miller wrote:
>
> I'd add one small caveat to that. Its possible that the panel feeder may
> have been sized to supply a group of balanced three phase in addition to
> single phase loads. Under certain conditions, the NEC will allow the
> neutral to be reduced so long as it can carry the maximum unbalanced
> load. In such a case, loading one phase to its maximum capacity will
> overload the neutral.
>
> Generally, I don't downsize neutrals serving tennant spaces. Even if the
> original design includes significant 3 phase balanced loads, one can
> never be certain what the next tennant will modify.
>
> --
> Paul Hovnanian mailto:Paul@Hovnanian.com
> ------------------------------------------------------------------
> I think you left the stove on.
>
NEC is one thing and local codes are another. You won't
be getting away with downsizing neutrals around here.
Downsize grounds? Sure anytime.
MLR
Northern CA
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