mivey
Senior Member
Have you actually run the numbers? It should clear it up for you.
250MCM for 21.7 amps? Voltage drop calc must be wrong?
- Thread starter Bri22
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Run 2 wires line-N out of a 120/208 panel to a load
calculate the V drop based on 1 way length
then measure it
do that for each phase with a balanced load
obviously you have not
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- Placerville, CA, USA
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- Retired PV System Designer
I was very clear at the start that I was referring to a "full boat" (three out of three phases) MWBC for the three phase. The two out of three 120/208 panel does not meet those conditions.
And, FWIW, if you have two line to neutral loads in such a panel, connected to opposite phases, each drawing current I, then the current in the neutral is also I, not 2I or 1.73I or 1.73I/2. But I am not counting that as "balanced".
And, again in the case you propose, which I did not intend to consider, the voltage drop seen by the load will (first guess, not 100% confirmed) be 1.73IR rather than 2IR since the phase VD and the neutral VD are not in phase with each other.
PS: OR is is 1+ 1.73/2?? I do not feel like doing the vectors right now.
The assertion was that for a line-n load off a balanced 3 phase source only 1 way distance need be considered
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- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Not quite. You do not get to define my assertion, I do.
My assertion was that for a balanced set of line-n loads (i.e. three loads) off a three phase source only one way distance need be considered.
Elsewhere (earlier) in the discussion I stated the basic condition that for a single, unbalanced, isolated, line to neutral load (whether single sided 120, 120/240 or 208Y/120), the two way distance should be used.
mivey
Senior Member
I have not put pencil to paper. Started to but as soon as you actually think about it the results you will get are clear so I did not need to actually write it out.
I just thought it would help you. If I get froggy I'll run TD analysis and share the results. Maybe that will clear it up for you.
The OP was about a 2 wire extended ckt derived from 120/208
morphed into discussions of various methods to mitigate
then onto v drop calcs in general
a comment was made for a line-n load sourced from a balanced wye only 1 line need be considered (not sure by whom, don't care, doesn't matter)
you nor I get to define the 'assertion'
it was defined by the thread in totality
perfectly clear
a remote line to neut load sourced from a balanced wye needs both line Z factored into the V drop calc between source-load
elementary my dear Watson
walk away from it for a while
when revisited you'll be on board
pretty much the crux of the OP and his 250 kcmil quandry for 20/120 load A lol
he was not talking about a 3 ph 4W feeder to a balanced wye load all of which are line-neut
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mivey
Senior Member
Of course. That has been covered. But is not what GoldDigger was talking about in part #2.
sure it was
it goes without saying (so no idea why it was brought up)
wye to wye 4W balanced
convert to 1 ph equiv
line will have line Z
neut 0 Z since no i flow, hence no v drop
a mental but pointless excercise
the OP was about a l-n load extended (250 kcmil 120/20 extended lol) from a 3 ph wye pnl
when calculating v drop for the real world it is calculated across ph-ph, so 2 line Z are needed
and with the typical full size n the rest is moot
But the n will carry 0-100% of line
so in worse case 100% imbalance it is by default sized for essentially the same drop as the ph-ph drop
and if only sizing for line-n you would use 2 line Z's
it got so esoteric and far removed from getting 2.5 kva to a gate lol
I practice mental 'self abuse' but not to that degree
mivey
Senior Member
If you mean he was talking about only one single-phase load on a three-phase source, you are mistaken. Go back and read it again. He actually made the point more than once in the same post. I did not read it carefully the first time either.
Someone mentioned pulling a single phase load from a balanced source (balanced source normally meaning voltages are balanced). GoldDigger was talking about a balanced set of L-N loads across a three phase source.
If you are still saying you need two line Zs (out & back) or something other than one line Z to calculate the volt drop on one of the three L-N balanced loads, you are still wrong.
Then why did you argue against it? GoldDigger made the point about balanced loads and using the one-way (line Z) and no return (neither N nor the other two lines) to find the L-N drop.
Of course. And that has been stated already. The OP had one single-phase load, not a set of balanced loads across three phases.
read his item 2, if you have nothing better to do
And subsequent clarifications and elaborations
on something so elemental it is hard to fathom how many electrons were wastefully shuffled for this
You still don't get it
3 ph 4W panel
balanced
circuit pulled to remote load, 2W
both line Z must be considered MUST lol
Feeder 4W to balanced l-n wye load
to calc V drop you need to factor BOTH current carrying lines
the full neut is covered by default, 0% tp line I 100% unbalanced
read the OP
no mention of wye-wye 4W with balanced l-n loads and V drop across the neutral
Zippo
Nadda
Zilch
mivey
Senior Member
Hoorah! Hoorah! You are preaching to the choir brother! That point is not in dispute.
What you disputed was that the L-N voltage drop on three balance L-N loads on a three-phase MWBC only required a one-way calc. I don't know why this is a problem for you.
Yes, yes, yes, we all know what the OP talked about and we discussed that as well. The later discussion was about your insistence that the L-N voltage drop on a set of balanced L-N loads on a three-phase MWBC required a two-way calc.
In my previous post
1 ph equivilent ckt
Z in supply
no Z in return
0 idea why this was brought up
read the OP
A mwbc was never a topic, until I made the example of a remote load (which is the point of THIS thread)
when the he k will you use this knowledge?
lol
mivey
Senior Member
FYI, posts are available for all to review so there is no value in you trying to re-write history.
GoldDigger actually brought up the shared neutral consideration in post 25 when discussing the assumption made by the calculator concerning three-phase calcs. So the topic was broached when discussing the proper use of the calculator inputs.
kwire questioned if swnelson was talking about MWBC calcs in post 116 since he kept referring to a one-way calc. This prompted GoldDiggers' post covering the same.
GoldDigger posted in 118 about how a balanced MWBC only needed a one-way calc for L-N volt drop calcs. You erroneously disputed that and the rest, as they say, is history. It appears now you are trying to make out as if you were on board all along. For shame.
Fulthrotl
~Autocorrect is My Worst Enema.~
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my little sparky app on my phone comes up with this:
1317'
21.7a
120v
2.90% Voltage drop with copper
4/0 copper
with 350 mcm aluminum, you get 2.89%
if all you need is a bit of 120 now and again,
a battery, inverter, and solar cell...... ?
i don't see 58 amps for anything short of raising the
drawbridge on the death star...
kwired
Electron manager
- Location
- NE Nebraska
Are you saying a voltage regulator is for regulating voltage
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