Series Voltage Drop All Inclusive

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GoldDigger said:
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FWIW, in either a real or idealized system you can all but eliminate the neutral offset by rotating the phase order in each three pole group.
That is:
First set poke 1 is on A, pole 2 on B, pole 3 on C.
Next group uses B, C, A.
Third group uses C, A, B.
Every nine poles the neutral voltage at the last pole is equal to the neutral voltage at the source.
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Never really thought about it... don't know if it is a valid statement... will not investigate said validity because I don't know if anyone would actually do it.
 
Discussion here is on radial circuit for pole lights. Does the code permit to use ring circuit for pole lights to effect greater reduction in voltage drop?
 
The general consensus is no. Some argue that it constitutes non compliant parallel conductors.
Others don't give a reason but are sure anyway.
 
Gentlepeople...

You've "Lost The Forest For The Trees", i.e, 7 pages of responses! Run the numbers: 84 fixtures @ 2 per pole yields 42 poles. Discounting the distance from the source of supply to the first pole, requires a feeder length of (42-1) x 50 or 2,050 feet. And, feeder conductor size, you must agree is quite large!

Had you gotten the Excel Spread-Sheet, "V-Drop Calc for Evenly-Spaced Loads" offered in Nov '14, you would have discovered that the neutral V-Drop is nil!

My offer still stands... but remember, you must reveal your 'real' name and location!

Regards, Phil Corso
 
GoldDigger said:
The problem that I have is your premise that because there is zero current in the neutral at the source there cannot, therefore, be a non-zero voltage drop from end to source. There are still unbalanced currents at various points along the way.
What you can say is that the net current from the last group of three has no effect on the voltage in any other group of three. That is both clear and correct.
It is also true that the VD between the first pole and the source is zero. Fine. But the VD from third pole to source is not zero. I hope you can agree on that.

The zero current at the start of each group does mean that to calculate the voltage drop from the third pole to the source you do not have to (or want to) consider any contribution from downstream groups.

But if the calculation for one three pole group shows a voltage drop between the third pole and the source, then that same drop will be repeated for each group down the line.
As shown in the approximate but close calculation the VD for one group is small, so the VD for 14 groups is 14 times small, which is still small compared to the VD in ungrounded wires, which is proportional to 14 squared.
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I think if you perform KVL around pole in the middle of the installation (arbitrarily say pole 25) and return on the neutral you can see that the resistances add up, and therefore the VD? Just a thought on how to better visualize it.
 
Gentlepeople,

The V-drop Calc of series-loads, thus far used on this post, use what is called the "Approx" Solution! It relies on the assumption that Load-Current is constant, i.e., magnitude and Pf!

The "Exact" Solution, using Load-Impedance reveals a different result! There is current in the Feeder's Neutral-conductor, but its magnitude is small nil! It exists because of a different V-Drp and slight phase-angle shift, at each pole. The factor influencing neutral-current magnitude is the ratio of feeder-impedance to load impedance, and the degree (excuse the pun) of the phase-shift.

When the "Exact" solution is applied to Spraymax's example, the 1st pole's Voltage is 119.6, if 50-ft from the source. The 42nd's pole is 111.4 V! The aggregate phase-current for each of the 3-phases (Seq ABC…ABC… etc) is about 40-Amps at the source, however, the Net Neutral-Current at the source is about a 1/4 of an ampere!

Regards, Phil Corso
 
Gentlepeople... WISHING YOU ALL A HAPPY, PROSPEROUS, and more importantly, HEALTHY THANKSGIVING !!!

GoldDigger is correct. Older "Linemen" called transposed lines "A Barrel of Transposition"! But, the statement about Ph-N voltages being equal every 9th pole is only true when feeder or line impedances are ignored, or materially smaller than Luminaire impedance! See my Nov 24 post!

Regards, Phil Corso
 
Gentlepeople.,

There is no gain in using "Barrel Transposition", "Phase-Rollover", or "Asymmetrical-spacing" techniques for a multi-conductor cable installation. In fact, average voltage-drop increases!

The reason is quite simple! Consider Spraymax's example, i.e., Symmetrical-spacing, with poles 50 ft apart! Hence, the Luminaire's connected to, say A-Phase, are 150 ft apart... ditto for B and C phases!

However, using Asymmetrical-spacing, only 1/3 of the Luminaire's, connected in series, will be 50 ft apart, while 2/3, connected in series, wiil be 200 ft apart! The net result is a lower V-drop than that for Symmetrical-spacing!

Please note,

Regards, Phil Corso
 
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Phil Corso said:
Gentlepeople.,

There is no gain in using "Barrel Transposition", "Phase-Rollover", or "Asymmetrical-spacing" techniques for a multi-conductor cable installation. In fact, average voltage-drop increases!

The reason is quite simple! Consider Spraymax's example, i.e., Symmetrical-spacing, with poles 50 ft apart! Hence, the Luminaire's connected to, say A-Phase, are 150 ft apart... ditto for B and C phases!

However, using Asymmetrical-spacing, only 1/3 of the Luminaire's, connected in series, will be 50 ft apart, while 2/3, connected in series, wiil be 200 ft apart! The net result is a lower V-drop than that for Symmetrical-spacing!

Please note,

Regards, Phil Corso
Click to expand...
I can, I think, rationalize this to mybown satisfaction without rehashing the exact calculations as follows:
Although the Phase-Rollover will definitely reduce the voltage drop in the neutral, it will cause a corresponding (or greater) VD in the ungrounded wires.
But I do not buy your simple explanation of wire length differences based entirely on "average" device spacing.
 
GoldDigger...

How would you connect poles in series so that phase-rollover could be accomplished, yet maintain a maximum of 150 ft between poles having like phases?

Phil

Ps: I said neutral current was nil!
 
Phil Corso said:
GoldDigger...

How would you connect poles in series so that phase-rollover could be accomplished, yet maintain a maximum of 150 ft between poles having like phases?

Phil
Click to expand...
I cannot, but the average distance of wire per pole is still the same. The 50 foot short run makes the total length to the next connected pole shorter by that same 50 feet. You are not changing the total run length, just messing with the spacing.
 
GoldDigger,

SYMMETRICAL NETWORK (Poles of same phase are 150 ft apart)
Ph A: 1 – 4 - 7 –
Ph B: 2 – 5 – 8 -
Ph C: 3 – 6 – 9 –

ASYMMETRICAL NETWORK (Poles of same phase, ex, 1-5-9 and 2-6, are 200 ft apart, but 3-4 are 50 ft apart
Ph A: 1 – 5 – 9 –
Ph B: 2 – 6 –
Ph C: 3 – 4 –

Ii is the asymmetrical separation distances that cause different V-drops, hence neutral-current. Admittedly they are small, as posted earlier!

Phil
 
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GoldDigger... yes!

For the Symmetrical case the 1st pole V-drp is 0.33%, while the 42nd is 7.0 %!

For the Asymmetrical case the corresponding figures are 0.33% and 8.8 %, respectively!

Phil
 
GoldDigger... as well as others:

Did you want a copy of the study comparing Sym-Spaced to Asym-Spaced arrangements, using the "EXACT" method?

Although SprayMax was not responsible with the arrangement selected, the original designer was quite lax in approach. Had 277V luminaires been chosen instead of 120V, AWG # 8 could have been used, instead of #2!

BTW, the AWG #2 case resulted in V-drops that exceeded 5% for the second half of luminaires! In fact to satisfy the 5% tolerance, AWG 3/0 would have been required!

Phil
 
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