reduced neutral

[Smart $]

Perhaps a grounded 480/240 Delta.

I think it's just an all-around, bad idea to have 240V lamps w/screw bases. What's to stop Joe HO from wiring one to his 120/240 system?

 

[ramsy]

Light bulbs near 230vac are common abroad, however, owner & unlicensed wiring may be more efficiently prosecuted and discouraged. At least that was my experience in Germany, where there's no such thing as owner permits.

In the mid 80's, I lived off base near Bitburg where the natives seemed well prepared for human nature, and for enjoying or disciplining that nature in moderation vs deleterious excess. If they are accused of being pagans, it is for including Mother Nature in the holly Trinity, and indoctrinating themselves with it.

Later experiences, back here in the states, would lead me to eventually realize my welfare is much less relevant to other people's enrichment.

In this environment installing 240 or 277vac lights, at the brink of disaster, would not deter the pursuit of maxim profit, as long as the screw shell is connected to ground.

 

[hillbilly]

"In the mid 80's, I lived off base near Bitburg where the natives seemed well prepared for human nature, and for enjoying or disciplining that nature in moderation vs deleterious excess. If they are accused of being pagans, it is for including Mother Nature in the holly Trinity, and indoctrinating themselves with it".

Sounds like you liked it over there, why not go back?


"In this environment installing 240 or 277vac lights, at the brink of disaster, would not deter the pursuit of maxim profit, as long as the screw shell is connected to ground".

That's the way it is in America. Operating at the brink of disaster has paid a lot of scientific dividends.
Indoctrination is a synonym of brainwashing and propagandizing.
I'll take free thought and action if you please.
steve

 

[Smart $]

Lamps aren't high-precision loads.

The variation in voltage drop across a bulb in a network like what you've drawn -- based on plus or minus however many watts a 180w bulb actually consumes under operating conditions -- exceeds the amount of voltage drop needed to change the direction of the current flowing between pairs of pairs of bulbs on the neutral conductor.

I thought that might be what you were trying to point out. However, I suggest you reserve the term "uncertainty" for apparatus requiring high precision.

As to your point... I don't think so. I believe the variations in wattage will only change node voltage and the amount of current, but not direction. Let me put it to you in the form of a diagram where resistor symbol direction and position is more indicative of voltage change as a result of wire impedance.

To Larry: Note what appear to be the "balance points" of the neutral conductor: The connection nodes of every second lamp.

If I have and am giving the wrong impression here, I'll be glad to entertain corrective comments :smile:

 

[wirenut1980]

As I said before, the power factor of ballast-driven lighting coupled with the reactance of AC wiring could reduce voltage drop on a circuit (...it could also increase voltage drop, as either way depends on circuit and load parameters).

How could the power factor and load parameters reduce voltage drop? This would have to mean that the load would have a leading power factor, right? What loads have this parameter?

 

[Smart $]

How could the power factor and load parameters reduce voltage drop? This would have to mean that the load would have a leading power factor, right? What loads have this parameter?

Nope! Lagging power factor.

Go to NEC Chapter 9, Table 9 and compare Effective Z to it's respective Resistance column values, down to #2. In short Z is less than R. However, circuit parameters will change Effective Z for power factors other than 0.85 and a calculation per Note 2 would be necessary to determine such.

 

[ramsy]

Indoctrination is a synonym of brainwashing and propagandizing. I'll take free thought and action if you please.

Dis Controls is nix fer da finga poken. Dis controls is fer da train fessional. If der feels da erge, pudda der stiken hands inder pockets, sit back and watchin der blinkin lights.

 

[wirenut1980]

Nope! Lagging power factor.

Go to NEC Chapter 9, Table 9 and compare Effective Z to it's respective Resistance column values, down to #2. In short Z is less than R. However, circuit parameters will change Effective Z for power factors other than 0.85 and a calculation per Note 2 would be necessary to determine such.

Ah, I see. Table 9 clears things up. I did not know that you were talking in terms of a .85 pf

"Out of Chaos, Comes Cash!"

 

[tallgirl]

I thought that might be what you were trying to point out. However, I suggest you reserve the term "uncertainty" for apparatus requiring high precision.

Hey, you're the one who used "ultra-accuracy"

As to your point... I don't think so. I believe the variations in wattage will only change node voltage and the amount of current, but not direction. Let me put it to you in the form of a diagram where resistor symbol direction and position is more indicative of voltage change as a result of wire impedance.

I think you're assuming the conclusion with your drawing.

I assert, without proof, that the difference in wattage, bulb to bulb, is greater than the power lost to the wiring. If that's correct, and I put an ohm meter on 3 PARs I dug out of my kitchen and they varied in "cold" resistance by more than the ohms per kilofoot resistance for a fairly length piece of wire (0.3 ohms is what I measured), the voltage in the MIDDLE of a pair of lamps could be greater than or less than 0v relative to some other point within the "neutral" portion of that circuit.

Consider this -- if you have a pair of 180w nominal lamps and one is drawing 183w and the other is drawing 177w (for an average of 180w -- no great stretch here), what is the voltage at the midpoint of those two lamps with respect to the (unconnected) neutral, if they are connected in series between a 240v supply? Now, if you take another pair of 180w lamps, both of which are also actually draw 183w and 177w, but happen -- just because that's life -- to connect them in series oppositely, what's the voltage at the midpoint of those two lamps relative to the midpoint of the other two lamps?

 

[Bob NH]

Consider this -- if you have a pair of 180w nominal lamps and one is drawing 183w and the other is drawing 177w (for an average of 180w -- no great stretch here), what is the voltage at the midpoint of those two lamps with respect to the (unconnected) neutral, if they are connected in series between a 240v supply? Now, if you take another pair of 180w lamps, both of which are also actually draw 183w and 177w, but happen -- just because that's life -- to connect them in series oppositely, what's the voltage at the midpoint of those two lamps relative to the midpoint of the other two lamps?

The voltage across the lamp that was 177W at 120 Volts will be 122 Volts when 240 Volts is applied to the two lamps in series; while the voltage across the other lamp will be 118 Volts.

The original 183 Watt lamp will dissipate 176.95 Watts and the original 177 Watt lamp will dissipate 182.95 Watts.

The voltage between the midpoints of two pairs of lamps will be 4 Volts.

 

[LarryFine]

Consider this -- if you have a pair of 180w nominal lamps and one is drawing 183w and the other is drawing 177w (for an average of 180w -- no great stretch here), what is the voltage at the midpoint of those two lamps with respect to the (unconnected) neutral, if they are connected in series between a 240v supply?

"Pick me! Pick Me! Me! Me!" ~ Donkey in Shreck

Now, if you take another pair of 180w lamps, both of which are also actually draw 183w and 177w, but happen -- just because that's life -- to connect them in series oppositely, what's the voltage at the midpoint of those two lamps relative to the midpoint of the other two lamps?

In round numbers, there would be a 2v offset for each pair, for a total of 4v.

 

[tallgirl]

"Pick me! Pick Me! Me! Me!" ~ Donkey in Shreck
In round numbers, there would be a 2v offset for each pair, for a total of 4v.

Correct! I think. I didn't actually work it out myself, but that sounds about right.

The "trick" is that this isn't actually a balanced MWBC, except in theory. In reality it is slightly unbalanced due to the variation in lamp wattage, and as with all unbalanced MWBCs current goes in whichever direction needed.

THUS, depending on the lamps, the variation in the actual power consumed by the individual lamps, the resistance of the wiring, etc. the magnitude and direction of the current flow is just about anybody's guess.

Where this is all going goes back to Smart's headache. While an "ultra-accurate" calculation might be a fun way to burn a few milliseconds of computer time (and quite a bit of keyboard time entering the values ...), in practice an "ultra-accurate" calculation is impossible. A less accurate (but likely still within the margin of error for the lamp wattage) answer can be had by simplifying the circuit into 8 2 lamp networks arranged as a ladder.

 

[Smart $]

Where this is all going goes back to Smart's headache. ...in practice an "ultra-accurate" calculation is impossible.

Exactly!

I think the ONLY point you are missing is that current direction does not change just because the zero volt point moves, or the so-called midpoint voltage changes with lamp wattage variations.

Consider the above image. The fact is, TP2 can NEVER have a voltage potential closer to L1 than does TP1. Additionally, the only time TP2 and TP1 can be at the same potential is if the L2 circuit is not conducting, for whatever reason. Yes, current can change direction from TP1 to Neutral. Yes variations in lamp wattage will have greater effect as pairs are added. However, the current direction will remain the same from node to node on the neutral conductor.

Throw one more lamp on the end of the run and all bets are off :grin:

 

[tallgirl]

Exactly!

I think the ONLY point you are missing is that current direction does not change just because the zero volt point moves, or the so-called midpoint voltage changes with lamp wattage variations.

Consider the above image. The fact is, TP2 can NEVER have a voltage potential closer to L1 than does TP1. Additionally, the only time TP2 and TP1 can be at the same potential is if the L2 circuit is not conducting, for whatever reason. Yes, current can change direction from TP1 to Neutral. Yes variations in lamp wattage will have greater effect as pairs are added. However, the current direction will remain the same from node to node on the neutral conductor.

Okay, now add another

to the end of the one you just drew, and this time change the wattages of Lamp1' and Lamp2' to values within the normal variability of the lamps. Although TP1 < TP2 is a guaranteed relationship, that doesn't means that TP1' has any predictable relationship to TP1. The only predictable relationship for the second pair of lamps, Lamp1' and Lamp2' is that TP1' < TP2'. TP1' can be greater than, equal to, or less than TP1 and/or TP2.

The behaviors of the current on the neutral conductor between TP2 and TP1' when TP2 < TP1', TP2 = TP1' and TP2 > TP1' are left to the reader as an exercise (as my basic circuits EE prof would say ).