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#77432 - 06/01/01 09:28 PM V-Drop Q  
sparky  Offline
Joined: Oct 2000
Posts: 5,308
I need to size pipe & wire for some post lights. There are distances ,enough that V-drop is a concern.

The post lights, however, will incorporate the usual edison screw base, with the retrofit fluoresants of a whopping 17W. Or around 1.4 A @ 120V.

As V-drop calc's vary greatly due to the amount of "umph" introduced into the calc, this would allow ( per calc only) somewhat of a reduced conductor.

I am crusing 220 to apply a demand figure to this, would 220-13 require i start this calc @ 180W per???

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#77433 - 06/02/01 12:34 AM Re: V-Drop Q  
Scott35  Offline

Broom Pusher and
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA

Send me some numbers and I'll do a Volt-Loss calc. for you.

Need one way length[s], total load current [or Volt-Amps] per circuit, system voltage [nominal rating], voltage at the subpanel feeding these lighting circuits [under a high load would be best], type of conduit [magnetic or non-magnetic], power factor [list lamp wattage, then it's noted RLA and I'll figure PF].

If you want, I'll do one for the connected load, and one for max. circuit load @ 0.8 for LCL.

The 17 watt CFL [compact Fluorescent] must have had a typo' for the RLA. 1.4 Amps would put the line Volt-Amps at 168 VA, resulting in a PF of less than 10% [anything less than 50% is going to get the utility people raging mad!!].

Take an ampere reading yourself to get an idea of RLA.

Scott SET.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#77434 - 06/02/01 02:09 PM Re: V-Drop Q  
Bill Addiss  Offline
Joined: Oct 2000
Posts: 3,878
Just to put my 2 cents in here:

Shouldn't you figure the Voltage drop at some higher current rate? How can you be assured that this 17w lamp will always be there?
I would think the 180va (as originally stated) per fixture should be used to be sure.

That's probably .14 Amp


[This message has been edited by Bill Addiss (edited 06-02-2001).]

#77435 - 06/02/01 02:20 PM Re: V-Drop Q  
sparky  Offline
Joined: Oct 2000
Posts: 5,308
Thanks Guys;
there is much distance, and also a company main. man involved.
he is trying to squeeze a nickel for his company, which i can understand, that's everyday for me.
and your right, the fluor.elements may not always be in vouge, the posts may change to whatever...
all my bad math aside, i just need a code to stand on, and i'll figure it from there...
( i have a program, i cheat!)
[Linked Image]

#77436 - 06/02/01 05:22 PM Re: V-Drop Q  
Tom  Offline
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
There is no code to stand on when it comes to voltage drop, except by some really convoluted reasoning which probably wouldn't apply.

A real conservative voltage drop formula is 2KIL/circular mils. K is a constant & 12 would be nice & safe, I is amps & L is one way distance to the load. the answer is in volts, you figure the percentages.

You can also try the online calculator at


Few things are harder to put up with than the annoyance of a good example.

#77437 - 06/02/01 07:46 PM Re: V-Drop Q  
sparky  Offline
Joined: Oct 2000
Posts: 5,308
that is a good link, thanks.

i would rather explore convoluted vs. running 14-2 UF all over creation,,,

did you have something in mind???

[Linked Image]

#77438 - 06/02/01 08:39 PM Re: V-Drop Q  

I think you still need to give us some numbers.

Are you talking about 100 lamps about 1000' away? Or is this 10 lamps with one every 25'?

You might consider using 14-3 and 240 V then alternate the hot wire at each lamp.

You didn't say who will be inspecting the installation.

If no one, I am comfortable that if you put 20 lamps on a 14-2 or 40 lamps on a 14-3, it won't burn down anyone's house.

Someday might someone replace those 17 W bulbs with 75 W bulbs? It could happen. They will have a voltage drop.
But it still won't burn anything and even if someone sticks it in a 20 A breaker, the wire won't be melting.

#77439 - 06/03/01 09:04 AM Re: V-Drop Q  
electure  Offline

Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
I would suggest, rather, that you follow Bill's advice, using the 180va. figure. Whether the job will be inspected or not should NOT dictate the quality of work you do. Even if it calcs out that you should use #6 on the run, by all means do the job correctly. Just because it won't melt the wire or burn down the house is not a criteria for doing a half a** job.
(Yes, I stop at stop signs even if I don't see a cop)

#77440 - 06/03/01 10:54 AM Re: V-Drop Q  
sparky  Offline
Joined: Oct 2000
Posts: 5,308
I agree, it's not so much the calc i'm worried about, it's what i should be using as a load figure.
I will be pulling a permit for this, as it meets the criterior here.
The figures will be submitted at that time.
I WILL NOT be doing the work without this.

mama did'nt raise no fool!

[Linked Image]

#77441 - 06/03/01 10:58 AM Re: V-Drop Q  
Tom  Offline
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA

Here's convoluted.

Voltage drop is not normally enforceable because it is a fine print note.

However, NEC's stated purpose is "the practical safeguarding of persons and property..." 90-1(a).

If excessive voltage drop would cause operating problems in any equipment that is required for safety, then a case could be made for installing larger conductors.


[This message has been edited by Tom (edited 06-03-2001).]

Few things are harder to put up with than the annoyance of a good example.

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