Wiring for voltage drop when wiring for voltage drop?

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ritelec

Senior Member
Location
Jersey
Hello.

I have a 200 + foot run at 120v.

Calculations show that at up to 5 amps I can run 12's. Up to 7 amps - 10's. Up to 13 amps- 8's. Up to 20amps- 6's.

If I want to run a good 20 amp circuit and run the 6's, where does that leave me when terminating to the breaker (sq D #8 max), time clock (intermatic), 15 amp switches and or receptacles?

Thank you
 

ritelec

Senior Member
Location
Jersey
Yes, figured something like that would have to be done. Thank you.

Wonder how much it really affects things. 6's through out, 12's or 10's (or 8's) placed at feed, at remote time clock, out at load..

Sounds like a few well placed funnels.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
140930-1129 EDT

ritelec:

Funnel is probably the wrong way to view the problem.

The resistance of #12 copper wire at 20 C is about 1 ohm per 1000 ft, or 0.001 ohms per foot. So at 20 A the voltage drop is about 20 mV per foot.

With one foot of #12 at the end of each of two wires the total drop from the transition wires is 40 mV.

#6 at 20 C is about 0.4 ohms per 1000 ft. Your 200 ft run is a loop of 400 ft. Thus, resistance is about 0.16 ohms. This portion of the voltage drop is 3.2 V, or about 2.7%, and the 20 C resistance value is probably reasonably close. The four one foot #12 transition wires add only about 0.05% to your voltage drop.

.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Yes, figured something like that would have to be done. Thank you.

Wonder how much it really affects things. 6's through out, 12's or 10's (or 8's) placed at feed, at remote time clock, out at load..

Sounds like a few well placed funnels.
You are not able to create a "funnel" of current flow, but you can cause a voltage drop with resistance, which then indirectly affects current flow. So as gar said, the purpose of the larger wire is just to remove the resistance in the circuit

Your thinking is, by the way, not uncommon. Gar's explanation is perfect, it's just that this concept is often left out of training programs, other than maybe a generalized discussion that tells you "current is always the same at any point in a circuit", which is the deeper precept behind that.
 

fmtjfw

Senior Member
140930-1129 EDT

ritelec:

Funnel is probably the wrong way to view the problem.

The resistance of #12 copper wire at 20 C is about 1 ohm per 1000 ft, or 0.001 ohms per foot. So at 20 A the voltage drop is about 20 mV per foot.

With one foot of #12 at the end of each of two wires the total drop from the transition wires is 40 mV.

#6 at 20 C is about 0.4 ohms per 1000 ft. Your 200 ft run is a loop of 400 ft. Thus, resistance is about 0.16 ohms. This portion of the voltage drop is 3.2 V, or about 2.7%, and the 20 C resistance value is probably reasonably close. The four one foot #12 transition wires add only about 0.05% to your voltage drop.

.
Isn't #12 more like 2 Ohms / Kfoot?
 

ritelec

Senior Member
Location
Jersey
Thank you for the replies.

Splice to smaller conductors it is.


This is insane, but correct me if I'm wrong,
If this 20 amp circuit (or 3) is fed with 6's, I would need the ground to also be #6.

I believe that's the way it reads someplace.

Thank you.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
140930-2119 EDT

fmtjfw:

Check your wire resistance source and see what is actually defined. You will find that loop resistance is defined. That is the total resistance of two wires from a source to a destination. So if the destination is 1000 ft from the source, then there is 2000 ft of wire in series from the source to the destination and back to the source.

In the calculation that I did above I used 4 ft for the loop resistance of the #12 1 ft sections, then I used 400 ft for the loop resistance of the 200 ft run from source to destination.

.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Thank you for the replies.

Splice to smaller conductors it is.


This is insane, but correct me if I'm wrong,
If this 20 amp circuit (or 3) is fed with 6's, I would need the ground to also be #6.

I believe that's the way it reads someplace.

Thank you.

yes, you would need the ground to be #6.
this bit me in the ass a couple years ago...

i had a 500' emt run feeding a wifi repeater.
i did not have to use a ground, but if i used a ground,
it had to be #6.

that pipe made a phenomenal grounding path.

parallel conductors also need a larger ground than
you'd expect.
 

ritelec

Senior Member
Location
Jersey
Thanks Gar.

I have my old book which I took the test with many moons ago.

The equations in there somewhere (if I can locate it). think it was vd = 2L x constant (12) x I / by circular mills

I cheated and calculated with this..

http://www.southwire.com/support/voltage-drop-calculator.htm


I will try to get my brain around it and calculate as you did using both wires.

2 x 200 x 12 x 15 = 72000/26240 (6's) = 2.74 vd

2 x 2 x 12 x 15 = 720/6530 (12's) = .11 vd

Am I way off?

2.74 + .11 = 2.85 vd

120 x .03 (3%) = 3.6
120 - 3.6 = 116.4

120 - 2.85 = 117.15
 

ritelec

Senior Member
Location
Jersey
yes, you would need the ground to be #6.
this bit me in the ass a couple years ago...

i had a 500' emt run feeding a wifi repeater.
i did not have to use a ground, but if i used a ground,
it had to be #6.

that pipe made a phenomenal grounding path.

parallel conductors also need a larger ground than
you'd expect.

Thank you
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
141001-0852 EDT

ritelec:

I made an error in reading my resistance table. I read the #10 value which is 0.9989 ohms/1000 ft at 20 C.

My reference is "Reference Data for Radio Engineers", sixth printing 1960. The "Handbook of Chemistry and Physics", 40thn Edition, 1958-1959 provides the same value as "RDRE". The "Handbook ..." also has a 75 C column with 1.931 ohms/1000 ft.

#12 is 1.588 ohms/1000 ft at 20 C. The Southwire value of 1.9029 ohms/1000 ft is 1.1983 times the 20 C value. The Southwire value is for direct burial and appears be for an actual wire temperature of somewhat below 75 C.

To calculate the assumed wire temperature:

1.9029 = 1.588 ( 1 + 0.00393 (Tx - T20) ) or
Tx - 20 = ( 1.9029/1.588 - 1 ) / 0.00393 = 50.46
Tx = 70.46 C appears to be about the assumed actual wire temperature for #12 copper direct burial at 20 A.

Your memory of about 2 ohms/1000 ft was correct for full nominal load.

.
 

ritelec

Senior Member
Location
Jersey
yes, you would need the ground to be #6.

Was thinking. I will bring the conduits into the basement, then from there to the panel I wanted to run 6-2 nm or 6-3 nm depending on the circuits.

I won't be able to because they have a #10 ground.

As with cable assemblies, there are certain things you can do vs. individual conductors... would I be able to tape #6 in the 3 wire nm green? Or would it have to be a manufactured green?


Thank you.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Was thinking. I will bring the conduits into the basement, then from there to the panel I wanted to run 6-2 nm or 6-3 nm depending on the circuits.

I won't be able to because they have a #10 ground.

As with cable assemblies, there are certain things you can do vs. individual conductors... would I be able to tape #6 in the 3 wire nm green? Or would it have to be a manufactured green?


Thank you.
If I understand what you are wanting to do use 10AWG NM from the panel to where you are crossing over to conduits and you are good to go.

You get to use a larger wire than 12AWG and the egc is upsized automatically.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Hello.

I have a 200 + foot run at 120v.

Calculations show that at up to 5 amps I can run 12's. Up to 7 amps - 10's. Up to 13 amps- 8's. Up to 20amps- 6's.

If I want to run a good 20 amp circuit and run the 6's, where does that leave me when terminating to the breaker (sq D #8 max), time clock (intermatic), 15 amp switches and or receptacles?

Thank you
Are you really going to use all 20A on this circuit? Do you really need 120V at the end of it? I don't know of much equipment out there that would know or care if its voltage got down to 110V or even 105V.
 

ritelec

Senior Member
Location
Jersey
Are you really going to use all 20A on this circuit? Do you really need 120V at the end of it? I don't know of much equipment out there that would know or care if its voltage got down to 110V or even 105V.

I was thinking so ??

1) Planning on two lights on two columns ( as in the calculator, over 5 amps on 12's voltage would start to drop. Not knowing in the future if they would like to add more lighting on to it)

2) Planning on a receptacle on each column (depending on whats being plugged in could cause a substantial drop right. For instance, to go across the driveway I'm thinking of renting an electric jack hammer. Googleing shows these jack hammers a 15 amps. Not that when the job is done the owner would be in need of jack hammering later on. But may install other lighting or need for other equipment. (drag is this would have been the perfect opportunity to use a new eu2000i honda inverter generator I just picked up.. but can't cause I don't want to kill it)).

3) Planning on Gate openers. Not sure if they will be piston type that plug in, or hard wire units ??

What would you suggest?



At first, my thought or game plan was to bring out 4-1" conduits.

1 for HV, 1 spare, 1 for LV, 1 spare.

Then with the length of the pull and probably going with the 6's (and seeing 1" is good 6 conductors, which would be 3 circ's using 6's.. grd, h1-h2-n1, h1-n2) I'm now thinking to do 4- 1 1/4" instead.

Recommendations ?

I would sure hate after ripping up these people's lawn (actually it will be controlled) to have issues with under voltage or conduits that are to small.




..."If I understand what you are wanting to do use 10AWG NM from the panel to where you are crossing over to conduits and you are good to go.

You get to use a larger wire than 12AWG and the egc is upsized automatically."...


"If" the conduits have the #6 ground with the #6 wire circuits. I could feed that #6 ground with a #10 ground ( from the nm) even if the panel is 30' away from that splice point??


Again, any suggestions appreciated. When I first came across this (last year) my thoughts where to run 10's in a 1" out to the columns.
But now as you see it went from 10's to 8's to 6's....

I would much rather work with the 1" but... I'm ASCARED...

The insanity !

Thank you.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
Again, any suggestions appreciated. When I first came across this (last year) my thoughts where to run 10's in a 1" out to the columns.
But now as you see it went from 10's to 8's to 6's....

I would much rather work with the 1" but... I'm ASCARED...

The insanity !

Thank you.
Take my advice for what it costs you but I think you are just fine with 10's and 1" conduit. It's what I would do.
 

ritelec

Senior Member
Location
Jersey
Thank you for all your input.

Alittle vote for confidence please for "LV".

After thinking about this discussion, I'm going to do 2- 1" for high voltage, 10's or 8's or 6's. Use one and one for spare or use the spare if needed.

Not knowing in the future what they may want for intercom or camera or control of some sort. Should I be good with 2-1" for LV also ?

In reading and mentioned here they do may rf units.. but if it was all hardwired, should the two 1" get me through ?

Thank you.
 
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