14ga or 12ga...Which is more effiecient and why?

Status
Not open for further replies.

Wes G

Senior Member
A load in the mA, will the #14 be better?

If you compare the circular mil size of conductors (NEC table 8) with ampacities of conductors (NEC 310.16) you will see that as the size of the wire increases the efficiency decreases. This is due largely to eddy currents in AC wiring. Therefore, if my load is small enough that my voltage drop is not a factor, the smaller the wire, the more efficient. This is one of the considerations for using parallel runs in large installations.
 

iwire

Moderator
Staff member
Location
Massachusetts
If you compare the circular mil size of conductors (NEC table 8) with ampacities of conductors (NEC 310.16) you will see that as the size of the wire increases the efficiency decreases. This is due largely to eddy currents in AC wiring. Therefore, if my load is small enough that my voltage drop is not a factor, the smaller the wire, the more efficient. This is one of the considerations for using parallel runs in large installations.

Great point.

There is a lot more copper in one 600 Kcmil then two 4/0s but the two 4/0s give you 450 amps compared to 420 amps on the 600s.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090920-2035 EST

quogueelectric:

In so many of the discussions on this forum questions are asked without the author doing adequate initial analysis, measurements, and providing definitions and assumptions that it is hard to converge on useful answers. Similarly many answers are provided without providing supporting measurements or analysis, and also the problem of definitions and assumptions.

I think, but I do not know, that the original intent of this thread was --- How can I provide a simple explanation to a potential customer of why they should pay for the extra cost of using #12 instead of #14?

Most customers have no ability to understand the technical implications of one electrical design vs another.

Consider flickering lights, meaning a light momentarily dimming from some high inrush current when something turns on like an air conditioner. I have this problem from my neighbor's air conditioner. There is nothing I can do about the source of the problem, the pole transformer, except try to get the power company to install a larger lower impedance transformer. There is no valid reason for them to do this. Thus, I live with the problem. There is no wiring solution in my house to solve the problem. I could install a constant voltage transformer, or a motor generator, or some other possibilities. Most of these would be very costly, and might waste a lot of power, like the constant voltage transformer or a motor generator. Note: constant voltage transformers run very hot and are thus not efficient. Even a standard transformer has a moderate power loss. Today there is virtually no reason to use a constant voltage transformer except in some special applications.

Next suppose within my house I have a circuit that feeds a radial arm saw and on this same circuit I have an incandescent lamp to see my saw work. Make the circuit 100 ft of #12 Romex, 0.318 ohms. My light will dim greatly when the saw starts. Assume the main panel has a voltage drop of 0.8 V for a 12 A load, and inrush is 80 A. Thus, at the panel the voltage should drop about 5.3 V. If my light is on a separate circuit from the main panel, then I will get a noticeable flicker, but not severe. In this application I can do something to solve my problem, use the separate circuit from the main panel.

.
 

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
Just because office equipment is turned on 24/7, does not make them a continuous load. Practically all the equipent your are referring to do not draw their maximum current while on but not in use, and even while in use, the current draw often varies.

True, accurate and spot-on. I agree too.:grin:
---------------------------------------------
In my office, a good amount of the equipment is running at peak load for 3+ hours.

IF his office was like mine, we have 22 pieces of equipment. 3 of which do run 24/7 at their peak, 6 that get used in a continuous load manner plus lights and fan, and the rest intermittent.;)
---------------------------------------------
So, to back up here.

He must have a baseline continuous load (as in usage) on the circuit from all connected loads on the circuit that is contributing to the problem. Whether they operate in a "continuous load" state or not.

Which would lead me back to my original guess.

. . . thought comes to me that the load goes up, the slow trip of the breaker + the voltage drop allows the ups to engage and relieve the load of the computer off of the circuit creating your scenario. . . . maybe.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re-mind's me when we took waves 40 ft over the bow and rolled (see sawed) +/-28 deg in the North Atlantic. The deck almost left my feet in those rolls.

I can't even begin to imagine that, I can get sea sick just looking at post cards of the ocean.


Thanks for your service. :)
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Thems some big bullets!
wis28.jpg
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090921-1103 EST

We shot about 300 of those in one 24 hour period about 20 miles inland in North Korea. Roughly 1/3 of all our stock. If you were on deck when a gun was fired it was a big boom, not a sharp crack like the 5", and then you felt a swoosh of wind.

.
 

Besoeker

Senior Member
Location
UK
Great point.

There is a lot more copper in one 600 Kcmil then two 4/0s but the two 4/0s give you 450 amps compared to 420 amps on the 600s.
I think that's more to do with surface area.
The current carrying capacity of a conductor is ultimately determined by how hot it gets (or is permitted to get). Heat is dissipated through the surface. More surface area, more dissipation for the same temperature rise.

In simple terms, if you double the diameter of a conductor you will get four times the cross section but only double the surface area. I know this ignores factors like the type and thickness of the insulation material, but I'm assuming that we are comparing like for like.

Busbars are neither round nor square for a reason.
 

tom baker

First Chief Moderator
Staff member
14ga or 12ga...Which is more effiecient and why?

I specifically want to know how a 12ga wire is more or less efficient than 14ga, and how that effects the electrical equipment utilizing that circuit?

I am looking for the dummy version of this answer. I am too technical to explain this to my customers so they can understand it. It needs to be factual with simple examples please.

Thank you for your help.

There is a great article in a recent issue of the IAEI news on the cost savings by going to a larger conductor due to less volt drop, it was the July 2009 issue and I find it, but can't post a link to it.
 

Besoeker

Senior Member
Location
UK
090921-0954 EST

Re-mind's me when we took waves 40 ft over the bow and rolled (see sawed) +/-28 deg in the North Atlantic. The deck almost left my feet in those rolls. We lost all the high pressure gas bottles and some of the small boats from the main deck.
Off topic I know.....
But it reminds me the commissioning of some drives on a series of icebreaker vessels.
The drives were for deck main and auxiliary hoists.
I did the first vessel and proof tests were interesting.
To pass inspection the main hoist had to lift 25 tons off the dockside.
It was all hooked up and the hoist operator pushed the joystick to the lift postion. I was on deck at the time and nothing seemed to happen. But I thought I could hear the winch motor (below deck) running. OK. Down the ladder and sure enough it was running. Rope was being wound on to the drum. But, the 25 tons of concrete block had not moved by even one inch at that point. Suspension of belief......

It eventually all became clear. The vessel was being pulled over. At around 25deg the vessel dynamics matched the 25T
Walking across a deck even at just 25deg and stationary was more of a challenge than I would have expected.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090921-1346 EST

Besoeker:

We had problems with the tables and trays in the mess hall.

In calm waters about 1000 or 2000 yards from North Korean shore I went to breakfast and there were just some small fishing boats around us. On returning to the main deck after breakfast there were little red flags in the water all around us that identified mines that our minesweeper had located.

Our main search radar was at the highest part of the superstructure, about 155 ft above the water line. I had access to the transmitter and receiver that was just below this level, and slightly below was a hatch that allowed me to look out and see the wave activity. The Missouri was with us and they would disappear behind waves. A poor little destroyer escort in our group lost steering control and was going over the waves sideways. They probably had 45 deg rolls. Our ship length was great enough that we mostly went thru the waves rather than over them, thus pitch was not large.

On the AC/DC resistance ratio of single round wires see
http://www.okonite.com/engineering/ac_dc_ratios.htm
This is called the skin effect. The effect increases as the sq-root of frequency. This is one reason microwave components are silver plated. For #12 and #14 copper wire the effect is only in the range of 1.000 for the ratio.

For a theoretical derivation see
"Electric and Magnetic Fields", by Steven S. Attwood, 1949, Third Edition, John Wiley and Sons. p 267 thru 269.

.
 

iwire

Moderator
Staff member
Location
Massachusetts
I think that's more to do with surface area.
The current carrying capacity of a conductor is ultimately determined by how hot it gets (or is permitted to get). Heat is dissipated through the surface. More surface area, more dissipation for the same temperature rise.

In simple terms, if you double the diameter of a conductor you will get four times the cross section but only double the surface area. I know this ignores factors like the type and thickness of the insulation material, but I'm assuming that we are comparing like for like.

Busbars are neither round nor square for a reason.


We are saying the same thing, I just said it in simple terms. I know it's about heat.:)
 

iwire

Moderator
Staff member
Location
Massachusetts
On the AC/DC resistance ratio of single round wires see
http://www.okonite.com/engineering/ac_dc_ratios.htm
This is called the skin effect. The effect increases as the sq-root of frequency. This is one reason microwave components are silver plated. For #12 and #14 copper wire the effect is only in the range of 1.000 for the ratio.

For a theoretical derivation see
"Electric and Magnetic Fields", by Steven S. Attwood, 1949, Third Edition, John Wiley and Sons. p 267 thru 269.

.

I was under the impression skin effect has little impact on our 60 cycle systems.
 

Besoeker

Senior Member
Location
UK
090921-1346 EST

Our ship length was great enough that we mostly went thru the waves rather than over them, thus pitch was not large.
Pitch I can live with. Yaw isn't so comfortable.
On the AC/DC resistance ratio of single round wires see
http://www.okonite.com/engineering/ac_dc_ratios.htm
This is called the skin effect. The effect increases as the sq-root of frequency. This is one reason microwave components are silver plated. For #12 and #14 copper wire the effect is only in the range of 1.000 for the ratio.
At power frequencies skin effect isn't a big issue.
Even up to 500kcmil the table makes it about 2%.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090921-1506 EST

iwire:

Yes, skin effect at power frequencies is not significant until diameters are large.

Okonite shows the ratio as 1.326 for 60 Hz, copper and AWG 2500.

.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I was under the impression skin effect has little impact on our 60 cycle systems.
It comes into play a bit for higher currents. That's one of the reasons tubing is used in sub-stations for busbars; they weigh less than solid for a given ampacity.
 
Status
Not open for further replies.
Top