Interesting article...

[e57]

While searching the word "HANDYMAN" - to dig up the many reasons why they should all be lined up... I found this interesting article, based on propoganda from the copper industry...

I think it's a great tool to sell those 200A service changes in 500MCM....

Anyway - while it may be technically true, I think there is some wild speculation and fuzzy math attached to the examples - anyone care to disect it?

 

[nakulak]

that's hilarious. too bad no owner is going to pay for it (none that we work for anyway) (it would be nice to find a bunch of clients that want us to install one size up wire for everything !)

 

[Flex]

Can anyone verify that it is true?

 

[e57]

I wouldn't attempt it without a calculator and a refresher course...

 

[rwreuter]

the first hyper link doesn't work.

on the second link: YOU HAVE GOT TO BE KIDDING ME????

 

[Saturday Cowboy]

Very interesting. Altho I think it might be hyped up a little.

There also must be some increased safety margins with that kind of install.
Also some larger increases in installation than they quote. Ya'll know that landing a #10 on a recp is harder than landing smaller wire, harder to pull in, ect.

However If I were building my own house I would not use anything smaller than #12. But i can justify a installation using only 20A or larger, by running fewer circuts.

 

[ceb58]

There may be truth to the second link, but....
It's hard enough to win a bid doing just what is requried much less trying to break down every thing to show the customer the "savings" for upgrading the wire size.
The majority of runs that are installed, due to length of run, if there were any voltage drop it would be so minimal the savings cost could not justify the expense of the larger wire.
The one thing they do not take into account is the increased labor above the increase in pipe size. I can see some one in a resd. setting landing #10 on the recpts. for the sabc/ bath circ.
The only time IMHO the time to up-size is when there is a load that is close to the max. rating of the wire. Just the right thing to do.
On UPS systems we have the mfg. instructions list to up-size the wire ie.. 80amp ocp- #2 thwn. We have had several installs by contractor that we rejected because of the wire size. When we tell them it must be #2 they start with 310.16 .#4 is rated for 85 amp. and start shaking the code book at you. Then I must tell them to look at 110.3 B and then look on page 27 of the installation instructions that comes with every unit. That's why I install all of our UPS's now in our older sites.

 

[jaylectricity]

Until you go to insert it into the main breaker terminals only to find that it doesn't fit without cutting a strand or two or six off the end. And really, then what is the sense?

 

[JFletcher]

All of their math is correct, at least for the lighting circuit (example #2).

As for dissecting it, there are commercial and industrial applications where increasing wire size will result in savings. I don't see it happening in residences.

 

[rwreuter]

most resi loads don't come close to the capacity of the circuit.

 

[e57]

the first hyper link doesn't work.

on the second link: YOU HAVE GOT TO BE KIDDING ME????

Oh so is the first one....
http://www.handymanwire.com/articles/wiresize.html

 

[rwreuter]

i tried the link later and it worked

 

[jaylectricity]

most resi loads don't come close to the capacity of the circuit.

Do you mean capacity of the conductors or capacity of the overcurrent device?

 

[e57]

most resi loads don't come close to the capacity of the circuit.

Nor will they be operating at 104F ambient in most cases...

 

[dbuckley]

Some smoke and mirrors here.

Quoting... "Take the case of a single-phase, 15 amp lighting load operating continuously. To simplify, assume the load is concentrated 100 ft. from the panel"

The maths following looks correct, but makes a huge assumption, namely the load current remains at 15A. In the case of a real-world such as an incandescent lamp, the current consumed by the lamp is related to the voltage across it. So if you upsize your conductors, the I2R losses diminish, the voltage drop across the conductors reduces, so the voltage across the lamp increases, so the lamp consumes more current, so you dont save electricity - you use more of it!!! And (edited to note) since incandescent lamp life changes by (so I've been told...) the twelfth power of the voltage you'll be replacing lamps more often too - more money in the trash can.

Whats that smell around here? Oh yeah, someone let the cattle in...

Though to be fair, if the load was a PC, or a fluoro with electronic "ballast", then these class of device use the same power (KVA) irrespective of the supply voltage, so bigger conductors will save you money for that kind of load.

Better than bigger conductors is higher voltage to reduce the current, along with smaller conductors. I2R losses go up by the square of the current, so the conductor losses for a 10A 120V load (1200W) are four times as high as for a 5A 240V load also 1200W. Always use the highest voltage you can get away with.

 

[steve66]

The math does seem reasonable for the example they give. But I think that example is the exception rather than the rule for the following reasons:

1. The circuit they use is almost at its limit for current. (15 amps vs. the allowed continuous load of 16 amps for #12).

2. The circuit is almost at its limit for length: For #12, the 100' run causes a 5% voltage drop. That is reduced to 3% for #10.

3. The circuit they use runs 24 hours/day for 365 days a year. How many fully loaded circuits do you know that run constantly? Not many.

4. The circuit is single phase. There would be less voltage drop for a three phase circuit, or one that shares the neutral.

5. It's a 120 volt circuit. For higher voltages, the voltage drop is a smaller percentage of the input, so there would be fewer losses, and the payback would be longer.

6. How often can you upsize all the wires in a conduit and not have to upsize the conduit?? Maybe if you run a separate conduit for each circuit, but how often does that happen?

In my opinion, many times you could get an even faster payback by sharing the neutral wire, or by using a higher voltage. But they don't tell you that because you would be using less copper.

 

[LarryFine]

My random (as if there were any other kind) thoughts:


Unless one is going to compensate by using larger bulbs, voltage drop actually reduces power consumed by incandescent lighting.

For electric heating, less power over more time produces the same heat gain. The money would be better spent reducing heat loss.

If the heating-circuit wires are in the heated space, their heat contributes to heating the space anyway, so there isn't really a loss.

For cooling, compressor motors are basically contant-power devices. Less voltage at more current should be about the same power.

Now, if the cooling circuit wires are in the conditioned space, their heat could increase the cooling load a bit. But, how much, really?

Again, I thing money spent on better insulation and weather sealing goes much farther than does money spent on using larger wire.

Plus, if there are several circuits that long, a sub-panel can reduce installed costs and even voltage-drop losses, due to load diversity.

 

[rwreuter]

Do you mean capacity of the conductors or capacity of the overcurrent device?

I would say both. With a OCP you are never allowed to reach the actually capacity of the conductor.

 

[StephenSDH]

Its not outlandish. For continuous loads (where your savings would be) it is required. Most non-continuous loads the rated ampacity is far greater then the load.