> Sorry Lew, but I get suspicious when somebody says "trust me".
> Normally, I would let this one slide. After all, the worst that might
> happen if he follows your advice is that he might spend an extra few
> bucks on wire. But it's a slow day at the office, so I decided to run
> some numbers.
> 1. A 25 ft. 10-3 extension cord costs about $25.00 say $1.00 per
> 2. 14-2 w/g Romex costs about $0.27 cents a foot
> 3. The difference of $0.73 per foot x 15 feet equals a materials cost
> difference of $10.95 for the job.
> 4. #14 wire has a resistance of about 0.00258 ohms per foot
> 5. #10 wire has a resistance of about 0.00120 ohms per foot
> 6. 0.00138 ohms difference x 30 foot total run equals 0.0414 ohms
> difference in resistance between the two proposed types of wire.
> 7. The power lost in a wire equals the current (squared) x
> resistance. At 11 amps load, the difference in power lost is 0.0414 x
> 11(squared) equals 5.01 watts.
> 8. The national average for electricity cost is about $0.10 per
> kilowatt-hour or $0.0001per watt-hour.
> 9. The time required to recoup the initial investment in wire is
> $10.95/($0.0001 x 5.01) equals 21,856 hours at full load.
> 10. At an average of 10 hours per week at full load, it will only
> take him 42 years to recoup his investment. After that, it's all
A little knowledge and some extra time on your hands can produce some
Let's take it from the top.
No one has defined the application so we don't know if this is a case
where a cord out in an exposed area or conductors in a secure space such
as in a conduit or behind a wall are required.
If it is a cord application, then Romex would not be appropriate.
If it is a set of conductors in a secure space, then the cord would not
In either case, any attempt at comparison between the two would be moot.
BTW, if you are aware of what is happening in the raw materials market
these days, especially copper which has a history of being volatile, you
would also be aware that only a fool would quote anything but "price in
effect at time of shipment", and that includes the lowly hardware store
down the street that is going to cut a piece of something off a roll
that was purchased 6-9 months ago.
Never sold wire but was around the business. Not uncommon to have a
price on wire be good only for the day, sometimes two.
Electrical contractors typically make a buy on wire on a job as a
specific commodity, just like the apparatus or the lighting.
As far as the cost of power is concerned, think you will find the
residential/small commercial market is somewhere around $0.15-$0.17/KWH
unless it is being subsidized in some fashion.
The days of $0.10/KWH disappeared with the buggy whip.
Now, let's talk about line losses.
Line losses are a two edged sword.
First, you pay for the lost power and turn it into heat. Heating up a
conductor raises the temperature of the insulation around the
conductors, thus shortening the insulation life.
2nd, the line losses reduce the amount of power delivered to the load by
reducing the voltage at the terminals of the load, which in this case
would appear to be a saw or an air compressor.
Reducing the voltage delivered requires that the current be increased to
get the same amount of work done.
Again, increasing the current in the motor windings, increases the heat,
which reduces the life of the insulation of the motor.
Calculation of the economics is based on the ability of the buyer to get
a deal; however, the bottom line when it comes to electrical conductors
is that bigger is better when it comes to distribution conductors.