Potential electrical power saving by increasing the size of conductors NEC REQUIRED

[Rjryan]

Some 30 years ago the DOE introduced rules requiring dry type transformers to be most energy efficient at 35% loading as that is what researched showed was their typical usage in schools and other public buildings. This would imply that most NEC conductors, especially feeders and services, are already oversized compared to their actual loading.

If voltage drop was increasing heat loss through conductors why isn't it typically considered when performing heat loss/gain calculations or mentioned as an energy savings practice?

I worked for a school district with schools from over a hundred years old to new schools and they were not running at 35% load, almost every
panel and transformer was maxed out. Several reasons: 1. The addition of more computers in classrooms 2. Teacher allowed to have microwaves,
coffee pot, small refrigerators and hot plates in their classrooms. 3. Plugging in space heaters 4. More elevators and stair lift equipment for
special needs students. In most of the schools elevators were used extensively to take breakfasts and snacks to upper floors for students. The school district thought it necessary to feed students. 5. More energy consuming appliances in the cafeteria kitchens.

 

[Rjryan]

The NEC recognize the fact that temperature has an effect on conductors. I will sight two tables, but there are many examples: Table
310.15(B)(1)(2) Temperature Correction Factor, Table 310.15(C)(1) Adjustment Factor for More than Three Current Carrying Conductors.
Heat is resistance to a conductor if you can reduce the resistance by increasing conductor size and not causing the conductor not to
heat up as much, all I am saying it will be more efficient. I am looking for a way to accurately analyze this, to see if enlarging conductor size
is feasibly an economically beneficial option.

 

[jim dungar]

I worked for a school district with schools from over a hundred years old to new schools and they were not running at 35% load, almost every
panel and transformer was maxed out. Several reasons: 1. The addition of more computers in classrooms 2. Teacher allowed to have microwaves,
coffee pot, small refrigerators and hot plates in their classrooms. 3. Plugging in space heaters 4. More elevators and stair lift equipment for
special needs students. In most of the schools elevators were used extensively to take breakfasts and snacks to upper floors for students. The school district thought it necessary to feed students. 5. More energy consuming appliances in the cafeteria kitchens.

Do you have any actual amp readings to show the transformers run "maxed out" 24/7/365? More likely there are only some circuits which are used extensively, but even then for periods rarely more than 7 hours/day 5 days a week for roughly 42 weeks per year.

 

[Rjryan]

Do you have any actual amp readings to show the transformers run "maxed out" 24/7/365? More likely there are only some circuits which are used extensively, but even then for periods rarely more than 7 hours/day 5 days a week for roughly 42 weeks per year.

Do you have any actual amp readings to show the transformers run "maxed out" 24/7/365? More likely there are only some circuits which are used extensively, but even then for periods rarely more than 7 hours/day 5 days a week for roughly 42 weeks per year.

During school hours, the panels were maxed, not all the time. Should have stated during regular hours of use.

 

[Rjryan]

During school hours, the panels were maxed, not all the time. Should have stated during regular hours of use.

Some schools may be designed for microwaves, coffee pots, small refrigerators and hot plates in classrooms our's were not and between space heaters, breakers were constantly tripping.
Our new schools were designed to handle computer loads, but the older schools had electrical upgrades, but not large enough to handle increasing loads. Administration was not willing to address the problems created in the classrooms. It got so bad with space heaters, my boss,
the supervisor of the electrical shop, when he found a space heater would cut the cord off, until he was reprimanded. I don't know the actual power draw, but my bosses hard pressed to find power for new equipment.

 

[LarryFine]

I don't think anyone has mentioned the most important thing, which is the characteristics of the load.

​

 

[electrofelon]

Yet another thing to consider is there is likely "lower hanging fruit". I am in lots of buildings where there is still old fluorescent lighting that should be upgraded, poorly designed heating systems where one thermostat is set to hot and others are set to cool at the same time (energy wars!), ventilation fans that are left on continuously that don't need to be and are sucking out heated or cooled air all night and on weekends, the list goes on and on.

 

[Rjryan]

Yet another thing to consider is there is likely "lower hanging fruit". I am in lots of buildings where there is still old fluorescent lighting that should be upgraded, poorly designed heating systems where one thermostat is set to hot and others are set to cool at the same time (energy wars!), ventilation fans that are left on continuously that don't need to be and are sucking out heated or cooled air all night and on weekends, the list goes on and on.

Your right there was still old fluorescent lighting, but the utility company helped with low wattage florescent make over for about 70 portable units
(trailers) and the old t-12 when they failed had a blast change with low wattage lamps. We had an energy management department that monitored and controlled over a 100 schools and support building from a central location. Every HVAC had a monitoring device, energy management controlled. New schools had LED lighting and older school auditoriums were being converted to LED. Energy codes made classroom have monitors that shut off light when no one is present.
Getting away from my point, if an increase in conductor size when building would pay for itself in a few years and schools are around for 50+ years, that could be a large operational savings and a reduction in energy use.

 

[winnie]

Bringing in old buildings which are overloaded for their original design intent is a red herring. These buildings with their current loads are presumably undersized per the NEC.

The original question restated: what is the formula for calculating the economic benefit of increasing conductor size?

IMHO there isn't a simple formula because there are so many relevant factors. Previous posts in this thread have already listed them.

My guess is that you will not see a benefit (payback in short enough time to justify the additional cost) with the exception perhaps of heavily loaded circuits operating nearly full time.

IMHO this thread could provide a useful answer by suggesting and reviewing the chain of equations the OP will need.

Jonathan

 

[Rjryan]

Thanks everyone for your input, and list of potential problems. Without a mathematical equations this premise will be hard to prove.
I do think it is a real thing. Maybe someone with access to AI could feed in all the parameter into a computer and come up with a formula or
formulas. This hypothesis may have to be broken down to several stages of equations to come up with an answer.
Going to take someone smarter than me to get to an equation or equation.
Thanks again for your inputs.

 

[LarryFine]

This hypothesis may have to be broken down to several stages of equations to come up with an answer.

To put it in simple terms, look at how each load behaves when presented with different voltages.

The current of resistive loads varies proportionately with voltage. Raise the voltage, the current rises.

The current of inductive loads varies inversely with voltage. Raise the voltage, the current lowers (within limits).

 

[winnie]

Thanks everyone for your input, and list of potential problems. Without a mathematical equations this premise will be hard to prove.
I do think it is a real thing. Maybe someone with access to AI could feed in all the parameter into a computer and come up with a formula or
formulas. This hypothesis may have to be broken down to several stages of equations to come up with an answer.
Going to take someone smarter than me to get to an equation or equation.
Thanks again for your inputs.

You can do this.

It is not going to be a single equation.

It will be a spreadsheet of several equations expressing the simple known physics and your assumptions.

Post #31 describes the equations for how loads will respond to voltage drop.

You need an equation for voltage drop and losses in the wires. Those are easily found.

You need a description of how the load changes vs time.

You just go step by step with pieces you can understand and put them together.

Jonathan

 

[Flicker Index]

Desktop computers of today are much more similar to laptops than it was years ago. The major difference is the housing and durability. The parts touched by people and things likely being spilled into are commercially off the shelf goods that can be bought from Office Depot and easily replaced.

Then, 120v ac to whatever voltage DC adapter might be inside the case, because there's space. For laptops, that's externalized, because it's undesirable to carry around the extra heft of AC/DC power adapter while working off the grid on battery.

Computer labs of 90s and early 2000s assumed CRTs and assumed diodes and capacitor front end and 400W/800VA to 1kVA per station with oversized neutral. It was common for 90s design monitors to remain powered 24/7/365, unless switched off by hand. It wasn't until EnergyStar monitors that shut down of monitors by signal was made possible. Otherwise, the only other way to shut down monitor was with a relay built inside the computer itself and the monitor powered with a female-male IEC cable from the back of the desktop computer.

Due to EU regulations, many laptop and desktop power supplies are not plain rectified input, but have harmonics and power factor control. Since Manufacturers would rather not produce separate IEC and US versions, they tend to have those features built in globally.

These days, computer monitors no longer use gas discharge backlight and when user steps away and computer goes into log-in screen for security reason, backlight shuts off too. So, the 50W/60VA per workstation isn't unreasonable for new setups. Modern classroom/office workstations vary in input power greatly on the CPU work load. It might do 125W if you run stress test, but 50W/50VA average per workstation is pretty reasonable these days.

Facility wise, each 4xF40T12 luminaires being replaced by whatchamacallit solid state fluorescent (L.E.D. ) type fixture sheds enough load to support a computer workstation at facility level, although that reduction would be on 480/277 side, and computers are on 208/120 side, unless the facility is small enough to not be on 480.

These days, I think only electron tubes in common use in households and offices is the magnetron in microwave ovens.

 

[kingpb]

Keep in mind the NEC is not and never has been a design guide and the conductors are minimum size needed to maintain a safe system.

 

[ggunn]

The last question is easy: #1 wire has an area that is very close to the cube root of 2 times the area of #2 wire.

Or you could just look up the cross sectional areas on Table 8.

 

[wwhitney]

Or you could just look up the cross sectional areas on Table 8.

Easier to remember it's a geometric series and that an increase of 3 AWG doubles the cross-sectional area.

Cheers, Wayne

 

[Tainted]

Yea but you have to also worry about short circuit current. If you increase wire gauge, the available short circuit current will be larger

 

[junkhound]

500 feet of 10 AWG feeder = 1 ohm
24A continuous max per NEC @240 V input = 10 ohm load total, 9 ohms is the load, line loss = 576 watts
double 10 AWG, 0.5 ohms. Amps total = 240/9.5 = 25.26 A, line loss = 320 watts; 246W sawings

Say $600 for 1000 ft of 10 AWG. Say 15 cent kw-hr/

Continuous load, 8760 hours * 0.246 *0.15 = $323
Interest at 5% on $600 = $30 year, rounding gives about 2 year payback for cpntinuous loads.

For never a payback, saving would need to be less than $30 a year, or load factor of about 10%.

If loads are internal resistance space heating loads, there is obviously NO savings, and a loss of $30 per year.

 

[brycenesbitt]

Administration was not willing to address the problems created in the classrooms. It got so bad with space heaters, my boss,
the supervisor of the electrical shop, when he found a space heater would cut the cord off, until he was reprimanded. I don't know the actual power draw, but my bosses hard pressed to find power for new equipment.

This is NOT an electrical problem, this is an HVAC and environmental air design problem.

 

[Hv&Lv]

Electrical: Energy Efficiency - One Wire Size Up Means Big Savings

Installing wire only one size larger than has been required by the National Electrical Code increases energy efficiency with dramatic paybacks.

copper.org

Electrical: Energy Efficiency - High-Efficiency Wiring for Energy Savings

Now let's look at upsizing the wiring above code minimum to achieve further energy savings.

copper.org