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

[hillbilly1]

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

The dramatic payback is only for loads that are high amp draw for hours at a time, such as EV chargers. Most residential ovens would not meet that goal, or if your local poco has high per kw rates. Ours does not meet that because of the many local hydroelectric plants, and we have cheap electricity. But the outrageous rates on the left coast it might actually have a pay off.

 

[Hv&Lv]

The dramatic payback is only for loads that are high amp draw for hours at a time, such as EV chargers. Most residential ovens would not meet that goal, or if your local poco has high per kw rates. Ours does not meet that because of the many local hydroelectric plants, and we have cheap electricity. But the outrageous rates on the left coast it might actually have a pay off.

I agree completely.
There is also the part where the owner doesn’t want to pay the extra for the larger conductors when building a house initially.

I know an electrician that wired his house with #10 for lights and receptacles. Said it was the biggest mistake he ever made when it came time to dress out.

 

[wwhitney]

OK, say you drive your EV car 12,000 miles / year, and say it gets only 3 miles / kWh wall to wheels. So that's 4,000 kWh/year ; at $0.25/kWh, that would be $1,000/year in fuel costs. Say you charge at 32A continuous (40A circuit). At 240V, that's 7.68 kW, so 521 hrs/year.

If you wire your circuit with #8 Cu it has an AC resistance at 75C of 0.78 ohms/kft; #6 Cu would be 0.49 ohms/kft. The difference is 0.29 ohms/kft; at 32A, that's (0.29)*(32)² = 297 W/kft difference. At 521 hrs/year, that's 155 kWh/year/kft, or $38.70/year/kft.

Home Depot (probably a poor source of price info, but easy to look up) advertises #6 THHN at $882/kft, and #8 TTHN at $491/kft. So a difference of $391/kft. The return period is just over 10 years with a constant price model and zero cost of funds.

Now if you're driving an EV pickup truck and do some hauling and average 8,000 kWh/year, then the return period is half as long.

Cheers, Wayne

 

[jaggedben]

Home Depot (probably a poor source of price info,[ ...]

Nah it's a pretty good source, at least for those wire sizes.

 

[gadfly56]

It is sometimes--maybe not for code minimum houses, where the effect is comparatively small, but in high performance, well insulated, well air-sealed houses. And surely for things like office towers, where the extra heat gain can increase A/C demand.

Cheers, Wayne

To the point where the building has no heating demand in winter. In my youth, I had heard that this was the case for the Twin Towers.

 

[hillbilly1]

I agree completely.
There is also the part where the owner doesn’t want to pay the extra for the larger conductors when building a house initially.

I know an electrician that wired his house with #10 for lights and receptacles. Said it was the biggest mistake he ever made when it came time to dress out.

My cousin did that, he had a roll of #10 so he used it for the outlets! Real pain to trim out. Never doing that again!

 

[Flicker Index]

What about the cost savings by using aluminum core steel reinforced, by itself or copper cladded in EV charging stations' user interfacing cables?
I'm talking about theft and vandalism insurance by the deterrent effect on meth tweakers.

Utilities are already using copper clad steel cables for certain applications to deter just that.

 

[gadfly56]

OK, say you drive your EV car 12,000 miles / year, and say it gets only 3 miles / kWh wall to wheels. So that's 4,000 kWh/year ; at $0.25/kWh, that would be $1,000/year in fuel costs. Say you charge at 32A continuous (40A circuit). At 240V, that's 7.68 kW, so 521 hrs/year.

If you wire your circuit with #8 Cu it has an AC resistance at 75C of 0.78 ohms/kft; #6 Cu would be 0.49 ohms/kft. The difference is 0.29 ohms/kft; at 32A, that's (0.29)*(32)² = 297 W/kft difference. At 521 hrs/year, that's 155 kWh/year/kft, or $38.70/year/kft.

Home Depot (probably a poor source of price info, but easy to look up) advertises #6 THHN at $882/kft, and #8 TTHN at $491/kft. So a difference of $391/kft. The return period is just over 10 years with a constant price model and zero cost of funds.

Now if you're driving an EV pickup truck and do some hauling and average 8,000 kWh/year, then the return period is half as long.

Cheers, Wayne

Your calculations are per 1,000 feet. I doubt anyone is running 1,000 feet to their charging station. More like 50 feet. So, divide by 200 and now you're at $0.19 of savings. For some reason, that doesn't get my juices flowing.

 

[wwhitney]

Your calculations are per 1,000 feet. I doubt anyone is running 1,000 feet to their charging station. More like 50 feet. So, divide by 200 and now you're at $0.19 of savings. For some reason, that doesn't get my juices flowing.

The payback period doesn't depend on the length, as both the cost of materials and the energy savings are proportional to length.

Cheers, Wayne

 

[LarryFine]

My cousin did that, he had a roll of #10 so he used it for the outlets! Real pain to trim out. Never doing that again!

I would suggest using it up with receptacle-circuit home runs, and pigtail at the load end.

 

[gadfly56]

The payback period doesn't depend on the length, as both the cost of materials and the energy savings are proportional to length.

Cheers, Wayne

I understand that, but it's easy to lose sight of the units when you want an idea of what you're getting back on a per installation basis. $38 is paltry enough, but $0.20 per year really drives that home.

 

[Flicker Index]

I understand that, but it's easy to lose sight of the units when you want an idea of what you're getting back on a per installation basis. $38 is paltry enough, but $0.20 per year really drives that home.

That's how it is with a lot of green/alternative energy stuff.
How much of MY money does it save regardless of how much of it is paid for by others (subsidies, grants)?

 

[wwhitney]

$38 is paltry enough, but $0.20 per year really drives that home.

Your "divide by 200" gives a circuit one-way length of 30", which is at the opposite extreme from my 500' one-way calculation.

Maybe a 25' one-way circuit length is more typical, in which case we are talking about spending $19.50 in materials to save $1.90 per year, given the assumptions I made

Cheers, Wayne

 

[jaggedben]

That's how it is with a lot of green/alternative energy stuff.
How much of MY money does it save regardless of how much of it is paid for by others (subsidies, grants)?

The calculation could apply to any constant current load, an EV circuit is just a good example. The customer should be paying for all of it in this situation.

 

[jaggedben]

Maybe a 25' one-way circuit length is more typical, in which case we are talking about spending $19.50 in materials to save $1.90 per year, given the assumptions I made

$19.50 on what is likely to be a $1500 install is basically not a sig fig. I bet the variation between quotes from different contractors, and the corresponding customer experience, will greatly outweigh that amount.

 

[Flicker Index]

$19.50 on what is likely to be a $1500 install is basically not a sig fig. I bet the variation between quotes from different contractors, and the corresponding customer experience, will greatly outweigh that amount.

If there's $1,500 in purpose specific grant funds sitting around that just has to be spent, don't think that they won't spend it if it translates to $10/year available in their unrestricted funds from savings

 

[hillbilly1]

I would suggest using it up with receptacle-circuit home runs, and pigtail at the load end.

But that’s not what he done, he did the living room outlets! LOL!

 

[jim dungar]

I understand that, but it's easy to lose sight of the units when you want an idea of what you're getting back on a per installation basis. $38 is paltry enough, but $0.20 per year really drives that home.

This is why it is really only a concern for very heavily loaded circuits that run for several hours.
Let's see an analysis for an on-demand water heater that probably runs for less than 1 hour per day. And also for the service entrance conductors.
How much of the US pays .25/kWH?

 

[jaggedben]

..
How much of the US pays .25/kWH?

Rough guess: a quarter.

 

[readydave8]

My cousin did that, he had a roll of #10 so he used it for the outlets! Real pain to trim out. Never doing that again!

Even worse, DIYs around here will use their 10 UF left over from well pump