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Forrest
Re: Rewire Entire House

Great reply above, I was thinking how can bigger wire save money! In fact I have heard using bigger wire that is not properly rated for the load you are putting on it, can have negative effects and 'draw' more causing heat? or other issues. Meaning if you are putting a load that could easily run on a 12 or 14/2 wire on a 10, might cause more draw etc. Again I am not an expert.

Anyways here are my questions.

How do you determine to run 12 or 14/2 in the house? I need to re-wire my entire house as well. I know for kitchen where there will be toasters, water kettles, and more running appliances you wold want to probably use 12/2 between 2, 20 amp circuits??

Other general question

I like the idea of having all the lighting on one circuit and outlets on another.

so I know you can't exceed 80% of total circuit load. So If I take 2 bedrooms, each running a computer (700 Watt PSU /120 = 5.8 Amps), clock radio maybe a few other electronics but nothing out of normal besides the higher wattage computers, maybe another laptop running at 90Watts = .75 Amp, alarm clocks .041 amps, misc stuff etc... I shouldn't have more than 12 amps consumed at any given time. That fits under the 80% continuous load code. Would I be fine using 1, 15 Amp circuit running both of those rooms for the outlets? I would imaging I could run at least 3 rooms on another 15 amp circuit for the lighting. (3 rooms no more than 100 watt lighting) - I could probably run 4 rooms?

Any thoughts here on this?

MtMan54
Re: Rewire Entire House
pcride wrote:

Great reply above, I was thinking how can bigger wire save money! In fact I have heard using bigger wire that is not properly rated for the load you are putting on it, can have negative effects and 'draw' more causing heat? or other issues. Meaning if you are putting a load that could easily run on a 12 or 14/2 wire on a 10, might cause more draw etc. Again I am not an expert.

Anyways here are my questions.

How do you determine to run 12 or 14/2 in the house? I need to re-wire my entire house as well. I know for kitchen where there will be toasters, water kettles, and more running appliances you wold want to probably use 12/2 between 2, 20 amp circuits??

Other general question

I like the idea of having all the lighting on one circuit and outlets on another.

so I know you can't exceed 80% of total circuit load. So If I take 2 bedrooms, each running a computer (700 Watt PSU /120 = 5.8 Amps), clock radio maybe a few other electronics but nothing out of normal besides the higher wattage computers, maybe another laptop running at 90Watts = .75 Amp, alarm clocks .041 amps, misc stuff etc... I shouldn't have more than 12 amps consumed at any given time. That fits under the 80% continuous load code. Would I be fine using 1, 15 Amp circuit running both of those rooms for the outlets? I would imaging I could run at least 3 rooms on another 15 amp circuit for the lighting. (3 rooms no more than 100 watt lighting) - I could probably run 4 rooms?

Any thoughts here on this?

Hi, Just because you use #10 wire doesn't mean you have to use a 30amp breaker and a larger wire doesn't draw more and cause heat, it is just the opposite, using a smaller wire will draw more and cause heat. Thanks

Seth
Re: Rewire Entire House

He's right in that there would be less resistance and heat, but let's do some math as to how much...

According to wikipedia:

# Ω/kft
10 0.9989
12 1.588
14 2.525

So, 100 feet of #14 would have 0.15 ohms more resistance than #10, 100 feet of #12 would have less than 0.06 more ohms of resistance.

0.15 ohms at 15 amps is 33.75W, compared to the ~1800W being used at 15A, or 1.875%.
0.06 ohms at 20 amps is 24W, compared to the ~2400W being used, or 1%.
(Did I do that part right? I was expecting smaller percentages.)

Assuming I did that right, that means if I use all #10 I can save around 1.5%. So, if I spend $800 a year I will save $12/yr.

Now, what is the added cost in materials and labor? 10/2 seems to cost $50 more per 100ft than #12 and $65 more than #14, but it might be cheaper in bulk. I imagine in addition to being more expensive and harder to snake, wiring outlets would be slower too as you can't fit #10 in the back of those little quick-connects (but I don't know if real electricians use those).

I need to stop wasting time.

JLMCDANIEL
Re: Rewire Entire House
skintigh wrote:

He's right in that there would be less resistance and heat, but let's do some math as to how much...

According to wikipedia:

# Ω/kft
10 0.9989
12 1.588
14 2.525

So, 100 feet of #14 would have 0.15 ohms more resistance than #10, 100 feet of #12 would have less than 0.06 more ohms of resistance.

0.15 ohms at 15 amps is 33.75W, compared to the ~1800W being used at 15A, or 1.875%.
0.06 ohms at 20 amps is 24W, compared to the ~2400W being used, or 1%.
(Did I do that part right? I was expecting smaller percentages.)

Assuming I did that right, that means if I use all #10 I can save around 1.5%. So, if I spend $800 a year I will save $12/yr.

Now, what is the added cost in materials and labor? 10/2 seems to cost $50 more per 100ft than #12 and $65 more than #14, but it might be cheaper in bulk. I imagine in addition to being more expensive and harder to snake, wiring outlets would be slower too as you can't fit #10 in the back of those little quick-connects (but I don't know if real electricians use those).

I need to stop wasting time.

First, the calculation you used is based on DC current resistance not impedance in AC wiring.
Second, seldom is a circuit load at 80% full capacity let alone full capacity normally reached.
Third, any good electrician will tell you not to use the stab connections in the back of the receptacle.
Fourth, the code size rating already has a significant safety margin built in, going to #10 will only add to the cost and make installation many times harder.

Most common practice is to use all 12 gauge cables because it is cheaper to buy in bulk one size cabling.

Jack

Re: Rewire Entire House
MtMan54 wrote:

Hi, If this was not important, then I would not say anything. Thanks

While #10 wire would save energy lost because of long runs it would:

1) very easily create "box fill" Code violations using standard boxes

2) probably necessitate all connections to switches and receptacles to be "pigtailed" with stranded wire so they could be inserted into a box, without breaking the terminals off of the devices.

3) very easily double the cost of labor and material for branch circuit wiring

4) not allow the branch circuits to be protected with a breaker larger than 20A or have more than 13 outlets (receptacles or lights) on the circuit.

5) take decades to break even, compared to using #12 or #14 wire.

MtMan54
Re: Rewire Entire House

Hi, There is one thing that people do today and that is they double or triple the number of outlets on a circuit with these power strips. Thanks

Seth
Re: Rewire Entire House
JLMCDANIEL wrote:

First, the calculation you used is based on DC current resistance not impedance in AC wiring.
Second, seldom is a circuit load at 80% full capacity let alone full capacity normally reached.
Third, any good electrician will tell you not to use the stab connections in the back of the receptacle.
Fourth, the code size rating already has a significant safety margin built in, going to #10 will only add to the cost and make installation many times harder.

Most common practice is to use all 12 gauge cables because it is cheaper to buy in bulk one size cabling.

Jack

1) You're right, that would change the impedance to 3.1, 2.0 and 1.2. Roughly the same ratio but I don't feel like redoing the math.

2) Obviously, but the ratios are the same for any length or use. I just picked 100 feet at random and full current as I don't know what a typical use or run would be. What would be better? 20 feet and 25% load? If someone has real numbers maybe I'll make a spreadsheet.

3) I have heard that, do they work loose?

4) I think I already showed that's not entirely true -- it would save a tiny amount of money. I'm just wondering how that compares to additional costs.

Maurice: if it doubles the costs like you are suggesting, I think your estimates on payback are low. Assuming wiring a house will cost in the 4-5 digit range, while yearly savings are in the 1-2 digit range, then payoff may take a millennium...

JLMCDANIEL
Re: Rewire Entire House
skintigh wrote:

1) You're right, that would change the impedance to 3.1, 2.0 and 1.2. Roughly the same ratio but I don't feel like redoing the math.
Cute but no cigar, impedance calculations require much more than length and resistance. Code wiring has a greater than 50% load rating safety margin based on a wide temperature range.
2) Obviously, but the ratios are the same for any length or use. I just picked 100 feet at random and full current as I don't know what a typical use or run would be. What would be better? 20 feet and 25% load? If someone has real numbers maybe I'll make a spreadsheet.
The calculations have already be done in establishing the cabling needed to meet code. 12/2 costs are half of what 10/2 costs, so that double the installation material cost. Because of the extra labor required (making pig tails to connect devices, adding extra boxes to meet fill requirements, and harder to pull) that increases the installation cost.
3) I have heard that, do they work loose?
Over time due to vibration and heat they loose proper contact.
4) I think I already showed that's not entirely true -- it would save a tiny amount of money. I'm just wondering how that compares to additional costs.
If you spend 3600/yr on electric and can save 1.5% (if possible) you would save $54/yr, with installation and material cost cost of the 10/2 adding $10,000 to the cost the pay back would take 185 years.
Maurice: if it doubles the costs like you are suggesting, I think your estimates on payback are low. Assuming wiring a house will cost in the 4-5 digit range, while yearly savings are in the 1-2 digit range, then payoff may take a millennium...
See number 4 above

I hope this helps you understand a little better.
Jack

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