Electrical Code

[reicherb]

Ok, I posted here a couple of weeks ago looking for advice on home electrical. I've since bought a book with some NEC info. I'm wondering how people are able to wire houses using 14awg or 12awg wire. According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long. I don't have a huge house, but that wouldn't even make it to many of my rooms on the second floor, let alone to each light/receptical. What am I missing here? Is it common practice to run a larger wire to a junction box and then distribute the power to each receptical with a smaller wire?

How do they wire houses and still meet code?

Thanks.

 

[Iron Woode]

Wire is generally run to where it is supposed to go, reguardless of length.

Junction boxes are to be kept to a minimum. General house wiring is NMD7 or 9 14/2 for a 15 amp circuit. Unless a device needs a higher current draw, then this should be enough.

Common sense says keep the wire from injury and use the proper guage wire for the expected load.

 

[reicherb]

What is NMD7 or 9?

 

[Iron Woode]

Originally posted by: reicherb
What is NMD7 or 9?

I can't remember. It is supposed to identify the conditions the wire is able to work in.

It is typically seen on wire in Ontario Canada.

 

[Iron Woode]

I forgot to add that there is a limit on the number of outlets on a single circuit. I shoot for 5 or 6/room and I calculate the combined load. You can have more but I play it safe.

 

[Kwatt]

According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long.

What book?

That info is not correct! Or out of context....


As far as I know the NEC does not limit how long a wire can be run. Only the installtion, overcurrent,etc.....



Kwatt

 

[Iron Woode]

Originally posted by: Kwatt

According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long.

What book?

That info is not correct! Or out of context....


As far as I know the NEC does not limit how long a wire can be run. Only the installtion, overcurrent,etc.....



Kwatt

Some might, but it is stupid in a residential construct.

The only limitation with length would be an increase in resistance.

 

[Kwatt]

Some might, but it is stupid in a residential construct.

Now I'm confused

I was referring to the National Electrical Code.

The only limitation with length would be an increase in resistance.

Exactly, because of voltage drop.


Anything less than 100 feet will be fine. Maybe a lot more. I forget its been a long time since I had to do voltage drop calculations.







reicherb


More info. will be needed. What type of insulation does the wire you are using have?

And I would forget about using 14 AWG. Max overcurrent protection is 15 amps and max load is12 Amps. Most people wish they had installed 12 AWG before too long. And just have to change it later. Save some trouble for yourself later install 12 AWG. The cost difference is not too large. Compared to replacing the wire.


DISCLAMER: The above load ratings depend on the type of insulation.



Kwatt











EDIT: Because leaving out a word or two in the wrong place makes a lot of difference

(Note to self) Use the preview button.

 

[Iron Woode]

Originally posted by: Kwatt

Some might, but it is stupid in a residential construct.

Now I'm confused

I was referring to the National Electrical Code.

The only limitation with length would be an increase in resistance.

Exactly, because of voltage drop.


Anything less than 100 feet will be fine. Maybe a lot more. I forget its been a long time since I had to do voltage drop calculations.







reicherb


More info. will be needed. What type of insulation does the wire you are using have?

And I would forget about using 14 AWG. Max overcurrent protection is 15 amps and max load is12 Amps. Most people wish they had installed 12 AWG before too long. And just have to change it later. Save some trouble for yourself later install 12 AWG. The cost difference is not too large. Compared to replacing the wire.


DISCLAMER: The above load ratings depend on the type of insulation.



Kwatt











EDIT: Because leaving out a word or two in the wrong place makes a lot of difference

(Note to self) Use the preview button.

He was refering to his home. I can understand that commercial/industrial wiring would entail long legnths, but not home wiring.

Load is determined by wire guage. Insulation is for mechanical injury protection. You can draw 13-14 amps on 14/2 no problem, just don't have a sustained load for any great length of time.

The only problem with wire of a larger guage is that some electrical products may not fit the wire correctly. Personally I would wire a house using 12/2 wire.

I learned all this stuff so I could get my electrical technologist degree. 2 years of studing this crap. I forgot some of it, but remember most though.

 

[Armitage]

Originally posted by: reicherb
Is it common practice to run a larger wire to a junction box and then distribute the power to each receptical with a smaller wire?

Definitely do not do this! You must run the same gauge wire for the entire circuit.
I don't know what context you're seeing the length limits in. I don't have the actual NEC books, but my codecheck book doesn't indicate anything like that.

 

[morkinva]

Originally posted by: reicherb
Ok, I posted here a couple of weeks ago looking for advice on home electrical. I've since bought a book with some NEC info. I'm wondering how people are able to wire houses using 14awg or 12awg wire. According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long. I don't have a huge house, but that wouldn't even make it to many of my rooms on the second floor, let alone to each light/receptical. What am I missing here? Is it common practice to run a larger wire to a junction box and then distribute the power to each receptical with a smaller wire? How do they wire houses and still meet code? Thanks.

This book you are reading is really the LILLIPUTION NEC book, that's the problem

 

[woodie1]

If you use Romex 12/2 with ground in a house and a 20amp breaker there really isn't any limit on length unless you have a 5,000 sq. ft. house.

 

[Kwatt]

reicherb


You need to hire someone to do this or get a copy of the latest NEC. Check your local libary.



For allowable ampacities:

Table 310-16

Allowable ampacities of insulated conductors rated 0 through 2000 volts, 60 deg C through 90 deg C. Not more than three current-carrying conductors in raceway, cable, or earth(directly burried), Based on ambient temperature of 30 deg C.

For Branch-Circuit Ratings: 219-19

For Permisssible Loads: 210-23

For Protection of Conductors(Circuit breaker): 240-3

From the 1999 National Electrical Code (the latest copy I have handy)


for my reference's 20+ years field work and 4+ years of schooling(don't hold the schooling against me I tried not to let school interfere with my education)


Kwatt

 

[Kwatt]

Voltage Drop Calc.

per NEC 210-19 (a) FPN No. 4- Conductors for branch circuits as defined in Article 100. Sized to prevent voltage drop exceeding 3 percent at the farthest outlet of power,heating, and lighting loads....



Kwatt

 

[reicherb]

Originally posted by: Kwatt
Voltage Drop Calc.

per NEC 210-19 (a) FPN No. 4- Conductors for branch circuits as defined in Article 100. Sized to prevent voltage drop exceeding 3 percent at the farthest outlet of power,heating, and lighting loads....



Kwatt

That calaulator does basically the same thing as the book I have, but the books is based no 2% voltage drop.

Since it sounds like you know what you are talking about, is it common practice to use wire heavier than 12awg in homes? I'm going to do the wiring myself and had planned to run 12awg everywhere on 15 and 20amp circuits, but maybe the longer runs need to be 10 or even 8awg? I put 6 florescent lights in my basement on a 15amp circuit and used about 60ft of wire to do so. Apparnently that circuit was too long?

Thanks for the help.

 

[Kwatt]

I'm going to do the wiring myself and had planned to run 12awg everywhere on 15 and 20amp circuits, but maybe the longer runs need to be 10 or even 8awg?

You can use 10 or 8 or whatever you need to reduce voltage drop.
If you use 10 for 50' and then reduce the wire to 12 you should use a breaker based on the rating for the 12.
If use the 10 all the way you may have a problem connecting the wire to the device. Most devices are for 12 and smaller.

For pure lighting loads there is a few exceptions that allow for smaller wire size. I don't remember what they are or know if they would apply.


When house's are being wired you can take the shortest route. When you are adding to a house the wire route is usually longer.
Tearing out walls and ceiling's to save money on wire size is a poor choice.


Kwatt

 

[Analog]

Originally posted by: reicherb
Ok, I posted here a couple of weeks ago looking for advice on home electrical. I've since bought a book with some NEC info. I'm wondering how people are able to wire houses using 14awg or 12awg wire. According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long. I don't have a huge house, but that wouldn't even make it to many of my rooms on the second floor, let alone to each light/receptical. What am I missing here? Is it common practice to run a larger wire to a junction box and then distribute the power to each receptical with a smaller wire?

How do they wire houses and still meet code?

Thanks.

the NEC does not say this.

 

[reicherb]

Originally posted by: yellowfiero

Originally posted by: reicherb
Ok, I posted here a couple of weeks ago looking for advice on home electrical. I've since bought a book with some NEC info. I'm wondering how people are able to wire houses using 14awg or 12awg wire. According to the book, a 20amp circuit using 12awg wire can only be 35' long and a 15amp circuit using 14awg wire can only be 30' long. I don't have a huge house, but that wouldn't even make it to many of my rooms on the second floor, let alone to each light/receptical. What am I missing here? Is it common practice to run a larger wire to a junction box and then distribute the power to each receptical with a smaller wire?

How do they wire houses and still meet code?

Thanks.

the NEC does not say this.

It may not specifically say that, but in order to only have 2% voltage drop, apparently those are the restrictions.