We had to re-wire our new kitchen and the areas of our house that were gutted for structural repairs. Of all the work that we did, I enjoyed the wiring the most. I did, however, want to make sure that everything was on the up and up, so I purchased the latest version of the National Electrical Code or NEC.
So very often a simple home owner can be flummoxed by technical jargon from contractors. This bla bladdy bla bla bla is not to code. Code? What does that mean? The National Electrical Code is really a minimum standard for electrical wiring and workmanship in the US. It is revised every three years with the next revision due out in 2008. I say it is the minimum standard because cities, counties and states can override the NEC with their own, more strict electrical code. The only way to know what code is used in your jurisdiction is to check with the building department.
Like all professions, electricians have there own phraseology which can be confusing for the non-electricians among us. Things like voltage drop, box fill, ground fault, service entrance, conduit fill, just to name a few, can leave you scratching your head. I will try to explain these things in more every day terms. Any questions regarding this should be referred to the NEC section cited. I also strongly suggest that anyone engaged in a re-wiring project on there own purchase a copy of the lastest NEC and read it throughly. There are several books explaining the residential sections of the NEC available as well. I do not condone or recommend non electrical workers to attempt to re-wire their houses, if you don’t understand what you are doing, it is time to call a professional.
The Basics
The electrical service entrance for a house is where the electric meter is located. This feeds the electrical panel, or service entrance panel. The size of the service entrance panel is determined by the size load, or amount of power, the house is calculated to need. These calculations are done in Volt Amps which is nearly the same thing as Watts.
Load calculation
General load for every 1 square foot of floor space is 3 VA. Example: The total square footage of the house is 1525 SqFt x 3 VA = 4,575 VA. (NEC 220.82). The General load includes things like lamps, radios, televisions, kitchen appliances, etc.
Kitchens require the most circuits of any room in the house. Each kitchen is required to have two 20 amp appliance circuits to feed the counter top receptacles only (NEC 210.52). Those are calculated at 1,500 VA each, therefore 1,500VA x 2 = 3,000 VA. (NEC 220.82)
Other loads in the kitchen are electric range, typical 7,500 VA (each range is different, all ranges will have a name plate with the maximum load specified in Watts which can be as high as 15,000 watts or VA). Dishwasher, typical 1,200 VA, clothes washing machine, typical 1,500 VA, clothes dryer, typical 5,000 VA. (NEC 220.82)
A separate 20 amp circuit is needed for the refrigerator and if you have one of those whole house central vacuums installed, that should be on its own 20 amp circuit as well. (NEC 220.82) Those two loads are 1,500 VA x 2 = 3,000VA. Those circuits are heavy loads. Other appliances that require separate circuits are garbage disposal, built in microwave oven, trash compactor, stand alone freezer, and anything with a 1/2 HP or bigger motor. When they are run on separate circuits it will prevent circuit breaker trips and dimming lights when the appliance turns on.
Other non-kitchen house loads include electric hot water heater, typical 4,000 VA, well pump, typical 1,500 VA. Each bathroom is required to have a 20 amp circuit, so if the house has two bathrooms that would be 1,500 VA x 2 = 3,000VA. (NEC 210.11)
Heating and cooling loads are based on the size of the heating or cooling appliance. Each appliance will have a name plate rating. If the house is using electric base board heat, each base board unit has a rating. Example, there are 4 2,000 watt base board heaters and 1 1,200 watt baseboard heater, so the heating load would be 9,200 VA. Heat pumps and AC units need to be calculated by there name plate rating as well. If the house has an oil fired furnace that will require one 15 amp circuit to run the burner and circulator pumps or air blowers.
Next step, add all of the general loads together:
| Load | VA |
| General lighting | 4,575 |
| Kitchen Appliance | 3,000 |
| Electric Range | 7,500 |
| Dishwasher | 1,200 |
| Clothes Dryer | 5,000 |
| Clothes washer | 1,500 |
| Refrigerator | 1,500 |
| Central Vacuum | 1,500 |
| Heating (non-electric heat) | 1,200 |
| Bathroom | 3,000 |
| Hot Water Heater | 4,000 |
| Well Pump | 1,500 |
| Total | 35,475 |
To convert that load to Amps, we refer to ohms law which states: P = I x E where P is the power in watts (or in this case VA), I is the current in Amps and E is the voltage. Most incoming residential service voltage is 240 volts, so divide 35,475 VA by 240 volts which results 147 Amps. (NEC 220.82C) Therefore the minimum service panel for this house should be 150 amps.
Circuit breakers
Minimum required wire size for circuit breaker (copper wire) (NEC 240.3):
| Minimum Wire Size (AWG) | Breaker size (Amps) |
| 14 | 15 |
| 12 | 20 |
| 10 | 30 |
| 8 | 40 |
| 6 | 50 |
| 4 | 60 |
(AWG stands for American Wire Gauge)
Outlets or receptacles
All living areas must have an outlet placed so that no point measured horizontally along the floor line is more than six feet from any receptacle. (NEC 210.52) This is because most lamps, Televisions, radios, etc have six foot cords and extension cords should not be used.
Kitchen counter tops must have receptacles installed so that no point along the wall line is more than 24 inches from any receptacle. (NEC 210.52) This is because all kitchen appliances come with 2 foot cords.
Arc Fault Circuit Interrupter (AFCI) circuits are required for receptacles installed in all bedrooms. (NEC 210.12)
Ground Fault Circuit Interrupter (GFCI) circuits are required for receptacles located in kitchens, bathrooms, unfinished basements, outdoors, garages, unfinished accessory buildings, and within six feet of any sink in laundry rooms or wet bars. (NEC210.8 )
Wiring methods
All wiring including splices must be terminated in enclosures, i.e. junction boxes, breaker panels, etc. Splices shall be made with an approved splice cap or “wire nut.” (NEC 110.14)
Junction boxes must be installed so that access to wiring in the box is possible without removing any part of the house structure, e.g. no burying boxes behind sheet rock in walls or ceilings (NEC 314.19).
All boxes must be securely attached (NEC 314.23).
When cables are installed through bored holes in studs, joints or rafters, the hole must be at least 1 ¼ inches away from the nearest edge of wood member. Where this is not practical, a metal plate not less than 1/16 of an inch thick must be installed over the area of the cable. (NEC 300.4) This is to prevent nails and screws from penetrating the cable.
Cable types are NM (or non-metallic) also known as Romex and MC (metal clad) also known as BX. They are usually specified by their gauge and number of conductors, not counting the ground conductor. For example 12/2 NM wire will have two twelve gauge wires plus a ground wire in some sort of plastic sheath. 14/3 MC will have three 14 gauge wires plus a ground in a spiral metal clad enclosure.
Cables must be secured every four and a half feet and within 1 foot of each box (NEC 334.30).
The outer jacket of NM cable must be secured to the box and extend into the box at least ¼ inch (NEC 314.17)
The minimum length of all conductors, including ground conductors at all boxes is 6 inches with at least 3 inches extending outside of the box (NEC 300.14)
Only one conductor can be secured under each screw terminal (NEC 110.14)
All electrical equipment, metal boxes, cover plates, outlets, switches shall be grounded (NEC 250.134, 314.4, 404.9)
Service entrance panel
Minimum conductor sizes for entrance service (NEC 310-15)
| Copper wire (AWG) | Aluminum wire (AWG) | Rating (amps) |
| 4 | 2 | 100 |
| 1 | 2/0 | 150 |
| 2/0 | 4/0 | 200 |
A listed anti-oxidant compound must be used on all aluminum conductor terminations (NEC 110.14)
Service entrance conductors must be rain tight (NEC 230.54)
Electrical panels must be readily accessible and shall not be located in bathrooms or in the vicinity of easily ignitable materials such as clothes closets. (NEC 230.7, 240.24)
All electrical equipment, including service entrance panels must have sufficient working space around them. The depth of that space in the direction of access shall be a minimum of 3 feet, with a minimum width of 30 inches or the width of the equipment, which ever is greater. (NEC 110.26)
All grounding electrodes that are present must be bonded together to form a single grounding system (NEC 250.50) A grounding electrode consisting of one or more of the following must be installed: metal underground water pipe in direct contact with the earth for 10 feet or more; metal frame of the building; concrete encased electrodes; ground ring; ground rod or pipe driven at least 8 feet into soil; plate electrode. (NEC 250.50).
A metal underground water pipe shall be supplemented by an additional grounding electrode (NEC 250.64).
Minimum size for the grounding electrode conductor is based on the service conductor. The conductor sizes are (NEC 250.66):
| Service conductor | Ground conductor |
| Copper (AWG) | Aluminum (AWG) | Copper (AWG) | Aluminum (AWG) |
| 4 | 2 | 8 | 6 |
| 1 | 2/0 | 6 | 4 |
| 2/0 | 4/0 | 4 | 2 |
Underground wiring
Direct buried cable or conduit must have the minimum cover requirements (NEC 300.5):
| Type cable enclosure | Depth of cover (inches) |
| Direct burial (UF) | 24 |
| Ridged metal conduit | 6 |
| Non-metallic conduit (PVC) | 18 |
Underground service laterals must have their location identified by a warning ribbon placed at least 12 inches above the underground installation (NEC 300.5)
These are the minimum guide lines. There is nothing wrong with using 12/2 NM wire on a 15 amp circuit. For longer cable runs with heavy loads such as an electric range or dryer, it is good to go up one wire size to minimize the voltage drop.
update
There is no way that the entire NEC can be covered in a blog post. This is an informational post that explain some of the jargon used in the electrical industry. I did it to help the average non-electrical homeowner when talking with an electrician.
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I have a question regarding access to junction boxes. Can they be left behind kitchen cabinets. My remodling contractor has left them there and it just doesn’t seem right to me.
No. The way the current electrical code is written, no active junction boxes can be located where parts of the structure need to be removed to access the box (NEC 314.19). Examples of this would be placing dry wall, molding, carpet, etc over a box cover. I would say that placing cabinets over top of junction boxes fits that description also. As always, if you have any questions regarding this, contact a licensed electrician or the electrical inspector for your area.
The article does assume some basic knowledge of electricity. I also used the terms that most electricians or code inspectors would use. There are several books available that can explain the basics of electricity, etc.
Can I add something about the National Electric Code?
The National Electrical Code (NEC), or NFPA 70, is a United States standard for the safe installation of electrical wiring and equipment. It is part of the National Fire Codes series published by the National Fire Protection Association (NFPA). “National Electrical Code” and “NEC” are registered trademarks of the NFPA. While the NEC is not itself a U.S. law, NEC use is commonly mandated by state or local law, as well as in many jurisdictions outside of the United States. [The NEC codifies the requirements for safe electrical installations into a single, standardized source.
The “Authority Having Jurisdiction” inspects for compliance with these minimum standards.
I am wondering if “dead” wires can be capped with wire nuts in the Main Service Panel?
On my older house, someone cut the wiring at the detached garage. It seems safer to detach the wiring from the breaker and cap those there, rather than leave them live with power to the cut ends at the garage?
Thanks for the great NEC review…very helpful.
Hi Chris,
The NEC states that old wiring must be removed, however, I know many electricians that would do exactly as you are proposing, remove the wire from the breaker, label it for reuse later and securely cap it to prevent the bare ends from coming into contact with any live parts of your panel.
thanks for the response.
It will be quite another project to remove the old wiring from the box and completely out of the connected conduit etc. so I am hoping it will be acceptable to cap the wires inside the Panel.
The inspection with the City is set for Monday…so we’ll see what they have to say???
I’ll post the response if it’s okay.
thanks again for the great page Paul.
Okay, good luck with the inspection, Chris, let me know how it turns out.
Paul,
Thanks for the blog. Do you happen to know if National Electric Code requires outside electrical boxes to be labeled?
Mike
Paul,
Thanks for the blog. Do you happen to know if National Electric Code requires outside electrical boxes to be labeled?
(Do the breakers inside the box need to be labeled?)
Mike
Michael,
All breakers inside a panel need to be labeled, that is the code (NEC 225.37 among others). Is the question “Do outside breakers need to be labled “Outside breakers’? Not specifically, but they should be labeled according to purpose or location. Besides, it makes life easier if you need to do work or reset.
ELECTRICAL WORK IS NOT A HOBBY WIRE A LICENSED ELECTRICIAN
Chad,
you probably mean “hire” and not “wire” which would make more sense, unless you really didn’t like electricians.
By the by, just because a homeowner has hired a licensed electrician, does not mean the job will be done right… Best to hire a licensed, bonded electrical contractor with good references.
Hi Paul,
Ohm’s law relates voltage and current in a resistor.
When dealing with ac voltages & currents, S=I*V is the definition of apparent power (VA) and it takes into account the “real” (or “average”) power and the “reactive” power. The “real” power, P, represents the power which is used to do work and has units of watts. The reactive power, Q, represents the energy which is absorbed into magnetic fields on one half cycle and then returned on the next half cycle. (The energy could also be stored / returned using the charge in an ac capacitor, but this would be very unlikely in residential situations.) Reactive power has the units of “VAr” or Volt-Ampere reactive. P, Q & S are related like the sides of a right triangle: S*S=P*P+Q*Q
When sizing a circuit, what is important is the apparent power, VA, since the circuit needs to handle both the real (watts) as well as the reactive (VAr). Choosing a circuit only on the watts will result in too small of a circuit!
Also, I agree with your comment about licensed electricians — my house was previously owned (and worked on) by a licensed electrician. Cleaning up the code violations has kept me quite busy… Junction boxes? who needs junction boxes?
I need to know if you can run a #14 wire from switch to light that is wired on a 20 amp circuit using #12 wire for all other in the bedroom?
Hi Joe – I wouldn’t. That circuit is still protected by a 20 circuit breaker, thus if there where an intermittent short or high resistance fault, the wire still could become very hot without tripping the circuit breaker. It is better to be safe than sorry when it comes to electrical installations.
What section of the code covers removing old wiring?
Ray, Good question. I have always been told by electricians that “code” required old wiring be removed. Yet, when I looked through the 2008 code, I cannot find any section that mentions that. Perhaps it is the section on workmanlike installations. Anyway, I believe it is simply good practice to remove the old wiring
On a garage wall there are several 1900 boxes each separated by a run of conduit. Each box has two duplex receptacles in it. I always run pigtails from the main feeds to and from each box.
What NEC code mentions how the feeds should be terminated in each box? I thought I once read in the code that pigtails shall be used when tying in switches/receptacles so that the main feeds are not interrupted if a switch/receptacle has to be changed in a box. The thought was that there would be no ciruit interruption on the hot or neutrals down the line. Is what I read correct? And what code references it?
Not that I can tell. The only thing I see in the NEC about outlet terminations is “Only 1 wire allowed under a screw terminal.” (NEC 110.14) Since most outlets have four screws (2 each for hot and neutral) then the wires could be “looped” through the outlet. I think this is the most common way. You could use pigtails as well, but the wires would still need to be cut and spliced using a wire nut. I would think the circuit would need to be turned off to replace an outlet or switch no matter which method is used.
Hi Paul,
Thanks for the blog.
I bought a brand new house recently. We found that the lights in the bedroom go dimmer and brighter as the iron goes on and off while I do the ironing. I did the measurement. The drop is over 7 volts when the iron is on. I was told the outlet is 15 amps. Does the drop of voltage meet the NEC standard? How should I deal the issue with the builder? Please advice. Thanks.
I forgot to tell you that the iron is 1200 W.
Voltage drop is an interesting part of the NEC. The recommendation is that no greater than 3% voltage drop exists in all branch circuits and not more than 5% in any feeder/branch circuit combination. That being said, it is a recommendation only and not generally part of the enforceable code because the NEC does not view it as a safety issue. (NEC 210.19)
Your situation is out of the 5% range. If your normal voltage is 120, then 120 volts x 0.05 = 6 volts. Chances are you have a long run of #14 wire feeding this circuit, which is perfectly legal for a 15 amp breaker.
hi,This post is very helpful. i would like to know what the NEC says about what a homeowner can do himself before a licensed electrician is needed. can a homeowner living in his home wire his house (basement remodel) and can he add new circuits to the service panel?Thanks,
Hi Phil,
The NEC really does not specify what a homeowner can or can’t do. That is more or less up to the Jurisdiction having authority, usually the local building inspector or code enforcement officer. If you live in a small town, chances are he/they are your neighbor and you can come to an agreement. Often cases, you would need to be inspected regardless of whether you do the work or an electrician does the work.
It is best to check with your local building department.
in my bathroom my light fixture box is 1/4″ away from a water main
i live in a 4 floor condo is this to code?
thanks
When running wiring along a concrete block wall, does it have to be in conduit?
Thank You
Whne adding a circuit to a residential main panel, can you use knockouts on the rear of the panel?
Paul:
We did a whole house rewire with a licensed bonded electrical contractor, passed all City inspections. Now selling the house, a home inspection was done, some old alum. wiring was left in the attic at the eaves, it’s not hot of course. Does the NEC stipulate we must remove dead wire?
Thanks,
Cathy
Paul:
Sorry, I just read the Ray blog of Jan. 09. I’m glad someone is willing to put up with “the masses”. Thanks, Cathy
Hi Kathy,
No worries :) Removing old wire is an often asked question. I think if it is exposed, it should be removed. If it is buried in the wall somewhere, don’t worry about it.
this question would reffer to 2002 nec since the permit was pulled in 2004. romex in a one hr fire wall in a comercial building wood framing. INSPECTOR SAYS NO, I SAY YES. WHO IS RIGHT?
SORRY THE BUILDING FALLS UNDER 300 ACCUPANT LOAD
I am not an expert on the code, you might want to try one of the electrician’s forums. That being said, usually the Jurisdiction Having Authority (JHA) e.g. the inspector, is the ultimate judge on what is right or not. You could always ask to see what part of the code he is basing his assertion on. If he has it in his mind that the wiring should be in conduit, you might just have to do it that way.
In reply to the question about old wiring. NEC 800.2 Abandoned communications cable. Installed communications cable that is not terminated at both ends at a connector or other equipment and not identified for future use with a tag. NEC 645.2 Covers the same issue with information technology circuits. However the NEC does not make any clear rule about branch circuits for dwelling units. It is standard practice to remove any abandoned circuits not tagged or marked for future use. Remember also that excessive “dead” circuits in panels or conduit will create confusion for the next guy.
Remember to do things fair and safe just not fairly safe!
Because Romex needs to be kept 1 1/4″ from the edge of the framing member it is attached to (2 X 4 wall stud) do I need to take this into consideration in sizing the non metallic electric boxes? If they are too deep the Romex will be within the 1 1/4″ between the studs where it enters the box in the back. Thanks in advance for any advice.
Jean,
If Romex passes THROUGH a framing member, not just attached to it, the edge of the HOLE must be 1 1/4 inch from the edge of the stud, or else a nail plate should be used on the stud to prevent drywall or wall hanging fasteners from contacting the cable within the stud. Where the Romex enters the back or top of a plastic or metal outlet box is not limited by this 1 1/4 inch.
Mark
Does the code give any guidelines as to a wall heaters distance from a regular bathroom bathtub? I’m referring to a little 1000 watt flush mount wall heater. Thanks
Paul:
I recently cleaned up my furnace(oil) room and decided to replace the old power feed. The electrical panel is in the same room. The old setup was MC out of the panel to a junction box over the furnace and EMT from the junction box to another junction/emergency disconnect switch mounted to the side of the furnace. Flex ran to the motor/burner. The old conduit was bent and the wires were real old….so I ran a new circuit using MC from the panel directly to the furnace (away from anything real hot). It is secured on the furnace within several inches of the junction box and every few feet back to the panel. Is this ok? Thanks.
Paul,
We just installed a stacking washer/dryer. The intent is to make room for a utility sink in the place where the old dryer was located. Unfortunately, the 240v dryer connection is right behind where we’d want to install the sink.
Can this outlet stay where it is and just run a longer cord to the dryer (it has a 6′ one that fits OK, but can’t be neatly tucked out of the way)?
If not, can a junction box be placed in the crawl space in order to extend the run for a new outlet placed behind the new dryer location?
Thanks!
A truth-in-housing inspector recently flagged the electrical wires running power from our house to our garage. The wires are in bad shape and hanging too low. My question, which no one can seem to answer, is can we have an electrician install upgraded wiring and raise the height of the wires, or do we need to bury the wiring? This being Minnesota, our ground probably won’t be thawed enough for that until mid-April and we’d like to sell our house before then. Thanks
Greetings from Vermont; Is it against the code to put a clothes washing machine in the same room as the entrance panel? Thanks, Bob Pomykala Go Duke!!!!
Greetings from Long Island, New York.
A house inspector recently flagged that my service entrance line is Aluminum, as well as the water ground wire. Is this against the code? We never had any work done with the wiring since we purchased the house. Thank you!
Are there any NEC requirements that a #4 insulated conductor, used to bond sections of raised access flooring to a ground bar, have to be identified?
Hi
Your article lists “Minimum required wire size for circuit breaker (copper wire) (NEC 240.3)” is this for 120V circuits or does it also apply to 230V single phase circuits? It seems to me it should be perfectly legal to use 14 gauge wire for a 240V 20A drop as long as the length of the run/voltage drop does not exceed requirements, is that correct or is there some other rule that I am unaware of? Thanks
That is not correct. A split phase 240 volt circuit consists of two 120 volt circuits that are 180 degrees a part in phase relationship. A 120 volt 20 amp circuit requires a 12 gauge wire or greater. In fact any 20 amp circuit, regardless of the voltage requires at least 12 gauge wire.