Minimum wiring required if electricity serves that detached structure

The minimum wiring required in a detached garage, that has electricity installed to the structure, would include switches at the service [human] door to control a light inside the structure, Article 210-70-A-2and a light serving the stoop outside the garage service door. Vehicular doors of a garage are exempt from any lighting requirements. A minimum of one GFCI protected receptacle somewhere inside the attached garage is also required. Article 210-52 Article 210-8-A-2The light that is installed to serve the inside of the garage, and controlled at the service door may be wired as a three way switch { two switches controlling the same lighting } to serve as any second switch located at a second service door controlling the same light. You may decide on an option to install two lights inside the garage, one inside light controlled at the service door and the second inside light controlled at the garage’s second service door. The first option { using a three way switch serving the same light } is the most common choice to reduce confusion in switching systems and a possible reduction in wiring cost. Any second switch at any second service door is only voluntary and not required to meet minimum safety standards. There is an exception available considering the stoop light. If you have a dusk to dawn light that is always on automatic such as a photo cell, then that dusk to dawn light may serve as that garage stoop light if that dusk to dawn light is left in automatic control and if that dusk to dawn light also lights that stoop area outside the garage service door. Article 210-70-A-2-Exception

If you desire to provide more wiring you might want to check the following electrical requirements, if present, in an attached garage:

All readily accessible receptacles in an attached garage must be GFCI protected.

Article 210-8-A-1: The following exceptions can apply, if they meet the requirements of the exceptions. If a duplex receptacle is located behind a large appliance such as a combination of any two, refrigerator, freezer, washer, gas dryer etc., making the duplex receptacle “not to be readily accessible”and if this duplex receptacle is located behind the large appliance, then the GFCI protection is not required to protect that duplex receptacle serving those two appliances. Article 210-8-A-2-Exc. 2 If a single receptacle is located behind a single appliance, and made not readily accessible, then a GFCI protection is also not required. Article 210-8-A-2-Exc. 2 If a receptacle serving that large appliance is located so that it is “readily accessible”then that receptacle must be a single receptacle, and not a duplex receptacle, and again is not required to be protected by a GFCI. Article 210-8-A-Exc. 2

If you have a washer and a gas dryer, and the receptacle is designed so that both appliances are going to be left plugged into the same duplex receptacle on a permanent basis, and this receptacle is located behind either the washer or dryer, then the GFCI protection is not required, in this particular scenario. If you have receptacles out of reach {not readily accessible} such as located on the wall or ceiling and located above approximately 8’, then the GFCI protection is not required. These receptacles would not be considered as readily accessible. If you use normal lighting fixtures that are constructed without a receptacle mounted on the fixture, then GFCI protection is not required. A light fixture with a receptacle mounted on the fixture must be GFCI protected, if readily accessible as described above. Article 210-8-A-2Any receptacle dedicated as large appliance equipment, and that is not GFCI protected will not fulfill the one receptacle requirement serving that detached garage if power is installed in that detached garaged. Article 210-8-A-2
Hazardous Locations Involving Garages

There is a statement in the NEC that says you must not have electrical wiring, or an open flame appliances within 18”of the floor because that area is considered as a Class 1 hazardous location. Article 511-3-A This NEC requirement applies only to commercial garages, not residential garages. Residential garages are exempt from this requirement. Code Mute Be careful of this rule. A detached garage may be declared by the “authority having jurisdiction”to be a commercial garage even if located in your back yard. Article 90-4 This ruling as to whether a detached garage is a commercial or a residential garage would depend on the design, size of the structure, or the apparent use of the structure, or even the master plan assigning the zoning classifications of your property.
Special Circuits and Considerations in Design

Outside receptacles, basement receptacles, and garage receptacles can be run on the same circuits if found in the same structure, and those devices can be protected by the same GFCI device. If a kitchen or a bathroom is installed in this detached garage, then these receptacles in that kitchen or bathroom must be dedicated as their own circuits. Kitchen and bathroom receptacles must not be wired on the same circuits as the garage, basement or outside receptacle circuits, not even a combination including both the kitchen and bathroom are allowed. Kitchen and bathrooms must have their own 20 amp receptacle circuits. Article 210-52-B-2 and Article 210-11-C You should refer to wiring a kitchen or wiring a bathroom, in the heading of wiring a dwelling, if you have a kitchen or bath in this detached garage.
Type of GFCI Protective Devices to Choose From

There are two forms of GFCI protective devices. You may use a receptacle style GFCI protective device, or a breaker style GFCI protective device. Both devices are designed to be installed at the beginning of the circuit to be protected, only. Do not install GFCI receptacles for more than the first receptacle on that certain circuit, just install one GFCI receptacle as the first receptacle on that circuit and then install a normal receptacle on all the rest of that circuit.

A breaker style GFCI protective device is designed to be both the overcurrent device [breaker or fuse], and the GFCI protective device incorporated as one unit, and installed in the distribution panel.

The receptacle style GFCI protective device is designed to serve as both the first duplex receptacle, and the GFCI protective device, incorporated as one unit and installed as the first receptacle on the circuit. The receptacle style GFCI protective device is designed to protect itself as a receptacle, and it is designed to also protect all receptacles located the loads side of that GFCI device installed on that same circuit coming from that same GFCI protective device located as the first receptacle on the circuit.

You might want to compare the cost factor between a breaker style GFCI protective device, and the receptacle style GFCI protective device. When you compare the difference in cost remember to price the normal breaker, and the receptacle style GFCI device compared to the breaker style GFCI protective device, and a normal receptacle as required in each wiring design you may choose. I suspect you will find the GFCI receptacle, and normal breaker to be much cheaper than the GFCI breaker. Both devices will do the job, and should meet the NEC minimum requirements. Its your choice.
Special Receptacle Configuration Designs Exempt From GFCI

If you are using a circuit that is rated 220 volts, or over 30 amp rated, or a circuit that is hard wired without a receptacle, then no GFCI protection is required.
Number of Receptacles Allowed on a Branch Circuit

Calculating the maximum number or receptacles allowed on a circuit in a garage
If you have a question as to how many receptacles are allowed on a circuit, then you may wire your dwelling’s garage by designing your general use receptacles in that garage with no more that 10 receptacles on a 20 amp circuit or no more than 8 receptacles on a 15 amp circuit. This is allowed in Article 220-13 for commercial style building or as a non dwelling design of receptacle circuits.

Actually if allowed by your Electrical Inspector you could discard the 80% rule required for continuous use on these circuits because they are really general use convenience receptacles located in a dwelling setting that should normally be considered as non- continuous use and should be allowed to be calculated at 100% of the circuits ampacity. If you discarded the 20% reduction as described for continuous use and design your receptacle circuits as residential use at 100%, then you could put 13 receptacles on a 20 amp circuit and 10 receptacles on a 15 amp circuit and still use the 180 volt amp rule calculated at 100% for residential use, instead of the 80% for continuous use design. Just consider what you plan to do in that garage and don’t install more than the 13 receptacles on a 20 amp circuit or 10 on a 15 amp circuit if you are allowed to calculate your general use receptacles in your garage at 100%. If your inspector requires the 20% reduction considering your general use receptacles, then you may install 10 on a 20 amp circuit or 8 on a 15 amp circuit using an 80% load calculation per circuit. Article 210-19
Special Design Requirements Involving Motors

Dedicated branch circuit design for motors only.

If you are utilizing motors, or other such equipment, then you would have to calculate the load on that circuit created by all motors {full load current rating}, plus any other equipment on that circuit called other loads, then add 25% of the full load current of the largest motor on that circuit, then divide that answer into either the 1,920 Va. for 12 ga., or 1,440 Va for 14 ga. for continuous use at 80%

Branch circuit conductors serving a single motor would be sized by Article 430-22 taking the full load current of that motor, and increasing that full load current rating times 125%. That answer will tell you the required ampacity of that dedicated motor branch circuit conductor then refer to Table 310-16, using the 60 degree column if smaller than a 1 awg conductor or the 75 degree column if larger than a 1 awg conductor and only if that conductor is rated at least in temperature rating of that column, to obtain the minimum size of the conductor required. Article 110-14-C. Remember the ampacity of a circuit is rated by the smallest ampacity associated to that conductor. Also remember that Article 240-3-D is not exempt from consideration of its ampacity limitations of 14 amps on 14 awg, or 20 amps on 12 awg or 30 amps on 10 awg because if other loads are added to this motor circuit the exemption found in Article 240-3-D would not be allowed to be used. This exemption is for motors, only .

If you have more than one motor, or motors and other loads on that feeder circuit, then just take the largest motor’s full load current, and add 25% to that motors full load current, then add the connected load of utilization equipment, or full load current of each additional motor added onto that feeder circuit. The total amps you come up with would be the ampacity requirement of the conductor serving as that feeder circuit. Article 430-24 Also remember that using 15 or 20 amp circuits, when installing motors or motors and other loads or more than one motor on a branch circuit, no one motor may be sized in amps more than 50% of the total ampacity of that branch circuit. Article 210-23-A Remember, also, that for dwelling premises you are not allowed to install lighting on any circuit larger than 15 or 20 amp circuits. Article 210-23-B & C For single circuit motors only on a certain circuit, also remember that Article 240-3-D is exempt from consideration of its ampacity limitations of 14 amps on 14 awg, or 20 amps on 12 awg or 30 amps on 10 awg because motors are the when otherwise specifically mentioned in the Code. When dealing with motors you may use the actual ampacity rating found in Table 310-16 which is a bit higher in ampacity ratings for these smaller conductors. Remember these higher ampacity ratings found in Table 310-16 concerning these conductors are only valid if these conductors are used as a branch circuit conductor carrying a single motor that has an overload built into that motor, or is with a separate overload protection device designed for motors. Most single phase motors contain a built in overload protective device as required in Articles 430-32 and 430-34. Check the name plate of the motor, and you should find a block on that name plate that says thermal protection with a “T”in that block on the name plate, or check to see if that motor has a red reset button on that motor. If so, then you have a thermally protected motor. For circuits with more than one motor or motors, and other loads on the same circuit, 14 Ga. is good for 15 amps and 12 Ga. is good for 20 amps and 10 Ga. is good for 30 amps and 8 Ga. is good for 40 amps. Article 240-3-D

A single motor load using the larger ampacity of conductors 14 Ga.,12 Ga, or 10 Ga found in Table 310-16., would be air compressors, drill presses, small wood planers, table saws, etc.

An arc welder would usually be rated at 60 amp, and does not have any 120 volt loads on that arc welder unit. Therefore a 6 Ga. Romex with an equipment grounding conductor containing a black, white and bare conductor in that cable would fulfill the needs for that welder. No neutral would be used. Most wire style welders are much smaller in amp loads. Check you wire style welder such as a mig or tig for the amp rating on its name plate, and whether it has any 120 volt loads on that machine requiring a neutral conductor in its feeder. You can now find available a wire welder that is 240 volt rated with no 120 volt equipment in that machine that also requires only a 20 amp 240 volt circuit. A 20 amp breaker with 12/2wGrnd Romex installed as the garage wiring may be all that is needed for this type of wire welder. Just check your name plate, checking amp rating, and if 120 volt equipment is in that machine to decide what branch circuit size, and conductor is required.

A thought for future, if you build a detached garage try to keep in mind that you would often find yourself working just outside the overhead door in the driveway with you welder, or even hand tools requiring 120 volts. You might want to install your welder plug, and or a 120 volt GFCI protected convenience receptacle at your overhead door for this work practice, that you might be doing outside your garage.
Another thought, if you have a welder, that you may weld both inside and outside, and if your garage is large enough to make distance a consideration limiting your welder cord length, then a trick of the trade may be used. An article in the code allows you to install two welder plugs in opposite ends of your garage, and install both welder plugs on the same 60 amp circuit for an arc style welder, or even a 240 volt wire welder that is 20 amp rated. The reason you can do this is that you most likely would only have one welder, and one person welding. This should be considered as a non-coincidental load as referred in Article 220-21 allowing both welder plugs on the same circuit without consideration of making those two welder plug locations bigger but just considering them as one welder load as an either or scenario. Just an extra thought for you to ponder.
Form of Disconnect Required for Motorized Equipment

Please keep in mind that the Code requires a form of disconnect on all equipment. Article 422-30 There is an exception allowing the breaker of a panel to serve as a disconnect if that breaker is within sight. Article 422-31-B If you were to research, you should find the definition of “in sight”is only if you can see the breaker at that motor, and only if that motor is within 50’of the breaker. Both requirements must be met to be considered as “within sight”. Article 100

A receptacle may serve as a form of disconnect, {if it is not a convenience style duplex receptacle, example would be a twist lock receptacle or a 220 volt style receptacle or a single receptacle located behind the equipment making that receptacle not readily accessible}.

A non-fused disconnect may serve as a disconnect Article 422-30, if the circuit is protected at the beginning of the circuit by an overcurrent device such as a fuse or breaker at the beginning of that branch circuit, and if that motor is with an overload such as a thermal device in the motor, or a red reset button on the motor. Article 240-21 A second fuse or breaker is not required on a circuit to serve as a form of disconnect, only a form of disconnect is required. Article 422-30
Wiring Style and Type of Conductors Allowed

Non-metallic sheathed cable [Romex] is an accepted wiring practice, if not subject to physical damage in garages. Article 336-4 Most inspectors will consider type NMB cable [Romex] as not subject to physical damage, if ran within a wall space, whether dry walled or not. Most inspectors will react to a type NMB cable that is ran on the front edge surface of the studs or posts. The inspector will most likely consider this wiring method to be exposed to physical damage. Article 336-6-B You might lean a ladder, or similar item against that stud or post, and be laying against the cable. This, commonly, would be considered to be exposed to physical damage. Any wiring exposed to the outside elements, weather or sun, would be required to be approved for sunlight resistance and approved for a wet location. Article 310-8-C & D This sunlight resistant rated wire will commonly have the words “sunlight resistant”written on the cable itself. If you are installing a cable or wire underground in a conduit that cable must be approved for a wet location having an initial “W”in its classification initials. Article 310-8-C If you are installing wiring as direct buried wire, then that wire or cable must have a “U”rating in its classification initials, such as UF or USE or URD. Article 310-B-1-D

If you are passing a non-metallic sheathed cable through a metal siding or wall covering, then you must use a rubber grommet or chase nipple where it passes through the metal to protected the plastic sheath of the cable from being cut by the metal. Article 336-6-B .

Designing The Service To A Detached Garage/Separate Meter Or Power Fed From The Main Dwelling?
You have several options and / or decisions to make on the power source, and design, of a service to a detached structure. We might consider the power source first. You must consider the frequency of use and the amount of electrical usage before you should design the type of service you might pick to supply electricity to your detached structure. One thing that you might consider are the probability of a minimum bill sent to you each month by your serving Utility Company, if you opt to have a separate meter serving your detached structure. Most Utility Companies will charge you both a construction charge for supplying a separate service to your structure, and a minimum bill each month regardless whether you use electricity in the detached structure, that month or not. You might want to check to see if the per kilowatt charge for the detached structure, and the per kilowatt charge for your dwelling are the same. You might find a substantial increase in the per kilowatt charge for the detached structure, than what they charge for your dwelling. It may even be a commercial rate of charge per kilowatts used, and / or for a minimum bill if no electricity is used. If you opt to install a separate meter you most likely will be charged a minimum bill for that service whether you use any electricity or not for the rest of the time you own the property, or as long as you keep the electricity on the detached structure. You also should confirm with your serving Utility company whether there will be any construction cost charged to you, by them, during the installation of that Utility power source serving that new detached garage. This may be a rather substantial amount of cost involved in their construction charges for that Utility company to energize a new meter base serving that detached garage. You should confirm any questions you have with your local Electrical Inspector, and your local Utility company before you finalize the plans of your detached structure.

If you supply the detached structure from your original dwelling, then there would be no monthly minimum charge involved from the Utility company, concerning that detached garage. If you supply the detached structure from your dwelling, then you should be conscience of the load capacity of your dwelling’s service panel, and whether the dwelling’s service is strong enough to supply the detached structure considering the extra load expected to be added to that dwelling’s service. Most dwelling services will be large enough to serve a detached garage for personal use, considering it is common that very little actual sustained electrical load is actually added by the adding of that detached garage to your dwelling’s service, normally. Any construction cost would have to be absorbed by you, whether the Utility Company serves the detached structure considering construction charges that may be charged, or if your dwelling serves the detached structure.

If you are using the new detached garage for business use, then you would want to talk to your accountant about the tax advantages. Most often the accountant is reluctant to take a tax credit for a detached structure that is being served electrically from your dwelling. It is hard to defend the exact amount of electric usage tax credit when the electrical cost is absorbed into your dwelling’s total electrical cost. You might want to consider paying the minimum bill of the separate meter to use the electrical usage as a tax deduction. I am told that the separated services metered by the Utility company as two different services, would be much easier to defend a tax credit from that detached garage’s electrical usage on your commercial taxes. Please check with your accountant to help you make this decision.
Sizing the Service for Your Detached Garage

The following is an attempt to provide several scenarios involving electric usage of a detached structure. The first thing to consider is what the maximum electrical loads are planned that will truly be utilized in the detached structure at any one given time. In deciding this maximum, you must consider, truly, how many people will be using electricity in that detached structure at the same time.

You could have a total of 600 amps or more worth of individual motor loads in the detached structure, and only need a 60 amp service considering the fact that only one person would be using the equipment at a time, therefore only one motor would be used at any given time, normally. You may have 600 amps or more worth of motors, but you most likely will only be using one motor at a time if you are the only one working in the structure.

You must keep in consideration any automatic start equipment such as air compressors etc. that would likely be running at the same time you may be using a second motor to perform work. When you size the service requirements involved to serve a detached structure, you should be truthful with yourself as to the likely maximum electrical load applied to that service at any one given time frame. How many machines are you going to operate at once ? Article 220-21
Examples Described Concerning Different Service Designs For A Detached

Most people over-wire their detached garage and spend money on a service 10 times larger than is needed, then don’t have the money to install the equipment they want in the structure when they have way more than enough electricity available to run that equipment. Don’t under rate, but also don’t over rate your detached garage power supply.

Example # 1 If you are only going to have several convenience outlets in the detached structure with some lighting to see while you work but nothing else is planned, you might consider a special application allowing for a single 12 Ga. 20 amp circuit coming from the dwelling to the detached garage. This 120 volt {1 circuit} could most likely run a freezer or refrigerator and lighting and maybe one power saw or power drill etc. Most detached garages would fit in this category.

Example # 2 If you are only going to have several convenience outlets in the detached structure with some lighting to see while you work, and maybe an air compressor, and / or an electric range or welder and maybe one power tool but nothing else planned, then a 220 volt 60 amp service would probably be plenty large enough to serve this type of load, considering the intermittent usage of the equipment.

Example # 3 If you are only going to have several convenience outlets in the detached structure with some lighting to see while you work, and maybe an automatically operated air compressor and an electric range and a welder and maybe some power tools but nothing else planned, and with a couple of people working at the same time, then a 100 amp service may be required.

Example # 4 If you are only going to have several convenience outlets in the detached structure with only some lighting to see while you work, and maybe an automatically controlled air compressor and / or an electric range or welder and maybe several power tools [like planers, table saws, etc.], and two or more people running the machinery at the same time then a 200 amp service may be required.

You just have to be honest with yourself and don’t spend money on a size service that you won’t use. If you have questions the section called “Calculating the demand load part two”explaining the use of Article 220 of the NEC and showing a format to perform that calculation will tell you the minimum service size. You may even be able to have an electrician or the local Inspector calculate the minimum service size for you.

If you have question as to whether your dwelling service is large enough to serve the detached structure, feel free to call the Code Enforcement Div., in your area, or ask for an estimate from an electrical contractor, and often times they will calculate the minimum service size for you for both the dwelling with the detached structure load added to that dwelling service, or for a separate service fed detached garage. Just be able to provide the square footage, a list of the fixed equipment you have in your dwelling and the type of heat, cooking range, and type clothes dryer, and often times they will calculate the minimum service size dwelling’s service size and for your detached structure.

Please keep in mind to have available for the calculations a list of only fixed appliances and single circuits involved. Convenience outlets and general lighting is already calculated in the demand load calculation as per Table 220/3/B of the NEC in direct relationship to the type of usage and the square footage of your structure. Be sure to inform he or she that is calculating that demand load including your detached garage as to how many people will be working in that detached garage as one given time.

If you opt to supply the detached structure with the utility company serving a meter base on the structure, then you might want to refer to the link in this site referring to wiring a Service or Meter base for that service design.

Designing a Service to the Detached Garage Using a Common Service from the Main Dwelling's Service
If you opt to supply the detached structure from your dwelling’s service supply, then the following might be of some help to you.

Before you proceed further with this article. Please be informed that the white wire is either a grounded or neutral conductor. A neutral carries the unbalanced load of two hot feeders. A grounded conductor is only the return path back to the panel if only one hot conductor is served by that grounded conductor.

All grounded conductors or neutrals must be insulated and identified with a color of white or gray. Article 200-6-A

A Grounding conductor is the equipment grounding conductor or the grounding electrode conductor supplying the structure from the grounding electrode system. A grounding conductor must be identified with a color of green or be bare and without insulation. Article 250-119

An ungrounded [hot] conductor may be any color available except white, gray, green, or bare.

Special Note: A grounded conductor [is a current carrying conductor]{white or gray}(neutral or return path of a circuit) must be insulated except that section of the conductor that is isolated in free air as a duplex, triplex, or quadraplex, and is a service entrance neutral conductor on the line side of a main service rated panel. Articles 230-30 & 230-41 & 250-140 & 250-184 and many more Articles in the NEC.

A grounding conductor [is a non-current carrying conductor]{green or bare}(bonding ground or equipment ground) Article 250-119

Special Note: There are a few exceptions such as Article 547 for agricultural buildings concerning livestock requiring insulated grounding electrode conductors. Also special wiring considerations must be considered such as PVC conduit or NMC cable {UF cable} if concentrations of animal excrement are present. If you have this scenario or suspect you may have this scenario then contact your local AHJ {Electrical Inspector} to confirm your wiring style before you install wiring in that agricultural style building

Designing the Service to That Detached Garage Whether a Separate Metered System or Fed from a Common Service Of The Main Dwelling's Service
You have several options in the designs to supply power to the detached structure from your dwelling.

You should also refer to a link in this site called “WIRING A SERVICE”for details involving services, and common services, serving two or more buildings or structures. There is a detailed section included at that link providing the explanations that you may desire related to the service in the dwelling or in the detached structure or both.

Pictorial Example of One Single Circuit 120 Volt 15 or 20 Amp Branch Circuit with Overhead Conductors Supplying the Detached Structure