Usually, a ten gauge wire can handle 30 amps at 240V. 2021 Using 12 AWG THHN copper, what is the voltage drop on the wire? Thus according to the NEC, an ungrounded conductor or hot circuit with a live current must be black or red. This is where he found his passion for home improvement and a keen interest in DIY projects. Some homeowners or contractors may be tempted to use a thinner wire gauge to save costs. What happens if the wire used in the circuit is too large for the circuit breaker? So you can never be too careful, even if the wire is white until youve tested it to be sure. No, a 12/2 wire is not rated for 30 amps. Using copper and aluminum means you are using two dissimilar types of metals. (NEC 220-2). However you may see some here in Canada labeled as 220V but they are actually 240V. The mistake is understandable: #10 AWG wire has a 35A ampacity. 30 Amp Breaker Wire Size (110v,120v,240v,Single & 2 Pole) - PortablePowerGuides 30 Amp Breaker Wire Size (110v,120v,240v,Single & 2 Pole) Written by stellar in Wire Before you install the breaker, you must first select wiring of the correct size. Founded by Hubert Miles, Certified Master Inspector. This is a good question! A 30-amp circuit intends to provide power to medium-sized appliances in the home. You can use an 8 AWG gauge copper wire for a 30 amp breaker. Contractors use the following steps to identify the correct wire gauge for a particular application: Showing you how I installed a new 240v 30a circuit in my basement for my new air compressor. Reset GE Front Load Washer For Error Codes E2/E23/E31/E54. Not necessarily. For a 20 amp, you will need a 12-gauge wire. Check the owner's manual. Remember that there will be a trade-off in cost for futureproofing the electrical system this way. This situation will cause the breaker to trip frequently, and heat build-up in the conductor. This metal is a stronger conductor of electricity, which makes it a natural choice for electrical wire. A high voltage drop is not the only consequence of a long distance. This metal, however, has gotten more and. The wire size for 200 amp service is #2/0 AWG copper or #4/0 AWG for aluminum wire inside a minimum of 1.5-inch schedule 40 or 80 PVC conduit for underground electrical service. A 240-volt branch circuit supplies a resistive heating load of 10 amps. Since 25 amps are below the breakers 30-amp capacity, the breaker will not detect the overcurrent and will not trip. That's why motors larger than 2HP are wired only for 220V.BruceT. We will look at how to wire this as well as some other 240 volt circuits. What size wire for 240 volts? The wrong wire size can destroy everything you own. Its best to use eight gauge copper wires to be on the safe side. The thicker the wire, the smaller the gauge. The air compressor is rated at 15.5a and according to NEC code,. To use a 30 amp breaker, we need a wire that can handle at least 37.5 amps. Each supply wire may carry the maximum rated capacity of the circuit breaker. Furthermore, while ten gauge wires can handle up to 50 amps when naked, its advisable not to use them for such a high current. And you account for it by increasing the amperage (boosting the amps, so to speak). There are the safety considerations, the locations and the appliances themselves. However, a naked ten gauge copper wire such as a power line can handle up to 50 amps of current. Yes, the size of the wire will change with heavy-duty applications. If you are unfamiliar with electrical wire sizes, then rewiring your home is not the best DIY project for you to learn on. Additionally, certified electricians are well-versed in your local electrical codes. Wire size for 60 amps, with 240V example and 100 feet from sub panel. However, it would be best to keep in mind that this is not a rigid rule because there are a few different 240V circuits, and some require a neutral while others do not. You can not place a 30-amp single-pole breaker on a #12 AWG wire size, regardless of a residential, commercial, or industrial building. The 240-volt circuit supply is a double-pole circuit breaker. Tom Gaffey is an expert writer who currently resides in Washington D.C. Tom has a passion for real estate and home improvement writing, as well as travel and lifestyle writing. This is due to the fact that aluminum is not as powerful of a conductor as copper is. Three or four wires signify a three-phase system. The customers also consider the wire length and AWG when installing the 30 AMP circuit breaker. What Size Of Wire Do I Need For A 30 Amp 220V Circuit? What size wire you should use? Later in this article, you will learn about some factors you should consider before selecting the proper gauge wire for your home electrical project. You cant just use 30A ampacity wire for 30 amps service. There are copper wires and aluminum wires, and each requires different circuit sizes. Find many great new & used options and get the best deals for TS-30-Pre-wired TS-30 A- GO Power - Automatic Transfer Switch- or House or Boat at the best online prices at eBay! Remember that dryers require dedicated circuits, which are circuits that serve only a single fixture or appliance. These electrical appliances draw a substantial current, requiring a wire gauge capable of withstanding the current demand. You should call an electrical professional any time you have a little bit of uncertainty when it comes to electrical work. For instance, contractors use 40A and 50A circuits to operate hot tubs, hence the 6-gauge wiring. The #12 gauge wiring for a 20-amp circuit is undersized for a 30-amp breaker. link to Can You Wire Lights With 12/2 Wire? No. . The same goes for a 240V single-phase setup which needs two wires. Proper connection of wires ensures low resistance to the flow of electric current. PV Wire, Cables & Connectors; Anderson Connectors; Ring Terminals; Wiring Accessories . A 240 volt unit draws a full 240 volts and is used as a single phase circuit. Luckily, the #8 AWG wire has a 50A ampacity. If it's a multi-outlet device, we can install a 20-amp circuit to protect the #10 conductor. For a 40 amp-240 volt circuit, an eight gauge wire is best. These are the more power-hungry devices such as toasters, space heaters, large microwave ovens, and even some air conditioning units. This is known as the 80% NEC ampacity requirement. The NEC mandates that a dryer have a dedicated 30 AMP 240 volt circuit. With 50A ampacity, the #8 AWG wire is the perfect wire size for 30 amp service. This regulation protects from heat build-up in the conductor and prevents tripping the breaker when appliances turn on and generate a temporary spike in the current draw. Using a larger gauge wire rated for higher amperage than the circuit breaker is possible. If you want to give your electricians the strongest guarantee, we recommend that you provide #14/2 gauge with ground. A 30-amp 240-volt circuit can handle up to 7,200 watts of electrical power. You cannot completely ignore the voltage because you only get the wattage when you divide the watts by the volts. A 240 volt, 30 amp circuit would require 4/3 AWG wire. For a 120v breaker it takes 6.8 amps to turn on and 15 amps to trip, in a 120V circuit. But they work as expected in most cases, and only because you paired them with the correct wire size. You can install an 8-gauge wire for a 40A welder and a 6-gauge line for a 50A welder. The recommended wire gauge for a 30 amp breaker is 10 AWG. For 60 amp, the correct wire size is 4. 120 volt 30 amp wire can deliver 3,600W wattage. However, for longer runs, you should use thicker wires, such as eight gauge copper. One line of 3 phase from the utility is converted into single split phase. The intention of the wiring standards stipulated in the National Electrical Code is not to be an inconvenience but rather to improve the safety standards of the electrical systems in our homes. But that is to be expected. The correct 40 amp wire size needed to operate with a 40-amp breaker safely is an 8-gauge wire. Equal Power & Positives What is Positivity? Other circuits, such as the 120V, require a neutral wire, but a 240V circuit doesnt. https://en.wikipedia.org/wiki/American_wire_gauge, https://en.wikipedia.org/wiki/Single-phase_electric_power, How Many Amps Can 12 Gauge Wire Handle? Does that mean 240V outlets, circuits, and appliances use 10 gauge wiring? (Explained), 8-gauge wire for a 40A welder and a 6-gauge line for a 50A welder, well pump because their breakers are just 15 or 20 amps. Breakers can fail, permitting wires to melt and allowing fires to start. The exact gauge of the wire is measured in thousands of ohms. But it is also possible to run generators up to 8000 watts with a 30 AMP circuit breaker. 200 amp wire size and breaker size. The NEC requires that dryers have a dedicated circuit with a minimum of 30 amps. The distance and amperage go hand in hand. Fortunately, the guide below has all the information you need. Your feedback is greatly appreciated. This system is not foolproof. Selecting the correct wire gauge for the circuit requires more care as the amperage rating of your breaker increases. Some online calculators will ask you to specify the phase before they can calculate the wire size. Good wiring means a safe electrical system and a secure home, which is worth its weight in gold, or in this case, copper. In commercial and industrial buildings, 30-amp single-pole breakers can power 120v appliances and tools above the 20-amp outlet rating. The gauge changes in response to the amperage, not the voltage. The box with the circles on the front of the breaker box is the polarity on the breaker. Solar Lighting Controllers Wind . If you purchase copper wire, using a minimum of a 10-gauge wire is sufficient. NEC 310-16 Code. In addition, this standard is used in the measurement of wires. This system may be a residential electric supply or a small commercial electric supply. This setup consists of simpler, lightweight units with a compact design. (std. 9000 watts: When you buy a 9000 watts generator, you must use a 50 AMP circuit . Because this is the frequency most of our current devices operate on. When cutting heating cable, we use a minimum length of double the circuit module length to ensure that the cable contains at least one full module. You can use your oven for heating, your A/C unit for cooling, your clothes dryer to dry your clothes and your washing machine to wash clothes. Ampacity is a term that tells you the maximum volume of electricity a conductor can transmit. The correct wire gauge for each typical household circuit is as follows. There are specific codes you must adhere to when it comes to installing new electrical in your home. At 230 or 240 volt single phase you will draw just over 20 amps, so it should be installed on a 30 amp circuit with appropriate sized wire. 110 volt 30 amp wire can deliver 3,300W wattage. Modern standards also require electrical compliance certificates to ensure the electrical system is up to code before selling a house. As such, for a 30-amp circuit, the minimum should be ten gauge wire copper wire or an eight gauge aluminum wire. This determines what size wire for 30 amp service at a distance. Besides, it can only accommodate 30-amp receptacles if it's a single-outlet circuit breaker. Password. A Nema 6-30R has two straight, horizontally aligned prongs above its ground prong. Electricity that is not up to code is subject to all sorts of issues, including fines, to difficulty selling your home to difficulty collecting on electrical or fire-related insurance claims. 30 amp 240 volt circuit. Using a larger wire will reduce the amount of heat build-up in the conductor as the current passes through it. Approximate For 240 volt 120 volt circuits you get 240 volts at one foot when the wiring is at 240 volts. Yes. The circuit breaker installed on a circuit is of a specific size to protect a certain wire gauge. Can 14 gauge wire handle 30 amps? The proper wire size for a circuit that requires 30 Amps is 10 gauge wire. Contractors use the term Residential Voltage when they refer to single-phase power. What Size Wire Is Needed For 200Amp Electrical Service Home Inspection Insider, Southwire 25' 10/3, Type NM-B, Orange & 30 Amp Dryer Receptacle Outlet | Residential Commercial Industrial Grade, Outdoor/Indoor, https://www.youtube.com/watch?v=KSYAqQ4xyJI, Wire Gauge AWG, Amperage, Diameter Size, & Resistance Per Unit Length (https://www.youtube.com/watch?v=KSYAqQ4xyJI). Electric clothes dryers, electric water heaters, 240-volt window air conditioners: 30 amps: 10-gauge: Ranges and Cooktops: 40-50 amps: 6-gauge: Large electric heaters: 60 amps: 4-gauge: Want to know the wire sizes of other amperages? What AWG Wire Do I Need For 40 Amp Circuit? No, you cannot use 12 gauge wire on a 30 amp breaker. Eaton Crouse-Hinds series Arktite CPH plug, 7A/30A, 0.375-0.875" cable diameter, Three-wire, four-pole, Brass or copper contacts, Style 2, 1 HP/3 HP, Copper-free alum, 3-phase, Mechanical cable grip and neoprene bushing, 120-240/480 Vac Log In . A higher voltage produces fewer amps. A ten gauge wire is perfect if it is a copper wire. . Although, you can use those recommended gauges to select a suitable extension cord if you need to use these devices to run the heavy-duty application. The wire size for a 30 Amp 240 volt circuit is 10-gauge or larger because each wire and each circuit breaker may carry up to 30 amps. If you are trying to provide 120 volt service this will not work but on larger power supplies this can be very dangerous. This means they require an electrical circuit providing (2) hot wires, (1) neutral, and (1) ground wire. Wiring Gauge Chart. Thats not a #10 AWG wire since it only has 35A ampacity. Most 30 Amp tools make use of a 220V circuit, and a ten gauge copper wire is the best conductor for 30 amps or currents even as high as 35-40 amps. This is why the length is so important. 40 amp typically requires an 8 gauge wire. As you can see, the voltage wont inform your gauge selection. As well see, you shouldnt even use #10 AWG wire with 35A ampacity. Be sure to consult your local electrical codes and contact a professional if you have any questions. (State-By-State Chart), How To Convert Therms To kWh? Note: The results of this calculator are based on conductor temperatures of 75C. An old breaker not replaced in time could also cause issues. The outlet will fail if you connect a 25-amp appliance to a 20 amp or 15 amp outlet. Available with 4, 5, 7 or 10 copper conductors and in 50-, 100- and 500-foot lengths. It is not safe nor practical to run the circuit at maximum ampacity for extended periods. 18.75 x 1.25= 23.5 Amps. Privacy Policy, Maximum Ampacity 25'. They discourage the use of extension cords. The recommended wire size for a 30-amp circuit breaker is 10 gauge wire. Wire size for 100 amps, 100 feet and 150 from sub panel. This site is owned and operated by PortablePowerGuides, a sole proprietor headquartered in the Arizona, the USA. As you can see, the voltage appears in both equations. This circuit can handle up to 7,200W of electrical power. 2/0 A 200-amp breaker protects a feeder that originates in a 120/240 volt, 3 ph, 4 wire service panel in a movie theatre. A 30-amp breaker can handle a substantial amount of current before tripping the circuit. There is no such thing as the best gauge for a 240V wire at a specific distance. Since the 30-amp single-pole breaker only provides 120 volts, you can not use it to run an electric dryer. Wiring breakers and outlets is dangerous. The first wire is the conductor, which is the wire that carries the current, and the second wire, which is the neutral wire, returns the current. In short, the perfect wire size for most 30 amp services is the #8 AWG wire with 50A ampacity. Accommodates heavy machinery in commercial settings. (Lets Find Out). For a 30 amp 240V circuit, what size wire do I need? Source: NFPA 70, National Electrical Code, Chapter 9, Table 8. However, if you choose to use aluminum wires, use an eight gauge aluminum wire instead. This higher current can damage the thinner wire, melt the insulation, cause short circuits, electrical fires, and even lethal shock. 220 volt 30 amp wire can deliver 6,600W wattage. Whether or not you can use 10ga wire for something that is 160' away is another issue relating to what's called "voltage drop" and is caused by the natural resistance of the wire based on the actual load at the other end. Unless you are an electrician, where you do not have access to 220V, a 240 volt power supply is best. Use 12-gauge wire for a 20-amp circuit, 10-gauge for 30 amps, 8-gauge for 40 amps, and 6-gauge for 50 amps. However, once you get the amps, tables like the one above will take care of the rest. See more at How Many Outlets Can Run on a 20-Amp Circuit? Length of Run. Minimum, * maximum circuit length, in feet. On the back end you will want to connect the breaker. Many appliances express their energy consumption in wattage. It is sometimes cheaper to run 120V because an accessory like a lighting switch, or a fan with a 240V cord may be able to power your devices without charging. The longest wires have the most significant voltage drop because their resistance is so high. In most cases, you will need an #8 AWG wire for a 30 amp 240V circuit. Therefore, you must select the correct wire size to protect your home. This is due to the fact that aluminum is not as strong of a conductor as copper is. Do you have a project that requires a 240 volt power feed? On the other hand, heaters can run on 20A and 30A circuits. This means that if you use aluminum wire for your 30 amp 240v circuit you should purchase a minimum of an 8-gauge wire to be safe. Some older receptacles use only three wires; codes now call for four wiresblack and red hot wires, a white neutral wire, and a ground wire. Therefore, the wire size for 60 amp 220v, for example, is still 6 to 4 awg. What size wire for 240 volts. You should not use a 30-amp circuit breaker on a 12-gauge wire. This article will answer these and more questions. (4 Common Issues). That combination is never a safe one. Some questions even ask how far can you run 10 gauge wire for 30 amps? The key for 30 amp wire sizing is to account for 2 NEC codes, namely: The first step in checking what size wire you need for a 30 amp circuit is to look at the AWG wire size chart here. A ten gauge wire is perfect if it is a copper wire. When wired properly, a 30 amp circuit can handle a load at a distance of 100 feet or 150 feet. What Size Wire Do I Need For A 30 Amp 240V Circuit? What Size Wire Do I Need For 30 Amp Sub Panel 100 Feet Or 150 Feet Away? The first wire connects to the switch (left) and the second wire connects to the line (right). The NEC recommends at least a 10 gauge wire for 30-amp connections An 8 gauge wire is a perfect pick for a 30 amp service to account for the 80% NEC rule You can pick a gauge higher to account for voltage drop when the connection is a distance away So, what's the proper length, gauge, and voltage for a 30 amps connection? A 175- amp breaker protects a feeder that originates in a 277/480-volt, 3-ph, 4 wire service panel in an office building. When these two metals touch and interact with each other, they oxidize over time. Below are several reasons why you need to be very careful when selecting the right wire. Wrong. Roger Bliss Engineer / Programmer (1987-present) Author has 16.1K answers and 4.5M answer views 1 y Related How do I wire a 30 amp breaker for a water heater? In most cases, you will need an #8 AWG wire for a 30 amp 240V circuit. In fact, the type of metal you choose will likely affect the gauge size you need. Here is the screenshot from that part of the chart: The most common mistake homeowners make is this: They choose a #10 AWG wire for a 30 amp circuit. Installation of 240 volt outlets usually includes the following steps: Determining of the best location for the new 240v outlet. Each circuit breaker requires a different wire, especially as the electricity or power passing through varies. This requirement is one of the most critical indices considered in the sale of cables: the AWG, the American Wire Gauge, or simply the gauge. According to the American Wire Standard, or AWS, a 30-amp circuit breaker requires a 10-gauge minimum wire size for shorter distances. Most house hold circuits (Typically 15 - 30 amp) can safely handle95% to 100% of it's max rating - but only for an hour or so at a time.Loads that require long periods of 'on' time (like an air conditioner,ballasts, etc) should not exceed 80% to 85% of the max rated load ofthe wire/cable. These are generally the two wires that are used for all 220 volt circuits. voltage at the load. A 30 amp 240 volt circuit requires a minimum of a 10-gauge wire. Find many great new & used options and get the best deals for EATON 250 AMP 208/120 VOLT 3 PHASE 3 WIRE 30 CIRCUIT MAIN BREAKER PANEL..P-670 at the best online prices at eBay! Can I replace a 20 amp breaker with a 30 amp breaker? Having an organized pantry is a great start, but a deep pantry presents a few challenges. A 30 amp breaker requires a minimum of 10 AWG gauge copper wire. When you select your electrical wire, there is more to consider in addition to the proper gauge number. Heavy-duty applications are dangerous because the electricity they use is significant enough to melt the wires and start a fire. This calculator also calculates the voltage drop and the resulting voltage at the load. Currently, Tom resides in Washington D.C, and also working on his debut fiction novel. However, people still use the old 110/220 volt terms in . It is because of this that wires are gauged in different sizes. Please take the time to talk with your local electrical contractor to determine the safest way to utilize 14 gauge. Daffodils and tulips make their early presence known, and of course, there is your is normally viewed as the superior choice between the two metals. The choice of the wire size is irrelevant of the voltage. Part 1 Choosing The Correct Wire Size For A Dc Circuit Blue Sea Systems. 120 Volt, Conductor size (AWG or kcmil) Single Phase, Max 3% Voltage Drop*. In residential construction, a 30-amp breaker is not used for 110v 15amp or 20amp receptacles. How do I determine what wire is the current or hot wire? At the end of the day, you need to pick a wire that has a high enough gauge to match the breaker and its capacity. You can use the #8 AWG wire for sub panel 50 feet, 100 feet, and even 150 feet away. You can use this strategy for the future expansion of the circuit should additional tamper-resistant outlets be needed. Remember Me. For 4560 starting watts at 120V, you need a wire that can handle at least 38 amps. This is shown in this chart above, however different building codes use different AWG (american wire gauge) standards so these wires are not all the same. Free shipping for many products! Wire gauge refers to the physical size of the wire, rated with a numerical designation that runs opposite to the diameter of the conductorsin other words, the smaller the wire gauge number, the larger the wire diameter. Some 240-volt circuits, however, are described as 120/240-volt circuits. I've been conducting professional home inspections since 2002. If you want a conductor to carry more amps, you must secure a thicker wire with a better gauge. This includes your wire selection, and how that wire is installed. The breaker ranges from 30 to 50 amps and typically has two poles that provide 240 volts. Now you have to increase the amps by 20% on top of that to account for 100 feet distance away from sub panel: 30 Amp Wire (100 ft away) = 37.5A 1.2 = 45A Amperage. This will help reduce voltage drops and ensure a safe installation. My current county building dept requires #10 with the breaker to be 25 amp. Lets use the 2nd NEC rule to figure out 30 amp wire sizes some distance away from sub panel. You cannot use 12ga wire on a 30A breaker, 10ga is the minimum size. You check the wire sizes with 30 or more ampacity. Most heavy-duty instruments include manuals that recommend an appropriate gauge. This is the only way for you to know what size wire for 125 amp breaker. What will I get if I use an earthed conductive wire instead of a grounded wire? 120 volt 30 amp wire can deliver 3,600W wattage. Perhaps most importantly, bad wiring can lead to some major safety problems. . Why not just use the controller to control the power to your circuits? Always use the minimum 10-gauge wire on a circuit with a 30-amp breaker. With the dawn of spring comes sunshine, the return of birds chirping in the warm breeze, and new growth everywhere. The NEC, or National Electrical Code, stipulates that a circuit must only conduct current up to 80% of its rated capacity for an extended period. The wire size for a 30 Amp 240 volt circuit is 10-gauge or larger because each . What 30 amp circuit wire size do you need? This is due to the fact that aluminum is not as strong of a conductor as copper is. Wire and Cable Gauge: 8-gauge. Increase amps by 10% for 30 amp wire size 50 feet away from sub panel. What Size Wire Do I Need For A 30 Amp 240V Circuit? Typically, a 30-amp breaker is designed for heavy-duty appliances like HVACs and water heating systems. Not necessarily. . It tells us that those 30 amps have to represent at most 80% of the ampacity of the wire (copper or aluminum wire). Tankless Water Heater Wire Size Calculator: What Gauge Wire (AWG)? Two of the most common kiln firing problems that we encounter are related to mismatched voltage between the kiln and the building. This is because single-phase power frequently appears in residential settings. Check your local building codes and electrical inspection authority codes in your area. You can tell that particular wire size is correct because its ampacity matches the breakers rating. 30A circuits can use 8AWG. The wires that are inside of the 240 outlet are the same type of wire that connects to a North American Standard 240 volt circuit. Any breaker that can take 110 volts ac will also take 240 volts ac if it is double pole. How Many Amps Can A 12 Gauge Wire Handle 240 Volts. link to Can You Leave Doorbell Wires Exposed? If you were to use 8/2 wire for a 150 foot run to a shed on a 20 amp breaker, chances are you wouldn't notice the drop. air). It is important to note that all wiring must conform with NECs National Electrical Code. Get Free estimates from licensed electricians in your area today. Its excellent for powering 240-volt large appliances and carrying more current than thinner gauge wires used for lights and electrical outlets. Increase amps by 30% for 30 amp wire size 150 feet away from sub panel. Haphazard electrical work is quite common when done by amateurs and can lead to all sorts of very expensive problems. PortablePowerGuides is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. Copper is a bit more expensive, but it is a stronger metal and a better conductor. (80% NEC Code). Common sizes include 16-, 14-, 12-, 10-, 8-, 6-, and 2-gauge wire. A 4500 watt element draws 18.75 amps at 240 volts. The time that it takes for a charge to build up a negative voltage on the battery is called discharge time and it varies with a number of factors. SIEMENS 400 AMP 240 VOLT PANEL 3 PHASE 3 WIRE 30 CIRCUIT MAIN BREAKER .P-665. The importance of using the perfect wires when wiring cant be overemphasized; picking the correct wire size helps keep your electronics at home safe and protects yourself and your family from harm. For a 30 Amp-240 volt circuit, it is best to use a 10-gauge wire. This is the rating of the wire based on its resistance to current. Most laypeople have either never heard the terms Single Phase and Three Phase or they dont know what those words mean. DC Wire Gauge Calculator: What Gauge Wire (12V, 24V, 48V)? It runs the appliances that domestic circuits accommodate. Think of a wire as a pipe. air), Latent Heat (BTU/hr) = 0.69 x CFM x gr. How is it safe? For the 240V, you need two hots only. On the front end of the circuit you will want to connect the neutral to a 208/240 volt breaker and then ground or earth. The 240v breaker turns on. Any OCP installed on the secondary of this transformer should have an interrupting rating of at least this value. For longer distances, you will need a bigger wire, such as 8-gauge, to account for voltage drop over the length of the wire. Can You Use a 30-Amp Breaker on a 12-Gauge Wire? The standards resulted from experimentation on the ampacity that wires of various thicknesses could withstand before being compromised.