Wire size for 20 amp 100 feet2/5/2024 ![]() ![]() Air conditioner compressor and fan motors are largely inductive (magnetic) loads and have different characteristics than purely resistive circuits. NEC article 440 was added because air conditioning and refrigeration systems are different from typical loads, like lights and heaters. I know this goes against what many of you have been told and understood your entire career, but take a deep breath and read on. ![]() This means it is allowable to install this unit on a circuit breaker rated at 50 amps and a conductor rated at 28.6 amps, according to the NEC’s NFPA 70. Notice that the MCA is 28.6 amps and the maximum fuse or circuit breaker is 50 amps. Take a look at the Lennox air conditioning condensing unit tag on. These ratings on the data tag tell us exactly what minimum ampacity the circuit must be capable of carrying as well as the maximum size the circuit breaker or fuse may be able to protect the circuit against in an overcurrent condition. In air conditioning, we are given a gift by equipment manufacturers on the equipment data tags: the minimum circuit ampacity (MCA) and MOCP or max fuse/max circuit breaker rating. ![]() If any portion of the circuit utilizes non-metallic (NM) cabling - often known by the trade name Romex® - it must be rated at 60☌ (140☏) according to article 334.80 of the NEC. Keep in mind that for a circuit to have a rating above 60☌ (140☏), the wire as well as the breaker, disconnect lugs, and connection lugs in the equipment must all be rated at a temperature at or above the temperature rating being used. Of course, there are other considerations in addition to this, but it is clear the rules of thumb we often use can get us in trouble if we aren’t aware that exceptions exist and what those exceptions are. ![]() The rule-of-thumb sizes rely on the lowest allowable temperature rating of the wire in some cases, the circuit may have a higher ampacity if the insulation on the wire and the connection endpoints are all rated at 75☌ (167☏) or 90☌ (194☏).Īll of these ratings can be found in NEC (NFPA 70) Table 310.15(B)(16) in detail, but as an example, according to this NEC chart, a 6-gauge copper circuit rated at 90☌ (194☏) has an ampacity of 75 amps while a 6-gauge aluminum conductor rated at 60☌ (140☏) has an ampacity of 40 amps. Is the conductor aluminum or copper, and is the insulation rating 60☌ (140☏) or greater?Īluminum wire has a lower ampacity than the same gauge copper wire, meaning aluminum must be larger to accomplish the same ampacity job as copper wire. When we use a rule of thumb, we are missing two main areas as it relates to the conductor. What is the allowable voltage drop based on wire length? This is not dictated by the NEC but rather by the requirements of the connected load.What other thermal de-rating conditions exist? Are there multiple conductors in a raceway, high ambient conditions, etc.?.What is the ambient rating of the conductor (wire) and its termination (connection) points?.What is the conductor made of? Is it aluminum, copper, or something else?.Here are some additional factors to be considered: It’s not that simple according to National Electrical Code (NEC) NFPA 70 for several reasons. Sometimes, these general rules lead technicians to believe that if an appliance is rated for 50-amp breaker/fuse maximum overcurrent circuit protector (MOCP), you must use 6-gauge wire and a 50-amp circuit breaker. These rules of thumb are referring to the amperage capacity or “ampacity” of the conductor (wire) and are often correct. “Twelve-gauge wire is good for 20 amps, 10-gauge wire is good for 30 amps, 8-gauge is good for 40 amps, and 6-gauge is good for 55 amps,” and “The circuit breaker or fuse is always sized to protect the conductor. Note: View additional wire size charts from the list below.Many techs will repeat these rules of thumb and rely on them in all circumstances: Wire Size Chart and Maximum Amp Ratings Source: NFPA 70, National Electrical Code, Table 310.15(B)(16) SIZE Such as wire, tools, extension cords, and accessories. Search Amazon for your Electrical products The wire size chart below shows allowable ampacities of insulated conductors rated up to and includingĢ000 Volts, 60☌ through 90☌ (140☏ through 194☏), not more than three current-carryingĬonductors in raceway, cable, or earth (directly buried), based on ambient air temperature of 30☌ (86☏). The number of devices connected to the circuit usually determines how much current will flow through the wire. It is important to pick the correct size of wire so that the wire doesn't overheat. Limit that a wire can handle before damage occurs. Each wire size, or wire gauge (AWG), has a maximum current ![]()
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