Since you made it to this page, you may already know what a gauge wire is and how it works, but in case you don’t we’ll first start off by just covering some of the basics to make sure that everyone is on board. If you aren’t interested in reading this section, you can just jump to the section that answers the question you came here to have answered. We have conveniently named all the sections so you can skim the title and find the one that best fits what you came here to achieve.
Summary: A Rule of Thumb
The typical rule of thumb that techs will usually go by is that when you have a 30 amp circuit breaker, 10-gauge wire is the right size to go with. For a 40 amp you need a 8-gauge wire size and for a 20 amp, you will need a 12-gauge wire size. The corresponding size for 60 amp is a wire gauge size 4, however there are certain important assumptions that that rule of thumb relies on – we will expand on those in the rest of this article. For 50 amps, the rule of thumb is that you need a 6 gauge wire size.
NEC wire ampacity chart table & gauge size rating from NEC 310.16
Looking for the NEC wire ampacity chart and gauge size rating tables across the internet, these are the values that we have been able to find which outlines the values in slightly great detail than the previous charts did, as per the NEC 310.16 table. If you want a simpler chart for the standard type of wire, scroll down further.
|Wire Gauge Size||167°F||194°F||140°F||167°F||194°F|
The simpler chart further down in this article is for copper wires with an ambient temperature rating of 60 ℃ or 140 ℉, which is considered as the standard. But in some cases, the suitable wire gauge for a specific ampacity will change depending on the wire used and the ambient temperature rating, as you can see from the detailed table above.
In those situations, it’s important to think about what the conductor is made of, and whether it is in fact copper or something else like aluminum. Other things like the type of load and the ambient rating of the wire as well as its termination points are other things you should be keeping in mind, as the above is only a rule of thumb.
High ambient conditions like multiple conductors as well as the allowable voltage drop should be considered so as to make sure you don’t run into any problems.
Copper is known to carry more ampacity than aluminum, that is why at the same wire gauge, it can handle more compared to its aluminum counterpart. This means if you have a 6-gauge copper wire and a 6-gauge aluminum wire, the copper wire will allow more current to flow through it.
Not only that, but wire gauges with a higher ambient temperature rating can be used at higher ampacity. This is why a 14-gauge copper wire with a 60 ℃ or 140 ℉ ambient temperature rating is suitable for a 15 amp breaker, while the same wire gauge but with an ambient temperature rating of 90 ℃ or 194 ℉ can be safely used with a 25 amp breaker.
These factors are what makes choosing the size of gauge wire to use for a 30 amp breaker not as straightforward as it seems. From the chart above, a 10-gauge copper wire with an ambient temperature rating of 60 ℃ or 140 ℉ is seen as standard in most conditions. However, you can also use a 10-gauge aluminum wire with a 90 ℃ or 194 ℉ ambient temperature rating, as well as wire gauges larger than these two sizes.
Always remember that it is fine to get a wire gauze bigger than the recommended size for a circuit breaker, but you should never use a gauge wire that is smaller for the available ampacity of the breaker.
So, what exactly is a gauge wire?
This is basically the measure of the wire diameter that you will be using and it comes in different measurements. People will usually refer to 12 gauge wire, 10 gauge wire, 14 gauge wire, 8 gauge wire and 6 gauge wire rather than referring to the actual thickness of it, where one number refers to a specific thickness.
Contrary to logic belief, the higher the number, the smaller the diameter, and the easiest way to determine the thickness of some wire you may have lying around is by using a thickness gauge, in case it is not clearly indicated on it already which thickness you are dealing with.
The reason you will want to make sure that you are using the right diameter is because the diameter determines the amount of current that can safely go through it, including the electrical resistance, and using the incorrect wire could have serious consequences, why different amounts of amps will require different diameters as well.
The unit of measure is AWG, or American wire gauge, which is the most popular measure in the US and is in fact used in more than 65 different countries. Other measures include the SWG and the IEC, the latter being the Imperial Standard Wire Gauge, which was introduced by the British Board of Trade. For this article, since most of our readers are from America, we will be focusing on AWG.
As the diameter of these wires determine how much electricity can safely be carried through them, it is obvious that not all diameters fulfill the purpose for every single machine.
Choosing the right size
A burned wire when you inspect your circuit breaker is a surprise that you do not want to get. Fortunately, this is an avoidable scenario if you know that having the right size of the gauge wire for a circuit breaker is important. The bad news is, this is something that a lot of people; they mistakenly believe that one wire is as good as any other so they attempt to make the connections themselves instead of calling for an electrician.
Anything involving breakers, such as its connections, should be taken seriously because it has to do with electricity. If you have the right components installed, you will avoid any known electric hazards and issues common to circuit breakers and faulty connections. In fact, many of these issues occur because of the wrong sized wire gauges used for the breakers. This is why it is important to know the right combination of the breaker and its compatible wire gauge sizes.
If you have a 30 amp breaker right for your air conditioner, water heater, or clothes dryer that needs to be wired but you are clueless about what size of the wire gauge is needed, allow us to help you out with not just that but also in understanding the basics involving wire gauges.
What Happens if You Use Too Small Gauge Wire?
People believe that as long as both ends of a certain wire will fit a connector, they can use it for their connections with no issue. Unfortunately, this is not the case for breakers. Those who are unaware of its importance often use too small gauge wires to connect their breakers, often because they want to save money since smaller wire gauges are cheaper.
Sadly, this only leads to costly mistakes for them.
If you use larger wires on your breaker, the only effect it will have is on your budget. This is because you ended up spending more than what you need to since larger wires cause more. It does not have an effect on your breaker nor will it cause damage to it, as it can handle the current that flows through it.
But if you use a wire gauge that is too small for your breaker, the following can happen:
- Melted Wires – the smaller the wire, the less amount of current it can handle and the higher its resistance to the flow of energy. But if the wire gauge is too small for your breaker, the current that flows through the wire is more than what it is designed to handle. Since the wire has a high resistance, heat is generated and this will eventually be enough to melt the wires.
- Performance Drops – any appliance or equipment that is connected to the circuit with the too-small gauge wire will not operate at peak efficiency. This is because it receives only a fraction of the energy it requires to run at full performance.
- May Damage Equipment – aside from affecting its performance, using a smaller wire gauge can eventually damage your equipment. Power being supplied improperly can cause them to go bust
- Can Start Fires – this is the worst that can happen when a wire gauge is too small to handle the current it receives. While circuit breakers have their own safety measures, such as tripping when it experiences an overload, this may not be enough to prevent a fire because of the wrong wire gauge used
These scenarios are totally avoidable, as long as you use the right wire gauge for a circuit breaker.
Simpler Wire Gauge Size Chart
While electrical work should ideally be handled by licensed electricians, it also helps to be personally aware of important aspects of your circuit breaker, such as the suitable wire gauge. To select the right wire gauge, professionals use different wire gauge size charts as their reference.
In the USA, the wire gauge size chart that is considered standard is the American Wire Gauge, commonly referred to as AWG. Also known as the Brown & Sharpe wire gauge, the AWG is a system that prescribes specific sizes or diameters of solid round wires, referred to as the wire gauge, to be used as electric conductors. The ampacity, or amperage capacity, is the maximum current that the wire gauges can handle.
What you should note is that the AWG numbering system does not directly represent the actual size of the wire. This means the higher the AWG number, the thinner or smaller the size of the wire and the smaller its ampacity. This is why a 2-gauge wire can carry a higher ampacity than a 14-gauge wire.
To better understand it, you can use the following chart to determine the diameter of a wire in inches and millimeters in terms of the AWG number. Whether you’re looking for 20, 30, 40 or 50 amp wire sizes, the chart below should help you out:
|AWG||Diameter (inches)||Diameter (millimeters)|
As you can see, the largest wire gauge in terms of diameter is 0000-gauge, while the smallest is 40-gauge. This means the 0000-wire gauge has a bigger ampacity than a 40-gauge wire, and this also means that the 0000-wire gauge allows more energy to flow through it.
Wire Gauge and Circuit Breaker
Now that you have a better understanding of the relationship between ampacity and the wire gauge, it is time to determine what wire gauge is suitable for specific circuit breakers.
If you have no idea where to find the amperage of your circuit breaker, look for the number on the handle of the breaker itself; this number is the maximum amperage of that breaker.
Once you find the amperage of your breaker, you can now determine what wire gauge to use. The most common wire gauge and their corresponding ampacity are:
|Wire Gauge (AWG Number)||Ampacity|
How Many Amps Can a 12-Gauge Wire Handle?
The amps that a 12-gauge wire can handle are:
- 20 for a copper wire with an ambient temperature rating of 60 ℃ or 140 ℉, which is the most common connection
- 25 for a copper wire with an ambient temperature rating of 75 ℃ or 167 ℉
- 30 for a copper wire with an ambient temperature rating of 90 ℃ or 194 ℉
- 20 for an aluminum wire with an ambient temperature rating of 75 ℃ or 167 ℉
- 30 for an aluminum wire with an ambient temperature rating of 90 ℃ or 194 ℉
Can I use 10 or 14 gauge wire on a 20 amp?
The rule of thumb is that you at least need a 12 gauge wire in order to handle 20 amps, why you would be able to use a 10 gauge, but not a 14 gauge wire. We still encourage you to refer to the detailed NEC table that we have included below when you are deciding which wire to go with.
Can a 10-Gauge Wire Handle 35 Amps?
Say you have a 35 amps breaker and a 10-gauge wire lying around. You may be wondering if this particular wire can handle that much current. It is possible but it will depend on the type of wire and its ambient rating.
Only a 10-gauge copper wire with either a 75 ℃ or 167 ℉ or 90 ℃ or 194 ℉ ambient temperature rating, as well as a 10-gauge aluminum wire with an ambient temperature rating of 90 ℃ or 194 ℉ can handle 35 Amps.
Can a 12-Gauge Wire Handle 25 Amps?
If you are wondering if your extra 12-gauge wire can also be used for a 25 amp breaker, it is possible to do so. A 12-gauge copper wire can be used if its ambient temperature rating is either 75 ℃ or 167 ℉ or 90 ℃ or 194 ℉, while a 12-gauge aluminum wire is compatible if its ambient temperature rating is 90 ℃ or 194 ℉.
Can 8, 10, 12 gauge wire handle 50 amps?
If you looked at our chart above, you can see that 50 amps hasn’t in fact been included in it, but we’re still finding that there are a lot of people out there asking the question of what the appropriate gauge wire size is for this amount of power. The truth is that 8, 10 or 12 gauge wire can’t handle 50 amps and that you will need a gauge wire size of 6 in this instance, given the same conditions that we stated earlier in the article.
What size wire do I need for 30 amps?
To answer this question, it’s important that you consider the same conditions that we previously noted with regards to ambient temperatures. The reality is that the rule of thumb is that you need a gauge wire size of 10 for 30 amps. So yes, you can use a 10 gauge wire for 30 amps, but you can’t use a 12 or 14 gauge for this amount of power as it simply cannot handle it.
Can 10 gauge wire handle 40 amps?
As you can see from our rule of thumb section, you will need a 8 gauge wire for 40 amps, why a 10 gauge wire will not be able to handle this amount of amperage.
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