Last Updated on October 22, 2023 by Kevin Chen
Image credit Portablepowerguide
When it comes to installing electric circuits, we usually focus on the size of the circuit breakers. The right size will guarantee your circuit full protection in case of an overload or short circuit. Another important consideration is the size of the wire. There should be a perfect match between the size of the breaker and the wire.
So, what is the perfect breaker size for the 8 gauge wires? Read on as we will give you the exact answer and the explanation.
The right breaker for the 8 gauge wire
Straight to the answer: You will need a 50 amps circuit breaker for your 8 gauge wire. Actually, circuit breakers between 40 amps and 50 amps should be connected using 8 AWG wires.
How have we arrived at this circuit breaker size?
The first thing you should know is that the wire gauge is not related to circuit breakers. The size of the wire has been determined by the American Wire Gauge (AWG) standard, so you can’t compare it with the circuit breaker. By looking at the table below, you will see that for a conductor size of 8 AWG, you should use breakers between 40 and 50 amps.
How are wires sized?
Image source D& F Liquiadators
From this explanation, probably you are curious about how the sizes of these wires are determined. The sizes simply refer to the thickness of the wires. Some wires are thick while others are thin.
As we have mentioned, the wires are classified by the American Wire Gauge. It puts the wires into different classes depending on their physical radius.
In this sizing nomenclature, 40 gauge is always the thinnest wire while 2-gauge is the thickest. When it comes to using, the thickest wire will be used with the largest circuit breakers. For example, a 2 -gauge wire will be used with the 95 amps circuit breakers as the 40 gauge be used on the 15 amps circuit breakers.
How are the breakers sized?
Circuit breakers are rated in terms of amperes. So, the higher the ampere number, the higher the amp circuit breaker. This is just the opposite of what you have seen with wire sizes.
Given their function, a circuit breaker should be sized at a minimum of 125% of its operational capacity.
This implies that if your breaker is rated 40 amps, it will incessantly trip once the current in the circuit reaches 40 amps. This tends to happen whether it is a continuous or non-continuous load. And this explains why the breaker should be 125% or more than 25% of the circuit amperage.
What are the dangers of using 8 gauge wire on a larger circuit breaker?
Let’s say you want to use your 8 gauge wires on a circuit breaker rated 75 amps. Is there anything wrong with this?
Usually, it is not advisable to use smaller wires on larger circuit breakers. The main reason for this is the amount of heat that is generated when there is a current flowing through the circuit.
Using 8 gauge wires on a 75 amp circuit breaker will not just be ineffective but it is also dangerous. The reason for this is that the wire will have to handle more than double the amperage it was rated for. This translates to increased heat which will eventually cause the wire to melt and even catch fire.
For the 75 amps breaker, you will have to upgrade your wires. Maybe get a 4-gauge wire or even a 3-gauge wire. Just make sure that the wire you get is approximately 150% of the amperage rating of your circuit breaker.
How can I tell the size of the wire?
If you are not sure what gauge wire you have, it is best to measure the wire. You can do this by using a wire gauge. The wire gauge will tell you what size of wire you are using.
Using a wire gauge to measure your wires is easy and straightforward. To use the tool, simply insert one end of the tool into the cable and twist until it contacts the copper inside the cable.
The tool will display an approximate number that represents your cable’s diameter in American Wire Gauge (AWG).
Will I be able to use my existing wires for my new circuit breaker?
You might want to check if your existing wires are still compatible with your new circuit breaker. The reason for this is that some circuit breakers require specific types of wires depending on their amperage rating.
For example, if you have a 20 amp circuit breaker and you want to upgrade it with a 40 amp one, then you should upgrade your wires too as well since they are only rated for 20 amps maximum.
To do this, just check if there is an “L” or “C” in front of any amperage ratings on the package of your current wires. If there is an “L” then that means that it can only be used on 15 amp or less circuits and also some dual voltage ones like 120/240 VAC circuits and vice versa for “C”. So make sure to check before buying new ones.
Check the quality of the wires
Do not just focus on the size of the wire. You should also check its quality. When you are buying a new circuit breaker, it is important to make sure that the wires that you are going to be using are not already damaged.
To check this, just run your hands along the wires. If they feel like they are already damaged then you should reconsider buying them.
Can I use a 30 amp breaker on 8 gauge wire?
Whenever you need a stable operation of the circuit breaker, you will definitely go for a larger wire. In this case, it is clear that the 8 gauge is too large for the 30 amp breaker. The good news is there are no strict rules regarding the use of larger wires. So, you can comfortably proceed to use the 8 gauge wire on your 30 amps circuit breaker. However, take note that this is the maximum size of wire that you can use with this breaker.
I hope now you know the right breaker size for the 8 gauge wire. You will be able to use the 40-50 amp circuit breaker accordingly. In case you have any questions, feel free to ask us.
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