Correct wire sizing is very important. Especially safety-wise. One of the most common questions we get about wiring is ‘what is the wire size for a 60 amp breaker?’.
A lot of homeowners make this very common mistake: They use 6 AWG wire for a 60 amp breaker because 6 AWG gauge wire has 65A ampacity. At first hand, that seems quite reasonable, and it’s an honest mistake to make. The problem is that we run a risk of frying our 60 amp breaker if we use the 6 AWG wire.
That’s why we’ll look at how to adequately choose a wire size for a 60 amp breaker using two National Electrical Code (NEC) CODE rules.
Knowing how to determine a 60 amp wire size will help you in any kind of situation. This may range from:
- 60 amp service wire size.
- 60 amp circuit wire size.
- Copper 60 amp wires.
- Even wire size for 60 amp sub-panel 150 feet away.
The size of the wire is always the same in theory (we’ll cover how big a wire you need for a 60 amp breaker further on):
60 amp wire size is
either 6 AWG or 4 AWG wire (AWG stands for American Wire Gauge; standard wire sizing is the US) for 220V voltage. An amateur will use a 6 AWG wire size for 60 amp 220V. A professional will always use 4 AWG wire size for 60 amp 220V.
As we’ll see further on, the choice of wire size for a 60 amp breaker shouldn’t only take the ampacity of a wire into account. It’s imperative that we also use ‘Chapter 3: NEC CODE Rules and Design Practice‘ rules (specifically NEC 220-2 and NEC 310-16 rules), that include:
- 80% breaker rating rule. Maximum loading for any branch circuit is 80% of the rating of the circuit for ampacity of wire for any load.
- Account for voltage drop. The rule of thumb for voltage loss dictates that if the length of the 60 amp wire is 100 feet, we will see a 20% voltage drop. That means that 4 AWG wire will not suffice; we might have to use 3 AWG wire for a 60 amp breaker at a 100+ feet distance.
Now, if you consult the AWG gauge wire size chart here, you can see that:
- 6 AWG wire has 65A ampacity.
- Bigger 4 AWG wire has 85 AWG ampacity.
Let’s look at these two rules closely. It will help illustrate why professionals always recommend using 4 AWG instead of 6 AWG for 60 amp breakers.
Note: In the end, you will be fully equipped to size any wire (including the 60 amp breaker wire size) yourself. If you’ll have any problems, you can pose a question in the comments and we’ll try our best to help you out.
80% Breaker Rating Rule For 60 Amp Wire Sizing (1st Rule)
It’s obvious why an amateur would use a 6 AWG wire for a 60 amp breaker at 220V. 6 AWG wire has a 65A ampacity, and you only need 60 amps for a 60 amp breaker, right?
Sadly, it’s not that simple.
We need to apply the most important rule in wire sizing: The 80% breaker rating rule, according to the NEC Code. This rule is to ensure electrical safety; you don’t want to fry an electrical circuit because you choose a wire gauge that’s too small.
Here is how this rule works:
Let’s say we want to determine the wire gauge for the 60 amp breaker. This can be anything from a 60 amp hot tub wire size to a wire for 60 amp service, you name it.
60 amps is 80% of the wire size you need. That means that for a 60 amp breaker, you will need a wire that can handle at least 75 amps. Here is how you make this very important calculation:
Adequate Wire Size = 60 amps ÷ 0.8 = 75 amps
This is what all those homeowners that mistakenly use 6 AWG gauge wire for 60 amp breaker don’t take into account. 6 AWG can only handle 65 amps.
Here’s what a professional will know:
The next wire size that can handle more than 75 amps (as required for a 60 amp breaker) is the 4 AWG gauge wire. 4 AWG can handle 85 amps; that’s more than enough ampacity to adequately wire a 60 amp breaker, even accounting for the 80% breaker rule.
Note: This principle also accounts for free air and direct burial wire size calculation.
In some limited cases, however, we also use a 3 AWG wire size for a 60 amp breaker. That’s because of the 2nd NEC CODE rule:
Account For Voltage Drop (2nd Rule)
If you have a short circuit, you can freely disregard the voltage loss. However, if you have a long wire connecting to a 60 amp breaker, you have to take the voltage drop into consideration.
By disregarding the voltage drop, you can mistakenly use the regular 4 AWG gauge wire when you should, in fact, be using a bigger 3 AWG wire.
Here is the rule of thumb for voltage drop that we should be using:
For every 100 feet of wire, the voltage drops by 20%.
Some factors like the choice of wire (copper, aluminum, iron, steel, etc.) and the number of wires may influence the exact percentage loss, but this is the general rule of thumb.
That means that we should increase the amps by 20% for every 100 feet of wire if we are to get the same power output (wattage) according to the basic electric power equation:
Power (Watts) = Current (Amps) × Voltage (Volts)
Let’s use an example to showcase what a voltage drop is and how to calculate the wire size for a 60 amp breaker that’s some distance from the power source.
Example: What is a wire size for a 60 amp sub-panel 150 feet away?
Alright, using the 80% breaker rating rule, we already know that we need a wire that can handle at least 75 amps. Now, we have to add the amps in order to balance out the voltage drop.
According to the rule of thumb for voltage loss, in 150 feet of wire, we lost 30% of voltage (100 feet = 20%, 150 feet = 30% loss). That means we have to increase the amps by 30%. Here’s how we calculate the final amps:
75 amps × 1.3 = 97.5 amps
This means that a wire for a 60 amp sub-panel 150 feet away must handle at least 97.5 amps. 6 AWG wire can handle 65 amps, 4 AWG wire can handle 85 amps. In this case, due to 150 feet distance, both of these wires have a too low amperage.
We need the next wire size: 3 AWG. This wire size can handle up to 100 amps. It’s perfect in this case.
In short, the wire size for a 60 amp sub-panel 150 feet away is 3 AWG gauge wire.
Now You Know How To Determine Any Wire Size
It’s notoriously easy to make mistakes when sizing wires and it’s not uncommon to see 60 amp breakers go up in flames as a result.
With these two simple NEC CODE rules – 80% breaker rule and voltage drop rule – you can adequately size a wire like a professional.
Hope this was helpful and will help you make the right choice for the size of your 60 amp breaker.