When you are installing appliances in your kitchen that take up a lot of power, there are generally very specific guidelines that need to be follows. One such guideline pertains to a common question: does a countertop microwave need a dedicated circuit?
The short answer to this question is yes! most countertop microwave oven do need a dedicated circuited i.e commonly a 15 amp or a 20 amp dedicated branch circuit.
However, the more detailed answer is a bit complex as having a dedicated circuit for a microwave depends on many factors i.e
- Its wattage
- Is it affixed or not?
- Are there more appliances on a general circuit?
- What does the manual recommend?
In order to answer this question in detail, we will keep the official standard and requirements in to consideration.
Branch Circuit vs Dedicated Branch Circuit
A branch circuit is simply an electric circuit that stretches from the breaker box in your house all the way to the outlets.
A branch circuit has a single breaker with one or many wall outlets.
A branch circuit can have many different appliances connected so long as the connected operating load does not exceed the amp rating of the breakers.
Dedicated Branch Circuit
A dedicated branch circuit also has a breaker but it only connects to a SINGLE appliance.
What Does the National Electric Code Has to Say?
To answer the question “does a microwave need a dedicated circuit”, the first course of actions must be to understand what the standard electric code says.
The following codes are the official National Electric Code (US).
Code in Question 210-23 Permissible Loads
The load on a branch circuit can never be higher than the ampere rating of that circuit.
1. Cord-and-Plug-Connected Equipment Not Fastened in Place
The rating of any one cord-and-plug-connected piece of utilization equipment must not exceed 80 percent of the branch-circuit ampere rating.
2. Equipment Fastened in Place
The total rating of utilization equipment fastened in place, other than luminaries (lighting fixtures), must not exceed 50 percent of the branch circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment (not fastened in place), or both, are also supplied
There are a few very important takeaways from the code 210-23 here.
Breaker Specifications Scenario 1
When designing a circuit, the total utilization of a breaker must no exceed 80% of its overall rating.
So for instance if the branch circuit has a 20 Amp breaker, then the total connected load (appliances) to this circuit should not exceed 16 amps.
Breaker Specifications Scenario 2
In case if an appliance is fastened in place, then its amp rating must not exceed 50% of the breaker rating.
Hence, if you have a 20 amp dedicated circuit for a fastened or an affixed appliance, then the amp rating of the appliance must not exceed 10 amps.
Over-the-Range and Built-in Microwaves
Over-the-range or built-in microwaves are fastened or affixed appliances. Hence they clearly fall in the second scenario.
Not only would they need a dedicated branch circuit, but you will also need to make sure that their amperage does not exceed 50% of the branch amperage.
In other words, on a 20 amp branch circuit, you will be limited to procuring a microwave that has a 10 amp current rating.
Now countertop microwaves have a certain leeway.
Since countertop microwave ovens are not necessarily fastened or affixed, they fall in the first scenario above.
In other words, a countertop microwave can utilize 80% of the branch amperage rating.
Hence, on a 20 amp branch circuit, you can get a countertop microwave oven that has a 16 amp current rating.
Whether they need a dedicated branch circuit or not is different aspect we discuss below:
So Does a Countertop Microwave need a Dedicated Circuit?
This depends upon a few things:
Read the manual. This is as simple an answer as it can be.
If the manual for your microwave says to install it on a dedicated branch circuit then stop arguing and connect it to a dedicated branch circuit!
Looking at the manual is particularly important when designing a fresh kitchen.
Of course, in many pre-built kitchens you cant just go out with a hammer and start breaking walls to build a dedicated branch circuit all by yourself.
What ‘dedicated’ here basically entails is that, when operating your microwave, make sure it is connected to a circuit that is NOT being utilized by another appliance at the time of operation.
Depends Upon the Input Power and Amp Rating
The next important consideration is the Input Power rating of the countertop microwave you have.
The input power power of a microwave oven ranges from 1100-1850 Watts. This corresponds to the current draw ranging from 9 amps to 16 amps (based on 120 volts).
A mini microwave oven that has an output power of 700 Watts draws 1100 Watts Input Power (9 amps) from the wall. A heavy duty microwave that has a 1200 Watt Output power draws 1850 Watts Input Power (16 amps) from the wall. Understanding the difference between input and output power of a microwave are important.
If you have a small microwave oven with low wattage, you can get away without using a dedicated branch circuit.
However, if you have a powerful microwave oven with a high power, then it is imperative that a dedicated circuit be used.
In View of the NEC Code Above
We have already established above that a countertop microwave oven, since it is not fastened, can be rated at 80% amperage of the total branch circuit amperage.
We also talked about the fact that power rating and the corresponding current rating dictates whether a countertop microwave needs a branch circuit or not.
Now understand that typically in US, kitchens have either 15 amps or a 20 amps branch circuits.
If you find that your microwave is utilizing about 12 amps of power, you will need at least a 15 amps dedicated branch circuit (80% of 15 is 12 amps).
If you find that your microwave is utilizing more than 12 amps and along the lines of 15 to 16 amps, you will need a dedicated 20 amps branch circuit.
Now if you have a 20 amp branch circuit but a mere 9 amp microwave oven, then you don’t to DEDICATE the circuit (unless the manual says so). You will still have 7 more amps of load that you can connect to reach the 16 amps threshold (80% of 20 amps = 16 amps).
If one day you decide that you need to affix the microwave inside a cabinet or a wall, then the entire scenario changes. Since the rule for fastened appliance changes to 50% utilization of branch circuit amperage, you will to re plan everything.
Important – Electric Codes are Different from Country to Country
It is worth noting that different countries have different electric codes on designing circuits.
These are very important to note particularly because different countries have different electric grid parameters.
For instance, US codes are primarily based on the 120 Volts wall voltage, whereas, the European codes are based on 220 Volts wall voltage.
Here we specifically answered a common question: does a countertop microwave need a dedicated circuit.
The simple answer, again, to this question is that YES, to be on the safe side, dedicate a circuit for your microwave oven.
This is particularly true if your microwave oven has a high wattage rating or if the manual specifically says so.
In any case, it is very important to look at your country’s national electric standards particularly if you are designing a fresh kitchen.