Each circuit breaker is built for a specific amperage, or current strength. When it is crossed by an intensity higher than that for which it was built, the switch turns off interrupting the flow of energy and avoiding damage to the wiring. Learn to calculate the real amperage of the switch and compare it with the rated one, to avoid unnecessary power outages.
Steps
Part 1 of 3: Finding the Nominal Amperage
Step 1. Inspect the electrical panel
Each switch should indicate its own amperage value on the toggle. This number refers to the maximum current that the circuit can withstand before the circuit breaker trips.
In Italy, standard domestic circuits are rated for around 16 amps
Step 2. Multiply the nominal amperage by 0.8
For daily needs it is better not to expose the circuit breaker to a current intensity greater than 80% of the nominal value. If this limit is exceeded for short periods of time, there is no problem, but a continued intensity above this value could trip the switch.
There may be a note on the electrical panel stating that the MCB is capable of withstanding 100% of the rated amperage; if so, you can skip this step
Step 3. Learn about bipolar switches
Some devices with a high electrical potential are connected to a bipolar switch, that is, to two thermal magnetic switches that share a single lever. Do not add the amperages of the two switches, because the circuit is still interrupted when the intensity of the current reaches the value written on the single lever.
Step 4. Compare these values to the current strength of the circuit
Now you know the amperage value that the thermal breaker can withstand. To understand if the circuit exceeds this limit, read the next section of the article.
Part 2 of 3: Finding the Current Strength of the Circuit
Step 1. Find the power of the device
Choose a device connected to the circuit you are controlling. Find the power, expressed in watts (W), which is usually indicated on a plate fixed on the back or inside the device itself. This value is the maximum power of the electronic device and you can use it to calculate the amperage.
Some appliances also report the amperage on the same plate, which can be indicated with the English abbreviation FLA (full load amperes). If this is your case, you can go directly to the next section to compare the real data with the nominal one
Step 2. Check the circuit voltage
In the case of the domestic system you can assume that it is the standard one of the country where you live. In Italy and in most European countries, the electrical voltage is 230 V. If you are working on a particular system or circuit, measure the voltage with a multimeter.
Step 3. Divide the power by the voltage
The result will give you the amperage, which is the amount of electrical current flowing through the device. For example, a device with a power of 150 watts connected to a 120 volt circuit will have a current of 150 ÷ 120 = 1.5 A.
Step 4. Repeat the calculations for each device connected to the circuit
Carry out the same division for all connected devices or, at least, for those with the highest power. Write down the results along with the device names.
Step 5. Add up the amperage of the appliances that are always in operation
Consider those that are permanently on or that are on for more than two hours a day and add up the current intensity. If the total value exceeds 80% of the maximum amperage that the circuit breaker can withstand, connect one of the devices to an outlet served by another circuit.
Step 6. Add the additional amperages
In addition to the intensity of current flowing through the devices that are constantly switched on, you should also consider that of the other devices that can be put into operation at the same time. If any of the possible combinations exceeds 100% of the switch rating, it will break the circuit. You can solve this problem by wiring an appliance to another circuit or by remembering not to use very powerful appliances at the same time.
Electrical circuits never work perfectly. Part of the energy is lost in the form of heat and for this reason the devices can be traversed by a greater amount of current. In almost all domestic systems the energy dispersion is rather low (less than 10%), but it is always possible that a magnetothermic switch interrupts the circuit when the amperage actually used is slightly below the nominal one
Step 7. Measure the amperage directly using a clamp multimeter
This instrument, also called amperometric clamp, is equipped with a "vice" at the top that closes to wrap a cable. When set to detect current, the meter shows the number of amps passing through the cable on the display. To test a circuit, find the wire that carries the current load to the miniature circuit breaker. Set the multimeter to detect amps and ask a helper to turn on another electronic device in the house. If this is connected to the same circuit, then you will notice an increase in the current strength values reported on the multimeter.
Do not perform this step unless you are wearing electrician gloves and are unfamiliar with basic electrical safety rules. These cables carry electrical energy and could be very dangerous
Part 3 of 3: Reading the Nominal Amperage of a Device
Step 1. Look for the metal plate with the device data
All appliances should have a metal label on the back or base with all electrical information. If you can't find it, consult your device manual. Thanks to this information you can understand the amount of current that flows through the appliance and consequently what is the necessary amperage for the magnetothermic switch.
- This part of the article refers to appliances that report the amperage directly on the plate, including electric motors. If the device only provides the power value (W), then you need to calculate the current intensity from this information.
- This is not the most appropriate technique for setting up safety devices to protect the motor itself. The magnetothermic switch is limited to protecting the wiring.
- Very powerful appliances, such as the air conditioner and oven, should be installed by an experienced electrician.
Step 2. Check the rated current voltage of the device
The intensity of the current depends on the voltage of the appliance. The expected current voltage should be indicated on the device itself to confirm that it conforms to that of your system. If it is an appliance that works with two different voltages, both are usually reported like this: 110V / 240V. According to this example, if you have connected the device to a 110 volt electrical system, then you only need to refer to the first number listed.
- Most regulations regarding electrical installations allow a tolerance of ± 5% regarding voltage. Do not turn on a device with a voltage that exceeds this tolerance.
- Most household electrical sockets in Italy and Europe have a voltage of 220-230 V; in the United States and other countries the outlets are set to 120 V.
Step 3. Look for the FLA (full load amperes) value
This figure indicates the number of amps that pass through the motor when it absorbs a certain power. In the United States, for example, if this device is on for more than three hours a day, the circuit breaker must have a nominal amperage equal to 125% of the FLA (just multiply the amperage at full load by 1.25). In this way it is possible to obtain a higher load due to various factors, especially heat.
- The full load amperage figure could be defined in several ways, such as nominal amperage, operating amperage or even simply amps.
- Some miniature circuit breakers are built to withstand 100% of the rated amperage, which means you can avoid proceeding with the calculation described above. This information is usually clearly expressed on the electrical panel where the switch is mounted.
Step 4. Check the locked rotor amperage or LRA value
This data indicates the amount of current that is absorbed when the motor is stopped. In practice, it is the energy needed to start the engine which can be much higher than that at full load. Modern miniature circuit breakers are designed to withstand this short peak load. If the one in your possession is rated to withstand the FLA, but trips when the device is connected, there may be a malfunction in the switch itself or it is simply an old model. Connect the appliance with a high LRA to another circuit or have an experienced electrician inspect the wiring.
Do not confuse this with the RLA which is indicated on the air conditioning units
Step 5. Consider the other appliances
If there are several devices connected to the same circuit, you need to add as follows:
- If the magnetothermic switch is able to withstand 100% of the nominal amperage, then add the amperages of the various devices together.
- If the circuit breaker can withstand 80% of the rated amperage or you do not know this value, you must add the current absorbed by the instruments that operate for more than three hours a day and multiply the total by 1.25. value obtained you must add the amperage of all the other devices that remain on for a shorter period.
- In both cases, if the final value you calculated exceeds that of the circuit breaker, then you need to connect the device to another circuit.
Step 6. Consider the maximum circuit amperage value and the maximum overload protection value
This data is almost never shown on air conditioners, except in North America. The first value, abbreviated MCA, indicates the minimum safety gauge of the circuit cables. The second, abbreviated MOP, informs you about the maximum possible value of the thermal magnetic circuit breaker. When in doubt about which switch to buy, use the MOP as a reference, to avoid unpleasant and unnecessary power outages.
These values often surprise people who have little experience with HVAC systems and have been made even more complex by new technologies that allow for lower amperages than indicated by the MOP. Consider getting help from an experienced electrician if you don't have the right knowledge
Warnings
- The amperage of the switch is also limited by the material and diameter of the cable to which it is connected. To avoid dangerous connections, always follow electrical safety codes. In Italy, the body that deals with electrical and electronic legislation is the CEI.
- Always use a switch of the same brand as the general panel you are installing, otherwise the warranty will not be valid.
