March 2nd, 2010 Home Electrical Newsletter and Tips
Understanding Circuit Sizes
Hello !
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In case you missed the last email, I was discussing what to do if you have an overloaded circuit. Below is the question and answer summary, however in this newsletter I will answer the next question: What the best solution is if you have an Overloaded Circuit?
Test your knowledge and lets see if you think this is a Hazard:
If you had a circuit that was blowing a fuse or tripping breaker, do you believe that the solution is to replace the fuse or breaker with a larger size? If you just said yes then you answered incorrectly. The answer is NO. A fuse or circuit breaker should never be replaced with another of a larger size or rating.
Ok, Next Question: Do you know why should never do this?
Here’s the quick answer: Because every circuit is protected according to the SIZE and TYPE of Wire that is installed. An over rated fuse or circuit breaker would allow an under rated wire to exceeded its rated capacity which could cause an overheated condition which could lead to a fire.
Do you know what the best solution is if you have an Overloaded Circuit?
Many times an overloaded circuit is due to adding more load to the circuit, especially a new appliance such as a space heater or an air conditioner. Usually these devices come with a regular plug that will fit into an electrical outlet, but many times the manufacturer states that a isolated circuit will need to be installed usually stating what size the circuit should and the voltage. Isolated or Dedicated means a circuit that is not shared by any other device, its dedicated entirely for the appliance that you wish to operate. This applies to all areas of the home, garage or workshop.
As I have discussed above, the manufacturer’s specifications and the label which is found on the device will indicate the required voltage and watts or amperage of the circuit that is needed to operate the device safely and without causing a fuse to blow or circuit breaker to trip off.
The new dedicated circuit will then be sized according to the information given from the manufacturer. At this point the required circuit is compared to the size and types of wire that is commonly installed in the home. The circuit should not be undersized and we must understand that most electrical circuits are sized so that the load will never go above 80% of the capacity of the circuit components. The required circuit should not be oversized either because this can create a problem. Here is an example: I have an air compressor that requires a dedicated 20 amp circuit. I know that because the motor draws a lot of amperage when it starts that maybe it would be a good idea to install #10 wire which is rated for 30 amps. Well here is the problem – the outlet that I will be wiring to is a 20 amp outlet to accommodate the 20 amp plug that came with the air compressor, and it is designed for #12 wire, so if I were to try to attach #10 wire to the outlet there may be a problem where the outlet screws may be too small and this would not allow the best possible connection which could create a burnt connection in the near future.
Wire Size:
The most common general purpose home electrical circuit wire sizes are #14, and #12, then larger sizes for larger electrical loads. A wire size is selected according to the load specifications which are indicated by the device being added.
Circuit Breaker or Fuse Size:
The most common home electrical circuit breakers and fuses are available in 10 amperage increments except for the 15 amp circuit. Sizing the required fuse or circuit breaker will always be determined after selecting the wire size. Selecting the correct circuit breaker size is essential in order to protect the selected wire from an overloaded condition which could lead to overheating which could lead to a fire hazard.
Sizing the Circuit - Summary:
Determine the required load or circuit size as stated by the device manufacturer.
Select the correct wire size and type that will safely provide the required load.
Select the correct circuit breaker or fuse to protect the selected wire.
I hope this helps you understand a little more about circuit sizing.
For more information about wire type and sizes:
For more information about circuit breaker types and sizes:
Answers To Your Questions: Keep them coming, I love getting them!
Enjoy!
Dave
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