Wire Type and Sizing Considerations

When a professional electrician looks at a job to wire a house or a new circuit in any structure the primary consideration in the wiring job is the size and type of wire to be used for job. The same for a plumber when looking at a job the plumber will size the pipes based on the number of gallons needed to carry the proper amount of water to its destination. If the pipe is too small then the water needed will not reach its destination. This is almost the same for electrical wire except under-sizing electrical wire is dangerous. Electrical wire carries voltage but it is the current rating of the power loads which is the primary factor in determining the size and type of wire to be used for the job. The current or amps, like the water pipe, is measured by how much flow there is in the wire. If the wire is too small and the flow too fast then wire gets hot. If it gets too hot then the insulation melts and a dangerous condition exists. If the wire runs for a prolonged period of time at a higher than rated temperature there are also corrosive effects at terminal connections. Eventually the corrosion and the excessive heat will cause the wire to become brittle. Solid wire will become brittle enough to eventually break off completely while stranded wire will lose strands one strand at a time from this effect. This causes the wire to become smaller and the heat increases. Eventually the current becomes too much for the wire and it breaks off again creating a dangerous condition. The equipment or device being supplied electricity from this wire, when it breaks, ceases to function while a live wire is hanging inside a control panel or other panel. This is why it is very important to properly size electrical wires for any type of electrical work and not to overload existing circuits in homes and businesses. Imagine a wire inside of a wall getting too hot and the insulation melting. This creates a dangerous electrical situation and also is a fire hazard.

Wire Type for the Application 

One other consideration in electrical wiring is choosing the right wire type. This usually refers to the insulation of the wire and its temperature rating. Selecting the approapiate insulation type and temperature rating is important and depnds on the environment and application of where the wire will be used. Romex is an all purpose wire almost used exclusively in residential wiring where the heat is not excessive and the wire is not subject to damage. Each specific type of wire has its own application and temperature rating and must be used in accordance with the NEC (National Electrical Code). Some wire is rated for direct burial underground while other wire is not rated for direct burial and must be used on conduit when run underground. Always refer to the NEC or your local electrical inspector for rules pertaining to the type of wire and the application.  

Wire Sizing Chart

The following chart  shows the proper wire size or wire guage ( awg ) for the desired current or amperage.

* The national electric code (NEC) specifies that the over-current protection device (breaker, fuse, or motor over-load) not exceed 15A for 14 AWG wire, 20A for 12 AGW wire, and 30A for 10 AGW wire.

Your resource for Electrical Wire Sizing

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Electricity Safety Basics

Electrical Control Panels

Electricity is a mystery to many people. Perhaps the most common reason electricity is a mystery is because it is invisible and can only be felt if touched. Something that you can feel and causes pain when touched generally causes fear in many people. At least with a hot stove we can feel the heat as our hand gets closer to the heat source but with electricity there is no warning until the wire is touched and the human body completes the circuit to ground. This causes pain and our natural instinct is to let go of the thing which is causing us pain. Additionally, another common reason electricity is a mystery to many people is that many people do not understand it. A little education about electricity goes a long ways to dissolving the mystery surrounding electricity.

Electricity Safety

Electrical safety is of the utmost importance when we are working around electricity. It is important that you shut down any electrical circuits which you are working on. As a licensed HVAC Master and Journeyman Electrician there are times when I had to work on the equipment while it was operating to solve mechanical and electrical problems with the machine. Extreme care was taken to ensure my safety from electrical shock. I remained hyper-aware of every place I touched and of my balance. Losing your balance and falling into an electrical control panel that has 460 volts can be a life ending experience. Unless you are a professional with many years of experience it is never recommended that anyone work on a live panel. Shut the power off first, lock out the switch so no one comes behind you and restores power to that circuit, and double check the circuit with a volt meter to ensure the circuit has no electricity. Additionally, also remember that some control panels can have more than one power source or the breaker or switch may be mislabeled. This is why it is important to double the circuit and control panel before touching anything inside the panel.

Electrical Accidents

Electrical Disconnect Box

A professional acquaintance was working on a rooftop air conditioning and heating package unit that was supplied by three-phase electrical power. The main electrical disconnect box has the knife blade switching mechanism in it. He threw the switch to the off position and thinking power was disconnected proceeded to open the electrical control panel for the rooftop unit. Throwing caution to the wind thinking power was not on in the unit because he had turned the disconnect switch to the off position, he began working which meant touching some of the wires in the panel. Zap! He got a surprise electrical shock and luckily he was able to pull his hand away. He got in a hurry and did not check the electrical circuit or main electrical power coming into the electrical control panel and he paid for that oversight by being shocked. After further investigation by this acquaintance, he found that one of the knife blades of the three phase power in the electrical disconnect box was stuck in the on position and had broken away from the switching mechanism. This acquaintance was very lucky considering the amount of electricity he was dealing with. 460 volts of electricity can shake you up and make you feel bad for a couple of days, albeit, it is not the voltage that is dangerous to humans but the current. The moral of this electrical accident story is that is always best practice to follow the safety rules to the T. This man was lucky and followed the rule of turning the power off but didn't follow through and double check the electrical circuit with a volt meter. The lesson and moral of the story is to never assume, always check the circuits with a volt meter!

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Prevent Home Electrical Fires

Inadequate electrical capacity is mainly due to increasing the number of devices that consume electricity in your home like new heating and cooling equipment, frost free refrigerators, clothes dryers, water heaters, electric ranges and ovens, dishwashers, and other powerful electric motor driven tools and appliances.

As you add devices to your home, the power supply may become inadequate. If you have indicators like fuses or circuit breakers tripping, or lights dimming, it’s time to carefully look at your circumstances before equipment failure, fire, or other problems arise.

- 5 Causes of Inadequate Power in Your Home -

1.Limited service panel capacity

When the overall demand from total electrical devices is greater than what the panel is able to supply, the main service panel will likely fail, frequently. Excess demand indicates that the panel rating is less than needed or the panel might be limiting capacity because it has no space left for more fuses or circuit breakers.

In either case it’s time to make a circuit map to calculate demand and compare it with the capacity of the main panel to supply. If you find the power demand is less than the capacity and there is no room for more breakers, then a sub-panel might be the answer. Conversely, if the overall demand is greater than the main panel ability to supply, then you will need a licensed electrician to install a new main panel.

2. Overloaded circuits

Another use for the circuit map is to determine if demand on the circuits are greater than the amperage rating of the circuit controlling it. It is important to note peak demands of appliances that may draw more power on starting and create a power surge that trips the breaker.

A power surge that doesn’t trip the breaker is indicated by lights dimming when an appliance turns on. Appliances that produce surges should have their own separate circuit designed to tolerate the surge.

To prevent the risk of fire do not exceed the safe amperage of the circuit. Blown fuses or tripped breakers indicate an overloaded circuit. Do not replace breakers with ones of higher amperage just because they fail. Instead run a new circuit from the main panel that is within the supply capacity.

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Ground-Fault Circuit Interrupter (GFCI)

Non-GFCI Breaker

GFCI are purchased as GFCI receptacles or special GFCI circuit breakers for shock protection and are required by the National Electric Code in locations where there exists a shock hazard because those locations generally can become wet in some way. Locations where GFCI's are required are (but not limited to):

 Ground-fault Circuit Interruper Locations

• Outdoor receptacles

• Kitchen receptacles

• Bathroom receptacles

• Unfinished basements

• Detached wired garages

• Crawl spaces

• Garages (some exemptions apply for garages)

• Receptacles permanently installed but used temporarily in construction processes

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