100 AMP wire.
Why would you need add a Sub-panel?
There are various circumstances in which you need to add up a sub-panel. A few such circumstances are cited below:
1) Running out of space on main panel:
Houses are built in a way to meet current needs. Plans regarding installation of panels does not differ to planning regarding building house. So if your main panel runs of space for circuits you may want to install a sub-panel to create some space for the additional circuits needed.
2) Proximity:
Running wires all the way from the main panel to ■■■■ and corner of the home not only makes a mess of the house but also causes a drop in voltage. The best way to avoid these issues is installation of a sub-panel. Additionally it assists you create many circuits in your desired location if you add a sub-panel.
3) Tripping the breaker:
Typically circuits draw too much current against that desired for amperage rating of circuit breaker so the circuit breaker trips. While wiring aggravates the situation in such event, installation of sub-panel placate by providing you ease as you can easily access the target sub-panel and reset it there.
4) Cost-saving:
The set-up costs substantially decrease in installing a sub-panel. Additionally usage costs are also lesser in setting up a sub-panel as power wastage due in wire is more than that in the panel.
Caution:
Your safety is a primary concern!
It is always recommended to consult a professional when working with electricity because of inherent dangers and threats posed by accidents and minor mistakes.
Setting Up sub-panel:
For any of the above reasons or some other reason you are committed to setting up a sub-panel, the next important step is the calculation of load which the sub-panel will draw. You just need to add all the inputs that will connect to the circuits on the sub-panel. In case it is given to you in watts, divide it by voltage given on service boards to convert it into amps since the main panel and sub-panel are measured in amps. Make sure that the amperage of sub-panel exceeds the load of required for all circuits and appliances which will be connected to the sub-panel.
Size of the wire:
The length and width of the wire connecting the main panel to the sub-panel is the next main consideration when setting-up a sub-panel. It is advised to use a 4-wire cable consisting of a brace of hots, a neutral and a ground wire; the last of which is to minimize risks in the event of any mishaps as it provides a safe, low resistance passage when any fault occurs in the system.
The other main factor affecting the performance of the panel is the temperature ratings of the insulation system. Friction in the wire and resultant heat generated in the wire as more current flows pushes these systems to limits. Of the multiple temperatures listed on the equipment, use the lowest one for your safety.
The last consideration is thickness of the wire. Higher temperatures ratings require a high gauge wire to minimize resistance and consequent heat to support same capacity and vice-versa for lower temperature ratings.
When deciding on the length of the wire it is advisable to use next gauge, thicker wire to accommodate greater travelling distance and avoid voltage drops. The recommended distance for this increase is when the length of the cable exceeds 50 feet.
The surroundings of the wire:
The surrounding temperatures of conductors also affect them and their ampacity. For example if the conductor works in a surrounding temperature of 85F you will need a thicker wire to support the same amperage. Usually the environmental temperatures are not significant consideration in this matter but if the conductors are in proximity of other conductors emitting heat, you either need to create some distance between them or shift to lower gauge.
Consult an Electrician:
When working with electricity, safety of the human life is utmost consideration. Even minor mistakes can be fatal not only for the operator but also for others. It is highly recommended to consult professional for accomplishing the task safely and well.
Summing-up:
Various factors affect the installation of a sub-panel including but not limited to thickness, length, surrounding temperatures and required load. The average wire gauge for in ordinary circumstances is 3AWG, subject to alteration in changed circumstances.
Hence it is important to consult a professional when working on the panels.