How To Wire a Subpanel?
How To Wire a Subpanel?
Wiring a subpanel is a standard electrical task for every homeowner. This blog will assist you in wiring a subpanel and selecting the best cables for this goal based on type, gauge, ampacity, conductor, and budget.
What is a subpanel?
The definition of the subpanel is found in the NEC, where it is known under the name small panel. This is a circuit breaker panel that is derived from the main one with the assistance of two regular circuit breakers.
The subpanel primarily serves the same functions as the main panel, with the difference only in scale. Subpanels are mainly used if the main panels no longer have space for additional circuit breakers, which, let's be honest, is the case for most houses larger than two bedrooms. Subpanels help to take the load off the main electrical circuit, prevent overloading, protect from electrical incidents, and add more circuit breakers in the specific area of the building.
A subpanel is fed through a 240-volt circuit breaker from the main panel. It is not to be confused with the second or third main panel in the building, which is fed separately. For feeding, the subpanel uses two hot bus bars from the main panel. It also has a separate ground bus bar of its own, which helps with the neutral/ground separation.
Which type of cable to use when wiring a subpanel?
When it comes to wiring a subpanel, there are many types of suitable cables to choose from.
The main recommendation for subpanels is to choose a 600V copper wire. However, even though copper works best for house applications, many will still use aluminum cables when wiring houses because they help save costs on an electrical project (on average, the savings will amount to $200-$300 per sub-panel).
Typically, you will need a 4-wire cable with a neutral separated from the ground wire. The gauge of the wire depends on the expected ampacity overviewed in the chart below:
Common types of cables used in subpanels are:
SER Cable
Service entrance SER cable is a very popular option for a subpanel. After all, subpanels are one of the main types of applications for this cable. SER is a non-expensive option that gets the job done incredibly well. No conduit is needed, even outdoors. SER is available both with copper and aluminum conductors. SER has no direct burial rating and cannot be used underground.
THHN Cable
THHN is a widely available option that works well for most subpanels. However, you need to use it in conduit. Works both indoors and outdoors. Easily pulled. Available in copper and aluminum versions. It can be used underground in conduit.
XHHW Cable
As with most applications, XHHW in a subpanel will be a more expensive and high-quality alternative to THHN. Like the latter, it should be used in conduit. Available in copper and aluminum versions. It can be used underground in conduit.
NM-B Wire
Another very popular option. Since non-metallic sheathed cable is an interior cable, it works only with indoor panels. The National Electric Code prohibits the outdoor use of the NM-B wire. NM-B Wire is only available with a copper conductor.
MHF mobile home feeder and URD cables are not the best options when wiring a subpanel. If you have decided to use aluminum, your best bets are aluminum SE, THHN, or XHHW. MHF and URD do not work for a variety of reasons. URD that does not have double ratings is not permitted to enter the building. It also does not carry a neutral wire. MHF, while allowed indoors, does not have the optimal wire assembly for subpanel uses.
An Example of The Installation of A Subpanel
The proposed example uses 60A Subpanel for 120V/240V. The breaker receives power from the two hot wires of the main panel. The neutral and ground wires from the main subpanel are connected to the neutral and ground individual terminals found in the subpanel.
Wiring a subpanel requires electrical expertise and cannot be done by a complete rookie out of safety and financial concerns. To complete the process, you will need a set of tools, including a screwdriver, a hammer, a voltage meter, a flashlight, a pair of strippers, and pliers. Other than that, you need a subpanel itself, mounting screws, cables, feeder breakers, circuit breakers, and clamps are required.
Steps Of Subpanel Wiring
- Mounting. The subpanel needs to be located approximately a foot away from the main panel.
- Route Planning For Two Hot Wires, Ground Wire, and a Neutral Wire. Make sure that the wires are routed in an organized manner, as it helps the later maintenance immensely. Chaotically routed wires will cause you problems down the road.
- Stripping Hot Wires and Attaching Them To Ground Breakers. Clamps are used to finish this process.
- Connecting Hot Wires to Hot Bus Bars. The wires are cut and stripped throughout this process.
- Connecting Neutral and Ground Wires To Their Respective Terminals. Cut and strip the wires accordingly. Make sure that the wires are tight enough at this stage.
- Connecting All Wires and Finishing.
