All You Need To Know About Commercial Sub Panel Wiring
March 1, 2021 | Cristina Dinulescu
As your business grows and expands, it’s not just the capacity of your electrical system that you have to think about, but also the efficiency of its distribution. This especially applies if you’re expanding your space, whether it’s new offices, a new wing or relocating an entire area of your business. This is where a sub panel comes in, which is a smaller service panel that serves a specific area of your business or commercial property. It usually connects to the main panel with a thick, three-wire cable, but sub panel wiring can get more complicated than that.
Before installing one, make sure you consult with a professional and experienced commercial electrician to make sure not only that you don’t overload your electrical system, but also that this is the right solution. This smaller panel is essentially a satellite circuit panel with its own breakers. It’s generally fed by a 240 volts, double-pole breaker in the main panel.
Sub Panel Wiring: Connections
Although most often the sub panel is installed to deliver power to a certain area of your business, as mentioned above, sometimes its purpose is simply to host additional circuit breakers, if there’s no more room in the main panel. In this case, the electrician may decide to install it right next to the main panel, which makes the sub panel wiring less expensive, as obviously you don’t have to run long feeder cables.
However, if it is installed in order to serve a dedicated space, then your electrician will want to install it as close to that area as possible. In this case, the feeder cable, which is a three-wire cable, is run from the main panel to the sub panel’s location.
The wires are 2 hot wires and a neutral one, but the connection also requires a ground, so the correct terminology would be a three-wire cable with ground. The two hot wires, which are also called feeder wires, are connected to the 240-volt double-pole breaker in the main service panel. These provide the power to the sub panel through two hot bus bars. The individual breakers are connected to these bars and distribute the power to the additional branch circuits.
When all connections are made, the sub panel is ready for its circuit breakers, which will branch out and deliver power to the additional circuits. Remember, the sub panel does not bring more power to your overall system, it simply distributes it, so make sure that your electrical system can support the load to begin with.
Sub Panel Wiring: Indoor vs Outdoor
The main difference between indoor sub panels and outdoor ones is that the indoor panels are not weathertight. But since they are protected from the elements, the sub panel wiring is not an issue of concern. Your electrician only needs to make sure to mount it according to local and national codes. For instance, if the sub panel is surface-mounted, it must be attached to the structure and it can’t be mounted on drywall, where it’s possible that the enclosure pulls loose.
Outdoor sub panels are weather resistance, which does not necessarily mean waterproof, which is why it’s best to install them in sheltered, shaded locations. Some codes will require that steel outdoor sub panels are bonded to a ground wire that’s connected to a nearby ground rod.
There are other requirements that need to be met when installing a sub panel, such as all wire entering the panel need to be fixed with a wire clamp or conduit, so that they can’t move, and the conduit needs to be attached to the structure in order to not pull loose. This is because movement within an electrical installation is usually a cause of faults, fire, and injury.
This is one of the main reasons why you need to find and hire a licensed, experienced commercial electrician for the job. They will know all of these requirements and best practices, as well as be up to date with the applicable codes. They’ll know to only use 600 volt copper wire for instance, or never to use an extension cord inside a sub panel. It’s not advisable to use aluminum wire inside the sub panel, unless it’s rated for CU-AL, because this type of wiring expands more than the copper does, which means higher chances to come loose.
3-Phase Sub Panel Wiring
Commercial sub panels are generally 3-phase panels, which are made for 3-pole, 2-pole and 1-pole circuit breakers. They’re also usually rated for any electrical service up to 600 volts. The commercial 3-phase panels need 3 out-of-phase hot wires, which means increased efficiency, because the average power is higher compared with single phase. Not only that, but 3-phase panels also deliver smoother or more continuous power.
Instead of two hot wires, this type of panels have 3, and these hot wires are attached to a 3-pole breaker. Then, the neutral wire is connected to the neutral busbar, while the ground wire connects to the ground busbar.
They’re not used for residential purposes because the cost is higher as well. They’re made from heavier materials, require more wires and have more complicated load factors, as well as more transformers. These panels are highly efficient and they’re used in industrial and commercial applications. They are suitable for motor applications and large area uses.