An electrical sub panel, also known as a service or circuit breaker sub panel, is a system of separate breaker panels distributing power to electrical circuits. It is in effect a mini service panel, situated between the main service panel and the electrical circuits at a property.
It is similar in structure to the main service panel, with a main feed wire that splits into bus bars and circuit breakers which protect the supply system from any power overload. Wires for each separate circuit lead out of the sub panel box.
When do you need a sub panel?
Where your existing breaker in your main panel doesn’t have enough slots to add new circuits, and when you wish to add multiple circuits, a sub panel is the answer. Although it does not increase the amount of power delivered to the property, it can give far greater versatility, allowing more power outlets to be set up and additional circuits put in place in different parts of a property.
A sub panel is usually installed to provide power via a circuit to a room or part of a property that has a separate function. For example, rooms such as garages, kitchens, utility rooms or offices can benefit from their own circuit and may require more power sockets than were originally provided.
The sub panel can be sited in or near the area it services, meaning that should a breaker be tripped or there is a need to turn off the power to a particular circuit, the control panel is near to hand. The power will be run from the main panel to the sub panel through a heavier, more expensive wire, rather than through several lighter wires.
This means that less wiring is required where the required circuits are some distance from the main panel. A further advantage is that there will be less voltage drop, a decrease in voltage that happens naturally over distances when power is put through smaller wires.
Installing a sub panel
A sub panel should be installed by a qualified electrician who is able to inspect the existing power supply and confirm that it is capable of supporting further circuitry. He will also be able to assess the amount of power available and identify how much can be put through the sub panel.
He will calculate how much wattage will be required by listing the appliances to be run and the power sockets to be supplied through the sub panel. A buffer of 25% extra wattage will be allowed to cope with any voltage drop in the power feed.
He will also be aware of the restrictions in positioning the sub panel. For example it is not permitted to site the sub panel in a bathroom or where easily ignitable material may hang over it, such as in a closet or behind curtains.
Points to consider when planning for a sub panel
You need to gauge suitable power levels for any sub panels, based on the amount of electricity available. Any increase will need to be arranged with the service provider; the sub panel is merely involved in distribution of the power.
All additional breakers in the sub panel should be clearly labelled. This allows easy turning off and on of particular circuits as needed and means that if a breaker is tripped then it can be quickly identified. A minute or two spent labelling the switches will save time and frustration later on down the line.
When planning the installation of a sub panel, allow space to expand the amount of breakers in the future. This will allow the easy addition of more circuits without having to replace the sub panel with a larger one.