Sub-Panels – What are They? – The Most Common Defect

Sub panels are very much like a main electrical panel, but they are subordinate to a main panel. In other words, they get their power from a main panel somewhere on the property. You’ll find sub-panels in garages, basements, next to main panels, and in condominiums. The benefit of a sub-panel is that they allow for more circuits to be added to the electrical system than the main panel can hold, and/or allows you to run one power cable to a remote location and then add circuits to the system from there. This can save on the amount of wiring that needs to be installed and gives you access to the breakers where it is needed the most.

Sub-Panels are Wired Differently!

The main difference between a main panel and a sub-panel is that the neutral wires and the ground wires are not connected together inside a sub-panel. In a main panel the neutral wires and ground wires are connected together. The neutrals and grounds are connected in a main panel so that the neutral wires are always at ground, or zero, potential. The reason they’re separated in a sub-panel is that the neutral wires carry electricity. They complete the circuit so that electricity can flow. We want ground wires to only carry electricity in the case of a defect in the system. So, if the neutral wires in a sub-panel were connected to the ground wires in the sub-panel the ground wire in the cable that brings electricity to the sub-panel from the main panel would always be carrying electricity, just like the neutral wire. This is wrong. You don’t want electricity to flow through ground wires except in the case of an emergency.

The Main Defect Found in Sub-Panels

Besides the other typical problems found inside a main panel, the main defect I see in sub-panels is that people connect the neutral wires and the ground wires inside the sub-panel. People that don’t understand how a sub-panel is supposed to be wired install them, and wire them incorrectly. This can be easily fixed if the cable supplying the sub-panel has a separate ground wire in it. If there is no separate ground wire in that cable, grounding somehow needs to be supplied to that panel, and that can sometimes be challenging.

Disconnecting a Sub-Panel for Service

Most sub-panels don’t have a main disconnect in them, but some do. If you need to work on a sub-panel you can turn off power to it in the main panel, or at the service disconnect for the property.

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