Pull four conductors to ground a subpanel within a detached building. Then, separate the grounded from the dropping bus. Although it is covered in National Electrical Code article 253.22, it is the grounding chapter’s most challenging and longest part.
The National Electrical Code requires that both main panels and subpanels adhere to specific standards (NEC). A sub-panel attached to a detached structure requires its ground rod. Three or more wires can feed it.
How to ground a subpanel in a detached building
Four conductors are required: one grounded (neutral), two ungrounded, and one grounded (hot). The grounded (neutral), and grounding buses must all be disengaged from the sub-panel. A GFCI breaker is only required on the main panel if your local code allows it. A grounding electrode system must be installed at the second structure.
Grounding of a Subpanel by Conditions
Any 250.52(Grounding electrodes must be connected to form a grounding system.
A grounding electrode must be installed if there is none. The 250.32(A) grounding electrode exemption applies to any structure or building connected by one branch circuit, individual or multiwire.
The Reasons for the Separation Of Grounds and Neutrals
When ground and neutral are connected, the current can travel on neutral and ground back to the main panel. If the load is too heavy and neutral and the ground is bonded, current can flow through all related items to the sub-panel (enclosures, ground wires, pipes, etc.) and back to the main panel, which is dangerous.
NEC Article 250.32B(1) states that a feeder or branch circuit serving a separate structure or building must have an equipment grounding conductor. An EGC could be wire or any other wiring method listed in section 250.118. It must be sized according to the 250.122 if it is wire.
One exception allows the grounded conductor of feeders/branches to be used for dropping at other buildings or structures. The circuit that powers a building does not include an EGC. A second reason is that continuous metallic routes do not connect the feeder source and the destination.
Grounding System for Separate Structures
A ground wire is not required in the cable that supplies electricity to the panel. The subpanel’s separate structure must have a GES (or Grounding Electrode System) installed. The NEC 250.66 Table must be used to size the remote panel’s grounding conductors.
The ground system of the detached building must be connected to the neutral and ground at the panel. Article 225.31 of NEC states that the main breaker must also be placed if there are more than six Circuit Breakers within the sub-panel.
Ground Rod for a Subpanel
Grounding electrodes are required for all detached building sub-panels. Whether you need two or one will depend on the soil conditions and local codes.
Grounding Rod for Subpanels within the Same Building
In all cases, a ground wire must be run from the main panel to each sub-panel. It doesn’t matter how far it’s being run, no matter if you’re running it to an outbuilding or up a lift. Without a ground, you’ll be exempt from the code.
Specific bonding and grounding regulations must be followed for any buildings or structures served by feeders or branch cables. Grounding electrodes are not required unless the construction or installation is powered by one branch circuit that meets the requirements of 250.32 (A).