Okay, let's break down the grounding requirements for your shed subpanel and address your proposed grounding plan. It's crucial to get this right for safety.

Understanding the Requirements (based on NEC - National Electrical Code)



Separately Derived System vs. Non-Separately Derived System

Because you are feeding the subpanel from an existing breaker in your main panel, this is considered a

non-separately derived system. The neutral wire is fed from the main panel, so the neutral and ground in the subpanel should be kept separate. Grounding Electrode System

Because this is not a separately derived system, the grounding electrode system does not go to the ground bus in the subpanel.

Equipment Grounding Conductor (EGC)

You must have a properly sized equipment grounding conductor (EGC) running with the circuit conductors (hot and neutral) from the main panel to the shed subpanel.

Bonding

Bonding ensures that all metallic parts of the electrical system are at the same electrical potential, providing a low-impedance path for fault current to return to the source (main panel).

Ground Rod

In addition to the equipment ground, you are required to add a grounding electrode to the subpanel enclosure and connect it to ground rods.

Analyzing Your Plan and Correcting It

Here's a breakdown of your plan and what needs to be changed to meet code:1.

3-Wire Feed and the Missing EGC

This is your biggest problem. You cannot rely on the metal conduit as the sole equipment grounding conductor. Even though it's metal, it's not a guaranteed continuous, low-impedance path. The code requires an actual equipment grounding conductor to be included in the conduit.

Solution

You must install a fourth wire (typically green or bare) inside the conduit along with your two hots and neutral. This will be the EGC. This is non-negotiable for safety and code compliance.If there is space in the conduit, this is the only way to safely perform this task.Otherwise, the best option would be to run a new conduit with 4 wires from the main panel.2.

Bonding the Conduit

Your plan to bond a bare wire to the metal conduit at the main panel end and run it to the shed subpanel is partially correct. This wire acts as a bonding jumper to ensure the conduit is bonded. However, this is NOT the equipment grounding conductor that needs to run with the circuit conductors.

The conduit should be bonded at both ends (main panel and shed subpanel).3.

Ground Rod at the Shed

Driving a ground rod is required for a subpanel located in a separate building. According to NEC 250.32, you must install an additional electrode system at the shed. If there is only one ground rod, it has to measure 25 ohms or less in order to be considered a sufficient ground. If the soil is resistive or other conditions make it difficult to get a reading less than 25 ohms, a second ground rod 8 feet away must be installed. You are correct to drive a ground rod at the shed. The rod(s) should be connected to the subpanel using the appropriate sized grounding electrode conductor.4.

Connecting the Grounding Electrode Conductor (to ground rods)

The grounding electrode conductor should be connected to a grounding bus within the shed subpanel enclosure, not the neutral bus (neutral and ground should be isolated in the subpanel).

Revised Plan (NEC Compliant)


Install a 4-Wire Feed

Run a 4-wire circuit (2 hots, 1 neutral, 1 EGC) inside the conduit from the spa panel to the shed subpanel.2.

Properly Size Wires and Breakers

Ensure all wires are properly sized for the 30-amp breaker. (Consult a wire ampacity chart).3.

Bond Conduit at Both Ends

Bond the metal conduit at the main panel end and at the shed subpanel end using grounding bushings and bonding jumpers.4.

Isolate Neutral and Ground

In the shed subpanel, isolate the neutral bus from the enclosure. Do not bond the neutral bus to the enclosure.5.

Connect EGC

Connect the green (or bare) EGC wire from the main panel to the grounding bus in the shed subpanel.6.

Install Ground Rod

Drive one or two ground rods at least 8 feet apart at the shed.7.

Connect Ground Rod(s) to Grounding Bus

Connect the ground rod(s) to the grounding bus in the shed subpanel using the appropriate sized grounding electrode conductor.

Important Considerations



Conduit as a Grounding Path

While the conduit can contribute to the overall grounding system, it is not a substitute for the required equipment grounding conductor. The EGC is the primary path for fault current.

Professional Help

If you are not comfortable working with electrical wiring, hire a qualified electrician. Electricity is dangerous, and incorrect wiring can lead to fire, electrocution, or equipment damage.

Local Codes

Always check with your local building department for specific requirements and permitting. Local codes can sometimes be stricter than the NEC.

Wire Size and Conduit Fill

Make sure the conductors you are using are correct for the breaker size (30 amps) and that the conduit is not overfilled (consult conduit fill tables).

Weatherproof Connections

Ensure all connections are weatherproof, especially at the point where the conduit enters the shed and the main panel.

In summary, you MUST run a dedicated equipment grounding conductor (EGC) with the circuit conductors. Ground rods are in addition to, not a replacement for, the EGC. Flag for review