Okay, let's break down the best options for splitting your 1000A feed into two 600A panels, considering code compliance, practical considerations, and your goal of maximizing available capacity.

Understanding the Key Considerations



NEC (National Electrical Code)

This is the primary guiding document for electrical installations. You MUST adhere to NEC requirements.

Overcurrent Protection

Each conductor must be protected against overcurrent. This means breakers or fuses sized appropriately for the conductor's ampacity.

Load Calculations

You need to know the actual expected load on these panels. Oversizing everything is costly and doesn't necessarily improve safety if it leads to inadequate overload detection.

Ampacity of Conductors

The wire you use must be rated to carry the current it will be subjected to.

Accessibility and Serviceability

The solution should be easy to maintain and troubleshoot.

Options and Analysis

Here's a detailed look at the options you mentioned and some alternatives, along with pros/cons and code considerations:

1. 600A Panel with 1000A Feed-Through Lugs (with 600A Main Breakers)



Description

You bring the 1000A feeder into the first 600A panel. The panel has large lugs specifically rated to pass through 1000A. From these lugs, you run conductors to the second 600A panel. Each panel has a 600A main breaker.

Pros

Simple wiring. Potentially less expensive than other options.

Cons



Limited Capacity in First Panel

The first panel's 600A main breaker is the bottleneck. Even though the lugs are rated for 1000A, you can only draw a maximum of 600A out of that panel before the breaker trips. The 400 amps are available for the second panel.

Feed Through Lugs

The 1000A feed through lugs must be rated for two sets of conductors, one set of 1000A conductors in, and one set of 600A conductors out to the second panel.

Code Compliance Concerns

While technically compliant if executed correctly (proper wire sizing, overcurrent protection), it's not ideal because it doesn't fully utilize the available 1000A.

NEC Considerations



110.3(B) - Installation and Use

Equipment must be installed according to its listing and labeling. Make sure the feed-through lugs are specifically listed for 1000A pass-through and the intended conductor sizes.

240.4 - Protection of Conductors

The 600A breaker protects the 600A-rated conductors leaving the first panel to the second panel. The 1000A cable is protected in the main switchgear.

Verdict

Not the best option due to the limited capacity in the first panel.

2. Wiring Trough/Junction Box with Tap Rule (with 600A Main Breakers)



Description

You bring the 1000A feeder into a large wiring trough (or appropriately sized junction box). You then use the NEC tap rules to tap off conductors to each of the 600A panels. Each panel has a 600A main breaker.

Pros

Can potentially utilize more of the 1000A capacity.

Cons



Tap Rule Complexity

The tap rules in NEC are very specific and require careful calculation and execution. You must meet all the conditions of the chosen tap rule.

Space Requirements

The wiring trough/junction box must be large enough to accommodate the conductors, bending radii, and terminations.

Potential for Confusion/Error

More complex wiring increases the chance of errors.

Labor Intensive

Terminating multiple conductors within the trough can be time-consuming.

NEC Considerations



240.21 - Location in Circuit

This is where the tap rules reside. You'll need to carefully review this section. Commonly used tap rules are 240.21(B)(1) (10-foot tap rule) and 240.21(B)(2) (25-foot tap rule).

314 - Junction Boxes, Pull Boxes, and Conduit Bodies

This article governs the sizing and installation of the junction box. It must be appropriately sized and accessible.

110.14 - Electrical Connections

All connections must be torqued to the manufacturer's specifications.

Verdict

Feasible if you can meet all the requirements of a tap rule. Be prepared for a detailed calculation and potentially a more complex installation.

3. (Recommended) Distribution Block/Power Distribution Block (PDB) with 600A Main Breakers



Description

This is the best option. You bring the 1000A feeder into a Listed and Labeled Distribution Block or Power Distribution Block. From the PDB, you run conductors to each of the 600A panels. Each panel has a 600A main breaker.

Pros



Simplest and Safest

Provides a clean, organized, and code-compliant way to split the feeder.

Listed and Labeled

The PDB is specifically designed and tested for this application, ensuring safety and reliability.

Easy to Install

Typically, PDBs have clear instructions and require less complex wiring than the tap rule method.

Flexibility

Allows for future modifications if needed.

Maintains Capacity

The full 1000A is available to the combined load of the two panels, up to the limit of each panel's 600A breaker.

Cons



Cost

PDBs have an upfront cost.

Space

Requires space to mount the PDB, though they are typically relatively compact.

NEC Considerations



110.3(B) - Installation and Use

Install the PDB according to its listing and labeling.

110.14 - Electrical Connections

Torque connections to the PDB's specifications.

408 - Switchboards and Panelboards

While not technically a panelboard, the PDB functions as a distribution point and should be installed in a manner consistent with good practices for switchboards/panelboards.

Verdict

This is the recommended option. It's the safest, most reliable, and easiest to install, and it provides the best utilization of your 1000A capacity.

Example using Option 3


Select a PDB

Choose a PDB rated for at least 1000A input and with sufficient output lugs to feed two 600A panels. Make sure the PDB's lugs can accommodate the conductor sizes you plan to use.2.

Mount the PDB

Install the PDB in a suitable enclosure or on a backboard near the two panels. Ensure adequate working space.3.

Run the 1000A Feeder

Run your 1000A-rated conductors from the switchgear to the PDB input lugs. Terminate them per the PDB manufacturer's instructions, including proper torque.4.

Run Conductors to Panels

Run appropriately sized conductors (at least 600A ampacity) from the PDB output lugs to each of the 600A panels.5.

Terminate Conductors

Terminate the conductors at the PDB and the panel main breakers, again following torque specifications.6.

Labeling

Clearly label all conductors and the PDB.

Important Considerations Before Proceeding



Load Calculation

Perform a thorough load calculation for each panel to ensure that the 600A main breakers are appropriately sized. You don't want nuisance tripping.

Conductor Sizing

Consult the NEC Article 310 for conductor ampacity. Consider derating factors for ambient temperature and the number of conductors in a raceway. It's generally a good idea to use larger conductors than the minimum required for better voltage drop performance.

Overcurrent Protection

Verify that the overcurrent protection in the switchgear feeding the 1000A feeder is sized appropriately for the conductors and downstream equipment.

Grounding

Ensure proper grounding of all equipment, including the PDB and panels, according to NEC Article 250.

Permitting and Inspection

Contact your local electrical inspector to determine permit requirements and schedule an inspection.

Qualified Electrician

This work must be performed by a qualified and licensed electrician.

*In summary, using a Power Distribution Block is the most practical and code-compliant solution for splitting your 1000A feed into two 600A panels. It provides the best balance of safety, ease of installation, and utilization of your available capacity. Flag for review