Okay, let's break down this setup and see if it works and identify potential issues. Your goal is to use a 4-pole double-throw switch to alternate between a 3-phase 208V source and a single-phase 240V source, powering two single-phase panels.

Here's a breakdown of the proposed wiring, assuming standard North American wiring conventions, followed by potential concerns and considerations



Source 1 (3-Phase 208V)

L1 (A) -> Pole 1, Terminal 1 (Position 1) -> Panel 1 Breaker L2 (B) -> Pole 2, Terminal 1 (Position 1) -> Panel 1 Breaker L1 (A) -> Pole 3, Terminal 1 (Position 1) -> Panel 2 Breaker L3 (C) -> Pole 4, Terminal 1 (Position 1) -> Panel 2 Breaker Neutral -> Neutral terminal for 3ph source

Source 2 (Single-Phase 240V)

L1 (A) -> Pole 1, Terminal 2 (Position 2) -> Panel 1 Breaker L2 (B) -> Pole 2, Terminal 2 (Position 2) -> Panel 1 Breaker L1 (A) -> Pole 3, Terminal 2 (Position 2) -> Panel 2 Breaker L2 (B) -> Pole 4, Terminal 2 (Position 2) -> Panel 2 Breaker Neutral -> Neutral terminal for 1ph source

Conceptual Analysis

In the 3-phase position, each panel receives power from two different phases of the 3-phase source. When switching to single-phase, both panels get power from the same two legs of the single-phase source. The switch moves ALL poles and the neutral at the same time.

Potential Issues and Considerations


Voltage Compatibility

This is the biggest concern. You're switching between 208V 3-phase (effectively 208V single-phase line-to-line) and 240V single-phase. Are the devices connected to your panels rated for both 208V and 240V? Many devices can handle a voltage range (e.g., 200-240V), but you must confirm this for every piece of equipment. Running devices designed for 208V on 240V could lead to overheating, reduced lifespan, or immediate failure.2.

Neutral Handling

Your plan to switch the neutral along with the phases is critical. However, you must ensure that the neutral from the 3-phase and single-phase sources are never connected together. The switch must isolate the neutrals from each source. Using a 4 pole switch with the 4th pole being the neutral should achieve this.3.

Panel Neutral-Ground Bond

Do not bond the neutral to ground in both panels. Only the main service (either the 3-phase source or the single-phase source when it's acting as the main) should have the neutral-ground bond. If you bond the neutral to ground in both panels, you'll create a parallel neutral path, which is a safety hazard and violates electrical codes.4.

Switch Rating

The 4-pole double-throw switch must be rated for the voltage (240V minimum) and current (100A minimum) of the larger of the two sources. It must also be suitable for the intended application (i.e., switching electrical loads).5.

Code Compliance

This setup may violate local electrical codes. Specifically, the NEC (National Electrical Code) has rules about how services are configured and how loads are connected. A qualified electrician must review the design and installation to ensure it meets all applicable codes.6.

Load Balancing

When on 3-phase, load balancing between the panels might be an issue. Try to distribute the loads as evenly as possible between the two panels so that each panel isn't overloaded. On 1-phase, both panels will be loaded on the same legs of the power which may require load shedding to prevent overdraw.7.

Safety

Make sure all work is performed by a qualified electrician and proper lockout tagout procedures are followed.

Recommendations


Consult an Electrician

This is non-negotiable. A qualified electrician must review the entire setup, verify component ratings, ensure code compliance, and perform the installation.2.

Verify Voltage Compatibility

Double-check the voltage rating of all devices connected to the panels.3.

Single Source of Bonded Neutral

Ensure that only one neutral-ground bond exists in the entire system – only in the main source being used at the time.4.

Proper Switch Selection

Choose a 4-pole double-throw switch that is specifically rated for switching between sources and meets all relevant electrical standards.

In summary, while the general idea can work, there are many critical details that must be addressed. A qualified electrician is essential to ensure safety and compliance with all applicable codes. Flag for review