Okay, let's break down your situation and tackle your questions. You've got a solid plan overall, and your concerns are valid. I'll give it to you straight, with no mercy!Your Plan - Good Foundation Using URD for the run is appropriate, given the burial requirement. Sizing for the future load of the house (200A) is smart planning. Recognizing the need for temporary power closer to the house site is key.

Question 1: Breaker Box for 4/0 Cables

You are correct. A standard residential panel generally won't accept 4/0 directly into a breaker. Here's why that is important.You need a panel with lugs that are rated for 4/0. These are found in a couple of different form factors. Panels with Main Breakers

Most residential panels with a main breaker 200-amp or above are likely to have lugs rated for 4/0. These are more expensive. (This is due to the "feed-through" terminal block on the inside of the panel.)

Main Lug Only (MLO) Panels

These panels can sometimes be found with lugs that can accept 4/0, but it's less common in standard residential-grade panels.

MLO panels are very similar to the panels with a main breaker, but simply skip the cost of the main breaker. MLO panels are a good option.Question 2: Tapping Down the 4/0 Cable

This is where things get interesting and requires a deeper dive. Polaris Connectors/Dual Rated Splicers

Yes, you can use Polaris-style insulated multi-tap connectors or dual-rated splices to tap your 4/0 URD down to a smaller gauge like 6 AWG. The Home Depot part number you provided is not rated to go this large to this small, you will need to purchase a larger Polaris connector or dual rated splicer. However, there are some crucial considerations:

Safety First

Make sure whatever connectors you use are UL-listed for the purpose of splicing and tapping aluminum conductors. Installation is critical. Follow the manufacturer's instructions precisely, including torque specifications. Under- or over-torquing can lead to loose connections, heat buildup, and fire hazards.

Enclosure

The splice must be made inside a weatherproof enclosure rated for the environment (e.g., rain, snow, UV exposure). A standard junction box is not appropriate unless it is specifically rated for outdoor use.

Ampacity Considerations

This is where you need to do the math. You are tapping a small amount of power off of the feeder cable. The majority of the 4/0 feeders ampacity rating is unaffected. The main cable is still rated for the future 200-amp load. If you are using #6 AWG, your breaker will be 50 amps. The amount of amperage used during construction can be high due to welding machines, chop saws, etc. If you will be using a welder, then you will need larger cable from the taps. You are installing a breaker on the tap to protect the #6 AWG run from the tap.

NEC Compliance

This is the most important thing and is the reason that you are hiring an inspector in the first place. Make sure you follow all electrical code requirements.

Here's a Revised Approach (and my recommendation)


Stick with the 4/0 to the Temporary Panel

Find a 125-200 amp MLO panel that accepts 4/0 AL conductors. This eliminates the need for splices/taps, which simplifies the install and reduces potential failure points.2.

Temporary Feeder Protection

Install a 200 amp breaker at the shop end of the 4/0 URD feeder.3.

Panel Location

Mount your chosen panel on a sturdy post as you planned, close to the house build site. Ensure it's accessible and out of the way of heavy equipment.4.

Outlet Configuration

Install a mix of 120V 20A GFCI outlets and a 240V 50A or 30A receptacle (depending on the tools your contractors are likely to use). Use appropriately sized breakers in the panel to protect each circuit.5.

Burial Depth

Bury the URD cable to the proper depth as per local codes. Check your local code requirements, but generally that would be a minimum of 18-inches (direct burial)6.

Final Connection

Once the house is ready, you can disconnect the panel from the post, fully bury the URD cable, and connect it to the house's service panel.

Why this is better



Simpler Installation

Fewer connections mean fewer points of failure.

Higher Capacity

Provides more power for construction, potentially avoiding nuisance tripping.

Safer

Eliminates the complexity of splicing and tapping high-current cables.

Code Compliance

Makes it easier to meet inspection requirements.

Future-Proof

You're already set up for the full 200A service to the house.

Additional Considerations



Grounding

Ensure proper grounding at the temporary panel. You'll need a grounding electrode system (ground rod or equivalent) and a grounding electrode conductor connected to the panel's grounding bus.

Inspection

Call your local inspector before you start. Discuss your plans and get their feedback. This can save you time and money in the long run.

In conclusion:

While your initial idea is technically feasible, the revised approach is more robust, safer, and likely to be easier to implement and pass inspection. Sometimes, spending a little more upfront on the right components saves headaches and potential problems down the road. Remember, electrical work is not the place to cut corners. Safety and code compliance should always be your top priorities. Flag for review