Okay, let's break down this scenario. It's tricky because you're dealing with existing concrete and limited space. Here's a detailed look at the code implications and possible solutions.

Code Considerations (Assuming US NEC - National Electrical Code)


Conductor Ampacity and Sizing (NEC 310.15, Table 310.16, and related articles)



4/0 Aluminum is a common choice for service entrance conductors but you would need to use a 200 amp breaker. This is a critical point. You must ensure the ampacity of the 4/0 aluminum conductors is sufficient for your load calculation for the house. If your service calculation demands a 200A service, the 4/0 aluminum is acceptable if terminations are rated for it. 2/0 Aluminum Neutral

Similar to the hot conductors, verify the 2/0 aluminum is sufficient for the calculated neutral load.

4 AWG Bare Copper Ground

The size of the grounding electrode conductor (GEC) to a grounding electrode (ground rod, water pipe, etc.) is dictated by NEC 250.66. For a 200A service supplied by 4/0 aluminum, a 4 AWG copper GEC is likely sufficient. This is the minimum size. Using a larger size is never a problem.



Terminations

All conductors must be terminated in equipment listed and labeled for the conductor material (aluminum or copper) and size. Using the proper anti-oxidant paste (e.g., NOALOX) on aluminum terminations is critical.2.

Conduit Fill (NEC Chapter 9, Table 1 and Annex C)

This is where the 1 1/2" conduit becomes a potential problem. You must calculate the fill percentage. The NEC limits the percentage of the conduit's cross-sectional area that can be occupied by conductors. For new installations, this limit is typically 40% for three or more conductors. However, existing raceways can, under certain conditions, be filled to a higher percentage (See Annex C).

Calculating Fill

You'll need the exact outer diameter (OD) of each conductor with insulation. Conductor manufacturers publish this data. Then, calculate the cross-sectional area of each conductor (Area = π (OD/2)^2). Sum the areas of all conductors. Next, find the internal area of 1 1/2" Schedule 40 PVC or EMT conduit (whichever you plan to use). This information is in NEC Chapter 9, Table 4 (for rigid PVC) or Chapter 9, Table 5 (for EMT). Divide the total conductor area by the conduit's internal area and multiply by 100 to get the fill percentage.

Crucial

If you're close to the 40% limit (or exceeding it under the "existing raceway" rules), consult with the electrical inspector before proceeding. Overtight conduit fill makes pulling conductors extremely difficult and can damage the insulation, leading to potential shorts or ground faults.3.

Conduit Body Fill (NEC 314.16)

If you use conduit bodies (like LB, LL, or LR fittings) immediately after the reduction, they also have fill limits that must be observed. This becomes even more critical in an existing concrete situation.4.

Service Disconnecting Means (NEC 230.70)

The service disconnect (the main breaker in your Homeline panel) must be readily accessible and located at a specific point relative to the entry of the service conductors. Ensure the reduced conduit doesn't violate this accessibility requirement.5.

Physical Protection (NEC 300.4)

Conductors must be protected from physical damage. The conduit and any fittings must be suitable for the environment (e.g., wet location if exposed to moisture).

Is it Likely to Pass Inspection?

Uncertain. It depends on the specifics. If your fill calculation is okay, and the inspector accepts the reduction with proper fittings, it might pass. However, if the fill is too tight, or the inspector has concerns about accessibility or future maintenance, it will likely fail.

Possible Solutions & Considerations


Careful Conductor Selection

Use conductors with the smallest outer diameter that still meet the ampacity requirements. Some insulation types (e.g., THHN/THWN-2) are thinner than others.2.

Tapered Reducer

Use a properly listed and sized tapered reducer fitting that transitions smoothly from the 2" to the 1 1/2" conduit. This minimizes stress on the conductors during pulling. Make sure it's suitable for the type of conduit you're using (PVC or metal).3.

Conduit Body (Carefully Considered)

While a conduit body might seem helpful to make the transition, it can actually reduce the space available and make pulling harder. Only use it if absolutely necessary and ensure it's properly sized.4.

Pulling Compound

Use a high-quality pulling lubricant specifically designed for electrical conductors. This will significantly reduce friction during installation.5.

Professional Installation

This is a situation where hiring a licensed electrician is highly recommended. They have the experience to assess the situation, perform the calculations, and ensure the installation meets code. They also have the tools and techniques to pull the conductors safely and efficiently.6.

Variance

Worst case is asking for a variance. In my locale you can do this with an electrical inspector. They will need to be convinced that not allowing this will cause undue hardship and that the solution you propose will not jeopardize the integrity of the system. I don't like this option, but I am throwing it out there.

Recommendations


Perform the Fill Calculation

Get the actual OD of the conductors you plan to use and calculate the conduit fill percentage. This is the first step to determine if your plan is even feasible.2.

Consult with the Electrical Inspector

This is the most important step. Explain your situation to the local electrical inspector, show them your calculations, and ask for their opinion before you do any work. They are the final authority and can tell you what they will accept.3.

Consider a Licensed Electrician

Even if you're comfortable doing electrical work, this is a complex situation with code implications. A professional can ensure the job is done safely and correctly, and can navigate the inspection process.

Important Safety Note:* Working with electricity can be dangerous. Always disconnect power at the main breaker before working on any electrical equipment. If you are not comfortable working with electricity, hire a qualified electrician.Good luck with your project! Flag for review