Yes, you can tap off the 400 amp MLO panel with lugs to feed the 150 amp fused disconnect, provided you follow the requirements of NEC 240.21(B) and 240.21(C) regarding overcurrent protection of tap conductors. Because your distance is 225', the tap rule will be most critical. Here's a breakdown of what you need to consider

Key Considerations & Code Requirements:
Tap Rules (NEC 240.21(B) and 240.21(C)): You MUST comply with the NEC tap rules. The most common is the 25-foot tap rule. Since your distance is 225', you'll need to use the tap rules that allow longer distances. The options are the 10-foot tap rule or the outside tap rule. Outside Tap Rule (NEC 240.21(C)(2)): This is the most likely scenario for your situation. This rule permits taps up to 100 feet long (or more if certain conditions are met) without immediate overcurrent protection, provided the tap is installed outside of a building. 240.21(C)(2)(a): The conductors are suitably protected from physical damage in an approved manner. 240.21(C)(2)(b): The conductors terminate in a single circuit breaker or set of fuses that will limit the load to the ampacity of the conductors. This is fulfilled by your 150A disconnect. 240.21(C)(2)(c): The overcurrent device is an integral part of a disconnecting means or shall be located immediately adjacent thereto. 240.21(C)(2)(d): The disconnecting means shall be readily accessible. 240.21(C)(2)(e): The disconnecting means shall be located either outside of a building or structure, or inside nearest the point of entrance of the conductors. Conductor Ampacity

The conductors you use for the tap MUST have an ampacity equal to or greater than the load they will supply (150 amps in this case). You also need to ensure that the ampacity is sufficient for any future load increases that might occur. You must derate the conductors in accordance with NEC table 310.15(B)(1), and correct them in accordance with NEC table 310.
16.

Overcurrent Protection

Your 150 amp fused disconnect provides the overcurrent protection for the tap conductors. The fuses in the disconnect should be sized to protect the tap conductors, but no larger than 150 amps (the disconnect rating).

Proper Lugs

Ensure you use properly sized and rated lugs in the 400 amp panel for tapping the conductors. Use lugs UL listed for the conductor size and material. Torque the lugs to the manufacturer's specifications.

Grounding and Bonding

Ensure proper grounding and bonding according to NEC Article 250. This includes a properly sized equipment grounding conductor run with the circuit conductors.

Conduit

The conductors should be run in appropriate conduit (e.g., PVC, rigid metal conduit (RMC), or intermediate metal conduit (IMC)) for the environment and application.

Step-by-Step Considerations


Load Calculation

Verify that the 150 amp fused disconnect is adequately sized for the actual load it will supply.2.

Conductor Sizing

Determine the appropriate conductor size based on the 150 amp load and derating/correction factors. Using the 75°C column from NEC Table 310.16, you would need at least a #1/0 AWG copper conductor (rated for 150 amps) before derating or correction. With derating and correction, you may need to go larger.3.

Conduit Sizing

Select the correct size of conduit based on the number and size of conductors.4.

Lug Selection

Choose lugs that are rated for the conductor size and the amperage.5.

Installation

Properly install the lugs in the 400 amp panel, torquing them to the manufacturer's specifications. Run the conductors in the appropriate conduit from the panel to the fused disconnect. Terminate the conductors in the fused disconnect. Install the correct size fuses in the disconnect. Ensure proper grounding and bonding.

Important Considerations



NEC Article 310, Conductors for General Wiring. Be sure to follow the requirements for ampacity, derating, and correction. NEC Article 250, Grounding and Bonding. Critical for safety. NEC Article 300, Wiring Methods. Local Codes and Permits

Always check with your local electrical inspector for any specific local code requirements or permit requirements.

Qualified Electrician

This type of work should ideally be done by a qualified and licensed electrician. They will be familiar with the NEC and local codes, and can ensure the installation is safe and compliant.

Disclaimer: I am an AI chatbot and cannot provide electrical advice. This information is for educational purposes only and should not be considered a substitute for professional electrical services. Always consult with a qualified electrician for any electrical work. Improper electrical work can be dangerous and may violate local codes. Flag for review