Wiring a walk-in cooler that's physically separated from the building it serves by 18 inches presents a few challenges but is certainly doable. Here's a breakdown of the best practices, requirements, and considerations

1. General Considerations and Planning
Local Codes and Permits

This is paramount. Before you do anything, contact your local building department or electrical inspector. They will be the ultimate authority on what's required in your specific area. They'll likely have specific codes related to detached structures, underground wiring, and potentially even walk-in cooler installations. Don't skip this step! Failure to get a permit and comply with local codes can result in fines, rework, and potential safety issues.

Wiring Method

Underground wiring is practically the only option here. Surface wiring isn't allowed or recommended.

Disconnect Switch

A readily accessible disconnect switch for the cooler is crucial, ideally located right near the cooler itself.

Circuit Size

Determine the amperage requirements of the cooler. This information should be on the cooler's nameplate. Factor in the starting amperage, which can be significantly higher than the running amperage.

Voltage

Walk-in coolers can be 120V, 208V, or 240V depending on the size and model. Know what your cooler requires.

Grounding

Proper grounding is critical for safety. You'll need to run a grounding conductor with your power conductors.

Weatherproofing

Everything needs to be rated for outdoor use and protection from the elements.

2. The Best Way to Route Power: Underground Wiring Trenching

Dig a trench between the building and the cooler. The depth will be determined by local codes, but typically it's around 18-24 inches for residential applications. Commercial applications may require a deeper trench (30-36 inches).

Conduit

Conduit protects the wiring from physical damage and moisture. Rigid metal conduit (RMC), intermediate metal conduit (IMC), or Schedule 80 PVC conduit are all suitable options for underground burial. RMC offers the most physical protection.

Wiring

Use appropriately sized THWN or THWN-2 insulated wires inside the conduit. These are moisture-resistant and rated for wet locations. Never bury NM-B (Romex) cable directly underground, even inside conduit.

Sealing

Seal the ends of the conduit where the wires enter and exit to prevent moisture from entering. Use appropriate conduit sealant.

Expansion Joints

Consider expansion joints in long runs of PVC conduit, especially in areas with significant temperature fluctuations. This will help prevent cracking or separation due to thermal expansion and contraction.

Transition from Underground to Above Ground

Where the conduit comes out of the ground (at both the building and the cooler), use a suitable LB fitting or other weatherproof fitting to make the transition. These fittings allow you to make a 90-degree bend while keeping the wires protected.

Weatherproof Junction Boxes

At both the building and the cooler, you'll likely need weatherproof junction boxes to connect the underground wiring to the building's electrical system and the cooler's power supply.

3. Detailed Steps for Routing Power1. Determine Circuit Requirements

Get the voltage, amperage (running and starting), and any special circuit requirements from the cooler's nameplate. Size the wire gauge and breaker accordingly. Use a wire size chart that takes into account the amperage and the length of the run to minimize voltage drop.2.

Install Disconnect Switch

Mount a weatherproof disconnect switch near the cooler. This is essential for safely cutting power to the unit for maintenance or emergencies.3.

Run Conduit and Wiring

Dig the trench to the required depth. Assemble the conduit run, including any necessary couplings, elbows, and expansion joints. Glue PVC conduit securely with the appropriate PVC cement. Bury the conduit in the trench, making sure it's properly supported. Pull the THWN/THWN-2 wires through the conduit. Use wire lubricant to make this easier.4.

Make Connections

At the building, connect the wires to a properly sized circuit breaker in the electrical panel. At the cooler, connect the wires to the disconnect switch. From the disconnect switch, connect to the cooler's power supply.5.

Grounding

Ensure a proper ground connection throughout the entire system. This includes connecting the ground wire to the grounding bar in the electrical panel, to the disconnect switch, and to the cooler's chassis.6.

Testing

Before backfilling the trench, have an electrician inspect the wiring to ensure it's done correctly and safely. After the inspection, backfill the trench. Test the circuit with a multimeter to verify the voltage and continuity. Finally, turn on the circuit breaker and test the cooler to ensure it's functioning correctly.

4. Specific Requirements National Electrical Code (NEC)

The NEC provides the minimum safety standards for electrical installations. You must adhere to all applicable NEC requirements. Some relevant articles include:

Article 300

Wiring Methods

Article 310

Conductors for General Wiring

Article 344

Rigid Metal Conduit (RMC)

Article 352

Rigid Polyvinyl Chloride Conduit (PVC)

Article 430

Motors, Motor Circuits, and Controllers (if the cooler has a motor compressor)

Article 225

Outside Branch Circuits and Feeders

Article 250

Grounding and Bonding

Grounding Electrode System

Depending on your local codes, you might need to establish a separate grounding electrode system (ground rod) at the cooler location. This is more likely if the cooler is considered a separate structure. Your local inspector will advise.

GFCI Protection

Ground Fault Circuit Interrupter (GFCI) protection may be required for certain outlets or circuits associated with the cooler, particularly those in damp or wet locations. Consult the NEC and your local inspector.

5. Important Considerations Hire a Qualified Electrician

This project is complex and potentially dangerous. Unless you have extensive experience with electrical work and a thorough understanding of the NEC, it's highly recommended that you hire a licensed and insured electrician. They will ensure that the installation is safe, compliant with all applicable codes, and properly grounded.

Future Expansion

Consider running a larger conduit than you currently need. This will allow you to easily add additional circuits in the future if needed.

Marking the Conduit

Consider running tracer wire along with the conduit to allow for easy location of the conduit in the future. Alternatively, bury a detectable warning tape above the conduit.

Sleeves Through Walls

Where the conduit enters the building and the cooler, use appropriate sleeves to protect the conduit from damage and to seal the penetrations against water and air infiltration.

Voltage Drop

Calculate the voltage drop for the length of the run. Excessive voltage drop can cause the cooler to operate inefficiently or even damage its components. Use a larger wire gauge if necessary to minimize voltage drop.

In Summary:

Routing power to a walk-in cooler that's physically separate from the building requires careful planning, adherence to local codes and the NEC, and the use of appropriate materials and techniques for underground wiring. Hiring a qualified electrician is strongly recommended to ensure a safe and compliant installation. Prioritize safety, and always get the necessary permits and inspections. Flag for review