You're right to question this. While liability is a factor in many vendor decisions, in this case, the reasoning sounds a bit thin. Here's a breakdown of why the elevator vendor should be providing the disconnect size, and why you, as the engineer, might still need to verify it

Why the Elevator Vendor Should Size the Disconnect:
They know the equipment best

The elevator vendor is the expert on their equipment. They know the motor horsepower, FLA (Full Load Amps), locked rotor amps, control circuit power requirements, and any other critical electrical characteristics. This is essential information for proper disconnect sizing.

Code Compliance (NEC)

The National Electrical Code (NEC) requires proper overcurrent protection for electrical equipment. While the elevator vendor isn't solely responsible for overall project code compliance, they are responsible for ensuring their equipment is protected per the NEC within the scope of their supply.

Warranty and Liability (Indirectly)

Improper overcurrent protection can damage the elevator equipment and void the warranty. By providing a properly sized disconnect recommendation, the vendor helps protect their own interests and reduces the likelihood of problems down the road.

Typical Industry Practice

In most industries, the equipment vendor provides the electrical requirements, including the recommended disconnect size. It's considered part of their service.

Coordination with Internal Protection

The disconnect is the first line of defense. The elevator controller itself will have internal overcurrent protection (fuses, breakers). The disconnect needs to be sized to coordinate with that internal protection to ensure selective tripping (only the closest device to the fault trips). The vendor should have this information.

Why You, as the Engineer, Might Still Need to Verify



Overall System Coordination

You are responsible for the overall electrical system design. This includes ensuring that the elevator disconnect is properly coordinated with the upstream panelboard or switchboard. You need to consider the available fault current at the disconnect location and ensure the disconnect has an adequate interrupting rating.

Specific Project Requirements

Project specifications might dictate specific brands, types, or features for the disconnect. You'll need to ensure the vendor's recommendation meets those requirements.

Local Codes and Amendments

Local jurisdictions may have amendments to the NEC that affect disconnect sizing or installation requirements.

Voltage Drop

While not directly related to overcurrent protection, you should also verify that the wire size recommended by the vendor (which is partially determined by the disconnect size) is adequate to minimize voltage drop to acceptable levels.

Reviewing for Accuracy

Even though the vendor should provide the size, it's always good engineering practice to independently review their calculations and recommendations. Mistakes can happen.

What to Do


Push Back on the Vendor

Politely but firmly explain that providing the recommended disconnect size is a standard part of their service. Cite the reasons above. Ask them to provide the electrical characteristics of the elevator (FLA, locked rotor amps, etc.) and the recommended disconnect size based on those characteristics.2.

If They Still Refuse

If they absolutely refuse, request all the electrical characteristics of the elevator (FLA, Locked Rotor Amps, control circuit power, voltage, phases, etc.). Then, using the NEC (Article 430 for motor circuits is most relevant), you can calculate the minimum required disconnect size. Document your calculations clearly.3.

Document Everything

Keep a record of all communication with the vendor regarding this issue. This will be important if any problems arise later.4.

Consider a Change Order (if applicable)

If you are now required to do more design work than you originally anticipated, consider a change order to account for the additional engineering time.5.

Clarify Responsibilities

Before the project starts, ensure that the division of responsibilities is clearly defined in the contract documents. This should include who is responsible for providing the electrical requirements for the elevator.

In summary: The elevator vendor should provide the disconnect size. Their reluctance sounds like a way to avoid potential liability, but it's not a valid reason. You, as the engineer, need to verify their recommendation (or calculate it yourself if they refuse) to ensure overall system coordination, code compliance, and project requirements are met. Make sure you obtain all necessary electrical characteristics from the vendor. Flag for review