Okay, let's break down the disconnect requirements for your DC system feeding those touch displays, considering the NEC and your specific situation.

Understanding the Requirements and Key Considerations NEC 6930.31(D) is Relevant

You're right, this section likely requires MC cable for the DC wiring due to the specific voltage levels involved.

Non-Photovoltaic DC

Since this isn't a solar PV system, you'll need to look at general DC power distribution requirements and adapt them logically. While PV sections can provide insight, they aren't directly applicable unless the specific voltage and current characteristics are similar, and even then, you'd be applying them by analogy.

Disconnect Purpose

The main purpose of a disconnect is to provide a safe and readily accessible means of de-energizing the DC circuits for maintenance, repair, or in emergency situations.

Guidance for DC Disconnects

Here's a breakdown of where to find guidance in the NEC, and how it likely applies to your situation:1. Article 690 Part IV - Disconnecting Means

While much of Article 690 applies to PV, the general principles of disconnecting means are relevant to any DC system. Focus on understanding the underlying reasons for disconnect requirements.2.

Article 725 - Class 2 and Class 3 Remote-Control, Signaling, and Power-Limited Circuits

Check the DC voltage and current ratings of your inverter output. If the output of your inverter is low enough, Article 725 could potentially apply. These circuits may have less stringent disconnect requirements. However, never assume without carefully verifying the voltage and current limits.3.

Article 480 - Storage Batteries

If you have batteries in the equipment rack as part of the inverter system, Article 480 is certainly worth a review to see if any of the articles apply

Disconnect Requirements

These sections will outline requirements for the location, type, and rating of disconnects.

Addressing Your Specific Questions Does the Inverter in the Rack Serve as a Disconnect? Possibly, but unlikely as the only disconnect. The inverter could serve as a disconnect if it meets all the requirements of a disconnecting means:

Accessible

It needs to be readily accessible to qualified personnel. (If the rack is locked or in a restricted area, it might not meet this requirement.)

Labeled

It must be clearly labeled to indicate its purpose.

Simultaneous Disconnect

It must simultaneously disconnect all ungrounded conductors of the DC circuit.

Suitable Rating

It must be rated for the voltage and current of the DC circuit.

Lockable

The disconnect might need to be lockable in the open (off) position, depending on the application and local requirements. However, a single disconnect at the inverter may not be sufficient. Consider this: If a technician needs to work on the displays 4 floors up, forcing them to go all the way down to the rack to disconnect the power is inefficient and potentially unsafe.

Do We Require a Disconnect 4 Floors Up Where the Displays Are? Very likely, yes. Local Disconnect for Servicing

The best practice (and likely code requirement) is to have a disconnect located at or near the displays. This allows for safe and convenient servicing of the displays without having to travel to the equipment rack.

Accessibility

A disconnect near the displays makes it accessible to maintenance personnel working in that area.

Emergency Shut-Off

In some cases, a local disconnect might be required for emergency shut-off purposes.

Recommendations and How to Proceed1. Consult Your Local Electrical Inspector

This is the most important step. The NEC provides a foundation, but local codes and interpretations can vary. The inspector can provide definitive guidance on what's required in your jurisdiction.2.

Determine Voltage and Current

Accurately determine the DC voltage and current output of the inverter, and the voltage and current required by the displays. This will dictate the ratings of the disconnects and conductors.3.

Plan for Two Disconnects (Likely)



Equipment Rack

Use the inverter's built-in disconnect if it meets all the requirements. If not, install a separate DC-rated disconnect near the rack.

Display Location

Install a DC-rated disconnect in a readily accessible location near the displays (e.g., in the ceiling near the displays, in a nearby electrical box). Enclosed fused disconnect switches are a good option.4.

Labeling

Clearly label all disconnects to indicate what they control and their purpose.5.

Lockout/Tagout

Consider lockout/tagout procedures for both disconnect locations to ensure safety during maintenance.6.

MC Cable

Ensure the MC cable is properly grounded and bonded according to NEC requirements.

Example Scenario (Illustrative)

Let's say your inverter outputs 48V DC at 10A. You would need DC-rated disconnects suitable for at least 48V and 10A (and ideally sized with a safety margin). You would need to ensure the conductors are sized appropriately. You would need to verify that the MC cable is rated for the voltage and conditions. You would need to ensure proper overcurrent protection.

Key Takeaways DC disconnect requirements are driven by safety concerns. A disconnect at the point of use (the displays) is almost certainly required. Always consult your local electrical inspector for definitive guidance. Proper labeling is crucial. Focus on accessibility and ease of use for maintenance personnel. Think about potential emergency scenarios.By following these steps, you'll be able to design a safe and code-compliant DC power system for your touch displays. Good luck! Flag for review