Exception to NM Cable Use in Non-Dwelling Mobiles

Yes, there is an exception to the general prohibition on using NM cable in non-dwelling mobiles with suspended ceilings, as stated in Article 550.10(D)(2) of the National Electrical Code (NEC):> Exception

Where the exposed NM cable is installed above the suspended ceiling and within 6 feet of the underside of the ceiling joists.

Conditions for Exception

For this exception to apply, the following conditions must be met: The NM cable must be installed above the suspended ceiling (i.e., in the ceiling plenum). The NM cable must be within 6 feet of the underside of the ceiling joists. The suspended ceiling must not be used as a support for the NM cable.

Wiring Practices

When using NM cable in non-dwelling mobiles with suspended ceilings under this exception, the following wiring practices must be followed: Support

The NM cable must be supported by J-hooks, straps, or other approved means.

Stapling

NM cable must not be stapled to the suspended ceiling.

Securing

NM cable must be securely fastened to prevent it from sagging or being displaced.*

Connectors

NM cable must be terminated using approved connectors.

Reasoning for Exception

The exception to the general prohibition on NM cable in non-dwelling mobiles with suspended ceilings is based on the fact that the NM cable is not exposed to physical damage within the ceiling plenum. The 6-foot limitation is intended to ensure that the NM cable is within easy reach for maintenance and troubleshooting.

Compliance

Based on the information you provided, it appears that the office complex you inspected is not in compliance with the NEC exception for NM cable use in non-dwelling mobiles with suspended ceilings. The fact that hundreds of trailers on site are wired with NM cable does not make it permissible under the NEC. Flag for review