Class A SLC Wiring in a High-Rise With a Shared Riser
A 12-story high-rise uses an addressable signaling line circuit wired Class A. The contractor routes the outgoing and return legs of the SLC in the same 2 in conduit riser for floors 1 through 12, with a single conduit sleeve through each floor. The panel is on floor 1. During a pre-test, the contractor opens the SLC at floor 6 to demonstrate survivability; the panel reports a trouble but the devices on floors 7-12 continue to communicate. The AHJ asks whether the shared-riser routing satisfies the intent of Class A survivability and whether the demonstration is adequate.
1. Assess the shared-riser routing and the open-circuit demonstration.
Read the worked answer
Class A provides a redundant path so a single open does not disable the circuit. The demonstration shows the electrical redundancy works: opening at floor 6 leaves floors 7-12 communicating via the return leg. However, physical survivability is a separate question. Routing both legs in the same conduit through the same floor sleeve means a single physical event (fire, collapse, or mechanical damage at that sleeve) can sever both paths at once, defeating the purpose of Class A. The AHJ should require the outgoing and return legs to be routed separately, in different conduits and preferably different shafts or separated paths, consistent with the design documents and the adopted code's survivability provisions.
The open-circuit test is necessary but not sufficient. It proves electrical function, not physical protection. The AHJ should also require documentation of the raceway routing and separation, and a test that confirms the panel annunciates the correct trouble and that the surviving devices remain operational.
2. If the design cannot separate the risers, what should the AHJ do?
Read the worked answer
The AHJ should not simply accept the shared riser. Options: require a code-compliant alternative that provides equivalent survivability (for example, a listed circuit-protection or pathway-survivability method acceptable under the adopted code), require the designer to justify the arrangement in writing with a code citation, or require the affected portion to be rewired. If a variance is requested, it must be documented with the technical basis and approved by the authority, not decided in the field by the contractor. The inspection record should note the deficiency and the resolution.