I've come across strobes and horn/strobes speced to be wired alternating circuits..like a/b/a/b ...anyone familiar with this?
It was popular in NYC, or so I've been told. The Port Authority of NY and NJ has added a design guideline for fire alarm systems for the LaGuardia Terminal B project that says you can't lose more than 60% of the notification appliances in a space if there is a circuit failure. There is nothing in NFPA 72, the NYC building code or Appendix Q thereto that requires "A/B" circuiting. It may show up in a specification, or there may be an AHJ who has a "shirt-pocket" rule.