Can emergency and normal power share a gutter? What NEC 700.10 says about keeping them apart

As the electrician described it, half the room is fed from an emergency panel and the other half from a normal panel through an automatic transfer switch whose backup is the emergency system. The drawings label all of it EM.

In the 2017 NEC text, 700.10(B) requires wiring that runs from an emergency source, or the overcurrent devices distributing it, out to emergency loads to be kept "entirely independent" of every other wiring system and piece of equipment. Several emergency circuits from the same source may share a raceway, cable, box or cabinet. The exceptions are narrow: normal-source wiring inside transfer equipment, luminaires fed from two sources and the listed load control relay or junction box attached to them, and a junction box on unit equipment that holds only its supply circuit and the emergency circuit it feeds. A general-purpose gutter is not on the list.

The second transfer switch is the trap. In an EC&M column, Mike Holt explains that an Article 700 transfer switch may supply only emergency loads, and a generator that also serves other loads needs separate transfer switches. A switch that picks up nonemergency loads from the emergency source falls under 700.10(B)(5). Those loads must be split off in their own vertical switchgear or switchboard sections or in separate disconnect enclosures, and emergency circuits may not originate in the same panelboard enclosure as other circuits. The load side of that second switch does not become emergency wiring because its backup comes from the emergency side, so it stays out of the emergency gutter.

Article 700 covers systems that a government agency requires and classes as emergency, for life safety. Legally required standby (Article 701) and optional standby (Article 702) are separate classes, EC&M notes. That call belongs to the engineer of record, so an EM tag on every circuit should go back as an RFI before pipe goes in. Under 700.10(A), emergency boxes and enclosures must also be permanently marked.