National Electrical Code (NEC)Article 700 - Emergency SystemsSection 700.12(B)"Emergency circuits shall be kept entirely independent of all other wiring and equipment and shall not enter the same raceways, boxes, or cabinets with other wiring except as permitted in 700.12(B)(1) through (B)(4)."Exceptions



(B)(1) "Emergency circuits shall be permitted to occupy the same raceway, box, or cabinet with branch circuits supplying lighting or power within sight of the emergency luminaires or equipment."(B)(2) "Emergency lighting circuits shall be permitted to occupy the same raceway, box, or cabinet with branch circuits supplying power to Class 1, 2, or 3 alarm systems."(B)(3) "Emergency power feeders shall be permitted to occupy the same raceway, box, or cabinet with branch circuits supplying equipment within the emergency system."(B)(4) "Emergency circuits shall be permitted to occupy the same raceway, box, or cabinet with other circuits provided all of the following conditions are met:(a) The emergency circuits are installed in a metal raceway.(b) The emergency circuits are not fusible.(c) The emergency circuits are protected by a circuit breaker rated 100 amperes or less."Interpretation

Based on NEC 700.12(B), it is generally not permitted to use the same box for utility and generator power. However,

Exception (B)(4) allows for this in certain circumstances: The emergency circuits must be installed in a metal raceway. The emergency circuits must not be fusible.* The emergency circuits must be protected by a circuit breaker rated 100 amperes or less.In your case, if you are extending existing wiring to new ATS switches, and if the emergency circuits meet the requirements of Exception (B)(4), then you may use the same box for utility and generator power. Flag for review