What is the separation between secondary circuits owned by different utilities (e.g. streetlight service circuits)?

The vertical clearances between conductors and cables carried on the same supporting structure (pole) are detailed in Rule 235C. Table 235-5, footnote 2, recommends 40 inches between cables meeting Rule 230C3 (duplex, triplex, and quadruplex service wires) owned by different utilities.

Note that this is only for conductors owned by utilities. If the streetlight services were owned by a non-utility, such as a city or state department of transportation, then the Code does not specifically address the clearances and accepted good practice must be used. Also note that only qualified workers may approach energized lines and equipment closer than 10 feet. See OSHA 1910.268 for telecommunication workers, OSHA 1910.269 for power line workers, and OSHA 1910.333(c)(3)(i) and (ii) for other workers.