Do cable trays need to be bridging?

Yes, but can be bridged using lock nuts or lock washers.

When using galvanized cable trays, bridges can be achieved using lock nuts or lock washers. For stainless steel and aluminum alloy cable trays, dedicated grounding bolt holes should be used for grounding bridges.

When purchasing cable trays, for ease of installation, it is recommended to request that the bolts on the connecting plates be lock nuts; lock washers are not recommended.