Colocation and shared responsibility.
A colo floor runs multiple employers' electrical work through one power system. 70E's host and contract employer machinery was built for a contractor visiting a plant — a colo runs that relationship permanently, in both directions, across every cage boundary on the floor.
110.5 is the governing mechanism — use it in both directions
The standard's host and contract employer provisions put mutual duties on both parties: the host informs the contractor of the hazards, the installation's particulars, and the applicable program requirements; the contractor brings its own program, follows the host's rules, and reports what it finds. In a colo, every customer with electrical scope is a contract employer, every operator is a host — and the customer's own vendors nest a third layer beneath both. The documented exchange the standard contemplates cannot be a one-time onboarding PDF; it has to attach to work, per project, where the scopes actually meet.
The floor-level artifact that makes it real is a demarcation schedule: for every cage, which employer's electrical safety program governs which piece of equipment, from the operator's breaker to the customer's rack PDU, with the boundary devices named. Two programs at one boundary with no schedule means, in practice, zero programs at that boundary.
The classic colo failure modes
Three patterns account for most of what goes wrong. The orphan breaker: the operator owns the panel, the customer owns the load, and a trip at 3 a.m. finds the operator's tech resetting into a fault they cannot see and the customer's tech unable to reach the breaker at all — the post-trip reset being the likelihood table's abnormal-operation Yes, whoever's hand is on it. The imported electrician: a customer's contractor arrives with their own program, their own PPE habits, and no knowledge of the site's available fault current, labels, or permit process — competent, and uninformed, which 110.5's information duties exist to fix. The assumption gradient: each party assumes the other's maintenance program covers the shared gear, and the condition-of-maintenance condition — one of the seven — is satisfied by nobody.
Each pattern is a coordination failure wearing an electrical costume, and each is solved on paper before it is solved on the floor.
Access tiers are the enforcement layer
The colo's badge system is where 70E meets the front door. Tie electrical access to training tier: awareness-trained customer staff reach their cages and their rack PDUs; qualified persons — proven by documented, task-specific training under 110.4, not by job title on a work order — reach panels and distribution; permits gate anything inside a restricted approach boundary, with the operator holding approval. The permit's restrict-unqualified-persons element does real work on a multi-tenant floor precisely because the population is uncontrolled by any single employer — the badge tier is how the restriction survives shift change.
A colo cage where the customer's UPS vendor and the operator's electrician had each locked out 'their' side of the same maintenance bypass wraparound — two locks, two programs, and a wraparound path neither party's one-line showed completely. The gear was fine; the near-miss was procedural. One shared drawing at onboarding would have cost an hour.
Work crossing a cage boundary? Establish whose program governs and who holds the permit before the walk — then run it under that program.
This is the material of the 8- and 16-hour NFPA 70E classes — taught on the 2027 edition, against data center topology, about 55 times a year. Private onsite days run against your one-lines.