In the construction industry, Tier 1 is a Contractor referred in ISO 19650 as the Lead appointed party, who provide goods or services directly to the ultimate client.
The Tier 1 are equivalent of the PAS 1192‑2:2013 lead suppliers

In the construction industry, Tier 1 is a Contractor referred in ISO 19650 as the Lead appointed party, who provide goods or services directly to the ultimate client.
The Tier 1 are equivalent of the PAS 1192‑2:2013 lead suppliers
A fuse or circuit-breaker providing overload and fault current protection.
Introduction The COVID19 pandemic has impacted global health and the
American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)