Which code applies to the installation of all appliances downstream of the natural gas meter?

The applicable code for the installation of all appliances downstream of the natural gas meter is the CSA B149.1 Natural Gas and Propane Installation Code. This code specifically outlines the standards and requirements for the installation of natural gas and propane equipment, including appliances, venting systems, and gas piping systems. It addresses safety, operational efficiency, and the proper methods for installation to ensure that the appliances function correctly and safely.

The other choices refer to codes that apply to different aspects of construction or utility systems. For example, the National Building Code of Canada governs general construction practices but does not specifically address the installation of gas appliances. The CSA Z662 Pipeline Systems Code pertains to oil and gas pipeline systems, focusing on the infrastructure rather than the appliances themselves. Lastly, while B149.1 Gas Code might seem relevant, it is essentially referring to the same CSA B149.1 code; it's more accurate to identify it clearly as the Natural Gas and Propane Installation Code, as specified in the correct answer.