225.30 tells us that a multiwire branch circuit can be considered as 'a' branch circuit, and a disconnect is not required.
Structure- That which is built or constructed.
250.32(A) says that at each building or structure (trailer) that one or more feeders or branch circuits requires us to follow part III of 250. (paraphrased to shorten this post)
550.4(A)Mobile Homes Not Intended as a Dwelling Unit.
-for example, contractor's on-site offices,...
...shall meet all other applicable requirementsof this article if provided with an electrical installation intended to be energized from a 120v or 120/240v ac power supply system.
I can see that your in your post this is a refridgerated trailer, but I am interested in 'job' trailers as well
After reading all of these articles, it would seem they contridict each other.
Bottom line, I am still confused.
would a 'job' trailer with a 'single' branch circuit (whether from 3phase or single phase) require a ground rod?
I do understand the principle behind the reason for the installation of ground rods.