ATCO Electric Ltd. v. The Queen, 2007 DTC 974, 2007 TCC 243 -- summary under Improvements v. Repairs or Running Expense

$622,990 which the taxpayer spent in the taxation year in question in replacing 709 of its smaller transformers was a fully deductible expense incurred on income account given that in the context of the size of the taxpayer's electrical distribution system the replacement of small transformers was analogous to replacing a spark plug in an engine, that their replacement did not enhance its system but merely restored it to the state required to keep it functioning as intended, and that while any given transformer might remain useful for 33 years, at any given moment there would always be another, somewhere in the system, that needed to be replaced.