There are code rules that this condition applies to.
In Ontario, Canada we (the Inspection Department) base our decision on the follwing code rules:
A maximum of one conductor per breaker is permitted unless the breaker is approved for terminating more than one conductor. - Rule 02-034
Section #2 states:
2-034 Use of Approved Equipment (see Appendix B) No one shall use any electrical equipment other than approved electrical equipment of a kind or type and rating approved for the specific purpose for which it is to be employed.
Appendix B states:
As a condition of approval of certain types of electrical equipment, the manufacturer supplies instructions pertaining to its installation. It is of the utmost importance that the installer closely follow installation instructions supplied by the manufacturer to fulfill the terms of the approval agreement.
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