The cord on the trailer is too short to reach the plug so I bought a proper rated cord to extend it. Is this legal?
It greatly depends on the length of the cord, but assuming it is bought locally and not imported (other countries wiring may not comply to our needs here), and the length does not exceed a certain distance and is rated for extreme duty, it should be fine. Check the fusing matching the cord size. 30amp for #10, 40amp for #8, 50amp for #6. with extensions BIGGER is always better.
Yes, It is legal as long as use proper cable and connectors based on local electrical code.
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