Many places have an exemption for manufactured goods that are subject to testing. So for instance, a device doesn't have to be designed by a licensed engineer i

Many places have an exemption for manufactured goods that are subject to testing. So for instance, a device doesn't have to be designed by a licensed engineer if it meets and is verified by testing to meet CSA standards. But if you want to use something that's not CSA, then it does need to be reviewed and signed off by an engineer. A home's electrical design doesn't have to be signed off by an engineer, but it has to meet code and be inspected. If it doesn't meet code and you want an exemption (for instance because you are doing something that wasn't anticipated by the code), then you need an engineer to sign off confirming that what you're doing is safe and truly requires an exemption.