100 amp Cable question

#4 THHN is only rated for 95 amps, not 100. #3 THHN is rated for 110 amps. It is unlikely that you will ever reach a 95 amp draw in the panel making the #4s okay. But in my opinion, since you're in there and you're buying some #3 anyway...I'd replace the attached garage sub-panel #4 feeders with #3 ones and call it a job done well and done correctly.

Unlikely a problem, but does code allow that? In theory you *could* overload the cable.

If in doubt, go up a size. It'll reduce the drop when large loads are used. A motor that draws 10A running can draw close to 100A for a brief surge. Friend of mine had an air compressor in his workshop that despite being on a 15A circuit, would take a couple seconds to come up to speed. I measured and found the voltage at the receptacle would drop to around

85V when the motor first switched on. We rewired it for 240V and ran a new circuit with #12 and it starts instantly now.

Isn't it really time you learned a little basic electrical installation practice? The infinitely patient people in this group have done an enormous amount of work for you, and I don't recall seeing many expressions of thanks.

John

With all of the questions he's asked, I think he now falls into the category of having learned a little basic electrical installation. One of the reasons some of us are even here is to help people like him that don't have all the answers or don't know exactly what to do. I'd rather answer 100 questions instead of learning someone died because they didn't ask even one. Yes it's nice to hear a thank you once in a while, but at the same time it can get old and meaningless after so many times. To me, helping is it's own reward, I don't need anything beyond that.

I do appreciate everyone's help and through asking these questions have learned alot. That is one reason when I looked at that wire and it said 4-3 I knew that something might not be right.