I have three circuits in my shop, each dedicated to powering 2 duplex 110V receptacles. The circuits originate from a 100A subpanel inside the shop.
Two of the circuits are 15A, and one is 20A. Everything is wired with 12/2 MC cable with ground, and metal boxes. Each circuit is about the same length. Each circuit has a GFCI receptacle first, with a regular duplex receptacle downstream. the 15A circuits have 15A rated receptacles, the 20A circuit has 20A rated receptacles.
Funny thing is - the 20A circuit will sometimes trip using tools that might draw only 8 or 9 amps max, while I hardly ever trip the 15A circuits with the same tools, or even when using a tool that will draw 15A max (briefly, like a table saw).
What could cause this? I have a multimeter - Can it help me infer something here?